idsession
code

113

B-3-1

An optimal floating structure?

34

B-3-2

Blade Pitch Control of Floating
Offshore Wind Turbine by a Modern Mr. Ken Haneda
Control

National Maritime ResearchInstitute

57

B-3-3

Model tests of the Floating Axis
Wind Turbine (FAWT)

Graduate School of Engineering,Osaka University, Albatross
Technology LLC

82

B-3-4

Proposal of Common floating station
with Triangle connection andRectangular link mechanism forMr. Tatsuhiko Nagata
Offshore wind farm with VAWT indeep sea and Evaluation of VAWTwith Flip-up mechanism andIndividual55

B-3-5

Aerodynamic Design and Analysis ofDr. Koji Fukami
Offshore Wind Turbine Blades

Mitsubishi Heavy Industries, Ltd.

44B-3-6

Passive cooling system for 5MW
downwind turbine

Hitachi, Ltd.

title

Presenter name

Mr. Are Kaspersen

Mr. Hiromichi Akimoto

Mr. Shigehisa Funabashi

Affiliation

DNV GL

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1-Nov. 10:45 - 12:15 [ Innovative offshore wind technology (3) ]An optimal floating structure?
Are Kaspersen
DNV GL

Abstract:
Floating wind energy is moving closer to commercialization: the US, Japan and the EU all have ongoing demonstration
projects, and the first full scale pilot parks are underway.
As floating wind is gaining significance, the number of new and innovative floating structure designs is increasing, aspiring
to be more cost-effective and better than the competitors. DNV GL has gained unique insight into the industry working withmost novel concepts. It is expected that when the industry matures, only a handful of the concepts will survive. Can we predict
which? DNV GL will discuss some of the concepts out there, and discuss key parameters that will have to characterize theconcepts that will survive and emerge as industry winners.
Going deeper – finding the optimal solution for each project
Since its deployment over three years ago, Statoil’s Hywind concept has been tested very successfully, demonstrating astunning capacity factor of nearly 50 % in 2011. US technology Windfloat was deployed outside the Portuguese coast during
the fall 2011, and by this it became the world’s first large scale floating wind energy prototype based on the semi-submersible
technology. More initiatives are ongoing, including government funded programs in both the US, UK, France and Japan.
DNV GL will introduce the audience to the key technical concepts being developed in the industry - the spar-buoys, semisubmersibles and tension leg platforms (TLPs), as well as some dark horses. Each of these three fundamental concepts has its
own characteristics, strengths and weaknesses, and in order to choose the optimal floating wind turbine structure, the developer
will have to consider a number of important parameters, unique for his/her project. Based on the understanding of thesedifferent challenges, the optimal floating wind energy concept can be selected. This is vital for the project developer to becomesuccessful.
Based on studies DNV GL has executed for stakeholders developing floating wind technologies or projects, such as technicalevaluations and qualifications (e.g. Hywind, WindFloat etc), technical and commercial benchmarking studies, and standard andrules development, DNV GL’s paper will aim to present key learnings with regard to the three key philosophies’ respective
technical and commercial strengths and weaknesses, main cost drivers and development opportunities. Furthermore, DNV GL
will present its benchmarking methodology for assessing the different technical philosophies and concepts.
To conclude the presentation, DNV GL will elaborate on our view on the key success parameters for a floating wind concept,
as well as the cost of energy potential for floating wind energy in a future, mature market.

Blade Pitch Control of Floating Offshore Wind Turbine
by a Modern Control
Ken Haneda and Toshiki Chujo
National Maritime Research Institute

Abstract:
Floating Offshore Wind Turbine (FOWT) is a complex system because its support structure and aerodynamic load due torotor rotation affect each other.
Blade pitch control is one of the control system in a wind turbine and it aim to maximize power generation. But there is apossibility that the control system cause unsuitable motion of a FOWT according to the relationship between a motion
characteristics of the support platform and rotor characteristics.
A wind turbine founded on land or sea bottom can be assumed as a single input - single output system. On the other hand, aFOWT system should be assumed as a single input - multi output system (SIMO system). The multi output means power
generation and stability of the motion of the support platform. It is said that modern control system work well for the SIMO
system and a FOWT with modern control systems may be effective.
In this thesis, the authors introduced LQ control, one of modern controls. Motion of a FOWT was linearized and thecontroller was designed as a linear system. Water tank test using a FOWT model with LQ controller was carried out. From thetank test and simulation, the controller was found to be effective for suppressing large motion in waves.

