March 2023

Revision History
I. July 31, 2021 New issue (Document No.: NKRE-GL-WFC01, Edition: July 2021)* Correction of error and Minor change have applied on 1st October 2021 (No change of Document No.)II.

New issue dated March 31, 2023 (Document No.: NKRE-GL-WFC01, Edition: March 2023)

EFFECTIVE DATE and APPLICATION
1. These guidelines shall be enforced from April 1, 2023.
2. Notwithstanding the provisions of these guidelines, the provisions then in force shall remain applicable to power plants otherthan those falling under any of the following.

(1)

Power plants for which the application for examination pertaining to wind farm certification is accepted on or after June
1, 2023(2) Power plants for which the initial certification document of wind farm certification is issued on or after September 1,

2023
3. Regardless of 1 and 2 above, it should be noted that for provisions, etc., based on the requirements shown below
from Chapter 1, 1.1.1-3. of these Guidelines, the application shall be from the effective date of that provision, etc.
1)

20140328 Bureau of Commerce No. 1 "Interpretation of Technical Standards for Wind Power Generation Facilities"(revised 20230310 Bureau No. 2)

2)

Annotations to the Ministerial Ordinance Prescribing Technical Standards for Wind Power Generation Facilities and its
Interpretation (Ministry of Economy, Trade and Industry, revised on March 20, 2023)

Table of Contents
Chapter 1 General .............................................................................................................................................................. 4
1.1 General ................................................................................................................................................................. 4
1.1.1
Application .................................................................................................................................................... 4
1.1.2
Wind power generation facilities with a new concept .................................................................................... 4
1.1.3
Design life and service life ............................................................................................................................ 4
1.2 Normative References .......................................................................................................................................... 4
1.2.1
General ......................................................................................................................................................... 4
1.3 Definitions and abbreviations ................................................................................................................................ 5
1.3.1
Definition of terms ......................................................................................................................................... 5
1.3.2
Definition of abbreviations ............................................................................................................................ 7
1.3.3
Meaning and units of symbols ...................................................................................................................... 7
1.4 Wind farm certification ........................................................................................................................................... 8
1.4.1
General ......................................................................................................................................................... 8
1.4.2
Evaluation module ........................................................................................................................................ 8
1.4.3
Site conditions assessment .......................................................................................................................... 8
1.4.4
Design basis evaluation ................................................................................................................................ 9
1.4.5
Integrated load analysis evaluation............................................................................................................... 9
1.4.6
Wind turbine (RNA) design evaluation .......................................................................................................... 9
1.4.7
Support structure design evaluation ............................................................................................................. 9
1.4.8
Wind farm certification module for onshore wind power plants ..................................................................... 9
1.4.9
Certification subcommittees ........................................................................................................................ 10
1.5 Documents to be submitted................................................................................................................................. 10
1.5.1
General ....................................................................................................................................................... 10
1.5.2
Materials related to wind turbine type certification ...................................................................................... 11
1.5.3
Materials related to the site conditions assessment (wind conditions) ........................................................ 11
1.5.4
Materials related to wind turbine (RNA) design evaluation ......................................................................... 11
1.5.5
Materials related to the support structure (Tower) design evaluation .......................................................... 12
1.5.6
Materials related to the support structure (Foundation) design evaluation ................................................. 12
1.6 Correspondence to the Technical Standards for Wind Power Generation Facilities [Reference] ........................ 13
1.6.1
General ....................................................................................................................................................... 13
Chapter 2 Site conditions assessment .............................................................................................................................. 16
2.1 General ............................................................................................................................................................... 16
2.1.1
General ....................................................................................................................................................... 16
2.2 Wind conditions during power production ........................................................................................................... 16
2.2.1
Wind condition measurement ..................................................................................................................... 16
2.2.2
Measurement data evaluation..................................................................................................................... 16
2.2.3
Evaluation of topographic complexity ......................................................................................................... 17
2.2.4
Airflow analysis ........................................................................................................................................... 18
2.2.5
Calculation of the wind speed appearance frequency distribution .............................................................. 18
2.2.6
Calculation of turbulence intensity .............................................................................................................. 18
2.2.7
Evaluation of wind turbine wake effect from adjacent wind turbines ........................................................... 18
2.2.8
Calculation of the wind shear exponent ...................................................................................................... 19
2.2.9
Calculation of flow inclination angle ............................................................................................................ 19
2.2.10 Calculation of atmospheric density ............................................................................................................. 19
2.3 Wind conditions during parked by storm ............................................................................................................. 19
2.3.1
Calculation of extreme wind speed and turbulence intensity ...................................................................... 19
2.3.2
Calculation of atmospheric density ............................................................................................................. 20
2.4 Geotechnical and earthquake conditions ............................................................................................................ 20
2.4.1
General ....................................................................................................................................................... 20
2.5 Lightning environment conditions ........................................................................................................................ 21
2.5.1
General ....................................................................................................................................................... 21
2.6 Other environmental conditions........................................................................................................................... 21
2.6.1
General ....................................................................................................................................................... 21
Chapter 3 Design basis evaluation ................................................................................................................................... 22
3.1 General ............................................................................................................................................................... 22
3.1.1
General ....................................................................................................................................................... 22
3.2 Design basis requirements .................................................................................................................................. 22- 1 -3.2.1
General ....................................................................................................................................................... 22
3.2.2
Wind turbine (RNA) design basis ................................................................................................................ 22
3.2.3
Support structure design basis ................................................................................................................... 23
Chapter 4 Integrated load analysis evaluation .................................................................................................................. 24
4.1 General ............................................................................................................................................................... 24
4.1.1
General ....................................................................................................................................................... 24
4.2 Requirements for load analysis for RNA and tower evaluation............................................................................ 24
4.2.1
Comparison of the site conditions and the design values set in the type certification ................................. 24
4.2.2
Load analysis .............................................................................................................................................. 24
4.3 Requirements for load analysis for support structure evaluation ......................................................................... 25
4.3.1
General ....................................................................................................................................................... 25
4.3.2
Support structure load analysis................................................................................................................... 25
Chapter 5 Wind turbine (RNA) design evaluation ............................................................................................................. 26
5.1 General ............................................................................................................................................................... 26
5.1.1
General ....................................................................................................................................................... 26
5.2 Wind turbine (RNA) design evaluation ................................................................................................................ 26
5.2.1
Comparison of site loads with design loads at type certification ................................................................. 26
5.2.2
Strength evaluation of the components of the RNA based on the site load ................................................ 26
5.3 Nacelle cover strength evaluation ....................................................................................................................... 27
5.3.1
General ....................................................................................................................................................... 27
5.3.2
Wind load on the nacelle cover ................................................................................................................... 27
5.3.3
Load cases ................................................................................................................................................. 28
5.3.4
Strength evaluation ..................................................................................................................................... 28
5.4 Evaluation in the event of the electrical power network loss ............................................................................... 28
5.4.1
General ....................................................................................................................................................... 28
5.4.2
Power back-up ............................................................................................................................................ 28
5.5 Evaluation to secure a safe state on the wind turbine ......................................................................................... 30
5.5.1
General ....................................................................................................................................................... 30
5.5.2
Safe and automatic shutdown of wind turbines........................................................................................... 30
5.5.3
Protection against lightning strikes ............................................................................................................. 30
Chapter 6 Support structure design evaluation ................................................................................................................. 32
6.1 General ............................................................................................................................................................... 32
6.1.1
General ....................................................................................................................................................... 32
6.2 Support structure (Tower) .................................................................................................................................... 32
6.2.1
General ....................................................................................................................................................... 32
6.3 Support structure (Foundation) ........................................................................................................................... 32
6.3.1
General ....................................................................................................................................................... 32
6.3.2
Strength evaluation for support structure (foundation) ................................................................................ 32
6.3.3
Items to be considered in the design .......................................................................................................... 33
Annex A. Measurement data evaluation methods [normative] ......................................................................................... 34
A.1 Selection of measurement points ........................................................................................................................ 34
A.2 Wind speed measurement by measurement mast .............................................................................................. 34
A.3 Wind direction measurement by measurement mast .......................................................................................... 34
A.4 Measurement using remote sensing devices ...................................................................................................... 35
A.5 Measurements and evaluation report of measurement results............................................................................ 35
A.6 Measurement at a point affected by the wake of an existing wind turbine........................................................... 36
A.7 Reference documents ......................................................................................................................................... 36
Annex B. Airflow analysis and verification of its validity [normative] ................................................................................ 37
B.1 Airflow analysis ................................................................................................................................................... 37
B.1.1
Topographic data and ground surface roughness data ............................................................................... 37
B.1.2
Calculation region ....................................................................................................................................... 37
B.1.3
Calculation grid and resolution.................................................................................................................... 37
B.1.4
Boundary conditions ................................................................................................................................... 38
B.1.5
Direction division......................................................................................................................................... 38
B.2 Verification of airflow analysis validity ................................................................................................................. 38
B.2.1
Verification of validity of airflow analysis applied to the calculation of wind conditions during power
production ................................................................................................................................................... 38
B.2.2
Verification of validity of airflow analysis applied to the wind conditions during parked by storm ................ 39- 2 -B.3 Report on airflow analysis and its validity ............................................................................................................ 39
B.3.1
Report on the airflow analysis applied to the wind conditions during power production and its validity ...... 39
B.3.2
Report on the airflow analysis applied to the wind conditions during parked by storm and its validity ........ 40
Annex C. Evaluation method for wind conditions [informative / normative] ...................................................................... 41
C.1 General ............................................................................................................................................................... 41
C.2 Wind conditions during power production ........................................................................................................... 41
C.2.1 Wind speed appearance frequency distribution and average wind speed .................................................. 41
C.2.2 Calculation method for turbulence intensity ................................................................................................ 41
C.2.3 Calculation method for wind shear exponent .............................................................................................. 42
C.2.4 Calculation method for inflow angle ............................................................................................................ 43
C.2.5 Calculation method for atmospheric density ............................................................................................... 43
C.3 Wind conditions during parked by storm ............................................................................................................. 44
C.3.1 Calculation method for extreme wind speed (10 minutes average wind speed with a return period of 50
years).......................................................................................................................................................... 44
C.3.2 Calculation method for extreme wind speed (3 seconds average wind speed) .......................................... 45
C.3.3 Calculation method for 𝑈𝑈𝑈𝑈50 using wind condition measurement data [informative] ................................. 47
C.4 Reports on wind conditions ................................................................................................................................. 47
C.4.1 Report on wind conditions during power production ................................................................................... 47
C.4.2 Report on wind conditions during parked by storm ..................................................................................... 48
C.4.3 Other conditions.......................................................................................................................................... 48
C.5 Reference documents ......................................................................................................................................... 48
Annex D. Equivalent wind pressure coefficient for the nacelle cover [informative]........................................................... 49
D.1 General ............................................................................................................................................................... 49
D.2 Equivalent wind pressure coefficient [Wind direction: -15° to +15°] .................................................................... 50
D.3 Equivalent wind pressure coefficient [Wind direction: All wind directions] ........................................................... 51
D.4 Reference documents ......................................................................................................................................... 52
Annex E. Measurement testing for fluctuating pressure characteristics acting on a nacelle surface [informative] ........... 53
E.1 General ............................................................................................................................................................... 53
E.2 Selection of wind tunnel ...................................................................................................................................... 53
E.3 Model and test conditions ................................................................................................................................... 53
E.3.1
Model .......................................................................................................................................................... 53
E.3.2
Airflow similarity .......................................................................................................................................... 53
E.3.3
Wind speed and wind direction in test implementation ............................................................................... 54
E.3.4
Pressure measurement instrument ............................................................................................................. 54
E.3.5
Data processing and recording ................................................................................................................... 54
E.3.6
Maximum/minimum peak wind pressure coefficient.................................................................................... 54
E.4 Reference documents ......................................................................................................................................... 55
Annex F. Design methodologies for tower structures [normative].................................................................................... 56
F.1 General ............................................................................................................................................................... 56
F.2 Attenuation .......................................................................................................................................................... 56
F.3 Anchor bolt hole diameter ................................................................................................................................... 56
F.4 Design applying the fatigue equivalent design method in structural calculations for anchor bolts ...................... 56
F.5 Lever ratio of flange joint ..................................................................................................................................... 57
F.6 Design applying the fatigue equivalent design method in structural calculations for flange joints ....................... 57
F.7 Distance between flange bolt centers in circumferential direction ....................................................................... 58
F.8 Tower opening ..................................................................................................................................................... 58
F.9 Reference documents ......................................................................................................................................... 58
Annex G. Design methodologies for foundations [normative]........................................................................................... 59
G.1 General ............................................................................................................................................................... 59
G.2 Special earthwork such as ground improvement................................................................................................. 59
G.3 Handling of seismic response analysis for the ground ........................................................................................ 59
G.4 Handling related to time history response analysis ............................................................................................. 59
G.5 Pile design........................................................................................................................................................... 59
G.6 Reference documents ......................................................................................................................................... 60- 3 -Chapter 1

1.1

GeneralGeneral1.1.1
Application-1. These guidelines specify the requirements for onshore wind power plants that are subject to wind farm certification.
-2. The requirements specified in these guidelines apply to the case where the wind turbine is a propeller type horizontal shaft
with three blades and is supported by a monopole tower that is cylindrical (including conical) and made of steel.
-3. It should be noted that if there is a change in the requirements for the construction plan examination based on the Electricity
Business Act, those requirements shall take precedence over the provisions of these guidelines.
1.1.2

Wind power generation facilities with a new concept-1. For wind power plants that have a different type or facilities from those specified in these guidelines, the requirement
determination and evaluation may be implemented individually in accordance with the basic principles behind the provisions ofthese guidelines.
1.1.3

Design life and service life

-1. The design life and service life in these guidelines shall both be 20 years.
-2. If the design life or service life are to be different from those in -1 above, the requirement determination and evaluation shallbe implemented individually in accordance with the basic way of thinking behind the provisions of these guidelines.

1.2
1.2.1

Normative References
General-1. The following standards are the normative references for wind farm certification that are specified in the "Sector-specificguidelines for ‘accreditation criteria’ - Wind power generation systems: wind farms, projects -" (JAB PD366:2017) document
produced by the Japan Accreditation Board, excluding those for offshore and small wind turbines. Where an anno domini year is
written for these cited standards, the version of the year mentioned shall apply, and subsequent revised versions (including
Supplements) shall not apply. If there is no anno domini year written for a cited standard, the most recent version (including
Supplements) shall apply.
[J-01]JIS C 1400-1:2017 : Wind Energy Generation Systems - Part 1: Design requirements[J-02]IEC 61400-1:2019 : Wind energy generation systems - Part 1: Design requirements[J-03]

Ministerial Ordinance Prescribing Technical Standards for Wind Power Generation Facilities (Ministry of Economy,
Trade and Industry, Ordinance of the Ministry of International Trade and Industry No. 53, final revision: Ordinance ofthe Ministry of Economy, Trade and Industry No. 32 of March 31, 2017)[J-04]

20140328 Bureau of Commerce No. 1 "Interpretation of Technical Standards for Wind Power Generation Facilities"(Revision 20230310 Bureau No. 2)[J-05]

Guidelines for Design of Wind Turbine Support Structures and Foundation [2010 version] (Japan Society of Civil
Engineers)[J-06]

Germanischer Lloyd (GL) Guideline for the Certification of Wind Turbines 2010

-2. In order to meet the requirements of the standards listed in -1 above, the following standards referenced by these guidelines
shall form part of the provisions. Where an anno domini year is written for these cited standards, the version of the year mentioned
shall apply, and subsequent revised versions (including Supplements) shall not apply. If there is no anno domini year written for acited standard, the most recent version (including Supplements) shall apply.
[R-01][R-02]NKRE-SP-0003 Wind Farm Certification Procedures, Edition October 2021
Annotations to the Ministerial Ordinance Prescribing Technical Standards for Wind Power Generation Facilities and
its Interpretation (Ministry of Economy, Trade and Industry, revised on March 20, 2023)[R-03]

Recommendations for Design of Building Foundations (Architectural Institute of Japan, 2019)- 4 -[R-04]

Guidebook on Design and Fabrication of High Strength Bolted Connections (Architectural Institute of Japan, 2003)[R-05]

Structural Design Recommendation for Chimneys (Architectural Institute of Japan, 2007)[R-06]JIS C 1400-12-1:2010: Wind turbines - Part 12-1: Power performance measurements of electricity producing
wind turbines[R-07]JIS C 1400-24:2014: Wind turbines - Part 24: Lightning protection[R-08]IEC 61400-6:2020: Wind energy generation systems - Part 6: Tower and foundation design requirements[R-09]IEC 61400-13:2015: Wind turbines - Part 13: Measurement of mechanical loads[R-10]

ISO 273:1979: Fasteners - Clearance holes for bolts and screws[R-11]

ISO 4354:2009: Wind actions on structures[R-12]

EN 1993-1-9:2005: Design of steel structures - Part 1-9: Fatigue[R-13]

fib Model Code for Concrete Structures 2010 (CEB-FIP Model Code 2010)[R-14]

CEB-FIP Model Code 1990

[R-15]DNVGL-ST-0126 Support structures for wind turbines, Edition April 2016

[R-16]MEASNET Evaluation of Site-Specific Wind Conditions, Version 2, April 2016

[R-17]IEC 61400-12-1:2017: Wind energy generation system - Part 12-1: Power performance measurements ofelectricity producing wind turbines

1.3

Definitions and abbreviations

1.3.1

Definition of terms-1. The definitions of the key terms used in these guidelines are given in Table 1-1.

Term

Table 1-1 Definition of terms
Definition

Requester

A person who submits an application for examination pertaining to wind farm certification.

NK-PASSThe document submission and management system available on the ClassNK website.

Environmental conditions

Characteristics such as wind, altitude, temperature, humidity, and atmospheric pressure
which may affect the behavior of the wind turbine.
Factors affecting wind turbine operation, including the environmental conditions, the groundand geological conditions, and the power system conditions.
A value that is obtained by averaging measurement data sets containing enough datacollected over a sufficient period, and is capable of estimating the expected value of an item
to be measured. It is desirable that the period for calculating the average is an integer
multiple of one year unit, in order to smooth out unsteady effects such as seasonal
differences.
The statistical average of the instantaneous values of wind speed averaged over a given
period varying from seconds to years.
The wind speed averaged in accordance with the definition of the annual average.
The height from the ground of the center of the wind receiving surface of the wind turbine
rotor (the center of the plane projected perpendicular to the wind direction during one
rotation).
The minimum wind speed at the hub height at which the wind turbine begins to generate
power in the case of steady wind without turbulence.
The maximum wind speed at the hub height at which the wind turbine is designed togenerate power in the case of steady wind without turbulence.
The value of the output normally obtained when the components, equipment and facilities
specified by the manufacturer are operated under the specified conditions. In the case ofwind turbines, this is the maximum continuous output (of the wind turbine) designed to besupplied under normal operating conditions and external conditions.
The minimum wind speed at the hub height at which the wind turbine reaches the rated
output in the case of steady wind without turbulence.

External conditions
Annual average

Average wind speed
Annual average wind speed
Hub heightCut-in wind speed
Cut-out wind speed
Rated output

Rated wind speed

- 5 -

Term

Definition

Reference wind speed (𝑉𝑉𝑟𝑟𝑟𝑟𝑟𝑟 )The wind speed at hub height used to define the wind turbine class in JIS C 1400-1: 2017 [J01], which is set as the 10 minutes average wind speed with a return period of 50 years.
According to the Building Standards Act, this is the 10 minutes average wind speed with areturn period of 50 years at a height of 10 m that is specified by the Minister of Land,
Infrastructure, Transport and Tourism. It is specified within a range from 30 m/s to 46 m/s
according to the degree of wind damage and other wind characteristics in the area based on
the records of past typhoons, etc.
The average wind speed corresponding to a return period of 50 year.
The state in which a wind turbine is operating for power generation between the cut-in windspeed and the cut-out wind speed.
The state when the wind speed exceeds the cut-out wind speed and the wind turbine stops thepower generation and enters a standby state.
Surrounding terrain where the airflow is easily distorted due to the terrain having many
variations or the presence of obstacles.
The roughness and smoothness of the boundary such as surface roughness, trees andbuildings.
The extrapolated height at which the average wind speed becomes zero when the verticalwind speed profile is assumed to change logarithmically with height.
A classification of the ground surface in stages from a smooth state to a rough state.

Reference wind speed (𝑉𝑉0 )Extreme wind speed
During power production
During parked by storm
Complex terrain
Roughness
Roughness length
Ground surface roughnessclassification
Turbulence intensity
Turbulence standard deviation
Wind condition measurement
data
Effective data rate
Data sufficiency rate
Correlation coefficient
Coefficient of determination
Airflow analysis
Airflow analysis model

Ambient turbulence standard
deviation
Ambient turbulence intensity
Wind turbine wake effect
Effective turbulence intensity
Wind shear
Wind shear exponent
Flow inclination angle
Power back-up
Yaw control
Yaw misalignment

The standard deviation of the fluctuating wind speed divided by the average wind speed.
The standard deviation of the principal direction component of the turbulence wind speed at
hub height.
Time series data of the 10 minute average value for wind speed, wind speed standard
deviation, and wind direction for at least one continuous year.
The data sufficiency rate after filtering processing is conducted on the wind condition
measurement data to remove abnormal values, etc., or after data filling is conducted on thewind measurement data.
The value obtained by dividing "the number of 10 minute averages that can be used after
filtering" by "the total number of 10 minute averages corresponding to the measurement
period" during the relevant measurement period.
An indicator that measures the strength of the linear relationship between two data or
random variables.
The value which indicates the extent to which an independent variable contributes to adependent variable. It is a measure of the applicability of the regression equation obtained
from the sample value.
A numerical analysis that calculates the flow of air.
The equations applied to airflow analysis and their solutions. (A linear model is applied incases where flat terrain stretches over a vast area, such as in parts of Europe. However, anonlinear model is suitable in cases where the terrain has large slope gradients, such as inJapan.)The standard deviation of the main direction component of the wind speed at the windturbine position and hub height as predicted and calculated from the results of airflow
analysis using measurement data. (It is usually calculated per wind speed bin.)
The value obtained by dividing the ambient turbulence standard deviation by the wind speed.
When neighboring wind turbines experience disturbance due to the wind (wake) that has
passed the rotor plane of the wind turbine.
The value obtained by adding the turbulence intensity due to the wake effect from windturbines to the ambient turbulence intensity.
A mathematical representation that is assumed for the change in wind speed relative to theheight above ground level.
The index of the power law for wind shear.
The inclination angle of the inflow wind relative to the rotor plane at hub height.
A power supply system that supplies power to operate the wind turbine control system in theevent of a loss of electrical power network loss.
Control to make the wind turbine nacelle direction angle (angle of the rotor shaft) follow thechanges in the wind direction.
The error between the nacelle direction angle (angle of the rotor shaft) and the winddirection, generally shown as a 10 minute average value.