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1-Nov. 10:45 - 12:15 [ Innovative offshore wind technology (3) ]Model tests of the Floating Axis Wind Turbine (FAWT)Hiromichi Akimoto1, Manato Kanesaki2, Kazuhiro Iijima1, Kiyoshi Uzawa2 amd Yasuhiro Takata2
1Graduate School of Engineering, Osaka University, Albatross Technology LLC,
2Innovative Composite Materials Research and Development Center, Kanazawa Institute of Technology

Abstract:
Horizontal Axis Wind Turbine (HAWT) has been quite successful in onshore and bottom-fixed offshore wind farms.
However, the situation may not be the same in the future floating offshore wind applications which have huge potential in deepwater region. The present top-heavy design of HAWT requires a large float system to keep the upright position of turbine
system. Since the floater part is about twice as expensive as that of turbine system onboard, cost reduction of the floating
HAWT will not be easy. The maintenance work in the HAWT nacelle at the top of high tower will be also expensive because of
the floater motion. In the expected high-wind condition of offshore wind sites, safety concerns of maintenance workers and thenarrow window of maintenance schedule are not easy to solve.
To solve these problems, the authors are developing a new floating wing turbine system. It is the Vertical Axis Wind Turbine(VAWT) mounted on a rotating cylindrical float (spar buoy). The shape is like a rotating fishing float equipped with VAWTblades. The spar buoy rotates with the vertical axis rotor. Power take-off from the rotor is by multiple roller units contacting on
the cylindrical surface of the rotating float. The concept is called Floating Axis Wind Turbine (FAWT) because the rotor is
floating with the buoyancy of the shaft.
The structural weight of FAWT will be lighter than those of floating HAWTs because of its smaller float size. VAWT rotor
is not top-heavy and its allowable tilt angle (about 30 degree) is much larger than that of HAWT (about 3 degree). In addition,
FAWT does not require large mechanical bearings since the heavy weight of vertical axis rotor is directly supported by sea
water (or buoyancy).
To demonstrate the concept, the authors conducted a water tank test of 1/100 scale 5MW turbine model, model test of power
take-off system and the preliminary structural analysis of FAWT rotor. The results show that the economic performance ofFAWT will be competitive with the present bottom-fixed offshore wind turbines.

Proposal of Common floating station with Triangle connection and Rectangular linkmechanism for Offshore wind farm with VAWT in deep sea and Evaluation of VAWT
with Flip-up mechanism and Movable leading edge slat
Tatsuhiko Nagata and Yasuo Ueno
IndividualAbstract:
We have the responsibility to develop sustainable energy resources such as wind power for the benefit of future generations.
Since the Tsunami disaster on March 11, 2011, people in northern Japan have experienced very difficult hardships. Theaccident at the Fukushima nuclear power plant has made it clear that nuclear power is very difficult to control and alternatives
to both nuclear power and fossil fuels are essential. The prime candidates are renewable energy sources such as solar power andwind power. Seventy percent of the earth’s total area is ocean, of which about 64% is deeper than 200 meters. These expansive
ocean areas could be a major energy resource in future. If we can discover a better solution for offshore wind farms in the deepsea, we need not use nuclear energy. The Fukushima offshore wind power plant has introduced a horizontal axis wind turbine(HAWT) and actual operations have started. During the course of HAWT usage over time longer performance and stability
have been demonstrated. However, is HAWT the right technology for off shore deep sea wind farms? Perhaps not. Most of thecurrent onshore wind turbines are horizontal-axis. However, those systems have several problems such as unbalanced loadaround the rotating shaft and the need to yaw to face the direction of the wind. Floating structures with HAWT devices requirebig, heavy, expensive, and complex mechanisms to overcome these problems. Clearly another solution is required. Arequirement for an alternate solution should be that the axis of rotation of the windmill and buoyant structures should share thesame thing. Only vertical axis wind turbines (VAWT) could meet this requirement. Darius, Line Darius, and Line Darius with
Flip-up Mechanism are examples of high speed VAWT. Development of this solution would require at least 10 years or more.
The author, Nagata, has developed some VAWT designs with Flip-up Mechanisms and built prototypes in the past few years.
Satisfactory results have been obtained. The weak point of VAWT is the low torque in low wind velocity. A VAWT design
with a leading edge slat proposed by Mr. Ueno might be one of solution. The author made a prototype of a movable leadingedge slat (MLES) last year. VAWT with MLES could generate 1.9 times more torque compared to VAWT without MLES atlow wind velocity. The combination of MLES and VAWT with a flip up mechanism might be very useful for an off shore windsystem. Additionally, the author made a small system with three floating towers combined into a Try Angle Connection andFlexible Rectangular Link Mechanism. This floating tower was tested on the water in a small tank with promising results.
Additionally, good performance was achieved under several conditions at lake and river test sites. The author proposes the newconcept of an offshore wind turbine system with self-stable VAWT with the flip-up mechanism and MLES and floating
structure with flexible rectangular link mechanism and Triangle connection for deep sea locations. The author proposes to startthe discussion for offshore wind systems with various kind of VAWT for the benefit of future generations at WWEC2016 inTokyo.
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1-Nov. 10:45 - 12:15 [ Innovative offshore wind technology (3) ]Aerodynamic Design and Analysis of Offshore Wind Turbine Blades
Koji Fukami and Masaaki Shibata
Mitsubishi Heavy Industries, Ltd.