- 6 -

Term

Definition

Wind force coefficient

1.3.2

The aerodynamic force acting on a structure divided by the product of the velocity pressure
and the representative area. The average wind force coefficient means the time average.

Definition of abbreviations-1. The definitions of the main abbreviations used in these guidelines are given in Table 1-2.
Table 1-2 Definition of abbreviations
Abbreviations

Definition

RNA

Rotor Nacelle Assembly

DLC

Design Load Case

MCP

Measure-Correlate-Predict

1.3.3

Meaning and units of symbols-1. The meanings and units of the main symbols used in these guidelines are specified in Table 1-3.
Table 1-3 Definition of symbols
Meaning

Symbol
𝐶𝐶𝐶𝐶𝐶𝐶

Turbulent structure intensity parameter (See JIS C 1400-1:2017 [J-01] 11.2)

𝐼𝐼𝑟𝑟𝑟𝑟𝑟𝑟

90% quantile of the ambient turbulence intensity

𝑉𝑉𝑎𝑎𝑎𝑎𝑎𝑎

𝐷𝐷
𝐼𝐼𝑟𝑟𝑟𝑟𝑟𝑟

Rotor diameter

𝐼𝐼𝑒𝑒𝑒𝑒𝑒𝑒

Effective turbulence intensity

𝑉𝑉𝑖𝑖𝑖𝑖

Units

Expected value hub height turbulence intensity at a 10 minute average wind speed of 15 m/s [J-01]
Reference value of the turbulence intensity corresponding to the 70% quantile at 15 m/s [J-02]

𝑉𝑉ℎ𝑢𝑢𝑢𝑢Wind speed at hub height[𝑚𝑚/𝑠𝑠]Annual average wind speed[𝑚𝑚/𝑠𝑠]Cut-in wind speed[𝑚𝑚/𝑠𝑠]𝑉𝑉𝑜𝑜𝑜𝑜𝑜𝑜

Cut-out wind speed[𝑚𝑚/𝑠𝑠]𝑉𝑉𝑟𝑟
𝑉𝑉𝑟𝑟𝑟𝑟𝑟𝑟

Rated wind speed[𝑚𝑚/𝑠𝑠]Reference wind speed (JIS C 1400-1:2017 [J-01])[𝑚𝑚/𝑠𝑠]𝑉𝑉0
𝜎𝜎�1

Reference wind speed (Building Standards Act)[𝑚𝑚/𝑠𝑠]𝜎𝜎�Estimated wind speed standard deviation[𝑚𝑚/𝑠𝑠]𝜎𝜎�𝜎𝜎

[𝑚𝑚/𝑠𝑠]Hub height longitudinal wind velocity standard deviation at wind turbine position[𝑚𝑚/𝑠𝑠]𝜎𝜎�2Standard deviation of estimated wind speed standard deviation 𝜎𝜎�

Hub height lateral wind velocity standard deviation at wind turbine position[𝑚𝑚/𝑠𝑠]𝜎𝜎�3

Hub height upward wind velocity standard deviation at wind turbine position[𝑚𝑚/𝑠𝑠]Hub height 10 minutes average wind speed with a return period of 50 years at wind turbine position[𝑚𝑚/𝑠𝑠]Hub height 3 seconds average wind speed with a return period of 50 years at wind turbine position[𝑚𝑚/𝑠𝑠]𝐼𝐼ℎ1

Hub height turbulence intensity for 10 minutes average wind speed with a return period of 50 years
at wind turbine position.

𝑈𝑈ℎ𝑈𝑈𝑒𝑒50

- 7 -

1.4
1.4.1

Wind farm certification
General-1. Wind farm certification is a procedure whereby ClassNK issues a document to certify that one or more wind turbines (RNA)and their support structures (towers and foundations) meet the requirements for a particular site.
-2. In principle, the wind farm certification is for wind power plants in Japan that have an output of 500 kilowatts or more, where
one or more wind turbines (RNA) and their support structures (towers and foundations) are installed and are subject to theElectricity Business Act. Cases where the project is not in Japan shall be handled separately as judged appropriate by ClassNK.
-3. The purpose of wind farm certification is to assess whether the design of type-certified wind turbines (RNA) and support
structure (towers and foundations) are in conformity with the external conditions and the requirements under the Electricity
Business Act, specifically, to confirm compliance with Articles 4, 5 and 7 of the Technical Standards for Wind Power Generation
Facilities[J-03].
-4. The prerequisites for the issuance of wind farm certification are the conditions that the wind turbine (RNA) and tower musthave obtained type certification, and that the manufacturing of the wind turbine (RNA) and tower and their main parts andcomponents must have been carried out at a place specified in the type certification. The handling of deviations from these
conditions is specified in Chapter 5 for the wind turbines (RNA) and in Chapter 6 for the towers.
-5. Procedures related to wind farm certification which are not described in these guidelines shall follow the Wind Farm
Certification Procedures [R-01].
1.4.2

Evaluation module-1. In principle, wind farm certification shall consist of the following modules. The relationships between individual modules areshown in Figure 1-1.
(1) Site conditions assessment(2) Design basis evaluation(3) Integrated load analysis(4) Wind turbine (RNA) design evaluation(5) Support structure design evaluation

Figure 1-1 Module for wind farm certification
1.4.3

Site conditions assessment-1. The site conditions assessment evaluates whether the external conditions have been set appropriately based on the results offield measurements, field investigations, etc. The details of the assessment are given in Chapter 2.

- 8 -1.4.4

Design basis evaluation-1. The design basis evaluation evaluates whether the design basis has been properly documented and is sufficient for safe design
and power plant construction. The details of the evaluation are given in Chapter 3.
1.4.5
Integrated load analysis evaluation-1. The integrated load analysis evaluation evaluates whether the site-specific loads and load effects on the integrated windturbine, which includes the wind turbine (RNA), the support structure and supporting ground, have been calculated in conformity
with the design basis. The details of the evaluation are given in Chapter 4.
1.4.6
Wind turbine (RNA) design evaluation-1. The wind turbine (RNA) design evaluation evaluates whether the design of the wind turbine (RNA) is in conformity with thesite-specific conditions and design basis. The details of the evaluation are given in Chapter 5.
1.4.7
Support structure design evaluation-1. The support structure design evaluation evaluates whether the design of the support structure (tower and foundation) is inconformity with the site-specific conditions and design basis. The details of the evaluation are given in Chapter 6.
1.4.8
Wind farm certification module for onshore wind power plants-1. In the case of an onshore wind power plant, the certification may consist of the following modules [M1] to [M4], regardlessof the provisions of 1.4.2. The relationships between the modules in this case are shown in Figure 1-2. In addition, the contentsof the evaluations which constitute each module shall follow 1.4.3 to 1.4.7.
[M1] Site conditions assessment (Wind conditions)[M2] Wind turbine (RNA) design evaluation (including site conditions assessment, design basis evaluation and integrated
wind load analysis)[M3] Support structure design evaluation (Tower) (including site conditions assessment, design basis evaluation andintegrated load analysis)[M4] Support structure design evaluation (Foundation) (including site conditions assessment, design basis evaluation andintegrated load analysis)

Figure 1-2 Wind farm certification module [Limited to onshore wind power plants]- 9 -1.4.9Certification subcommittees-1. The certification subcommittees shown in Table 1-4 shall be held according to the items to be examined.
-2. In principle, the format when the Large Wind Turbine Certification Subcommittee and the Support Structure Certification
Subcommittee Tower Section Meeting are held shall be that the ClassNK secretariat explains the evaluation results to thesubcommittee/section meeting members.
-3. In principle, the format when the Support Structure Certification Subcommittee Foundation and Ground Section Meeting isheld shall be that the requester directly explains the contents related to the items to be examined to the members of the section
meeting. The only language accepted for the materials used for explanation in the relevant section meeting shall be Japanese.
Table 1-4
Certification subcommittee

Certification subcommittee/section meeting
Items to be examined

Large Wind Turbine
Certification Subcommittee[M1] Site conditions assessment (Wind conditions)[M2] Wind turbine (RNA) design evaluation (including site conditions assessment, design basis
evaluation and integrated wind load analysis)

Support Structure
Certification Subcommittee
Tower Section Meeting[M3] The Support structure design evaluation (Tower) [including site conditions assessment,

Support Structure
Certification Subcommittee
Foundation and Ground
Section Meeting[M4] The Support structure design evaluation (Foundation) [including site conditions

1.5

design basis evaluation and integrated load analysis] items that deviate from the Guidelines for
Design of Wind Turbine Support Structures and Foundation[J-05]*Among the items to be examined by the Tower Section Meeting as deviations from the
Guidelines for Design of Wind Turbine Support Structures and Foundation[J-05], the items forwhich the corresponding design methods have been established are summarized in Annex F. If
there is deviation in an item not listed in Annex F, or if a method that is different to the methods
listed in Annex F is to be applied, the requirements shall be determined separately by the Tower
Section Meeting.
assessment, design basis evaluation and integrated load analysis] items that deviate from the
Guidelines for Design of Wind Turbine Support Structures and Foundation[J-05]*Among the items to be reviewed by the Foundation and Ground Section Meeting as deviations
from the Guidelines for Design of Wind Turbine Support Structures and Foundation[J-05] theitems for which the corresponding design methods have been established are summarized in
Annex G. If there is deviation in an item not listed in Annex G, or if a method that is different to
the methods listed in Annex G is to be applied, the requirements shall be determined separatelyby the Foundation and Ground Section Meeting.

Documents to be submitted

1.5.1

General-1. In order to be examined for wind farm certification, the requester shall submit to ClassNK the documents listed in 1.5.2 to
1.5.6 in accordance with the items to be evaluated. In addition to these documents, the requester shall provide sufficient andaccurate information (documents, records, etc.) deemed necessary by ClassNK.
-2. The materials to be submitted to ClassNK shall satisfy the following conditions.
- The responsibility for the preparation or issuing of materials shall be clarified.
- The item has a document number.
- The date of issue is clear.
- The history (revision history) is written, and in addition to the revision date and the document number after the revision, theparts that have been revised and the contents of the revision are clear.
- In principle, the language of materials to be submitted shall be Japanese. However, English may be used if ClassNK deems it
appropriate. Other languages are not permitted.
- In principle, the SI unit system shall be used as the units in the documents to be submitted.
-3. In principle, NK-PASS shall be used to submit the documents requested by ClassNK.

- 10 -

1.5.2

Materials related to wind turbine type certification-1. In the examination for the wind farm certification, the design conditions in the wind turbine type certification become thebasis, so in order to check the details, the documents listed below that have been issued by the certification organization
concerning the type certification must be submitted to ClassNK.
(1)

Type certificate and final evaluation report(2)

Design basis evaluation conformity statement and its evaluation report(3)

Design evaluation conformity statement and its evaluation report(4)Type testing conformity statement and its evaluation report(5)

Manufacturing evaluation conformity statement and its evaluation report(6)

Component certificate and its evaluation report-2. Class NK will designate submittal documents those the drawings and calculation materials which shall be submitted from thewind turbine manufacturer to the type certification body and referenced in the evaluation reports in (1) to (6), according to eachwind turbine type.
1.5.3

Materials related to the site conditions assessment (wind conditions)-1. The following documents and data shall be submitted to ClassNK as examination materials related to the site conditions
assessment. The documents may be in a format that combines the following items.
(1)

Report regarding basic information on the planned site
*The following information shall be included.
-

Site location-

Type of wind turbine to be used and number of wind turbines-

Wind turbine layout-

Wind turbine coordinates (World Geodetic System: WGS 84 and UTM)-

Plan for wind turbine operation at the site (Cut-in and cut-out wind speeds, rated output, rated wind speed, power
curve, etc.)(2)

Report on field measurements (to include the items listed in Annex A.5)

(3)

Report on wind conditions during power production (to include the items listed in Annexes B.3.1 and C.4.1)(4)

Report on wind conditions during parked by storm (to include the items listed in Annexes B.3.2 and C.4.2)(5)

Report on storm duration (Only when the power back-up specified in 5.4.2 is installed)-2. The following data shall be submitted to ClassNK when deemed necessary by ClassNK for the examination related to the site
conditions assessment (wind conditions).
(1)

Field measurement data (Time series data of 10 minute average value corresponding to the measurement period applied
to airflow analysis)

(2)

1.5.4

Results data from CFD analysis performed as airflow analysis

Materials related to wind turbine (RNA) design evaluation-1. The following documents shall be submitted to ClassNK as examination materials related to the wind turbine (RNA) design
evaluation. The documents may be in a format that combines the following items.
(1)

Report related to design basis (Contents described in 3.2.2)(2)

The values of the design load set at the time of the type certification (certification design load), and the site-specific load

(3)

Report on strength calculations for the relevant RNA components in a case when the site load exceeds the certification

obtained from the integrated load analysis (site load), and a report on their comparison
design load
(4)

Report on the change in the vibration mode/natural vibration frequency from the type certification conditions(5)

Reports on any components or systems that comprise the RNA that are not fully covered in the type certification, or thathave been newly modified or enhanced for the site

- 11 -

(6)(7)

If a power back-up is provided, a report that confirms that the requirements specified in 5.4 are satisfied
Of the items among the wind turbine structural drawings and strength calculation documents (including details related toconstruction) to be attached to the construction plan notification based on the Electricity Business Act, the items which
are not included in (1) to (6) above.
(8) Materials summarizing the measures for safely stopping wind turbines specified in 5.5.2 and the results of the strength
evaluation associated with those measures (It is acceptable for this to be the "Explanation of the measures for the safe andautomatic stopping of the wind turbine when the rotational speed has increased significantly, and/or when the functioningof the control equipment for the wind turbine has significantly deteriorated," which is an explanation to be attached to theconstruction plan notification based on the Electricity Business Act)
(9) Materials summarizing the measures taken to protect against lightning strikes specified in 5.5.3 (It is acceptable for thisto be the "Explanation of the protection of the wind turbine against lightning strikes," which is to be attached to theconstruction plan notification based on the Electricity Business Act)
(10) Explanation of the power generation method, which is to be attached to the construction plan notification based on theElectricity Business Act
1.5.5
Materials related to the support structure (Tower) design evaluation-1. The following documents shall be submitted to ClassNK as examination materials related to the support structure (tower)
design evaluation. The documents may be in a format that combines the following items.
(1) Report related to design basis (which may be common with the wind turbine design evaluation, including the contents
described in 3.2.3-1)(2) If a tower described in the type certificate is to be used, the values of the design load set at the time of the typecertification (certification design load), and the site-specific load obtained from the integrated load analysis (site load),
and a report on their comparison(3) If the site load exceeds the certified design load in (2) above, or if a tower not mentioned in the type certificate is to be
used, a report on the strength calculation of the structural design of the tower with the site load applied(4) Report showing that the tower to be used satisfies the requirements of the Guidelines for Design of Wind Turbine Support
Structures and Foundation[J-05](5) Report including the results of consideration of the items specified in 6.2 (If there are items that deviate from the
Guidelines for Design of Wind Turbine Support Structures and Foundation[J-05], it must include items for the contents ofAnnex F.)(6) Report on the change in the vibration mode/natural vibration frequency from the type certification conditions(7) Of the items among the support structure structural drawings and strength calculation documents (including details
related to construction) to be attached to the construction plan notification based on the Electricity Business Act, theitems which are not included in (1) to (6) above.
(8) Materials summarizing the details listed below for the tower manufacturing evaluation.
1) If a tower described in the type certification will be selected (including the selection of the manufacturing plant
described in the type certification), then the expected timing of the decision on the manufacturing plant.
2) In cases other than 1) above, the policy related to the manufacturing evaluation, and the estimated timing of thedecision on that policy.
1.5.6
Materials related to the support structure (Foundation) design evaluation-1. The following documents shall be submitted to ClassNK as examination materials related to the Support structure(Foundation) design evaluation.
(1) Support structure structural drawings and strength calculation documents (including details related to construction) to be
attached to the construction plan notification based on the Electricity Business Act(2) Explanatory materials for the following items related to the support structure design (in case the Support Structure
Certification Subcommittee Foundation and Ground Section Meeting specified in 1.4.9-3. is to be hold)
Overview of the power plant plan
Items that deviate from the Guidelines for Design of Wind Turbine Support Structures and Foundation[J-05] related
to foundation design, and details of the handling policy and study items related to them (including the details
related to the applicable items in Annex G.)
Overview of structural design of support structure- 12 -

1.6

Correspondence to the Technical Standards for Wind Power Generation Facilities [Reference]

1.6.1

General-1. The correspondence between the Technical Standards for Wind Power Generation Facilities and the requirements of theseguidelines is as shown in Table 1-5.
Table 1-5

Correspondence between the Technical Standards for Wind Power Generation Facilities and therequirements of these guidelines
Technical Standards for Wind Power Generation Facilities(Excerpts from the original text, and temporary translation)(Scope)Article 1. This Ministerial Ordinance shall apply to electric facilities installed togenerate electricity by means of wind power.
2. The term "electric facilities" as used in the preceding paragraph shall refer to theElectric Facilities for General Use and Electric Facilities for Business Use.
(Definitions)
Article 2. The terms used in this Ministerial Ordinance shall have the same
meanings as the terms used in the Rules for the Electricity Business Act(Ordinance of the Ministry of International Trade and Industry No. 77, 1995).
(Hazard prevention measures for persons other than operators)
Article 3. When installing a wind power plant, the operator shall indicate that thewind turbine is dangerous at a place that is easy to see for persons other than theoperator, and shall take appropriate measures to prevent those persons from easily
approaching it.
2. If a wind power generation facility is the Electric Facility for General Use, theprovisions of the preceding paragraph shall be applied by replacing the phrase"wind power plant" in the paragraph with "wind power generation facilities" andthe phrase "those persons from easily approaching it" with "those persons fromeasily approaching the wind turbine".
(Wind turbine)
Article 4. Wind turbines shall be installed in accordance with the following items.
(i) To be structurally safe relative to the maximum speed when the load is cut off.
(ii) To be structurally safe against wind pressure.
(iii) To be equipped so that there are no vibrations that may damage the windturbine during operation.
(iv) To be equipped so that the wind turbine will not start up against the operator's
intention, even at the maximum wind speed normally assumed.
(v) To be equipped so as not to come into contact with other structures, plants, etc.,
during operation.

- 13 -

Related items in these guidelines---< Item (i) >[Interpretation] Article 3 Paragraphs 1
to 3- 1.4.1-3., 1.5.2- 5.5.2< Item (ii) >[Interpretation] Article 4 Paragraphs 1
to 2- 2.1, 2.2, 2.3- Annex A- Annex B- Annex C
[Interpretation] Calculation of windpressure in Article 4 Paragraph 1, andParagraphs 3 and 4- 3.2.2- 4.2- Chapter 5
[Interpretation] Article 4 Paragraph 5- Not covered< Item (iii) >[Interpretation] Article 5- 5.5.2-2.
< Item (iv) >Technical Standards for Wind Power Generation Facilities(Excerpts from the original text, and temporary translation)

Related items in these guidelines
[Interpretation] Article 6- 5.5.2-2.
< Item (v) >- 5.5.1(Ensuring the safety of wind turbines)
Article 5. Measures shall be taken to ensure that wind turbines stop safely and< Paragraph 1. >[Interpretation] Article 7 Paragraphs 1

automatically in the following cases.

to 3(i) When the rotational speed has increased significantly- 5.5.2-1.

(ii) When the functioning of the control equipment for the wind turbine has< Paragraph 2. >significantly deteriorated

[Interpretation] Article 7 Paragraphs 4

2. If a wind power generation facility is the Electric Facility for General Use, theprovisions of the preceding paragraph shall be applied by replacing the phrase

to 5"Measures shall be taken to ensure that wind turbines stop safely and- Not covered

automatically" in the paragraph with "Measures shall be taken to ensure safe

< Paragraph 3. >[Interpretation] Article 7 Paragraph 6

conditions".
3. For wind power generation facilities on which the highest part is more than 20- 2.5

meters above the ground surface, measures shall be taken to protect the wind

- 5.5.3

turbine from lightning strikes. However, this shall not apply in a case where thesurrounding conditions mean that there is no risk of lightning strikes damaging thewind turbine.
(Prevention of dangers of oil pressure systems and compressed air devices)-

Article 6. The oil pressure systems and compressed air devices used as wind power
generation equipment shall be installed in accordance with the following items.
(i) The materials and structures of the pressure oil tank and air tank shall be
sufficient to withstand the maximum allowable working pressure and be safe.
(ii) The pressure oil tank and air tank shall have corrosion resistance.
(iii) There shall be a function to reduce the pressure before it reaches the maximum
allowable working pressure in the case that the pressure rises.
(iv) There shall be a function to automatically recover the pressure in the case thatthe oil pressure of a pressure oil tank or the air pressure of an air tank decreases.
(v) There shall be a function to detect abnormal pressure at an early stage.
(Structure to support the wind turbine)< Paragraph 1. >Article 7. The structure supporting the wind turbine shall be structurally safe

[Interpretation] Article 9 Paragraph 1

against its own weight, loading capacity, snow and wind pressure, and against- 2.1, 2.2, 2.3, 2.4, 2.6

earthquakes and other vibrations and impacts.

- 3.2.3

2. If a wind power generation facility is the Electric Facilities for General Use,appropriate measures shall be taken to prevent a person other than the operator
from easily climbing the structure supporting the wind turbine.

- 4.3
[Interpretation] Article 9 Paragraph 2- Chapter 6
[Interpretation] Article 9 Paragraph 3- Chapter 6
[Interpretation] Article 10- 3.2.3
[Interpretation] Article 11- 3.2.3
[Interpretation] Article 12- 14 -

Technical Standards for Wind Power Generation Facilities(Excerpts from the original text, and temporary translation)

Related items in these guidelines- 2.4, 2.6- 3.2.3- 4.3- Chapter 6
[Interpretation] Article 13- Chapter 6
[Interpretation] Article 14- Chapter 6
[Interpretation] Article 15- Chapter 6
[Interpretation] Article 16 Paragraph 1- 1.2.2
[Interpretation] Article 16 Paragraph 2- Not covered
[Interpretation] Article 17 Paragraph 1- Chapter 6
[Interpretation] Article 16 Paragraph 2- Not covered< Paragraph 2. >-(Prevention of pollution, etc.)
Article 8. The provisions of Article 19, paragraphs (11) and (13) of the Ministerial
Ordinance Prescribing Technical Standards for Electric Facilities (Ordinance of the
Ministry of International Trade and Industry No. 52, 1997) apply mutatis mutandis
to wind power generation facilities installed in wind power plants.
2. If a wind power generation facility is the Electric Facility for General Use, theprovisions of the preceding paragraph shall be applied by replacing the phrase"Article 19, paragraphs (11) and (13)" in the paragraph with "Article 19, paragraph(13)" and the phrase "wind power generation facilities installed in wind power
plants" with "wind power generation facilities".

- 15 --

Not covered

Chapter 2

2.1

General

2.1.1

GeneralSite conditions assessment-1. Site-specific external conditions and parameters associated with the design must be considered to ensure an appropriate levelof safety and reliability.
-2. The external conditions must be specified in such a way that they are the most severe for the structure, with consideration ofan appropriate probability level.
-3.

2.2
2.2.1

The wind conditions shall be summarized in accordance with Annex C.4.

Wind conditions during power production
Wind condition measurement-1. The evaluation of the wind conditions during power production must be carried out using data acquired by using windcondition measurement masts installed at one or more points which are representative of the planned wind farm. The measurement
period shall be a sufficient period to obtain reliable data and shall be at least one year to include seasonal effects.
-2. The measurement points shall be selected to represent the site-specific conditions (Topography, elevation, surface roughness,annual average wind speed, turbulence intensity, etc.) of the planned wind farm and the reasons shall be clearly stated. It is
desirable to use airflow analysis in the selection of these representative points.
-3. As shown in Table 2.1, the observed height shall be not less than 2/3 of the planned hub height, regardless of the topographyclass. Also, in order to appropriately evaluate the wind shear, the principle shall be to perform observation at three altitudes ormore. In addition, the distance between the measurement point and the wind turbine construction point must be within the
representative radius corresponding to the topographic complexity as shown in Table 2.1.
-4. Anemometers for the wind speed and wind direction shall each be installed at multiple altitudes in a manner that minimizes
the effects from the measurement mast and boom. Annex A may be followed for the installation method for wind condition
measurement masts and measurement equipment.
-5. When it is difficult to take measurements at a position over 2/3 of the planned hub height when only using a wind condition
measurement mast, the measurements may be taken in combination with remote sensing equipment such as a vertical lidar. Evenin this case, the wind condition measurement mast must be made as tall as possible. In addition, the wind condition measurement
mast and remote sensing equipment must carry out simultaneous measurement, and these measurement data must satisfy therequirement concerning the correlation shown in 2.2.2.
-6. When measurement must be carried out in the vicinity of an existing wind turbine that is in operation, a point which is notaffected by the wake of the existing wind turbine must be selected. In addition, Annex A.6 may be followed if observations are to
be made at a point where the wake effect of an existing wind turbine cannot be excluded.
-7. The results of the wind condition measurement must be summarized in accordance with Annex A.5.
Table 2-1 Observed height and representative radius
Topography class*Measured height

Representative radius of the measurement mast

Simple / Flat terrain

At least 2/3 of hub height

10 km or lessComplex terrain

At least 2/3 of hub height

2 km or less*: The topography class is determined based on the evaluation of the topographic complexity shown in 2.2.3.
2.2.2

Measurement data evaluation-1. The evaluation of the external conditions at the site must be carried out using wind condition measurement data that has beenacquired in a form which satisfies the requirements in 2.2.1.
-2. The wind condition measurement data to be used as the input data in the airflow analysis shown in 2.2.4 must be from one
year or longer and the effective data rate must be 95% or higher. (In principle, the measurement data from the highest position on
the measurement mast is to be used.)- 16 -

-3. If there is a period in which the wind condition measurement data is missing, or a period that contains abnormal values, suchas due to the failure of measurement equipment, the wind condition measurement data must be complemented by an appropriate
method. The effective data rate after the complementation processing should be 95% or higher.
-4. In principle, the effective data rate of the anemometers for the wind speed and wind direction that are used to complement thedata in -3. above shall be 90% or more. Also, if the MCP method is used to complement the data by using other measurement datameasured within the site, or data from a nearby meteorological observatory, then in principle, the correlation coefficient shall be
0.8 or higher. In addition, for confirmation of the validity of the complementation method, the results of the comparison of thevalues applied with the measured values from a period without missing data shall be shown.
-5. Regarding wind condition measurement data, comparison with normal year values must be carried out using reference datathat have a correlation coefficient of 0.8 or higher with the wind condition measurement data, such as reanalysis data by ameteorological model and long-term measurement data from a meteorological observatory close to the site, and appropriate
corrections must be made.
-6. The cause must be investigated if the wind condition measurement data contains a peculiar tendency, such as a case in which
the wind direction of adjoining altitudes greatly differs, or a case in which the wind shear exponent of a part of the wind direction
greatly differs from the others.
-7. It must be confirmed that measurement data from remote sensing equipment is appropriate as measurement data byconfirming that there is a correlation with the measurement data from a wind condition measurement mast on which simultaneous
measurement was carried out in accordance with Table 2-2, according to the following conditions. In any case, the principle is to
use the measurement data from the highest position on the wind condition measurement mast.
(1)

When the measurement data from a measurement mast and from remote sensing equipment is combined and treated as
hub-height measurement data for the input data for airflow analysis(2)

When measurement data from a measurement mast is used as the input data for airflow analysis, and the measurement
data from remote sensing equipment is only used to verify the validity of that airflow analysis.

-8. The effective data rate of measurement data from remote sensing equipment shall be in accordance with -2. above. However,if the mast measurement data is used as input data for airflow analysis and the measurement data from the remote sensing
equipment is only used to verify the validity of the airflow analysis, then it is not necessary for the effective data rate to be inaccordance with the provisions of -2. above, provided that it is quantitatively shown that the effects of seasonality are sufficiently
obtained.
-9.

For measurement data from remote sensing equipment, it shall be kept in mind that appropriate correction will be required

according to the complexity of the topography and the characteristics of the observation methods of the equipment used.
Table 2-2 Correlation of measurement data from a measurement mast and remote sensing equipment
Condition(1)

Requirements for wind speed• Coefficient of determination R2: > 0.98
• Slope of the regression line: 0.98 to 1.02
• Coefficient of determination R2: > 0.97
• Slope of the regression line: 0.97 to 1.03

(2)

2.2.3
-1.

*When these requirements are not satisfied, the reason
must be quantitatively shown using the results ofairflow analysis, etc.

Requirements for wind direction• Coefficient of determination R2: > 0.97
• Slope of the regression line: 0.97 to 1.03
• Intercept of the regression line: < 5°
• Coefficient of determination R2: > 0.95
• Slope of the regression line: 0.95 to 1.05
• Intercept of the regression line: < 10°*When these requirements are not satisfied, the reason
must be quantitatively shown using the results ofairflow analysis, etc.

Evaluation of topographic complexity
In order to select a model for airflow analysis and to evaluate the number of wind direction sectors, the turbulence structure

correction parameters (hereinafter, 𝐶𝐶𝐶𝐶𝐶𝐶 ) must be calculated for the measurement position (measurement mast and remote sensing

equipment) and the wind turbine position in order to judge the topographic complexity at each position. The specific method of
judgment shall follow one of the following.
(1)

JIS C 1400-1:2017[J-01], paragraph 11.2 (IEC 61400-1 Ed.3.1, 11.2)- 17 -

(2)IEC 61400-1:2019 [J-02], 11.2

-2. If there is even one measurement mast or wind turbine in the planned site with 𝐶𝐶𝐶𝐶𝐶𝐶 ≥ 1.05, then the site shall be treated ascorresponding to complex terrain.

2.2.4

Airflow analysis-1. In order to predict the wind condition at the wind turbine position, the airflow analysis must be performed appropriately. The
model applied to the airflow analysis and the number of wind direction sectors to be considered shall be as shown in Table 2.3.
Table 2-3 Airflow analysis model and requirements for the number of wind direction sectors
Topographic complexity

Airflow analysis model

Number of wind direction sectors

Simple / Flat terrain

Linear model/Nonlinear model

12 or more

Complex terrain

Non-linear model

16 or more

-2. For the airflow analysis, the appropriate terrain model must be selected according to the terrain of the planned site and thesituation in the surrounding area, and also a sufficient analysis area must be secured. The details of the airflow analysis shall be inaccordance with Annex B.1.
-3. The validity of the airflow analysis must be fully confirmed. The validity of the airflow analysis must be verified by using the
airflow analysis to calculate the wind conditions at the position of the wind condition measurement mast and then comparing theresults with the measurement data regarding the average wind speed, turbulence intensity, and wind shear for each direction. The
details of this confirmation of the validity of the airflow analysis shall follow Annex B.2.
2.2.5

Calculation of the wind speed appearance frequency distribution-1. The site wind condition measurement data and airflow analysis results shall be used to calculate the appearance frequency bydirection and Weibull parameter by direction at the hub height at the wind turbine position.
-2. Annex C.2.1 may be followed for the calculation of the Weibull parameter.
2.2.6

Calculation of turbulence intensity-1. For the turbulence intensity by direction at the hub height at the wind turbine position, the site wind condition measurement
data and airflow analysis results shall be used to calculate each of the turbulence intensities corresponding to the normal
turbulence model (NTM) and the extreme turbulence model (ETM) prescribed in JIS C 1400-1:2017 [J-01]. Also, with regards tothe wind turbine operation, the effect must be appropriately considered if sector management will be set.
-2. In order to calculate 𝐼𝐼𝑟𝑟𝑟𝑟𝑟𝑟 , which is the turbulence intensity corresponding to the normal turbulence model (NTM), it isnecessary to calculate the ambient turbulence standard deviation 𝜎𝜎� in 𝑉𝑉ℎ𝑢𝑢𝑢𝑢 between 𝑉𝑉𝑖𝑖𝑖𝑖 and 𝑉𝑉𝑜𝑜𝑜𝑜𝑜𝑜 , and the standard deviation

𝜎𝜎�𝜎𝜎 of 𝜎𝜎�.

-3. For the turbulence intensity corresponding to the extreme turbulence model (ETM), it is possible to use the turbulence
intensity using the maximum value of the ambient turbulence standard deviation 𝜎𝜎� in 𝑉𝑉ℎ𝑢𝑢𝑢𝑢 between 𝑉𝑉𝑖𝑖𝑖𝑖 and 𝑉𝑉𝑜𝑜𝑜𝑜𝑜𝑜 .

-4. Note that for the standard deviation of turbulence, it is necessary to calculate not only for the principal direction component
𝜎𝜎�1 , but also for the lateral direction component 𝜎𝜎�2 and vertical direction component 𝜎𝜎�3 of the principal direction (See 4.2.2-3).
-5. Annex C.2.2 may be followed for the specific method for calculating the turbulence intensity.

2.2.7

Evaluation of wind turbine wake effect from adjacent wind turbines-1. The intensity of the surrounding turbulence at the hub height at the wind turbine position that was found in 2.2.6 shall be
used to appropriately evaluate the effect of the wake flow from adjacent wind turbines during power production. Also, withregards to the wind turbine operation, the effect must be appropriately considered if sector management will be set.
-2. Turbulence characteristics considering single or multiple wake flows from the wind turbines located upwind shall beconsidered for all the ambient wind speeds and directions related to power generation, including consideration of the effect of the
distance between wind turbines. Also, when evaluating the wake flow effect, it is necessary to consider all of the wind turbines
located within a distance of 10 D from the wind turbine being evaluated. In this case, D is the rotor diameter of the adjacent wind

- 18 -

turbines.
-3. For the consideration of the effects of ambient turbulence and discrete turbulent wakes, it is possible to use the effective
turbulence intensity (hereinafter, 𝐼𝐼𝑒𝑒𝑒𝑒𝑒𝑒 ). This 𝐼𝐼𝑒𝑒𝑒𝑒𝑒𝑒 shall be calculated using the model given in either of the following. Also, forthe extreme turbulence intensity including the wake effects, it is acceptable to use the maximum turbulence at the center of thewake in the most severe direction.
(1)

JIS C 1400-1:2017[J-01], Annex D (IEC 61400-1 Ed.3.1, Annex D)(2) IEC 61400-1:2019 [J-02], Annex E-4. In the case of a large-scale wind farm, for 𝐼𝐼𝑒𝑒𝑒𝑒𝑒𝑒 , the case when the Frandsen model is applied based on JIS C 1400-1:2017[J-01]
Annex D shall be compared with the case when the provisions concerning the large-scale wind farm effect are used, and thevalidity of these shall be verified to judge which method to use for the calculation.

2.2.8

Calculation of the wind shear exponent-1. The site wind condition measurement data and airflow analysis results shall be used to calculate the wind shear exponent bydirection vertically of the wind receiving surface of the rotor at the wind turbine position.
-2. When the weighted average based on energy density is calculated for the wind shear exponent by direction that was found in-1. above, if a value less than 0.2 is obtained, then the value shall be assumed to be 0.2.
-3. Annex C.2.3 may be followed for the specific method for calculating the wind shear exponent.
2.2.9

Calculation of flow inclination angle-1. The site wind condition measurement data and airflow analysis results shall be used to calculate the inflow angle by direction
at the hub height at the wind turbine position.
-2. When the representative value as all wind direction of inflow angle by direction that was found in -1. above, the weighted
average based on energy density may be calculated.
-3. Annex C.2.4 may be followed for the specific method for calculating the flow inclination angle.
2.2.10Calculation of atmospheric density-1. The atmospheric density at the site must be calculated using field measurement data.
-2. Annex C.2.5 may be followed for the specific method for calculating the atmospheric density.

2.3

Wind conditions during parked by storm

2.3.1
Calculation of extreme wind speed and turbulence intensity-1. It is necessary to calculate the 10 minutes average wind speed with a return period of 50 years at wind turbine position andhub height 𝑈𝑈ℎ , and the turbulence intensity 𝐼𝐼ℎ1 and 3-second average wind speed 𝑈𝑈𝑒𝑒50 for that 𝑈𝑈ℎ . The methods used to
calculate these must be in accordance with Annexes C.3.1 and C.3.2, which comply with the Guidelines for Design of Wind

Turbine Support Structures and Foundation[J-05].
-2. The validity of the airflow analysis used for the calculation in -1. above must be sufficiently confirmed. The validity of the

airflow analysis must be verified by using the airflow analysis to calculate the wind conditions at the position of the windcondition measurement mast and then comparing the results with the measurement data regarding the average wind speed,
turbulence intensity, and wind shear for each direction. The confirmation of the validity of the airflow analysis shall be conductedin accordance with Annex B.2.
-3. If a typhoon simulation is used in the calculation in -1. above, the validity must be sufficiently confirmed by comparing thesimulation results (upper air winds due to the hypothetical typhoon) with the measured values (upper air winds calculated fromthe atmospheric pressure in the typhoon database). If the result of the comparison of the simulation results and the measured
values is that the simulation results are an underestimation, additional consideration must be given to the effects of uncertainty
related to the number of years of analysis and the number of years of atmospheric pressure measurement. In addition, the validityof the setting of the wind direction to be verified must be sufficiently confirmed.
-4. For 𝑈𝑈𝑒𝑒50 , the value may be determined by calculating 𝐼𝐼ℎ1 in accordance with Annex C.3.3 and based on appropriate- 19 -

measurement data meeting the criteria given in 2.2.2.
-5. For the 10 minutes average wind speed with a return period of 1 year 𝑈𝑈1 , in accordance with JIS C 1400-1:2017[J-01], thevalue used shall be 0.8 times the 10 minutes average wind speed with a return period of 50 years 𝑈𝑈ℎ . In addition, instead of this, acalculated value based on long-term measurement data, etc., may also be used. However, in that case, the validity of themeasurement data itself and the validity of the analysis method, etc., must be sufficiently shown.

-6. For the wind shear exponent for extreme wind speeds with a return period of 50 years and 1 year, the highest value of thefollowing items shall be adopted.
(1)(2)

The wind shear exponent for the surface roughness category specified in Table C.1 of Annex C
The wind shear exponent corresponding to the 10 minutes average wind speed with a return period of 50 years as(3)

specified in JIS C 1400-1:2017[J-01]
The wind shear exponent corresponding to the 10 minutes average wind speed with a return period of 50 years as
specified in Annex C.3.2.3

2.3.2

Calculation of atmospheric density-1. The atmospheric density corresponding to the extreme wind speed at the site shall be 1.22 kg/m3 or higher.

2.4

Geotechnical and earthquake conditions

2.4.1

General-1. Geotechnical and earthquake conditions shall be set in compliance with the requirements of the following Ministerial
Ordinance and Guidelines.
(1)

Ministerial Ordinance Prescribing Technical Standards for Wind Power Generation Facilities[J-03](2)

Interpretation of Technical Standards for Wind Power Generation Facilities[J-04](3) Guidelines for Design of Wind Turbine Support Structures and Foundation[J-05]-2. The following points shall be taken into consideration when setting the conditions in accordance with -1. above.
(1)

An investigation must be conducted regarding the situation of damage caused by past earthquakes and any accompanying
liquefaction or tsunami, and the results must be used as a reference.

(2)

When setting the engineering base surface, as the conditions for applying one-dimensional wave theory, it must be
confirmed that the shear wave velocity is 400 m/s or higher, the layer thickness is 5 m or higher, and the inclination is 5
degrees or less. If there is deviation from the above conditions, the effect must be examined, and the applicability of onedimensional wave theory must be confirmed.

(3)

If the spread foundations are on sloping ground, the effect of the decreased ultimate bearing capacity must be considered.

(4)

If the planned construction site is weak ground, it must be taken into consideration that negative frictional forces may
become significant.

(5)

If the planned construction site falls within the target area specified in the MLIT Housing Bureau Building Guidance(6)

When borehole lateral load testing is carried out for the estimation of the modulus of deformation, the results must be
appropriately summarized and shown.

(7)

When Ota and Goto's equation is used to estimate the shear wave velocity, the validity of the estimation must be verified(8)

based on the results of ground investigations, and the effect of the dispersion of the estimated values must be evaluated.
When making a liquefaction judgment, it should be noted that the simplified method can only be applied to a depth of up

Division Notice No. 1111 of June 24, 2016, the existence of effects from long-period ground motion must be examined.

to 20 m. When making a liquefaction judgment when the liquefied layer is continuous beyond a depth of 20 m, the cyclic
shear stress must be calculated using ground response analysis.
(9)

When the planned construction site is near the edge of water line and there is a risk of liquefaction, the following points
must be checked and the existence of effects from lateral flow must be checked. In addition, if there is a possibility oflateral flow occurring, the amount of ground flow (flow power, residual deformation, etc.) must be appropriately
considered.
-

The inclination of the ground surface and the thickness and inclination of the liquefied layer. (For the inclination, both
the direction parallel to the edge of water line and the direction perpendicular to it must be checked.)-

Distance to the edge of water line.

- 20 -

-

If the edge of water line has shore protection, the shape of it.

(10) The impact of tsunamis must be considered. Also, when investigating that impact by using hazard maps, the grounds forthe hazard maps must be clarified.
-3. When the distinction between onshore and offshore is not clear for the planned construction site, the handling shall be as
judged appropriate by ClassNK.

2.5

Lightning environment conditions

2.5.1

General-1. Regarding the lightning environment conditions at the planned installation site for a wind turbine or wind farm, the regional
characteristics must be evaluated by using data such as the frequency of lightning and the distribution of lightning days.
-2. The frequency of lightning strikes in each area is classified into the three categories shown in Figure 2-1, which are the areas
surrounded by solid lines, the areas surrounded by dashed lines and other areas.

Figure 2-1 Frequency of lightning strikes by region

2.6

Other environmental conditions

2.6.1

General-1. Depending on the characteristics of the site, the possibility of effects from the following environmental conditions shall beconsidered.
(1)

Normal temperatures and extreme temperatures(2)

Design vertical snow depth and icing(3)

Humidity- 21 -

Chapter 3

3.1

General

3.1.1

GeneralDesign basis evaluation-1. The purpose of the design basis evaluation is to examine whether the design basis has been properly documented and issufficient for safe design and project execution.

3.2

Design basis requirements

3.2.1

General-1. The design basis includes the following items.
(1)

Site conditions(2)

Design methodologies and principles(3)

Codes and standards which form the basis for the project(4)

Wind turbine type; main specifications or type certificate with identifications of deviations(5)

Support structure specifications-2. The design basis shall include all relevant overall design aspects and the parameters to be applied in the calculation of site
conditions, loads, design load cases, partial safety factors applied to loads and materials, geometric tolerances, corrosion
allowance growth, etc.