Abstract:
Against the backdrop of rising fuel prices and the introduction of tighter regulations for greenhouse gas emissions, theexpectations for renewable energies have been growing all over the world. In Japan, this trend has become especially evident in
the aftermath of the Great East Japan Earthquake in March 2011. Among a variety of renewable energy sources, wind power is
one of the most widely installed around the world – in particular, offshore wind power has drawn growing interest in recent
years owing to its applicability over vast sea area with stable and powerful wind condition. Especially in Japan, the concept of
the floating offshore wind turbine will be more attractive because the country is surrounded by deep sea environment.
Since noise regulations for the offshore installations are less strict compared to the onshore case, it is possible to have ahigher blade tip speed, which is expected to lead to an alleviation of aerodynamic moment load by use of more slender blades.
In addition, an increase in the rotational speed allows us to reduce the design torque of the drivetrain, which will contribute toweight reductions of the rotational components. It should be noticed that higher tip speed would raise the erosion risk of theleading edge; however, this constraint could be relaxed with recently developed erosion-resistant coating agent. Major technicalissues remaining at this point were the trade-offs of the load, weight and deflection with aerodynamic performance, which
imposed on us the developments of more advanced technologies with regard to aerodynamics, blade structure, lightning
protection system design, manufacturing of blades and optimization techniques that coordinate all these requirements.
This paper focuses on aerodynamic design and analysis of offshore wind turbine blades. Airfoils were among thecountermeasures, which should provide higher structural integrity as well as improved aerodynamic performance. In the late2000’s, multi-megawatt onshore turbines with rotor diameters exceeding 100m became the mainstream of the onshore windturbines with intensifying the demand for load and noise reduction. As a result, it was required for the airfoils to realize (1) highdesign lift coefficients and (2) lower noise characteristics. We have developed MHI-F airfoil series that have high design lift
coefficients and low noise features as well as high performance (maximum lift-to-drag ratio). For the development of theoffshore wind turbine blades, two more requirements were demanded: (3) higher section modulus for the weight reduction of
the inner section and even also the tip section as well and (4) enhanced lift-to-drag ratio especially for the tip section tomaintain the aerodynamic performance with higher tip speed, which might causes the greater drag derived loss due to thedecreased inflow angle. While maintaining the advantages of the MHI-F airfoils, such as low noise and roughness resistantfeatures, etc., we obtained higher strength (section modulus) as well as enhanced performance (maximum lift-to-drag ratio).

Passive cooling system for 5MW downwind turbine
Shigehisa Funabashi, Shingo Inamura and Yasushi Shigenaga
Hitachi, Ltd.

Abstract:
The expectation to renewable energy increases is still rising with environmental problems such as the global warming.
Hereafter, offshore wind power is regarded as the main player of renewable energy and offshore wind turbine size is increasing
to generate more electric power. Large offshore turbines are required high reliability because of severe environment in offshore.
Hitachi has developed the bottom-mounted offshore wind turbine (HTW5.0-126) which generates 5MW electricity with therotor behind the nacelle (i.e. downwind-type). For this turbine, we have developed original passive cooling system to fit
downwind-type turbine. The radiators located in upstream of the nacelle is benefit to get enough air flow rate without coolingfan, because wind speed at radiator located upstream from rotor, is not decreased. The utilization of natural wind enables toremove electric fan motors rotating in humid and salty air. It brings not only reduction of energy consumption and maintenancefor electric fans, but also improvement of reliability of the cooling system.
At first, we designed the nacelle and radiator configuration to get enough air flow rate for a generator and gearbox cooling.
As a result of many flow calculations, we could get distinctive nacelle design which have the radiators in front of the nacelle,
and air outlet in the both side and the bottom of the nacelle. It looks like a mouse of whale shark.
In the prototype test of this turbine, we verified the performance of the passive cooling systems. The water temperatures atthe exit of radiators were higher in low wind speed condition than high wind speed condition. It is characteristic trend as
passive cooling system using natural wind, because this result means that high wind speed brings high cooling performance.
Measured performance of this cooling system has good agreement with calculated result by simple heat balance model, and wecould confirm that this system have enough performance to achieve target water temperature at the generator inlet.

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