3.2.2Wind turbine (RNA) design basis-1. The document which shows the design basis for the wind turbine shall describe how the following matters were decided.
(1)

Codes and standards(2)

Site conditions• Wind conditions during power production-

Turbulence intensity correction parameter: 𝐶𝐶𝐶𝐶𝐶𝐶 (at measurement position / at wind turbine position)-

Average wind speed (hub height at wind turbine positions)-Turbulence intensity [Normal turbulence model (NTM) and extreme turbulence model (ETM)] (hub height at windturbine positions)-Wind shear exponent (hub height at wind turbine positions)-

Flow inclination angle (hub height at wind turbine positions)-

Air density (hub height at wind turbine positions)-

Design temperature range (hub height at wind turbine positions)-

Other conditions set in the type certification• Wind conditions during parked by storm-

10 minutes average wind speed with a return period of 50 years (hub height at wind turbine positions)-

3 seconds average wind speed with a return period of 50 years (hub height at wind turbine positions)-

10 minutes average wind speed with a return period of 1 year (hub height at wind turbine positions)-

3 seconds average wind speed with a return period of 1 year (hub height at wind turbine positions)-Turbulence intensities for wind speeds with a return period of 50 years and 1 year (hub height at wind turbine
positions)-Wind shear exponents for wind speeds with a return period of 50 years and 1 year (hub height at wind turbine
positions)-

Air densities for wind speeds with a return period 50 years and 1 year (hub height at wind turbine positions)-

Other conditions set in the type certification- 22 -

(3)Wind turbine operating conditions-

Cut-in wind speed, cut-out wind speed, rated wind speed, rated power generation, etc.

-

Whether or not sector management has been set, and if it is set, details thereof-

If there will be operation at high wind speeds with the power generation lowered, the operating conditions in thatcase (Clear indication of power curve and operation control)-

Operating conditions and specific control logic when the turbine continues to operate with power back up during aloss of electrical power while parked (if applicable)(4)

If there is any change from the wind turbine specifications or the specifications at the time of the type certification, acomparison of the specifications before and after that change(5)

Design parameters related to the load calculations, and the validity of applying the load analysis method used

(6)

Load case table(7)

Load factors and load reduction factors(8)

Overview of the load analysis model(9)

Duration of the simulation and its time(10) Ultimate and fatigue design loads and response analysis(11) Other items deemed necessary by ClassNK

3.2.3
-1.

Support structure design basis
The document which shows the design basis for the support structure (tower) shall describe how the following matters were

decided. For the design basis for the support structure (Tower), it should be noted that there must be compliance with Articles 10,
11 and 12 of the Interpretation of Technical Standards for Wind Power Generation Facilities[J-04].
(1)

Codes and standards(2)

Site conditions(3)

Support structure specifications(4)

Design policy (Required performance and verification items, materials used and material constants, allowable tolerance of
shape and corrosion reserve thickness, etc.)(5)

Load analysis method, and the validity of the application of that method(6)

Partial safety factors and load reduction factors for each load, and the validity of the application of those factors(7)

Evaluation method for ultimate and fatigue strength, and the validity of the application of that method-2.

Regarding the design basis for the support structure (foundation), in principle, it is acceptable to follow the regulations in the

Guidelines for Design of Wind Turbine Support Structures and Foundation[J-05]. For the design basis for the support structure(foundation), it should be noted that there must be compliance with Articles 10, 11 and 12 of the Interpretation of TechnicalStandards for Wind Power Generation Facilities[J-04].

- 23 -

Chapter 4

4.1

General

4.1.1

GeneralIntegrated load analysis evaluation-1. The purpose of the integrated load analysis is to evaluate whether the site-specific loads and load effects on the integrated
wind turbine structure, which includes the rotor-nacelle assembly (RNA) plus the support structure and supporting soils, arederived in conformity with the design basis.

4.2
4.2.1

Requirements for load analysis for RNA and tower evaluation
Comparison of the site conditions and the design values set in the type certification-1. The load analysis based on site conditions prescribed in Chapter 2 is not required when the below two conditions are
satisfied. One is that the conditions and requirements of the design basis relating to the site conditions and load effects necessary
for the calculation of loads are lower than those set in the type certification. Another is it is confirmed by ClassNK that thecharacteristics including the control of the wind turbine are the same as those set in the type certification.
-2. In the confirmation of -1. above, it is necessary to follow JIS C 1400-1:2017[J-01] 11.9 and compare the site-specific design
conditions with the design values set in the type certification, based on the site conditions specified in Chapter 2. Of the site
conditions specified in Chapter 2, for the turbulence intensity, the value obtained by multiplying the principal direction
component of 𝐼𝐼𝑒𝑒𝑒𝑒𝑒𝑒 specified in 2.2.7 (or 𝐼𝐼𝑟𝑟𝑟𝑟𝑟𝑟 specified in 2.2.6 if there is no adjacent wind turbine), by the 𝐶𝐶𝐶𝐶𝐶𝐶 specified in
2.2.3 must be compared with the principal direction component of the turbulence intensity set in the type certification for eachwind speed bin.

-3. In the confirmation of -2. above, if it is found that some items deviate from the design values set in the type certification, or if
the characteristics including the control of the wind turbine are different from those set in the type certification, the load analysis
prescribed in 4.2.2 shall be carried out based on the site conditions prescribed in Chapter 2.
4.2.2

Load analysis-1. For the load analysis based on the site conditions, in principle, all of the design load cases applied at the time of typecertification shall be targeted, and the analysis model and analysis method applied at the time of type certification shall be used. If
a design load case applied at the time of type certification is omitted, the reason why it may be omitted shall be indicated.
-2. In the case of a wind turbine with a power back-up as a measure for use in the event of a loss of the electrical power network,
evaluation must be carried out according to 5.4, and a design load case to be applied in the ultimate load analysis must be decided.
-3. In the load analysis, the components of the turbulence intensity in three directions that were determined in 2.2.6 must be
properly considered. In a case where there is no site data for the turbulence components, and also the terrain is complex, for the
turbulence standard deviations of the lateral direction and vertical direction against the principal direction component, it can beassumed that the ratios to the principal direction component are 1.0 and 0.7 respectively. These may also be calculated by using
𝐶𝐶𝐶𝐶𝐶𝐶 and applying equations (2.1) and (2.2). In this case, it is not necessary to multiply the principal direction componentprescribed in 4.2.1-2 by 𝐶𝐶𝐶𝐶𝐶𝐶 .

𝜎𝜎�2 = 1.15 × 0.8 × 𝐶𝐶𝐶𝐶𝐶𝐶 × 𝜎𝜎�1

𝜎𝜎�3 = 1.15 × 0.5 × 𝐶𝐶𝐶𝐶𝐶𝐶 × 𝜎𝜎�1

(2.1)
(2.2)

-4. The definition of the site load to be calculated shall be clearly indicated, and the coordinate definition applied in that site load
calculation shall be clearly indicated in a diagram. In principle, the definition specified in IEC 61400-13:2015[R-09] shall be used
for the coordinate definition.
-5. For the extreme wind conditions at the site that are to be applied to the load analysis, the combinations that produce themaximum load shall be selected appropriately, by taking into account the highest of each of the 10 minutes average wind speed,
the 3 second average wind speed and the wind shear exponent.
-6. If the extreme wind speed at the site greatly exceeds the design wind speed in the type certification, it must be sufficiently- 24 -

verified whether it is possible to apply the load analysis method applied for the extreme wind speed condition that was applied
during the type certification.
-7. In the case of a wind turbine which carries out passive yaw control (free yaw, etc.) in the standby state, the setting of thedesign load case is based on what ClassNK separately approves as appropriate.

4.3

Requirements for load analysis for support structure evaluation

4.3.1

General-1. Load analysis concerning the evaluation of support structures shall be carried out in accordance with the requirements of thefollowing Ministerial Ordinance and Guidelines.

4.3.2
-1.

(1)

Ministerial Ordinance Prescribing Technical Standards for Wind Power Generation Facilities[J-03](2)

Interpretation of Technical Standards for Wind Power Generation Facilities[J-04](3)

Guidelines for Design of Wind Turbine Support Structures and Foundation[J-05]
Support structure load analysis

In addition to the load calculated in 4.3.1-1., the loading data for the foundation and the tower design load at the site shall be

set with appropriate consideration of the load applied to the tower at the time of the type certification, and the site load on thetower that was calculated based on the site conditions specified in 4.2.2.
-2. Annex F.2 shall be followed to calculate the structural damping ratio to be set for the tower in the analytical model applied tothe seismic response analysis carried out in accordance with the Guidelines for Design of Wind Turbine Support Structures andFoundation[J-05].
-3. In the seismic response analysis, appropriate consideration shall be given to the effects of the wind turbine blade mass andrigidity distribution.
-4. When equivalent linear analysis is carried out in the seismic response analysis, if the shearing strain exceeds 1% in the
results, then it is not possible to apply the response calculation flow for liquefied ground that is described in the Guidelines for
Design of Wind Turbine Support Structures and Foundation[J-05] (p. 170, Illustration 5.11). In this case, it should be noted that it isnecessary to use an alternative method such as effective stress analysis.
-5.

The handling of wind and wind turbine control loads combined with the seismic loads obtained from the results of seismic

response analysis must follow the Appended Table 3 of the Interpretation of Technical Standards for Wind Power Generation
Facilities[J-04]. Although the handling of the wind and wind turbine control loads shall be as described above, the specific method
for combining the seismic load and the wind and wind turbine control loads may be carried out in accordance with Paragraph5.5.4 of the Guidelines for Design of Wind Turbine Support Structures and Foundation[J-05]. When coupled analysis
simultaneously considering both the seismic and the wind and wind turbine control loads is performed, this shall be approved as
appropriate by ClassNK.
-6.

In the case of pile foundations, if ground springs and attenuation are set using the thin layer method, etc., and not by

following the provisions of the Guidelines for Design of Wind Turbine Support Structures and Foundation[J-05], the validity of thesetting should be appropriately indicated in accordance with Annex G.4.

- 25 -

Chapter 5

5.1

Wind turbine (RNA) design evaluation

General

5.1.1
General-1. The structural integrity of the wind turbine for the site conditions shall be indicated by comparing the site-specific loads
obtained by the integrated load analysis with the design loads used in the type certification. It is also a prerequisite that the main
components of the RNA are composed of components specified in the type certificate, and that they are manufactured at a
manufacturing site specified in the certification documents pertaining to the type certification.
-2. If there are new components, improved or reinforced components, or new or improved systems not listed in the wind turbine
type certificate, the relevant components and systems shall also comply with the requirements for type certification.
-3. However, in the case of a wind turbine that has not obtained type certification, where the wind turbine has acquired a design
evaluation conformity statement and is carrying out type testing for the acquisition of type certification, the wind farm
certification may be issued on the condition that the acquisition of the type certification is set as an outstanding issue and a time
limit for the solution of that outstanding issue is established. (However, it should be noted that conditional issuance is not
acceptable in an examination by a registered conformity assessment body.) In other cases, the handling shall be as judged
appropriate by ClassNK.

5.2

Wind turbine (RNA) design evaluation

5.2.1
Comparison of site loads with design loads at type certification-1. If the load from the integrated load analysis carried out based on the site conditions (hereinafter called the site load) does notexceed the design load applied at the time of type certification (hereinafter called the certified design load), the site conditions
may be considered to satisfy the design values at the time of type certification, and the structural integrity of the wind turbine
against the site conditions may be ensured.
-2. With regards to the points to be evaluated in a comparison of the site-specific load with the allowable design load in order toshow the contents of -1. above, at least the following items must be taken into consideration and also any evaluation points otherthan those below must be set as appropriate for the RNA specification and structure. In addition, it must be clearly shown that theitems selected are sufficient to show the structural integrity of the RNA.
(1)

Six or more cross-sectional positions including the blade root portion and the portion where the maximum load is applied
other than the blade root portion(2)

Blade bearing(3)

Pitch system(4)

Hub (when fixed) and hub (during operation and during idling)(5)

Main shaft and main shaft bearing(6)

Yaw system(7)

Tower top/Joining part between tower top and nacelle(8)

Nacelle frame(9) Other major components requiring evaluation-3. The design documents concerning the certified design load described in the certification evaluation report of the Design
Evaluation Conformity Statement shall be submitted to ClassNK as data for the confirmation of the certified design load.
5.2.2
Strength evaluation of the components of the RNA based on the site load
-1. If the site load exceeds the certified design load, the integrity of the affected components against the site load must be
verified. For the value obtained by dividing the site load by the certified design load in the load comparison, when it can be
confirmed that the value after the third decimal place does not affect the checking value as a strength evaluation result, then if thevalue does not exceed 1.00 after rounding off the third decimal place, it may be considered that the integrity against the site load
has been confirmed.
-2. In the verification in -1. above, the response and applied stresses, etc., from the site load must be obtained based on a strength
evaluation with the same design methodologies and thinking on safety factors, etc., as those applied at the time of the typecertification (hereinafter called the original design method), and the allowance for the proof stress peculiar to the components- 26 -

must be shown. When any judgment is made in this strength evaluation, the grounds for the validity of that judgment shall be
indicated by citing international standards and guidelines.
-3. When citing the original design methodology in the strength evaluation based on the site load, the documents which can beused to confirm the details of the original design method indicated in the type certificate, the related conformity statement and its
certification evaluation report shall be submitted to ClassNK as reference materials.
-4. In the report which summarizes the strength evaluation based on the site load, a table shall be included which lists eachindividual component verified and shows the excess ratio of the site load to the certified design load and the tolerance obtained
from the results of the strength evaluation shown in -2. above for each component as a summary. The basis for the values in thattable shall be clearly indicated in an appropriate manner, such as by attaching a detailed statement to the report or by citing aseparate volume.

5.3
5.3.1

Nacelle cover strength evaluation
General-1. The nacelle cover shall be of sufficient strength against the wind load established under the site conditions.
5.3.2

Wind load on the nacelle cover-1. The wind load factor for the nacelle cover shall be calculated by using equation (5.1).
1
𝑃𝑃𝑒𝑒 = 𝜌𝜌𝑈𝑈ℎ 2 𝐶𝐶̂𝑝𝑝
2

Where:
𝜌𝜌

𝑈𝑈ℎ
𝐶𝐶̂𝑝𝑝

(5.1)

: Air density, which shall be 1.22 [𝑘𝑘𝑘𝑘/𝑚𝑚3 ]: 10 minutes average wind speed with a return period of 50 years [𝑚𝑚/𝑠𝑠] as specified in 2.3.1: Peak wind force coefficient, determined by equation (5.2).
𝐶𝐶̂𝑝𝑝 = 𝐶𝐶̂𝑝𝑝𝑝𝑝 − 𝐶𝐶𝑝𝑝𝑝𝑝(5.2)

Where:: Peak external pressure coefficient𝐶𝐶̂𝑝𝑝𝑝𝑝
𝐶𝐶𝑝𝑝𝑝𝑝: Internal pressure coefficient, according to Table 5-1
Table 5-1 Internal pressure coefficient
Negative pressure side

Positive pressure side

There is no opening on the upwind side surface

0

-0.5

There is an opening on the upwind side surface

0.5

0-2. The peak external pressure coefficient shall be calculated by using equation (5.3).
𝐶𝐶̂𝑝𝑝𝑝𝑝 = 𝐶𝐶̂𝑒𝑒𝑒𝑒 (1 + 7𝐼𝐼ℎ1 )Where:: Equivalent wind pressure coefficient, a reference example of which is given in Annex D𝐶𝐶̂𝑒𝑒𝑒𝑒
𝐼𝐼ℎ1

(5.3)

: Turbulence intensity for 10 minutes average wind speed with a return period of 50 years shown in 2.3.1-3. The peak external pressure coefficient may be set based on the results of wind tunnel testing in place of the provisions given
in -2. above. Annex E can be used as a reference for conducting wind tunnel tests.

- 27 -

5.3.3

Load cases-1. The wind load acting on the nacelle cover shall be calculated with all of the load cases given in Table 5-2 taken into
consideration. Note that the load cases shown in Table 5-2 are those among the design load cases specified in JIS C 14001:2017[J-01] that correspond to the wind speed, wind direction, and turbulence intensity to be considered in DLC6.1 and DLC6.2,
with the wind directions being those that should be considered in the 𝐶𝐶̂𝑒𝑒𝑒𝑒 calculation.

-2. The wind load for each load case shall be calculated using equation (5.1) and multiplied by the partial safety factor shown in

Table 5-2.

𝐶𝐶̂𝑒𝑒𝑒𝑒No.

Table 5-2 Load cases to be applied to the nacelle cover load calculation𝐶𝐶̂𝑒𝑒𝑒𝑒 Wind direction to be taken intoWind
Turbulence
Partial safety factor for

NC.1-1

Positive value

NC.1-2

Negative value

NC.2-1

Positive value

NC.2-2

Negative value

consideration in the calculation-15° to +15°

*1

All wind directions *2

speed

intensity

wind loads

𝑈𝑈ℎ

𝐼𝐼ℎ1

1.35

𝑈𝑈ℎ

𝐼𝐼ℎ1

1.10

*1: Corresponds to the wind direction to be considered in DLC6.1 specified in JIS C 1400-1:2017[J-01]*2: Corresponds to the wind direction to be considered in DLC6.2 specified in JIS C 1400-1:2017[J-01]
5.3.4

Strength evaluation-1. In principle, the method used for the strength evaluation for the nacelle cover against the wind loads calculated based on thesite conditions and in accordance with 5.3.3 shall be the same as the strength evaluation method applied at the time of typecertification, and the setting of the tolerance values, etc., may also follow that method.
-2. Notwithstanding -1. above, if composite materials are used on the nacelle cover, the partial safety factors related to thematerial, manufacturing, and long-term deterioration, etc., shall be appropriately taken into consideration, and the product of thesepartial safety factors shall not be less than 2.0.

5.4

Evaluation in the event of the electrical power network loss

5.4.1

General-1. The wind turbine must ensure the safety of the wind turbine regarding the following items, even if the electrical power
network is lost.
(1)

Measures to automatically shut down in the event of a loss of electrical power network(2)

Maintenance of a safe state until the electrical power network returns-2. Regarding -1. (2) above, it shall be ensured as a design load case to be applied to the integrated load analysis by considering
the DLC6.2 specified in JIS C 1400:2017[J-01].
-3. In order to satisfy the requirements of -1. above, when the control of the wind turbine will be continued by using power backup in the event of the electrical power network loss, DLC6.2 may be omitted from the design load cases to be applied to theintegrated load analysis by satisfying all the requirements shown in 5.4.2.
-4.

When DLC6.2 is omitted from the design load cases applied to the integrated load analysis in accordance with -3. above, atest showing that the system using a power back-up operates as assumed in the design must be conducted before the start ofoperation, and a report must be made to ClassNK using time-series data on the operation of related equipment such as the yaw
control equipment and power back-up. The test plan for this testing must be submitted to ClassNK for approval before the test is
conducted.
5.4.2

Power back-up-1. When a power back-up will be used to continue the control of the wind turbine in the event of the electrical power network
loss, the following items (1) to (4) must be satisfied.
(1)

In addition to clearly stating the yaw misalignment at which the maximum wind pressure occurs in the design, the- 28 -

certainty of the yaw misalignment to be adopted as the design value must be verified by measurement data from a reliable
period and number of times.
(2)

Whichever is the largest of the yaw misalignment design value obtained from the results of (1) above and ± 8° must be
adopted as the yaw error parameter in the DLC6.1 specified in JIS C 1400:2017[J-01] among the design load cases used in
the integrated load analysis specified in Chapter 4.

(3)

The power back-up capacity must be set appropriately based on the site-specific conditions.

(4)

The reliability of the systems related to the power back-up must be ensured, and the parameters related to the supply of
the power back-up must be set appropriately.

-2.

When setting design values for yaw misalignment, the following items (1) to (8) must be evaluated and confirmed under site-

specific extreme wind speed conditions. In addition, the validity of the evaluation and confirmation of these items must be shownby measured data. If no measured data under conditions corresponding to the site-specific extreme wind speed have been obtainedat the time of the design, then in order to confirm after the start of operations that the operation control assumed in the design canbe appropriately performed under conditions corresponding to the site-specific extreme wind speed, an environment should be
prepared to enable the collection of measured data (the history of the wind conditions (wind speed and wind direction) near thewind turbine and the history of the wind turbine operation control (nacelle orientation) and operating conditions corresponding tothose wind conditions), and when this data has been obtained, it must be reported to ClassNK.
(1)

With regard to the anemometers for wind speed and wind direction which obtain the measurement values necessary for
yaw control, the usability and measurement accuracy in the extreme wind speed conditions specific to the site shall beensured, and the anemometers including their mounting portions shall have sufficient strength under the site-specificextreme wind speed conditions.

(2)

The yaw control logic to follow the wind direction and the control logic for the equipment related to yaw control must be(3)

The yaw drive and yaw brake specifications must be appropriate for the control logic for the yaw control.

(4)

Either the pitch control mechanism or lock mechanism necessary to maintain the blade feather state must be provided,able to ensure the design values for yaw misalignment.

and the mechanisms must have sufficient strength under the site-specific extreme wind speed conditions.
(5)

The load calculation must be performed by using a simulation method that can appropriately reproduce the conditions inwhich the extreme wind speeds specific to the site occur.

(6)

There must have been appropriate consideration of the driving force (when the wind torque acts in the opposite direction
to the direction of yaw movement) and braking force (when the wind torque acts in the direction of yaw movement)
necessary for yaw control under the site-specific extreme wind speed conditions, which are provided by the wind torque,yaw drive torque and yaw brake, etc., and the equipment related to yaw control must have sufficient strength in that state.

(7)

Even when a fail-safe approach is applied, there must be the driving force necessary for yaw control, for example, when apart of the yaw drive or yaw brake related to yaw control fails for some reason.

(8)

Other items deemed necessary by ClassNK for each individual wind turbine-3. The capacity of the power back-up shall be determined by calculating the amount of power required for yaw control and theother minimum control necessary based on the estimated storm duration and wind direction deviation during that time. Whencalculating that electric power, the larger of the storm durations or wind direction deviations calculated in (1) and (2) below must
be adopted, and sufficient capacity must be secured for the conditions.
(1)

Obtain the maximum storm duration and maximum wind direction deviation from a typhoon simulation using the sitespecific conditions and calculate the amount of electric power required for yaw control and related control underconditions where both of these occur simultaneously. The definition of a storm in this case must be set individually
because it differs depending on the control and design policy.

(2)

Use the reference wind speed 𝑉𝑉0 of the site and define the maximum storm duration as the numerical value obtained by"𝑉𝑉0 − 24". Assume that the wind direction deviation occurs 180° within that time, and calculate the amount of electric
power required for yaw control and related control under those conditions.

-4. If the electrical power network is lost and the system is operated with a power back-up, the system must not automatically
return to normal operation. The operation manual shall specify that normal operation can only be resumed when it has been
confirmed in inspections that there is no abnormality.

- 29 -

-5. When an upwind wind turbine performs downwind control during parked by storm, it must satisfy separate requirements
recognized as appropriate by ClassNK in addition to the requirements in -1. to -3. above.

5.5

Evaluation to secure a safe state on the wind turbine

5.5.1

General-1.

A wind turbine must be equipped so as not to come into contact with other structures, plants, etc., during operation.

5.5.2

Safe and automatic shutdown of wind turbines-1.

Even in the following cases, there shall be a function to stop safely and automatically, and also the safe state after stopping

shall be maintained. It should be noted that for these items, it is necessary to conform to Article 7 of the Interpretation of TechnicalStandards for Wind Power Generation Facilities[J-04].
(1)

When the rotational speed has increased significantly(2)

When the functioning of the control equipment for the wind turbine has significantly deteriorated-2. Appropriate measures shall be taken for the following items.
(1)

There must also be sufficient strength against the maximum rotational speed that is expected when the load is cut off.

(2)

There must be no occurrence of resonance which affects the structural strength during operation.

(3)

A startup shall not be allowed when the cutout wind speed is exceeded.

5.5.3

Protection against lightning strikes-1. The provisions of this section are based on the Annotations to the Ministerial Ordinance Prescribing Technical Standards forWind Power Generation Facilities and its Interpretation[R-02], and there is no change to those requirements.
-2. For wind power generation facilities on which the highest part is more than 20 meters above the ground surface, measures
shall be taken to protect the wind turbine from lightning strikes. However, this shall not apply in a case where the surrounding
conditions mean that there is no risk of lightning strikes damaging the wind turbine. [Ministerial Ordinance, Article 5, paragraph(3)]-3. "Measures to protect the wind turbine from lightning strikes" refers to wind turbines that satisfy all of the following
requirements specified for the categories of areas, taking into consideration the lightning strike conditions at the location where
the wind power generation facilities will be installed. [Interpretation, Article 7, paragraph (6) item (i)](1)

Regions enclosed by solid lines in Figure 2-1(a)

The design must assume a lightning strike on the wind turbine with an electric charge of 600 coulombs or more.

(b)

An appropriate receptor which is highly effective at protecting the wind turbine from lightning strikes and does noteasily fall off must be attached to the wind turbine.
(c)A down conductor, etc., through which the current generated by a lightning strike can flow safely into the groundwithout damaging the wind turbine must be provided.
(d)An emergency stop device, etc., that can be used to stop the wind turbine immediately in the event of lightning striking

the wind turbine must be provided.
(2)

Regions enclosed by dashed lines in Figure 2-1(a)

The design must assume a lightning strike on the wind turbine with an electric charge of 300 coulombs or more.

(b)

The requirements set forth in (1) (b) and (1) (c) shall be satisfied.

(3)

Areas other than those enclosed by solid or dashed lines in Figure 2-1(a)

The design must assume a lightning strike on the wind turbine with an electric charge of 150 coulombs or more.

(b)

The requirements set forth in (1) (b) and (1) (c) shall be satisfied.

-4. Lightning protection equipment which satisfies all of the following requirements must be installed for protection fromlightning on parts at a height of 20 m or more on the structure supporting the wind turbine (except for items that are subject to theprovisions of Article 2, Paragraph 1 of the Ship Safety Act (Act No. 11 of 1933).) [Interpretation, Article 7, paragraph (6) item (ii)](1)

The lightning protection through which the current generated by a lightning strike can flow safely into the ground without
damaging the structures that support the wind turbine must conform to JIS C 1400-24:2014[R-07].

(2)

The parts of the lightning protection facilities which are liable to be corroded by rainwater, etc., must either be made of- 30 -

corrosion-resistant materials or provided with effective measures for corrosion prevention.
-5. The provision in -2. above that, "this shall not apply in a case where the surrounding conditions mean that there is no risk oflightning strikes damaging the wind turbine" shall include cases where a lightning conductor tower, lightning rod or otherlightning arrester equipment is installed to protect the wind turbine concerned. [Interpretation, Article 7, paragraph (7)]- 31 -

Chapter 6

6.1

General

6.1.1

GeneralSupport structure design evaluation-1. The structural integrity of the support structure for the site conditions is confirmed by using integrated load analysis toindicate that there is sufficient strength against the site-specific loads. In addition, for the tower of the support structures, theprerequisites are that the design has obtained type certification, and that the tower has been manufactured at a manufacturing site
specified in the certification documents pertaining to the type certification.
-2. The design of the support structure (tower and foundation) shall comply with the following ministerial ordinances andguidelines, etc.
(1)

Ministerial Ordinance Prescribing Technical Standards for Wind Power Generation Facilities[J-03](2)

Interpretation of Technical Standards for Wind Power Generation Facilities[J-04](3)

Annotations to the Ministerial Ordinance Prescribing Technical Standards for Wind Power Generation Facilities and its
Interpretation[R-02](4)

Guidelines for Design of Wind Turbine Support Structures and Foundation[J-05]-3. Of the support structures, with regards to the tower design, if there is an item which deviates from the content approved in thetype certification, the result of design examination equivalent to that at the time of obtaining the type certification shall be shownfor the deviating item.
-4. Of the support structures, if the tower was not included in the type certification, it is necessary at the time of the wind farm
certification to separately carry out the evaluation items normally conducted at the time of type certification, such as a detailed
evaluation of the connection between the tower and the wind turbine (RNA). Therefore, the handling of such items shall not bebased on the provisions of these guidelines and instead shall be as separately deemed appropriate by ClassNK.
-5.

It should be noted that if -3. and -4. above apply, then it is necessary to conduct a separate manufacturing evaluation for the

tower in light of the prerequisites of -1. above.

6.2

Support structure (Tower)

6.2.1

General-1. In the design of the support structure (tower), if any item does not satisfy the provisions in 6.1.1-2., then it shall be shownthat the item satisfies the required criteria regarding safety that are defined by the provisions in 6.1.1-2.
-2. In the case of -1. above, if the design is based on the method shown in Annex F, and it is confirmed by the Support Structure
Certification Subcommittee/Tower Section Meeting that the contents of it are satisfied, then it may be considered that the required
criteria regarding safety that are defined by the provisions in 6.1.1-2 are satisfied for the item.
-3. If it is necessary to conduct a manufacturing evaluation for the tower, ClassNK will individually specify when and how theresults of the manufacturing evaluation shall be confirmed, based on the content indicated in 1.5.5-1. (8).

6.3

Support structure (Foundation)

6.3.1
-1.

GeneralIn the design of the support structure (foundation), if any item does not satisfy the provisions in 6.1.1-2., then it shall beshown that the item satisfies the required criteria regarding safety that are defined by the provisions in 6.1.1-2.
-2.

In the case of -1. above, if the design is based on the method shown in Annex G, and it is confirmed by the Support

Structure Certification Subcommittee/Foundation and Ground Section Meeting that the contents of it are satisfied, then it may
be considered that the requirements regarding safety that are defined by the provisions in 6.1.1-2 are satisfied for the item.
6.3.2

Strength evaluation for support structure (foundation)-1. Regarding the strength evaluation for the support structure (foundation), in addition to the regulations in the Guidelines for
Design of Wind Turbine Support Structures and Foundation[J-05], attention shall also be paid to the following points.

- 32 -

(1)The bearing capacity of piles must be additionally evaluated by the formula prescribed in the Recommendations for
Design of Building Foundations[R-03].

(2)

The pile material properties (linear and nonlinear) and setting of the stress calculation method at the time of the pile stressexamination must be appropriately considered.

(3)

The horizontal resistance of piles must be additionally evaluated by a method using the group pile frame model specified
in the Recommendations for Design of Building Foundations[R-03].

(4)

When the response displacement method is used for the consideration, the combinations of the same direction and the(5)

When the occurrence of lateral flow is anticipated in an earthquake, the residual displacement of the foundation obtained

opposite direction must be considered for each of the ground displacement and inertia force.
from the result of its examination must be evaluated.
(6)

When applying certified construction methods in the field of architecture, etc., it is necessary to sufficiently confirm thatthe application of those methods is acceptable. (In particular, it may be that the scope of certification is limited to theprimary design, so it must be checked whether it can be applied to the secondary design, etc.)

6.3.3

Items to be considered in the design-1. Regarding the design for the support structure (foundation), in addition to the regulations in the Guidelines for Design ofWind Turbine Support Structures and Foundation[J-05], attention shall also be paid to the following points.
(1)

When concrete foundation driving is carried out using a placing joint, the treatment method for it shall be specified in a
drawing.

(2)

If liquefaction is expected to occur, a note must be clearly indicated on the drawings to the effect that the clearance under
the foundation, etc., should be checked after the occurrence of an earthquake, and that restoration measures should betaken if a clearance, etc., is found.

- 33 -

Annex A.

A.1

Measurement data evaluation methods [normative]

Selection of measurement points-1. The measurement points for the wind condition must be planned so that it is possible to obtain the necessary measurement
data for all the wind turbines within a site.
-2. When determining the number of measurement points necessary, all wind turbines must be located within the representative
radius of at least one measurement point, based on the assumption that the wind conditions at the wind turbine position will be
estimated from airflow analysis, and on the idea that the uncertainty related to the estimation can be reduced if it is within the
representative radius from the measurement point.
-3. The representative radius values shown in Table 2-1 are determined according to the topography, and are the values for when
the ground surface roughness can be assumed to be uniform within the representative radius. It must be kept in mind that if theground surface roughness is not uniform within the site or within the peripheral region set as the analysis region in the airflow
analysis, then the representative radius may not be applicable in all directions, because the measured value at the measurement
point may be affected by a ground surface roughness that is different from that at the wind turbine position. In this case,appropriate prior examination must be conducted, such as by carrying out airflow analysis during the stage of the selection of themeasurement point.

A.2

Wind speed measurement by measurement mast

-1. The wind speed measurement is carried out by using a cup type anemometer, or an anemometer of which the equivalent
performance is guaranteed.
-2. The cup type anemometer is calibrated before the measurement period, and the calibration value is used in the wind condition
evaluation. The calibration of the cup-type anemometer shall be performed in accordance with the procedure described in Annex F
of JIS C 1400-12-1:2010[R-06] or in a procedure judged to be equivalent, and the calibration results shall be attached to the report.
-3. The cup type anemometer is installed at a position that is at least 2/3 of the hub height from the ground surface in order toreduce the uncertainty of the vertical extrapolation of the wind condition. When this is difficult, it becomes necessary to use
measurement in combination with remote sensing equipment such as a vertical lidar, but even in this case, the cup type
anemometer must be installed at the highest possible position. To evaluate the vertical profile of the wind shear at the planned site,
two or more anemometers are added at intervals of about 10 m from the top anemometer. An anemometer may also be installed ata height close to the top anemometer for backup purposes.
-4. The installation of a wind speed anemometer on a measurement mast shall be in a manner that minimizes the effect on the
anemometer from the mast and boom. It is desirable that the installation of a wind speed anemometer on a measurement mastfollows Annex G of JIS C 1400-12-1:2010[R-06]. It is desirable that the boom installation is at an orientation that is 45° from theprincipal wind direction in the case of a cylindrical mast, and 90° from the principal wind direction in the case of a truss structure.
When a lightning rod is installed, it is installed at a position where it will not affect the anemometer.
-5. The 10 minute average and standard deviation of the wind speed are measured. It is desirable that the sampling frequency is 1
Hz or higher. In addition, MEASNET[R-16], [A1] can be used as a reference for the calibration, installation method, equipment
configuration, and test method, etc.
-6. If the planned site is in a cold region, a cold region specification device such as one with a heater must be used in order tomaintain the response characteristics specified for anemometers.

A.3

Wind direction measurement by measurement mast

-1. The wind direction measurement is carried out by using a vane type anemometer. It is desirable to install one at each altitude
to form pairs with the wind speed anemometers described in A.2. The installation of a wind direction anemometer on ameasurement mast shall be in a manner that minimizes the effect on the anemometer from the mast and boom. It is desirable thatthe installation of a wind direction anemometer on a measurement mast follows Annex G of JIS C 1400-12-1:2010[R-06].
-2. The anemometer measures 10 minute averages. It is desirable that the sampling frequency is 1 Hz or higher.

- 34 -

A.4

Measurement using remote sensing devices

A.5

Measurements and evaluation report of measurement results-1. When measurement is carried out by remote sensing equipment such as a vertical lidar, it is necessary to confirm thecorrelation with the measurement mast, so it is desirable to install the remote sensing equipment as close as possible to themeasurement mast. However, since it is difficult to establish a general threshold value for the separation distance between themeasurement mast and the remote sensing equipment, the placement of the equipment must be appropriately determined
depending on the measurement mast guy lines and the surrounding conditions.
-2. For the measurement heights, the essential measurement heights shall be the height of the anemometer on the measurement
mast with which the correlation is being confirmed, and the hub height of the planned wind turbine. Other heights shall be set
appropriately up to close to the top of the rotor plane, with one every 10 m as the standard setting.
-3. When the correlation between the measurement mast and the remote sensing equipment such as a vertical lidar is confirmed,
it must be confirmed that the time stamp of the measurement mast data and the time stamps of the remote sensing equipment suchas the vertical lidar agree.
-4. If the correlation between the measurement data of the remote sensing equipment and of the measurement mast does notsatisfy the requirements, the effect of the topographic complexity, and of the characteristics of the measurement method of theusing equipment may be corrected using the results of airflow analysis, etc.

-1. Reports on the measurements shall contain at least the following items.
(1) Site status:

a. Photographs showing 360° around the measurement points, from all the measurement points
b. Topographical map of the site showing the measurement points
c. Separation distance between the measurement point and the planned wind turbine positiond. Terrain judgment results for the measurement points and wind turbine positions (This may follow 2.2.3)(2) Description of the measurement system:
a. Specifications of measurement equipment and data collection systems (Including calibration certificates formeasurement equipment)b. Arrangement of measurement equipment on the measurement mast and the confirmation results for itc. Drawings including the main dimensions of the measurement mast and mounting boomd. Method of maintaining anemometer calibration throughout the measurement period, and evidence to show that it
was maintained(3) Description of the measurement procedure:a. Description of the measurement procedure, test and inspection conditions, sampling rate, averaging time,measurement periodb. Significant events that occurred during the entire measurement period (if any occurred)c. Data removal criteria applied during data analysis and conclusion derivation-2. Reports on the evaluation of measurement results shall contain at least the following items.
(1) Long-term evaluation:
a. Details of the methods used in the evaluation and the long-term data appliedb. Results of statistical analysis with corrections using the long-term data appliedc. Significance of the results of the long-term evaluation performed(2) Wind direction and wind speed data:
a. The average, maximum and minimum wind speeds and the wind speed standard deviations described in tabularform, for the entire duration of the measurements and for each month.
b. The Weibull shape and scale factors for each direction, and the appearance frequency distribution and energy
density distribution (with a wind direction sector width of 30° or less) for each direction specified in tabular form
for each measurement mast. A wind direction distribution map (plot) is also required.
c. When a measurement mast and remote sensing equipment are being used together, a correlation diagram showing
the result of confirmation of the required values related to the correlation as shown in Table 2-2, and parameters
representing the regression line.
d. When the required values shown in Table 2-2 are not satisfied in c. above, the results of consideration of the reason- 35 -

why the required values were not satisfied, following the notes shown in Table 2-2.
(3) Wind shear exponent:a. The average value of the wind shear exponent, described in tabular form with a wind direction sector width of 30°
or less.
(4) Turbulence intensity:a. The ambient turbulence intensity for each direction (with a wind direction sector width of 30° or less) specified intabular form for each measurement mast.
b. Chart comparing the ambient turbulence intensity and IEC turbulence category with consideration of all winddirections.
(5) Temperature:a. The average value, minimum value, and maximum value of the temperature described in tabular form, for the entire
duration of the measurements and for each month.
(6) Atmospheric pressure:a. The average value, minimum value, and maximum value of the atmospheric pressure described in tabular form, forthe entire duration of the measurements and for each month.
(7) Humidity:
a. The average value, minimum value, and maximum value of the relative humidity described in tabular form, for theentire duration of the measurements and for each month.

A.6

Measurement at a point affected by the wake of an existing wind turbine-1. When measurement must be carried out in the vicinity of an existing wind turbine that is in operation, a point which is notaffected by the wake of the existing wind turbine should be selected, but, due to various constraints, there are cases where
measurement must be carried out at a point where the wake effect of an existing wind turbine cannot be eliminated. This
paragraph summarizes the items that should be considered in such cases.
-2. If the separation distance between the measurement mast and the existing wind turbine is 10D or more (D: Rotor diameter ofthe existing wind turbine), the measurement data may be treated as data that is not affected by the wake.
-3. If the measurement data within the disturbed sector specified in IEC61400-12-1: 2017[R-17] is rejected and the effective data

rate of the remaining data satisfies the provisions of 2.2.2-2., the measurement data may be treated as data that is not affected by
the wake.
-4. If neither of the items -2. and -3. above is satisfied, consider performing simultaneous measurement using a wind condition
measurement mast and remote sensing equipment and then performing correction for the wake effect of the existing wind turbine.
[A2]

A.7

Reference documents[A1] MEASNET, JWPA translation, Evaluation of Site Wind Conditions (Japanese version) (Original title: Evaluation of Site
Specific Wind Conditions. Version 1), 2016.
[A2] Yoshida et al., Study on the method of wind turbine wake effect exclusion from wind condition measurement data in anexisting wind farm, Proceedings of the 44th Wind Energy Symposium, pp. 199-201, 2022.

- 36 -

Airflow analysis and verification of its validity [normative]

Annex B.

B.1

Airflow analysis

B.1.1

Topographic data and ground surface roughness data

-1. Use the topographic data (numerical elevation data) and ground surface roughness data from around the planned site as input
data for the airflow analysis. Reproduce the surrounding terrain with high accuracy for as wide a range as possible.
-2. Topographic data shall not have a resolution greater than 50 m. In the case of complex terrain, it is desirable to use data witha high resolution, but it must be appropriately considered together with the setting of the calculation grid prescribed in B.1.3.
-3. Ground surface roughness data shall not have a resolution greater than 100 m. When the change in the distribution of groundsurface roughness is large, it is desirable to use data with a higher resolution. For the topographic data and ground surface
roughness data, it is possible to use the digital national land information and basic map information from the Geospatial
Information Authority of Japan.

B.1.2

Calculation region-1. The calculation region must be set as the range of the planned site, that is, the range including the measurement masts and allwind turbines. The distance from the measurement masts and all wind turbines to the calculation region boundary (inflow plane,
outflow plane, side plane) must be 20 times or more the hub height. In addition, it is desirable to set an additional region for theflow to enter and exit smoothly (including on the side plane). When the flow cannot be set to flow smoothly in and out, it is also
necessary to take a sufficiently long distance.
-2. For the distance to the inflow boundary, in addition to being more than 20 times the hub height as written above, the changes
in the terrain (elevation) in all directions around the planned site should be evaluated and the effect of the terrain on the upwindside must be taken into consideration in the distance. An example of a calculation region is shown in Figure B.1.
-3. For the upper air region, the ratio (blockage ratio) of the cross section of the reproduced terrain to the cross section of theanalysis region, which is decided by the lateral range and the vertical range, must be 5% or less in order to avoid theoverestimation of the wind speed above the terrain due to a blockage effect. Or else, a height that is at least 20 times the maximum
difference in elevation must be secured in the vertical direction. If it is difficult to do so, the evidence must be provided.

Figure B.1 Example of calculation region (Horizontal direction)

B.1.3

Calculation grid and resolution-1. In principle, the calculation grid size in the horizontal direction of the range that includes the measurement masts and windturbines (the minimum grid range) shall not exceed 25 m. It is possible to use a gradually rougher grid as the distance from theminimum grid range increases, but in that case, the elongation rate of the calculation grid size must be 1.2 or less.

- 37 -

-2. For the calculation grid resolution in the vertical direction, in the case of the k-epsilon model, the first calculation grid pointon the ground surface is set in a region where the average wind speed distribution can be approximated by a logarithmic or powerlaw, that is, around the roughness length, and then the grid resolution may be made gradually coarser with increased elevation. In
this case, the elongation rate of the calculation grid width must be 1.2 or less.

B.1.4

Boundary conditions-1. For the inflow boundary conditions, set the vertical distribution of the average speed and turbulence statistics, based on the
ground surface roughness at the inflow point. For the outflow boundary conditions, use either a free outflow condition orconvective outflow condition in order to avoid the generation of unnatural flow from the outflow boundary. For the lateralboundary conditions and upper boundary conditions, use slip conditions.
-2. For the ground surface boundary conditions, in the case of the k-epsilon model, use a wall function using the ground surface
roughness parameter.

B.1.5

Direction division-1. The direction division must be set appropriately according to the complexity of the terrain.
-2. There must be 12 or more directions for flat terrain and 16 or more directions for complex terrain. If it is difficult to do so, theevidence for that must be provided appropriately.

B.2

Verification of airflow analysis validity

B.2.1

Verification of validity of airflow analysis applied to the calculation of wind conditions during power
production-1. To verify the validity of the airflow analysis applied to the calculation of the wind conditions during power production, use
the airflow analysis to calculate at least the following items for the measurement mast position and then compare the results withthe measurement data.
(1) Average wind speed by wind direction(2) Vertical profiles of wind shear by wind direction(3) Turbulence intensity by wind direction-2. For the average wind speed by wind direction, when there are multiple measurement masts, they must be mutually combined
for the comparison of the measurement data and the airflow analysis results. When there is only one measurement mast, thecomparison should be made using measurement data at a height different from the height used as input data for the airflow
analysis.
-3. The vertical profiles of the wind shear by wind direction are normalized by the wind speed at the highest point on themeasurement mast, and then the comparison of the measurement data with the airflow analysis results must be conducted in aformat following the example shown in Figure B.2. However, if there is measurement data by a vertical lidar, it should benormalized by the wind speed at hub height in a format following the example shown in Figure B.3. The following points should
be kept in mind when preparing figures.
- In all cases, the horizontal axis should start at 0.
- The airflow analysis results should be displayed to the horizontal axis 0 position.
- An auxiliary line should be inserted at the position where the horizontal axis is 1.0.
- If displacement height is taken into account, it should be clarified that the value is consistent with the figure.
-4. With regard to the turbulence intensity by wind direction, use the turbulence energy k of the k-epsilon model, etc., in the
airflow analysis and obtain the standard deviation of the wind speed fluctuation in the principal wind direction that arises due to𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠the terrain and surface roughness 𝜎𝜎𝑢𝑢
by using equation (B.1). Also, the wind speed 𝑈𝑈 obtained from the airflow analysis andequation (B.2) must be used to calculate 𝐼𝐼𝑠𝑠𝑠𝑠𝑠𝑠 and then compare the result with the turbulence intensity obtained frommeasurement data. In this case, in principle, the wind speed bin corresponding to 15 m/s shall be applied, but the wind speed bin
may be changed depending on the measurement data (the number of measurement points per wind speed bin, etc.). However, thewind speed bin selected should be appropriately stated.
𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠

𝜎𝜎𝑢𝑢= √1.2𝑘𝑘- 38 -(B. 1)

𝐼𝐼𝑠𝑠𝑠𝑠𝑠𝑠 =B.2.2

𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠

𝜎𝜎𝑢𝑢
𝑈𝑈(B. 2)

Figure B.2 Measurement mast only

Figure B.3 Measurement mast + vertical lidar(Displacement height not set)

(Displacement height not set)

Verification of validity of airflow analysis applied to the wind conditions during parked by storm-1. To verify the validity of the airflow analysis applied to the calculation of the wind conditions during parked by storm, use theairflow analysis to calculate at least the following items for the measurement mast position and then compare the results with themeasurement data. For the details of each item, the provisions of B.2.1 shall apply.
(1)

Average wind speed by wind direction(2)

Vertical profiles of wind shear by wind direction(3)

Turbulence intensity by wind direction

B.3

Report on airflow analysis and its validity

B.3.1

Report on the airflow analysis applied to the wind conditions during power production and its validity-1. Reports on the airflow analysis applied to the calculation of the wind conditions during power production and on theverification of the validity of that analysis shall include at least the following items.
(1)

Details of the airflow analysis (including the following content):a. Topographical map with grid informationb. Roughness map and roughness length definitionc. CFD simulation settings
1) Software
2) Applied model
3) Analysis region definition
4) Horizontal grid size:- Area corresponding to the minimum grid size
- Rate of elongation- Maximum grid size
- Figures containing the above items
5) Vertical grid size:- 39 -

(2)

B.3.2

- Minimum grid size
- Rate of elongation- Figures containing the above items
Results of validity verification (including the following content):a. Results of comparison of the airflow analysis with the measurement data regarding the average wind speed by winddirection
b. Results of comparison of the airflow analysis with the measurement data regarding the vertical profiles of wind
shear by wind direction
c. Results of comparison of the airflow analysis with the measurement data regarding the turbulence intensity by winddirection

Report on the airflow analysis applied to the wind conditions during parked by storm and its validity-1. Reports on the airflow analysis applied to the calculation of the wind conditions during parked by storm and on theverification of the validity of that analysis shall include at least the following items.
(1) Details of the airflow analysis (including the following content):a. Topographical map with grid informationb. Roughness map and roughness length definitionc. CFD simulation settings
1) Software
2) Applied model
3) Analysis region definition
4) Horizontal grid size:- Area corresponding to the minimum grid size
- Rate of elongation- Maximum grid size
- Figures containing the above items
5) Vertical grid size:- Minimum grid size
- Rate of elongation- Figures containing the above items
d. The following items when a method that considers the wind directional characteristics shown in C.3.1-4. (2) isapplied1) Probability distribution function for typhoon parameters
2) Probability distribution chart for typhoon parameters from analysis results(2)

Results of validity verification (including the following content):a. Results of comparison of the airflow analysis with the measurement data regarding the average wind speed by winddirection
b. Results of comparison of the airflow analysis with the measurement data regarding the vertical profiles of wind
shear by wind direction
c. Results of comparison of the airflow analysis with the measurement data regarding the turbulence intensity by winddirectiond. The following items when a method that considers the wind directional characteristics shown in C.3.1-4. (2) isapplied1)
Figure comparing the typhoon simulation results (upper air winds due to the hypothetical typhoon) with themeasured values (upper air winds calculated from the atmospheric pressure in the typhoon database)2)
Figure showing the non-exceedance probability distribution of the annual maximum wind speed due totyphoons on flat terrain and on the actual terrain
3)
Figure showing the validity of the setting of the wind direction to be verified
e. When the simulation results are an underestimation in d. above, the results of consideration of the effects ofuncertainty related to the number of years of analysis and the number of years of atmospheric pressure
measurement- 40 -

Annex C.

C.1

Evaluation method for wind conditions [informative / normative]

General-1. The calculation method for the wind conditions during power production that is shown in C.2 is shown as a reference. This
does not deny any method that is not based on these rules.
-2. The calculation method for the wind conditions during parked by storm that are shown in C.3.1 and C.3.2 are based on the
Guidelines for Design of Wind Turbine Support Structures and Foundation[J-05], and not following this rule is not permitted.

C.2

Wind conditions during power production

C.2.1

Wind speed appearance frequency distribution and average wind speed-1. The wind speed appearance frequency distribution function 𝑝𝑝(𝑉𝑉hub ) shall be approximated by the Weibull distribution
expressed by equation (C.1).
𝑝𝑝(𝑉𝑉hub ) =𝑉𝑉hub 𝑚𝑚
𝑚𝑚 𝑉𝑉hub 𝑚𝑚−1��𝑒𝑒𝑒𝑒𝑒𝑒 �− �
� �
𝜂𝜂
𝜂𝜂 𝜂𝜂

(C. 1)

Here, 𝜂𝜂 and 𝑚𝑚 are the scale factor and shape factor of the Weibull distribution, respectively, and are obtained from theaverage wind speed 𝑉𝑉ave and average wind speed standard deviation 𝜎𝜎v obtained from measurement by using by equations(C.2) and (C.3).

�

∞

0

�

∞

0

𝑚𝑚 𝑉𝑉ℎ𝑢𝑢𝑏𝑏 𝑚𝑚−1
𝑉𝑉ℎ𝑢𝑢𝑢𝑢 𝑚𝑚��𝑒𝑒𝑒𝑒𝑒𝑒 �− �� � 𝑉𝑉ℎ𝑢𝑢𝑢𝑢 𝑑𝑑𝑉𝑉ℎ𝑢𝑢𝑢𝑢 = 𝑉𝑉𝑎𝑎𝑎𝑎𝑎𝑎
𝜂𝜂
𝜂𝜂
𝜂𝜂

𝑉𝑉ℎ𝑢𝑢𝑢𝑢 𝑚𝑚
𝑚𝑚 𝑉𝑉ℎ𝑢𝑢𝑢𝑢 𝑚𝑚−1��𝑒𝑒𝑒𝑒𝑒𝑒 �− �� � (𝑉𝑉ℎ𝑢𝑢𝑢𝑢 − 𝑉𝑉𝑎𝑎𝑎𝑎𝑎𝑎 )𝑑𝑑𝑉𝑉ℎ𝑢𝑢𝑢𝑢 = 𝜎𝜎𝑉𝑉2
𝜂𝜂
𝜂𝜂
𝜂𝜂

(C. 2)(C. 3)-2. The time series data 𝑈𝑈𝑅𝑅 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃, 𝑡𝑡) of the average wind speed at wind turbine position and hub height are obtained byusing equation (C.4).
Where:𝑈𝑈𝑀𝑀 (ℎ, 𝜃𝜃, 𝑡𝑡)

𝐶𝐶𝑉𝑉 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃)::

𝑈𝑈𝑅𝑅 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃, 𝑡𝑡) = 𝑈𝑈𝑀𝑀 (ℎ, 𝜃𝜃, 𝑡𝑡) ⋅ 𝐶𝐶𝑉𝑉 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃)(C. 4)

Time series data of wind speed obtained from measurement data at the measurement mast
position and measurement height
The wind speed ratio found from the wind speed 𝑢𝑢 𝑇𝑇 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃) in the wind direction 𝜃𝜃
at the wind turbine position and hub height found using airflow analysis and the windspeed 𝑢𝑢𝑀𝑀 (𝑥𝑥, 𝑦𝑦, ℎ, 𝜃𝜃) in wind direction 𝜃𝜃 at measurement mast position and measurement
height found using airflow analysis, which is found from the following equation [=𝑢𝑢 𝑇𝑇 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃)⁄𝑢𝑢𝑀𝑀 (𝑥𝑥, 𝑦𝑦, ℎ, 𝜃𝜃)]

-3. The average wind speed in each direction at the wind turbine position and hub height 𝑉𝑉𝑎𝑎𝑎𝑎𝑎𝑎 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃) is obtained by using
equation (C.5).

Where:
𝑁𝑁

C.2.2

:

𝑉𝑉𝑎𝑎𝑎𝑎𝑎𝑎 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃) =∑𝑁𝑁
𝑖𝑖=1 𝑈𝑈𝑅𝑅 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃, 𝑡𝑡)
𝑁𝑁(C. 5)

Number of measurement data included in the relevant direction (Number of items in timeseries data)

Calculation method for turbulence intensity-1. The time series data 𝜎𝜎𝑅𝑅 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃, 𝑡𝑡) of the ambient turbulence standard deviation at the wind turbine position and hub
height is obtained by using equation (C.6).
(C. 6)𝜎𝜎𝑅𝑅 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃, 𝑡𝑡) = 𝜎𝜎𝑀𝑀 (ℎ, 𝜃𝜃, 𝑡𝑡) ⋅ 𝐶𝐶𝑆𝑆 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃)- 41 -

Where:𝜎𝜎𝑀𝑀 (ℎ, 𝜃𝜃, 𝑡𝑡)

𝐶𝐶𝑆𝑆 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃)::Time series data of ambient turbulence standard deviation obtained from measurement dataat the measurement mast position and measurement height
Ambient turbulence standard deviation in wind direction 𝜃𝜃 at wind turbine position andhub height from airflow analysis
As 𝜎𝜎𝑇𝑇 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃), the wind speed ratio found from the ambient turbulence standard
deviation 𝜎𝜎𝑀𝑀 (𝑥𝑥, 𝑦𝑦, ℎ, 𝜃𝜃) in wind direction 𝜃𝜃 at the measurement mast position and themeasurement height found using airflow analysis, which is found from the following
equation [= 𝜎𝜎𝑇𝑇 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃)⁄𝜎𝜎𝑀𝑀 (𝑥𝑥, 𝑦𝑦, ℎ, 𝜃𝜃)]

-2. The turbulence intensity 𝐼𝐼𝑟𝑟𝑟𝑟𝑟𝑟 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃, 𝑉𝑉𝑖𝑖 ) representing the direction 𝜃𝜃 and the 𝑖𝑖th wind speed bin at the wind turbine

position and hub height is the 90% quantile of the ambient turbulence standard deviation and is obtained by using equation (C.7).

Where:𝜎𝜎(𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃, 𝑉𝑉𝑖𝑖 )𝜎𝜎𝜎𝜎 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃, 𝑉𝑉𝑖𝑖 )𝑉𝑉𝑖𝑖 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃)

𝐼𝐼𝑟𝑟𝑟𝑟𝑟𝑟 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃, 𝑉𝑉𝑖𝑖 ) =:::𝜎𝜎(𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃, 𝑉𝑉𝑖𝑖 ) + 1.28𝜎𝜎𝜎𝜎 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃, 𝑉𝑉𝑖𝑖 )𝑉𝑉𝑖𝑖 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃)(C. 7)

Ambient turbulence standard deviation at direction 𝜃𝜃 and 𝑖𝑖th wind speed binStandard deviation of the ambient turbulence standard deviation at direction 𝜃𝜃 and 𝑖𝑖 thwind speed bin
Wind speed representative of the 𝑖𝑖th wind speed bin in the direction 𝜃𝜃-3. The turbulence intensity 𝐼𝐼𝑟𝑟𝑟𝑟𝑟𝑟,𝑖𝑖 representing the 𝑖𝑖th wind speed bin representing all directions is weighted and averaged
using the wind speed appearance frequency in each direction and obtained by using equation (C.8).

C.2.3

Where:
𝐹𝐹(𝜃𝜃)

𝐼𝐼𝑟𝑟𝑟𝑟𝑟𝑟,𝑖𝑖 = � �𝐼𝐼𝑟𝑟𝑟𝑟𝑟𝑟 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃, 𝑉𝑉𝑖𝑖 )𝐹𝐹(𝜃𝜃)�
𝜃𝜃

:(C. 8)

Wind speed appearance frequency or energy density in direction 𝜃𝜃Calculation method for wind shear exponent-1. The wind shear exponent for each direction at the wind turbine position and hub height 𝛼𝛼(𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃) shall be obtained byusing the least squares method with the average wind speed of each direction 𝜃𝜃 at the top of the rotor plane, the hub height andthe bottom of the rotor plane. This can also be calculated by using equation (C.9), but it is preferable to handle that value as areference.

Where:𝑉𝑉𝑈𝑈 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻𝑈𝑈 , 𝜃𝜃)
𝑉𝑉𝐿𝐿 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻𝐿𝐿 , 𝜃𝜃)
𝐻𝐻𝑈𝑈
𝐻𝐻𝐿𝐿
𝑑𝑑

:
:
:
:
:

𝑉𝑉 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻𝑈𝑈 , 𝜃𝜃)ln � 𝑈𝑈�𝑉𝑉𝐿𝐿 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻𝐿𝐿 , 𝜃𝜃)𝛼𝛼(𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃) =𝐻𝐻 − 𝑑𝑑ln � 𝑈𝑈�
𝐻𝐻𝐿𝐿 − 𝑑𝑑(C. 9)

Average wind speed at the top of the rotor plane at the wind turbine position in direction 𝜃𝜃Average wind speed at the bottom of the rotor plane at the wind turbine position in direction 𝜃𝜃
Height of the top of the rotor plane
Height of the bottom of the rotor plane

Zero plane displacement (displacement height)-2. The wind shear exponent representing all directions 𝛼𝛼 is weighted and averaged using the wind speed appearance frequency
in each direction and obtained by using equation (C.10).

- 42 -

Where:𝐹𝐹(𝜃𝜃)

C.2.4-1.

(C. 10)𝛼𝛼 = ��𝛼𝛼(𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃)𝐹𝐹(𝜃𝜃)�
𝜃𝜃:Wind speed appearance frequency or energy density in direction 𝜃𝜃Calculation method for inflow angle
The inflow angle in each direction at the wind turbine position and hub height 𝜑𝜑(𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃) is obtained by using equation(C.11).

Where:
𝑢𝑢 𝑇𝑇1 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃)𝑢𝑢 𝑇𝑇2 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃)𝑢𝑢 𝑇𝑇3 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃)𝑢𝑢 𝑇𝑇3 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃)𝜑𝜑(𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃) = 𝑡𝑡𝑡𝑡𝑡𝑡−1 ⎛
:
:
:

2

2

⎞

�
⎝ �𝑢𝑢 𝑇𝑇1 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃)� + �𝑢𝑢 𝑇𝑇2 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃)� ⎠(C. 11)Longitudinal component of the wind speed in wind direction 𝜃𝜃 at wind turbine positionand hub height from airflow analysis
Lateral component of the wind speed in wind direction 𝜃𝜃 at wind turbine position andhub height from airflow analysis
Vertical component of the wind speed in wind direction 𝜃𝜃 at wind turbine position andhub height from airflow analysis-2. The inflow angle representing all directions 𝜑𝜑 is weighted and averaged using the wind speed appearance frequency in eachdirection and obtained by using equation (C.12).

Where:
𝐹𝐹(𝜃𝜃)

C.2.5

𝜑𝜑 = ��𝜑𝜑(𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃)𝐹𝐹(𝜃𝜃)�
𝜃𝜃

:(C. 12)Wind speed appearance frequency or energy density in direction 𝜃𝜃Calculation method for atmospheric density-1. The atmospheric density is calculated from the atmospheric temperature and atmospheric pressure observed at the site byusing the equation (C.13).

Where:
𝐵𝐵
𝑇𝑇
𝑅𝑅0

𝜌𝜌 =
:
:
:

𝐵𝐵
𝑇𝑇 × 𝑅𝑅0(C. 13)

Atmospheric pressure
Atmospheric temperature
Gas constant (287.05 [𝐽𝐽/𝑘𝑘𝑘𝑘𝑘𝑘])-2. When there is no measurement data regarding the atmospheric density at the site, there are cases in which the long-term
measurement data from a nearby meteorological observatory can be applied by carrying out altitude correction regarding theelevation. However, in this case, the basis for the applicability of the data shall be clearly stated.

- 43 -

C.3

Wind conditions during parked by storm

C.3.1

Calculation method for extreme wind speed (10 minutes average wind speed with a return period of
50 years)-1. The 10 minutes average wind speed with a return period of 50 years at wind turbine position and hub height 𝑈𝑈ℎ shall beobtained by multiplying the reference wind speed 𝑉𝑉0 by the topographic multiplier for the average wind speed 𝐸𝐸𝑡𝑡𝑡𝑡 and thealtitude correction coefficient 𝐸𝐸𝑝𝑝𝑝𝑝 and is determined by equation (C.14). However, the reference wind speed 𝑉𝑉0 shall be the 10

minutes average wind speed with a return period of 50 years at a height of 10 m above flat ground that has a ground surface
roughness classification of II, and the reference wind speed used shall be that shown per municipality in No. 2 of the Ministry ofConstruction Notification No. 1454 in 2000.
𝑈𝑈ℎ = 𝐸𝐸𝑡𝑡𝑉𝑉 𝐸𝐸𝑝𝑝𝑝𝑝 𝑉𝑉0(C. 14)-2. The ground surface roughness classification at the wind turbine position is determined according to the Ministry ofConstruction Notification No. 1454 in 2000 (Ministry of Land, Infrastructure, Transport and Tourism Notification No. 1437)
according to Table C.1.

Roughness classI

II

Table C.1 Categorization of ground surface roughness classifications
Ground surface conditions around the construction site
Areas specified in a regulation by a Designated Administrative Agency as being
extremely flat and having no obstacles
Of the areas other than the areas in the ground roughness classes I and IV, the areas where
the distance to the shoreline or lake shoreline (This is limited to cases where the distanceto the opposite shore is 1,500 m or more. The same shall apply hereafter.) is 500 m or less
(Excluding in cases where the height of the building is 13 m or less, or the distance to theshoreline or lake shoreline exceeds 200 m and the height of the building is 31 m or less.),or areas other than such areas which are specified in a regulation by a DesignatedAdministrative Agency as being extremely flat and interspersed with obstacles.

III

Areas other than roughness class I, II or IV

IV

Areas specified in a regulation by a Designated Administrative Agency as being
extremely urbanized-3. The altitude correction coefficient 𝐸𝐸𝑝𝑝𝑝𝑝 for the average wind speed at hub height above flat terrain is calculated according to

the ground surface roughness classification by using equation (C.15). Here, 𝐻𝐻ℎ is the hub height (m), and 𝑍𝑍𝑏𝑏 , 𝑍𝑍𝐺𝐺 and 𝛼𝛼 areparameters indicating the vertical distribution of wind speed and are defined by Table C.2 according to the ground surface
roughness classification. The altitude correction coefficient for the average wind speed at height 𝑍𝑍 is obtained by substituting 𝑍𝑍
for 𝐻𝐻ℎ in equation (C.15).
𝐸𝐸𝑝𝑝𝑝𝑝 =𝛼𝛼⎧1.7 �𝐻𝐻ℎ �⎪
𝑍𝑍𝐺𝐺

𝑍𝑍𝑏𝑏 𝛼𝛼⎨⎪1.7 � �
𝑍𝑍𝐺𝐺⎩

𝑍𝑍𝑏𝑏 < 𝐻𝐻ℎ ≤ 𝑍𝑍𝐺𝐺

𝐻𝐻ℎ ≤ 𝑍𝑍𝑏𝑏

Table C.2 Parameters to determine the altitude correction coefficient for average wind speed
Roughness class
I
II
III
IV
𝑍𝑍𝑏𝑏
5
5
5
20
𝑍𝑍𝐺𝐺
250
350
450
550
𝛼𝛼
0.10
0.15
0.20
0.27

(C. 15)-4. The topographic multiplier for the average wind speed 𝐸𝐸𝑡𝑡𝑡𝑡 and the wind direction to be verified 𝜃𝜃𝑑𝑑 are determined byeither of the following methods (1) and (2).
(1) Method that does not consider the wind directional characteristics
The topographic multiplier for the average wind speed 𝐸𝐸𝑡𝑡𝑡𝑡 is decided by the equation (C.16) based on the results ofairflow analysis by wind direction on the actual terrain and on flat terrain. Here, 𝑈𝑈 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃) is the average wind
- 44 -

speed obtained by airflow analysis for wind direction 𝜃𝜃 at the wind turbine position and hub height 𝐻𝐻ℎ on the actual
terrain, and 𝑈𝑈 𝑃𝑃 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ ) is the average wind speed at the hub height 𝐻𝐻ℎ at the wind turbine construction site that was
obtained by airflow analysis for flat terrain of ground surface roughness classification 𝑃𝑃. In addition, the wind direction to
be verified 𝜃𝜃𝑑𝑑 shall be the wind direction where the multiplier for the wind speed per wind direction is the largest.
′(2)

𝐸𝐸𝑡𝑡𝑡𝑡 = 𝑚𝑚𝑚𝑚𝑚𝑚 �𝐸𝐸𝑡𝑡𝑡𝑡 (𝜃𝜃𝑑𝑑 ), 1� ,′′𝐸𝐸𝑡𝑡𝑡𝑡 (𝜃𝜃𝑑𝑑 ) = 𝑚𝑚𝑚𝑚𝑚𝑚 �𝐸𝐸𝑡𝑡𝑡𝑡 (𝜃𝜃)� ,C.3.2.1

𝑈𝑈 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃)
𝑈𝑈𝑃𝑃 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ )(C. 16)

Method that considers the wind directional characteristics
The topographic multiplier for the average wind speed 𝐸𝐸𝑡𝑡𝑡𝑡 is decided by the equation (C.17) based on the results of
typhoon simulations for the wind turbine construction site. Here, 𝑈𝑈50 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ ) is the expected annual maximum windspeed with a return period of 50 years at the hub height 𝐻𝐻ℎ at the wind turbine construction site, which is obtained by
𝑃𝑃 (𝑥𝑥,statistical analysis from the result of the typhoon simulation, and 𝑈𝑈50
𝑦𝑦, 𝐻𝐻ℎ ) is the expected annual maximum windspeed with a return period of 50 years at the hub height above flat terrain of the ground surface roughness classification. In
addition, the wind direction to be verified 𝜃𝜃𝑑𝑑 shall be the wind direction corresponding to 𝑈𝑈50 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ ). The validity ofthe simulation results must be sufficiently confirmed by comparing them with the measured values. Further, if thecomparison of the typhoon simulation results (upper air winds due to the hypothetical typhoon) with the measured values(upper air winds calculated from the atmospheric pressure in the typhoon database) indicates that the simulation results are
an underestimation, additional consideration must be given to the effects of uncertainty related to the number of years ofanalysis and the number of years of atmospheric pressure measurement. In addition, the validity of the setting of the winddirection to be verified must be sufficiently confirmed.
′
𝐸𝐸𝑡𝑡𝑡𝑡 = 𝑚𝑚𝑚𝑚𝑚𝑚(𝐸𝐸𝑡𝑡𝑡𝑡, 1) ,

C.3.2′

𝐸𝐸𝑡𝑡𝑡𝑡 (𝜃𝜃) =′𝐸𝐸𝑡𝑡𝑡𝑡=𝑈𝑈50 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ )𝑃𝑃 (𝑥𝑥,𝑦𝑦, 𝐻𝐻ℎ )𝑈𝑈50(𝐶𝐶. 17)

Calculation method for extreme wind speed (3 seconds average wind speed)
Calculation method for turbulence intensity-1. The principal wind direction component of the turbulence intensity during a storm at the wind turbine position 𝐼𝐼ℎ1 shall beobtained by multiplying the turbulence intensity on flat terrain 𝐼𝐼𝑃𝑃 by the correction coefficient for the turbulence intensity due tothe terrain 𝐸𝐸𝑡𝑡𝑡𝑡 and is obtained by using equation (C.18).

(C. 18)𝐼𝐼ℎ1 = 𝐸𝐸𝑡𝑡𝑡𝑡 𝐼𝐼𝑃𝑃

-2. The turbulence intensity at hub height on flat terrain 𝐼𝐼𝑃𝑃 is calculated according to the ground surface roughnessclassification by using equation (C.17). Here, 𝐻𝐻ℎ is the hub height (m), and 𝑍𝑍𝑏𝑏 , 𝑍𝑍𝐺𝐺 and 𝛼𝛼 are parameters indicating thevertical distribution of wind speed and are defined by Table C.2 according to the ground surface roughness classification. The
turbulence intensity at height 𝑍𝑍 is obtained by substituting 𝑍𝑍 for 𝐻𝐻ℎ in equation (C.19).
−𝛼𝛼−0.05⎧0.1 �𝐻𝐻ℎ �⎪
𝑍𝑍𝐺𝐺
𝐼𝐼𝑃𝑃 =
𝑍𝑍𝑏𝑏 −𝛼𝛼−0.05⎨⎪0.1 � �
𝑍𝑍𝐺𝐺⎩

𝑍𝑍𝑏𝑏 < 𝐻𝐻ℎ ≤ 𝑍𝑍𝐺𝐺

𝐻𝐻ℎ ≤ 𝑍𝑍𝑏𝑏

(C. 19)-3. The correction coefficient for the turbulence intensity due to the terrain 𝐸𝐸𝑡𝑡𝑡𝑡 is determined by the equation (C.20). Of themethods shown in C.3.1-4., if the method selected is (1) Method that does not consider the wind directional characteristics, then′(𝜃𝜃𝑑𝑑 ) is obtained by equation (C.16), and if the method selected is (2) Method that considers the wind directional
𝐸𝐸𝑡𝑡𝑡𝑡characteristics, then it is obtained by equation (C.21). Here, 𝑈𝑈 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃) is the average wind speed obtained by airflow
analysis for wind direction θ at hub height 𝐻𝐻ℎ at the wind turbine construction site on the actual terrain, and 𝑈𝑈 𝑃𝑃 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ ) is theaverage wind speed at the hub height 𝐻𝐻ℎ at the wind turbine construction site that was obtained by airflow analysis for flat
terrain of ground surface roughness classification 𝑃𝑃.
′

𝐸𝐸𝑡𝑡𝑡𝑡 = 𝑚𝑚𝑚𝑚𝑚𝑚 �𝐸𝐸𝑡𝑡𝑡𝑡 (𝜃𝜃𝑑𝑑 )⁄𝐸𝐸𝑡𝑡𝑡𝑡 (𝜃𝜃𝑑𝑑 ) , 1�

- 45 -(C. 20)′𝐸𝐸𝑡𝑡𝑡𝑡 (𝜃𝜃𝑑𝑑 ) =𝑈𝑈 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃𝑑𝑑 )𝑈𝑈𝑃𝑃 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ )(C. 21)

𝜎𝜎𝑢𝑢 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃𝑑𝑑 )𝜎𝜎𝑢𝑢𝑃𝑃 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ )(C. 22)-4. The correction coefficient for the fluctuating wind speed due to the terrain 𝐸𝐸𝑡𝑡𝑡𝑡 is determined by equation (C.22) regardlessof whether the method selected is (1) Method that does not consider the wind directional characteristics or (2) Method thatconsiders the wind directional characteristics in C.3.1-4. Here, 𝜎𝜎𝑢𝑢 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃𝑑𝑑 ) is the standard deviation of the wind speed
fluctuation in the principal wind direction at the hub height 𝐻𝐻ℎ in the wind direction to be verified on the actual terrain 𝜃𝜃𝑑𝑑 , and
𝜎𝜎𝑢𝑢𝑃𝑃 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ ) is the standard deviation of the wind speed fluctuation in the principal wind direction at the hub height 𝐻𝐻ℎ on flat
terrain with a ground surface roughness classification 𝑃𝑃, which are obtained from airflow analysis.
𝐸𝐸𝑡𝑡𝑡𝑡 (𝜃𝜃𝑑𝑑 ) =-5. In order to obtain the standard deviation of the wind speed fluctuation in the principal wind direction 𝜎𝜎𝑢𝑢 from airflow
analysis, it is also possible to calculate it by using equation (C.24) after using equation (C.23) to calculate the standard deviation
𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠of the wind speed fluctuation in the principal wind direction caused by the terrain and the surface roughness 𝜎𝜎𝑢𝑢
from theturbulent flow energy k in the k-epsilon model, etc. However, in this case, the background turbulence intensity 𝐼𝐼𝑎𝑎 shall be 0.1.
𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠

𝜎𝜎𝑢𝑢(C. 23)= √1.2𝑘𝑘

𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 2

𝜎𝜎𝜎𝜎𝑢𝑢 = 𝑈𝑈 × �� 𝑢𝑢 � + 𝐼𝐼𝑎𝑎2
𝑈𝑈

C.3.2.2(C. 24)

Calculation method for 3 seconds average wind speed-1. The extreme 3 seconds average wind speed at hub height with a return period of 50 years 𝑈𝑈𝑒𝑒50 is calculated by equation(C.25) by using the 𝑈𝑈ℎ calculated using equation (C.14).
Where:𝐺𝐺𝑓𝑓 = 1 + 3.5𝐼𝐼ℎ1

C.3.2.3(C. 25)

𝑈𝑈𝑒𝑒50 = 𝐺𝐺𝑓𝑓 𝑈𝑈ℎ*Reference: In IEC61400-1:2019[J-02], 𝐺𝐺𝑓𝑓 ≒ 1.4 is used as 𝐼𝐼ℎ1 = 0.11.

Calculation method for wind shear for extreme wind speed-1. The wind shear exponent 𝛼𝛼(𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃𝑑𝑑 ) corresponding to the 10 minutes average wind speed with a return period of 50
years at wind turbine position and hub height 𝑈𝑈ℎ , is obtained by the least squares method using the horizontal wind speed withconsideration of the principal flow direction component 𝑈𝑈1 and the principal flow direction perpendicular component 𝑈𝑈2 at thefollowing three heights at wind turbine position and wind direction to be checked 𝜃𝜃𝑑𝑑 of hub height, which is obtained fromairflow analysis.
2

2

2

2

(1)

Horizontal wind speed at the top of the rotor plane:𝑈𝑈𝑈𝑈 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻𝑈𝑈 , 𝜃𝜃𝑑𝑑 ) = ��𝑈𝑈1 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻𝑈𝑈 , 𝜃𝜃𝑑𝑑 )� + �𝑈𝑈2 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻𝑈𝑈 , 𝜃𝜃𝑑𝑑 )�

(2)

Horizontal wind speed at hub height:𝑈𝑈ℎ (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃𝑑𝑑 ) = ��𝑈𝑈1 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃𝑑𝑑 )� + �𝑈𝑈2 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻ℎ , 𝜃𝜃𝑑𝑑 )�

(3)

Horizontal wind speed at the bottom of the rotor plane :𝑈𝑈𝐿𝐿 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻𝐿𝐿 , 𝜃𝜃𝑑𝑑 ) = ��𝑈𝑈1 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻𝐿𝐿 , 𝜃𝜃𝑑𝑑 )� + �𝑈𝑈2 (𝑥𝑥, 𝑦𝑦, 𝐻𝐻𝐿𝐿 , 𝜃𝜃𝑑𝑑 )�

2- 46 -

2

C.3.3Calculation method for 𝑈𝑈𝑒𝑒50 using wind condition measurement data [informative]-1. The method to use measurement data to calculate the turbulence intensity 𝐼𝐼ℎ1 during a parked by storm and find 𝑈𝑈𝑒𝑒50 isshown below.
(1) Use airflow analysis to calculate the ratio of the wind speed and the ratio of the turbulence standard deviation between themeasurement position and each wind turbine position for each direction.
(2) Create time series data for the wind speed and turbulence standard deviation at the wind turbine position by multiplying
measurement data (10 minutes value time series data) which satisfies the provisions of 2.2.1 by the ratio obtained in (1).
(3) When the method that does not consider the wind directional characteristics in C.3.1-4. (1) is used in the calculation of the
10 minutes average wind speed at hub height with a return period of 50 years (𝑈𝑈ℎ ), calculate the turbulence intensity bywind speed bin with consideration of all wind directions. When the method that considers the wind directional
characteristics in C.3.1-4. (2) is used, calculate the turbulence intensity by wind speed class for each wind direction.
(4) For the turbulence intensity by wind speed class created in (3), calculate the turbulence intensity corresponding to the 50%
quantile (non-exceedance probability of 50%) for each wind speed class, and calculate 𝐼𝐼ℎ1,𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚 from the turbulence
intensity value corresponding to the 50% quantile (non-exceedance probability of 50%) in the range that is not less thanhalf the wind speed of 𝑉𝑉0 at the site.
 For the calculation of 𝐼𝐼ℎ1,𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚 , the specific calculation method such as whether to use the average value or the
maximum value, etc., of the turbulence intensity corresponding to the 50% quantile (probability of non-exceedance
50%) in the range that is not less than half the wind speed of 𝑉𝑉0 shall be selected according to the trends in themeasurement data, with selection so that it is on the safe side.
 When the method that considers the wind directional characteristics in C.3.1-4. (2) is used in the calculation of 𝑈𝑈ℎ , itshould be noted that it is necessary to calculate 𝐼𝐼ℎ1,𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚 using the turbulence intensity by wind speed class in the winddirection to be verified 𝜃𝜃𝑑𝑑 , and that the number of measurement data in the wind direction must be sufficient, including
the data in the high wind speed region.
(5) Use whichever is the larger of the 𝐼𝐼ℎ1,𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚 obtained in (4) and the turbulence intensity above flat terrain according to theground surface roughness classification 𝐼𝐼𝑝𝑝 as 𝐼𝐼ℎ1 and use equation (C.25) to calculate 𝑈𝑈𝑒𝑒50 .

-2. In order to show the validity of the turbulence intensity during a storm 𝐼𝐼ℎ1 that was calculated using measurement data, afigure must be prepared which is a plot of the turbulence intensity values used in the calculation and also includes a plot showing
the 50% quantile (non-exceedance probability of 50%) of the turbulence intensity by each wind speed class, a line showing thevalues of 𝐼𝐼𝑝𝑝 and a line showing the values of 𝐼𝐼ℎ1,𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚 .

C.4

Reports on wind conditions

C.4.1

Report on wind conditions during power production-1. Reports on the wind conditions during power production shall include at least the following items for all wind turbine
positions and hub heights.
(1) Average wind speed (including the following content):a. The Weibull shape and scale factors for each direction, and the wind direction appearance frequency distribution(with a wind direction sector width of 30° or less and the first sector centered on true north) specified in tabularform for each wind turbine position (hub height).
b. Or else, the detailed appearance rate distribution (according to the bin method; wind speed bin width of 1 m/s, winddirection sector width of 30° or less, and first sector centered on true north) described in tabular form for each windturbine hub height position.
(2) Turbulence intensity (including the following content):a. The turbulence intensity at the wind turbine position hub height described in tabular form for each wind speed bin(bin width 1 m/s or less) and wind direction bin (bin width 30° or less). Also describe the characteristic
value/representative value of turbulence intensity applied to the design specified in the type certification for theplanned wind turbine.
(3) Wind shear exponent (including the following content):a.
The average value, minimum value, and maximum value of the wind shear exponent in the wind turbine position,
described in tabular form with a wind direction sector width of 30° or less.
(4) Flow inclination angle (including the following content):a. The average value, minimum value, and maximum value of the estimated value of the average flow inclination
angle at the wind turbine position at hub height, described in tabular form with a wind direction sector width of 30°
or less.

- 47 -

C.4.2

Report on wind conditions during parked by storm-1. Reports on the airflow analysis applied to the calculation of the wind conditions during parked by storm and on theverification of the validity of that analysis shall include at least the following items for all wind turbine positions and hub heights.
(1) 10 minutes average wind speed: 𝑈𝑈ℎ(2) Turbulence intensity: 𝐼𝐼ℎ1
(3)

(4)

3 seconds average wind speed: 𝑈𝑈𝑒𝑒50
Wind shear exponent-2. For the parameters defined in this Annex that are used for the calculation of each of the values in -1 above, all of the values
by direction shall be shown, and it must be possible to appropriately confirm the setting of the wind direction to be verified and its
calculation process.
-3. When calculating 𝑈𝑈𝑒𝑒50 using wind condition measurement data, it must be possible to appropriately confirm the basis for
the 𝐼𝐼ℎ1 calculation, including the figures specified in C3.3-2.

C.4.3

Other conditions-1. The following conditions must be included.
(1) Site temperature range based on field measurements, etc.
(2)

C.5

Site humidity range based on field measurements, etc.

Reference documents[C1] JIS W 0201: 1990

: Standard atmosphere[C2] Ishihara, T. and Yamaguchi, A., Prediction of the extreme wind speed in mixed climate region by using Monte Carlosimulation and Measure-Correlate-Predict method, Wind Energy, 2014.
[C3] Ueda et al., Validation of Evaluation Method of Turbulence Intensity by CFD with field measurements, proceedings of the37th Wind Energy Symposium, pp. 245-246, 2015.

- 48 -

Annex D.
D.1

Equivalent wind pressure coefficient for the nacelle cover [informative]

General-1. The equivalent wind pressure coefficient for the nacelle cover varies greatly depending on the shape of the nacelle cover. This
Annex shows the equivalent wind pressure coefficient (positive/negative) for a rectangular nacelle cover with rounded corners.
-2. In the calculation of the equivalent maximum/minimum wind pressure coefficient for this rectangular nacelle cover withrounded corners, wind tunnel tests have been carried out under the test conditions shown in Table D.1.
Table D.1 Main conditions for wind tunnel tests
Wind tunnel measurement section

W: 3.1 m × H: 2.0 m × L: 16.0 m

Model position

14.75 m from the upstream end of the measurement tunnel

Average wind speed

10.0 m/s (Hub height)

Turbulence intensity

12.7% (Hub height)

Vertical profile of wind speed

0.2 (Hub height center)

Test wind direction

72 wind directions with 5° pitch

Model (Scale 1/50)• Nacelle: 250 x 80 x 80 (mm)• Tower: 60 φ (mm)*A photograph of the model is shown in Figure D-1.

Hub height

Height above wind tunnel floor: 400 mm

Pressure measurement holes

200 points (with consideration of symmetry)

Sampling

800 Hz, moving average processing for 6 items

Data length

60 seconds (Equivalent to 600 seconds real time)

Data count1 sample (60 seconds) with 5 samplesa) Wind tunnel test modelb) Installation of turbulent boundary layer generator
Figure D.1 Wind tunnel test model- 49 -

D.2

Equivalent wind pressure coefficient [Wind direction: -15° to +15°]-1. The equivalent wind pressure coefficient [positive value] and the equivalent wind pressure coefficient [negative value]
obtained from the wind tunnel test results in the range of -15° to +15°, which are the wind directions to be considered in DLC6.1,
are shown in Figure D.2 and D.3, respectively.
-2. The equivalent wind pressure coefficient [positive value] shown in Figure D.2 corresponds to the "𝐶𝐶̂𝑒𝑒𝑒𝑒 - Positive value"

applied to NC.1-1 in Table 5-2, and the equivalent wind pressure coefficient [negative value] shown in Figure D.3 corresponds tothe "𝐶𝐶̂𝑒𝑒𝑒𝑒 - Negative value" applied to NC.1-2 in Table 5-2.

Figure D.2 Equivalent wind pressure coefficient [Wind direction: -15° to +15° - Positive value]

Figure D.3 Equivalent wind pressure coefficient [Wind direction: -15° to +15° - Negative value]- 50 -

D.3

Equivalent wind pressure coefficient [Wind direction: All wind directions]-1. The equivalent wind pressure coefficient [positive value] and the equivalent wind pressure coefficient [negative value]
obtained from the wind tunnel test results for all wind directions, which are the wind directions to be considered in DLC6.2, areshown in Figure D.4 and D.5, respectively.
-2. The equivalent wind pressure coefficient [positive value] shown in Figure D.4 corresponds to the "𝐶𝐶̂𝑒𝑒𝑒𝑒 - Positive value"
applied to NC.2-1 in Table 5-2, and the equivalent wind pressure coefficient [negative value] shown in Figure D.5 corresponds tothe "𝐶𝐶̂𝑒𝑒𝑒𝑒 - Negative value" applied to NC.2-2 in Table 5-2.

Figure D.4 Equivalent wind pressure coefficient [All wind directions - Positive value]

Figure D.5 Equivalent wind pressure coefficient [Wind direction: All wind directions - Negative value]- 51 -

D.4

Reference documents[D1]

RENEWABLE ENERGY 2019; 2019.10. Nippon Kaiji Kyokai[D2]

H. Noda and T. Ishihara:Wind tunnel test on mean wind forces and peak pressures acting on wind turbine nacelles, Wind
Energy 2014; 17:1-17- 52 -

Annex E.

Measurement testing for fluctuating pressure characteristics acting on a nacellesurface [informative]

E.1

GeneralE.2

Selection of wind tunnel

E.3

Model and test conditions

E.3.1

Model

E.3.2

Airflow similarity-1. The values and distributions of the equivalent maximum/minimum wind pressure coefficients for the nacelle cover depend on
the shape of the nacelle cover, so it is appropriate to carry out wind tunnel testing according to the wind turbine type in order to
conduct the calculations and set the values rationally and on the safe side. This Annex summarizes the contents to be referred towhen implementing wind tunnel testing.
-2. Note that the scope of this Annex is wind tunnel tests for the purpose of measuring the fluctuating pressure acting on thesurface of the nacelle cover. Wind tunnel tests for the purpose of other measurements are not covered.

-1. A wind tunnel with the performance to meet the following conditions shall be selected.
(1) Wind speed: The air blow capacity must be sufficient for 10 m/s or more in the measurement part(2) Blockage ratio: The cross-section of the measuring section must have a blockage ratio of 5% or less due to the model(3) Turbulent boundary layer: It must be possible to simulate and reproduce the various characteristics of natural wind in
the wind path (It must be a turbulent boundary layer wind tunnel)-1. Appropriate scale models that meet the following conditions must be selected and manufactured.
(1) Scale: Must be 1/50 or larger.
 Although a larger scale is desirable, it should be kept in mind that it is necessary to select an appropriate scalemodel, because there is a limit to the blockage ratio, and also a limit to the generation of a turbulent boundary layerin each individual wind tunnel.
 It should be kept in mind that if the scale is too small, then there may be a problem in the model fabrication
accuracy, and that there is a possibility that unreasonableness may occur in the appropriate arrangement andinstallation of pressure measurement holes.
 Any accessories, etc., may be omitted from the model if the effect is considered to be small for the test purpose.
(2) Pressure measurement hole size: The inside diameter shall be approximately 1 mm.
 The diameter commonly used in building-related pressure measurements is recommended.
(3) Pressure measurement hole arrangement: Holes must be arranged so that the pressure distribution characteristics can be
determined within 1 m2 of the actual machine.
 The fluctuating pressure characteristics on the nacelle shall be measured as accurately as possible, andconsideration shall be given so that the wind pressure characteristics can be appropriately evaluated according to
the area to be evaluated.
 The minimum size of a panel on the nacelle surface was assumed to be 1 m2, and this was set as the standard for thepressure hole arrangement.
(4) Materials used and fabrication accuracy: It is recommended to use materials generally used in wind tunnel testing ofbuildings, and to use the fabrication accuracy applied in relation to buildings.
 It should be noted that a surface roughness problem or corner fabrication accuracy problem may occur with somematerials.

-1. The wind tunnel tests are conducted by simulating and reproducing the various characteristics of natural wind in the wind
path, so the following conditions regarding the various characteristics must be satisfied at the wind speed used in the test
implementation.
(1) Wind shear exponent (α)
 The wind shear exponent (α) for the turbulent boundary layer generated shall be in the range of 0.15 to 0.2,
corresponding to the ground surface roughness classifications II to III. In consideration of the limit of wind tunnel
capacity, the standard for the allowable range of the wind shear exponent (α) shall be 0.125 or more and 0.235 or less.
(2) Turbulence intensity (𝐼𝐼𝑢𝑢𝑢𝑢 ) The turbulence intensity (𝐼𝐼𝑢𝑢𝑢𝑢 ) of the turbulent boundary layer generated must be in the range of 0.13 ± 0.03 at the
hub height.

- 53 -

(3)Spectral distribution of turbulence The spectrum of turbulence at hub height must be summarized in comparison with the general Karman-type
spectrum, and it must be shown that there is no peculiar frequency peak.

(4)

Turbulence scale The scale of the turbulence in the vicinity of the hub height shall be shown as a reference value.

E.3.3

Wind speed and wind direction in test implementation-1. The wind tunnel tests are conducted by simulating and reproducing the various characteristics of natural wind in the wind
path, so the following conditions regarding the various characteristics must be satisfied at the wind speed used in the test
implementation.
(1)

Wind speed: The average wind speed at the hub height after the natural wind simulation shall be 8 m/s or more.
 The simulation of the Reynolds number is impossible in general wind tunnels, so for nacelles without sharp edges
in particular, there is a possibility that disagreement between the simulation and the actual machines may become aproblem. However, it is currently difficult to properly complement (correct) that disagreement, so it shall be
acceptable to conduct the testing with the largest Reynolds number that is possible in the wind tunnel concerned.

(2)Wind direction: All wind directions (360°) shall be considered with a pitch of 5°.
 If the shape is symmetrical, the test wind directions may be reduced according to the symmetry.

E.3.4

Pressure measurement instrument-1. The pressure transducer used shall have a sufficient margin for the magnitude of the fluctuating pressure that occurs and also
have no problems regarding its resolution and frequency response characteristics.
-2. For the tube connecting a pressure measurement hole and a pressure transducer, use a tube with an inner diameter and lengththat takes the frequency response characteristics into consideration. In the pressure measurement, the pressure difference from thestatic pressure at the reference point is measured, so it must be shown that the reference point is at an appropriate position.

E.3.5

Data processing and recording-1. As with the selection of pressure measurement equipment, the setting conditions for the wind tunnel test shall be clearly
indicated for the following items so that it can be confirmed that the fluctuating pressure characteristics are being correctly
recorded and processed. The values in parentheses for each item were the values used in the tests described in Annex D and areprovided only as reference values.
(1)

Sampling frequency (800 Hz)(2)

Low pass filter (300 Hz)(3)Time scale (1/10)(4)

Data length per sample (60 seconds)(5)

Number of samples (Ensemble averaging of 5 samples)-2. The fluctuating pressure depends on the test wind speed and the shape and size of the model, so it should be noted that it isnecessary to record and process the fluctuating pressure correctly with consideration of those characteristics.

E.3.6

Maximum/minimum peak wind pressure coefficient-1. The fluctuating wind pressure measured in the test shall be subjected to the processing shown in E3.5, and the maximum
peak wind pressure coefficient 𝐶𝐶𝐶𝐶max and minimum peak wind pressure coefficient 𝐶𝐶𝐶𝐶min shall be obtained by thedimensionless equations shown in equations (E.1) and (E.2) for each measurement point and each wind direction.
𝐶𝐶𝐶𝐶max = (𝑝𝑝e − 𝑝𝑝s )max ⁄𝑞𝑞𝐻𝐻
𝐶𝐶𝐶𝐶min = (𝑝𝑝e − 𝑝𝑝s )min ⁄𝑞𝑞𝐻𝐻

Where:

𝑝𝑝e: Fluctuating wind pressure acting on the model walls (N/m2)- 54 -(E. 1)(E. 2)

(𝑝𝑝e − 𝑝𝑝s )max
(𝑝𝑝e − 𝑝𝑝s )min
𝑝𝑝s

𝑞𝑞𝐻𝐻

: Maximum peak wind pressure (N/m2): Minimum peak wind pressure (N/m2): Static pressure in the wind tunnel (reference point) (N/m2): Average hub height speed pressure (N/m2)-2. Note that the maximum and minimum peak wind pressure coefficients must each be calculated in the form corresponding to
the DLC6.1 and DLC6.2 design load cases shown in 5.3.3 (Specifically, with the range of wind direction limited).

E.4

Reference documents[E1]

H. Noda and T. Ishihara:Wind tunnel test on mean wind forces and peak pressures acting on wind turbine nacelles, Wind

[E2]

Energy 2014; 17:1-17
RENEWABLE ENERGY 2019; 2019.10. Nippon Kaiji Kyokai[E3]

Noda Hiroshi and Ishihara Tsutomu: Wind Tunnel Tests for Mean Wind Forces and Peak Pressures Acting on Wind
Turbine Nacelles, JAWE, Vol. 35, No. 1, 2010.1.

[E4]

Guidelines for Design of Wind Turbine Support Structures and Foundation [2010 version] (Japan Society of Civil
Engineers)[E5]

Architectural Institute of Japan: Recommendations for Loads on Buildings (2015), February 25, 2015 5th Edition, 1st
printing, Maruzen Publishing Co., Ltd.

[E6]

Japan Society of Civil Engineers: Structural Engineering Series 12 - Wind resistant design of bridges - Criteria and recent
advances -, March 31, 2003 1st edition, 1st printing, Maruzen Publishing Co., Ltd.

[E7]

Japan Road Association: Road Bridge Wind Resistant Design Handbook (Revised 2007), January 25, 2008 revised
edition 1st printing, Maruzen Publishing Co., Ltd.

[E8]
[E9]

The Building Center of Japan: Guidebook on architecture wind tunnel experiments for practitioners, 2008
Masakuni Yoshida et al.: Transfer function of a single PCB tube and the digital correction of fluctuating wind pressure,[E10]

Proceedings of 9th National Symposium on Wind Engineering, 1986
ClassNK Renewable Energy:Japanese requirements for Globe type nacelle cover- 55 -

Annex F.
F.1

GeneralF.2

Attenuation

Design methodologies for tower structures [normative]-1. This Annex summarizes the tower structure-related items where the method has been established for items that deviate fromthe Guidelines for Design of Wind Turbine Support Structures and Foundation[J-05].
-2. This Annex presents examples of methods based on past examination cases and does not deny the application of othermethods.

-1. For the first and second mode structural damping ratios for cylindrical steel structures, the values obtained from equation(F.1) and equation (F.2)[R-08] [R-11][F1] may be applied. When using values other than this, it is necessary to explain the validity ofthe values. In addition, for the modal damping ratio that consists of the structural damping and ground damping, evaluation ispossible in the method shown in the reference document[F2]. Furthermore, in the time history response analysis using the SR
model, the soil damping is considered as a dashpot[F2].
𝜁𝜁𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 1 (%) = max(2.0𝑒𝑒 −1.3𝑇𝑇1 + 0.15, 0.2)𝜁𝜁𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 2 (%) = 𝜁𝜁𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 1 (%)(F. 1)(F. 2)

F.3

Anchor bolt hole diameter

F.4

Design applying the fatigue equivalent design method in structural calculations for anchor
bolts-1. When the hole diameter of the anchor bolt exceeds the nominal diameter of the bolt + 5 mm, the following both [1] and [2]shall be satisfied.
[1] The hole diameter of anchor bolts shall not exceed the clearance based on the nominal bolt diameter specified in
ISO273[R-10].
[2] Following the Guidebook on Design and Fabrication of High Strength Bolted Connections[R-04], if the nominal bolt
diameter exceeds 24 mm, the hole diameter may be the bolt diameter + 8 mm on the premise that the slip resistance isreduced (reduction factor: 0.85). Therefore, in the most severer loading conditions based on the site conditions, thehorizontal force due to the shear force and torsional moment acting on the tower base, and the frictional force(resistance friction force) on the underside of the base plate should be compared considering the reduction factor of
0.85, and it must be confirmed that the "Resistance friction force considering horizontal force/reduction factor" is lessthan 1.0.

-1. For the design bolt tension and short-term allowable tensile force for anchor bolts, the approach of the "fatigue strength
design method" shown in (1) may be applied. However, in this case, it is necessary to satisfy the requirements concerning fatigue
strength evaluation shown in (2).
(1) There are regulations for tower flange bolts in item 7.3.2 of the Guidelines for Design of Wind Turbine Support Structuresand Foundation[J-05], and the short term allowable tensile force and design bolt tension when adopting the fatigue strength
design method for high strength bolts for flange joints are regulated as equation (7.2) and equation (7.3) shown below. In
addition, the allowable tensile force in extremely rare earthquakes in this case is determined as equation (7.a).
When fatigue evaluations that include strong winds up to the design wind speed have been carried out and it has been
confirmed that bolt fatigue damage will not occur during the service period, the short-term allowable tensile force is thevalue obtained by multiplying the effective cross-sectional area of the bolt thread part by 0.8 times the yield strength and isdetermined by equation (7.2).
𝑇𝑇𝑎𝑎 = 0.80 ∙ 𝜎𝜎𝑦𝑦 ∙ 𝐴𝐴𝑒𝑒

(7.2)

𝑁𝑁0 = 0.70 ∙ 𝜎𝜎𝑦𝑦 ∙ 𝐴𝐴𝑒𝑒

(7.3)

However, the design bolt tension is the value obtained by multiplying the effective cross-sectional area of the bolt threadpart by 0.7 times the yield strength and is determined by equation (7.3).

- 56 -

The force acting in the axial direction 𝑇𝑇 caused by the external force per anchor bolt in extremely rare earthquakes must

not exceed the allowable tensile force 𝑇𝑇𝑎𝑎𝑎𝑎 in extremely rare earthquakes.

𝑇𝑇𝑎𝑎𝑎𝑎 = max�0.80 ∙ 𝜎𝜎𝑦𝑦 ∙ 𝐴𝐴𝑒𝑒 , 𝐴𝐴𝑒𝑒 ∙ 𝐹𝐹𝑏𝑏𝑏𝑏 �

Where:
𝜎𝜎𝑦𝑦: Anchor bolt yield strength [N/𝑚𝑚𝑚𝑚2 ]𝐴𝐴𝑒𝑒
𝐹𝐹𝑏𝑏𝑏𝑏(2)(7. 𝑎𝑎): Effective cross-sectional area of anchor bolt [𝑚𝑚𝑚𝑚2 ]: Determined by the smaller of the anchor bolt reference strength [N/𝑚𝑚𝑚𝑚2 ], yield strength, and 70% of the tensile
strength.

When the design bolt axial force for an anchor bolt is set by adopting the fatigue strength design method shown in (1) above,
the requirements related to fatigue strength evaluation are as shown below.
1)

Principle for conducting fatigue strength evaluation
 According to the requirement by 7.4.1 in the Guidelines for Design of Wind Turbine Support Structures andFoundation[J-05], the degree of fatigue damage shall be determined by the cumulative fatigue damage rule.

2)

The requirements for each item to be considered shall be as shown in Table F.1.
Table F.1 Items to be considered for fatigue strength evaluation and their requirements
Items to be
Applicable specifications
Requirements
consideredand standards

Anchor bolts

EN 1993-1-9: 2005[R-12]

 When considering only the axial force on the anchor bolt and not
bending, apply DC36* as the S-N diagram. *1
 The size effect reduction factor: ks shall be considered.

Grout/ Concrete

MC2010[R-13] (MC1990[R14] is also possible)

 In principle, consideration of the three-dimensional restraint effect is
not accepted. *2
 The concrete strength applied to the fatigue strength consideration
shall be the concrete strength adopted at the site. Also, the basic ruleis the application of 28-day strength.

*1: See the column of requirements for DC50 on Table 8.1 of EN 1993-1-9: 2005[R-12].
(In addition, refer to the Guidance note in Paragraph 4.12.3.6 of DNVGL-ST-0126[R-15].)*2: When adopting fatigue design strength that considers the three-dimensional restraint effect, its validity must be shownby quantitative verification results based on fatigue experiment results, etc.

F.5

Lever ratio of flange joint-1. Regarding the tensile strength of a flange joint bolt, if the lever ratio (e/g) exceeds 1.25, checking can be carried out based on
the proposed equation in the reference document[F3] within the application range shown in this reference.

F.6

Design applying the fatigue equivalent design method in structural calculations for flange
joints-1. For the short-term allowable tensile force and design bolt tension for flange joints, the approach of the "fatigue strength
design method" shown in (1) may be applied. However, in this case, it is necessary to satisfy the requirements concerning fatigue
strength evaluation shown in (2).
(1) There are regulations for tower flange bolts in item 7.3.2 of the Guidelines for Design of Wind Turbine Support Structuresand Foundation[J-05], and the short term allowable tensile force and design bolt tension when adopting the fatigue strength
design method for high strength bolts for flange joints are regulated as equation (7.2) and equation (7.3) shown in F.4.
(2) When the design bolt axial force for a flange bolt is set by adopting the fatigue strength design method shown in (1) above,
the requirements related to fatigue strength evaluation are as shown below.
1) Principle for conducting fatigue strength evaluation
 According to the requirement by 7.4.1 in the Guidelines for Design of Wind Turbine Support Structures andFoundation[J-05], the degree of fatigue damage shall be determined by the cumulative fatigue damage rule.
2) The requirements for each item to be considered shall be as shown in Table F.2.

- 57 -

Table F.2 Items to be considered for fatigue strength evaluation and their requirements
Items to be
Applicable specifications
Requirements
consideredand standards
Flange bolt

EN 1993-1-9: 2005[R-12]

 When considering only the axial force on the flange bolt and not
bending, apply DC36* as the S-N diagram. *1
 The size effect reduction factor: ks shall be considered.

*1: See the column of requirements for DC50 on Table 8.1 of EN 1993-1-9: 2005[R-12].
(In addition, refer to the Guidance note in Paragraph 4.12.3.6 of DNVGL-ST-0126[R-15].)

F.7

Distance between flange bolt centers in circumferential direction-1.

If the distance between the centers of the flange bolts in the circumferential direction does not satisfy the dimensional

specifications in 7.3.3 (1) 2) of the Guidelines for Design of Wind Turbine Support Structures and Foundation[J-05], the following
must be satisfied.
(1)

For the tower flange connection, perform finite element analysis for each case where the distance between the centers of theflange bolts in the circumferential direction is 1) and 2) below, and indicate the effect that the difference in the center-tocenter distance has on bolt tension, stress, etc., against the site ultimate load (short-term, extremely rare earthquake, IECload). In the case of 2), also confirm from the results of the finite element analysis that the tower flange connection is
structurally safe.
1)

In the case of 2.0D (D: nominal bolt diameter), which is the dimensional specification in 7.3.3 (1) 2) of the Guidelines for
Design of Wind Turbine Support Structures and Foundation[J-05]

2)(2)

In the case where the planned distance between the centers of the flange bolts in the circumferential direction is (< 2.0D)
The validity of the model and analysis method for the finite element analysis used in (1) above must be verified bycomparison with the results of structural experiments, or by reproducing the contents of previous literature.

F.8
-1.

Tower opening
For the tower opening, in a case where the tower opening is not provided with a reinforcing material that satisfies thedimensional provisions of 7.3.5 (2) 1) of the Guidelines for Design of Wind Turbine Support Structures and Foundation[J-05], andthe plate thickness around the opening is increased, the following details must be satisfied in accordance with the provisions of
7.3.5 (2) 2) of those Guidelines.
(1) In accordance with 7.3.3 of the Structural Design Recommendation for Chimneys[R-05], the checking of the strength of the
opening in terms of bending moment and shear force must be performed for each load of the site ultimate load (long-term,
short-term, rare earthquake, extremely rare earthquake and IEC load) calculated based on the site conditions. For the positionof the cross-section check, perform finite element analysis for the opening and then the cross-section where the stressconcentration is confirmed to be the most severe must be selected and appropriate consideration must be given to the stressconcentration factor.
(2)

Fatigue strength checks against the site fatigue loads calculated based on the site conditions must be performed for the welds
at the opening end and around the opening.

F.9

Reference documents[F1]

S. Oh, T. Ishihara, Structural parameter identification of a 2.4MW bottom fixed wind turbine by excitation test using an[F2]

active mass damper, Wind Energy, 21(11):1232-1238, 2018.
T. Ishihara, L. Wang, A study of modal damping for offshore wind turbines considering soil properties and foundation[F3]

types, Wind Energy, 22(12):1760-1778, 2019.
Ikuo Tobinaga, Takeshi Ishihara: A study of action point correction factor for L-type flange of wind turbine towers, Japan
Wind Energy Association proceedings, Vol. 40, No. 2, August 2016

- 58 -

Annex G.

G.1-1.

Design methodologies for foundations [normative]

GeneralThis Annex summarizes the foundation-related items where the method has been established for items that deviate from the

Guidelines for Design of Wind Turbine Support Structures and Foundation[J-05].
-2.

This Annex presents examples of methods based on past examination cases and does not deny the application of othermethods.

G.2-1.

Special earthwork such as ground improvement
When ground improvement is carried out, in principle, the Foundation and Ground Section Meeting of the Support Structure

Certification Subcommittee must conduct an examination according to the situation of each site.
-2.

When strength correction using rubble concrete is performed for the foundation floor, the item -1. above shall not apply if

the depth of that concrete is less than 3 m.

G.3
-1.

Handling of seismic response analysis for the groundIf the shearing strain exceeds 1% in the results of the seismic response analysis for the ground, then it is not permitted tofollow the response calculation flow for liquefied ground that is described in the Guidelines for Design of Wind Turbine Support
Structures and Foundation[J-05] (p. 170, Illustration 5.11), so at the point, it is not permitted to apply equivalent linear analysis, or
simplified liquefaction analysis in which the equivalent stiffness of the liquefied layer multiplied by the stiffness reduction rate is
set.
-2.

In the case of -1. above, the following analyses must be performed, depending on whether liquefaction is considered or not.

(1)

When liquefaction is not considered: Sequential nonlinear - Total stress analysis(2)

When liquefaction is considered: Sequential nonlinear - Effective stress analysis (Time-history nonlinear analysis
considering the soil nonlinearity accompanying the increase in the shear strain and the increase in the excess pore waterpressure)-3.

In a case where sequential nonlinear - effective stress analysis is performed in -2. above, the basis for setting the groundmodel (stress-strain model) and its validity must be shown.
-4.

If the shearing strain does not exceed 1% in the results of the seismic response analysis for the ground, but the response

calculation flow for liquefied ground that is described in the Guidelines for Design of Wind Turbine Support Structures andFoundation[J-05] (p. 170, Illustration 5.11) is not followed and sequential nonlinear - effective stress analysis is applied, then thevalidity of the analysis results must be shown. (Example: For representative cases, perform comparisons of the equivalent linear
analysis, and simplified liquefaction analysis in which the equivalent stiffness of the liquefied layer multiplied by the stiffness
reduction rate is set.)-5.

When the inclination of the engineering base surface is 5 degrees or more, the existence of effects from the inclination of theengineering base surface must be checked. (Example: Perform seismic response analysis using the ground response at the windturbine site that was evaluated by finite element analysis (2-D), and then perform a comparison with the seismic response analysis
results evaluated using the ground response of a 1-D parallel stratified ground at the time of design.)

G.4
-1.

Handling related to time history response analysis
When setting ground springs and attenuation by using the thin layer method, the basis for that setting and its validity must

be shown. In particular, for attenuation, it must be clearly stated how the attenuation coefficient C was set in the form shown in
Illustration 5.19 of the Guidelines for Design of Wind Turbine Support Structures and Foundation[J-05].

G.5
-1.

Pile design
When the pile response is calculated using a separated model in which the wind turbine and foundation response analysis isperformed separately to the pile response analysis, the value of the ultimate bending strength Mu of the pile divided by the
maximum bending moment M during extremely rare earthquakes should not be less than 1.2. However, this does not apply when

― 59 ―

coupled analysis of the pile response is performed in an integrated model of the wind turbine, foundation and pile, and it has been
confirmed that the analysis is valid.
-2.

For the shear checks for piles during extremely rare earthquakes, the evaluation may be performed using the ultimate

strength rather than the short-term allowable value if the following items are satisfied.
(1)

The ultimate shear capacity of piles is evaluated based on each of the Pile Foundation Design Manual[G1] and Strength andDeformation Capacity of Foundation Structural Members[G2], and it is confirmed to be within the allowable value.

(2)

The tolerance to shear based on the allowable value evaluated in (1) above exceeds the tolerance to bending, and it has been
confirmed that it is a failure mode where bending failure will occur first.

G.6

Reference documents[G1] Pile Foundation Design Manual (Japan Road Association, September 2020)[G2] Strength and Deformation Capacity of Foundation Structural Members (Architectural Institute of Japan, 2022)― 60 ―

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