Volume 7, Issue 2 June 2022

Special Contribution

Research Projects at National Institute of Maritime, Port andAviation Technology, Japan, for Achieving Carbon Neutrality
Yoshiaki Kuriyama
President
National Institute of Maritime, Port and Aviation Technology

ABSTRACTTo meet the target of carbon neutrality by 2050 in Japan, the National Institute of Maritime, Port and Aviation Technology(MPAT), Japan, is conducting research activities in various fields such as offshore wind farm, zero-emission ship, blue
carbon and air traffic management. For the floating type offshore wind farm, a feasibility study of spar type floaters fora 15 MW wind turbine was carried out. To estimate a damage probability of a wind turbine as required by a newinternational standard, MPAT proposed a methodology and presented some calculation results. For the bottom-typeoffshore wind farm, the technical issues mentioned below were numerically investigated: the seismic stability of amonopile type wind turbine, the behavior of an open-ended pile penetrating the ground, and the dynamic response of amonopile to wind and wave. Blades of an offshore wind turbine may disturb signals from a radar for electronic navigation.
MPAT examined its potential using model tests. The vessels containing suspended loads for an offshore wind farm project
behave differently from those without the loads, and hence the movement of a vessel with a suspended load in the air
and in the water were examined. To reduce the amount of carbon dioxide (CO2) emitted from ships, the use of ammonia
and hydrogen as fuel as well as the injection of air bubbles from the bottom of a ship was investigated. Blue Carbon is CO2
stored in ocean and coastal ecosystems. The amounts of CO2 taken by shallow water ecosystems across the globe and inJapan were estimated. Before landing, an airplane descends stepwise and consumes fuel during the level flight to maintainits altitude. To reduce the amount of CO2 emitted for landing, MPAT proposed a fixed flight-path angle descent andconfirmed its usefulness.
Keywords: carbon neutrality, offshore wind farm, zero-emission ship, blue carbon, air traffic management, MPAT

1. Introduction

The Japanese Government declared in 2020 that Japan will achieve carbon neutral by 2050. To tackle with this challenge,
our research institute, the National Institute of Maritime, Port, and Aviation Technology (MPAT), is carrying out research
projects in various fields including offshore wind farm. In this article, after briefly introducing MPAT, I will describe theoutlines of some of the research projects.

2. National Institute of Maritime, Port and Aviation Technology (MPAT)MPAT was established on April 1, 2016, by merging the National Maritime Research Institute (NMRI), the Port and Airport
Research Institute (PARI), and the Electronic Navigation Research Institute (ENRI). Our mission is to implement researchand development for strengthening the international competitiveness oftransportation industry, enhancing the use of oceans, and preserving thecoastal and marine environment.

3. Research projects toward carbon neutrality

3.1 Offshore wind farm
The amount of carbon dioxide, CO2, emitted in the power industry is not
small, and thus the development and deployment of offshore wind farms
are highly expected. Offshore wind farm is classified into two types
according to its supporting structure: floating and bottom-fixed types,
which are suitable where the water depth is larger and smaller than 60 m,
respectively. MPAT experimentally and numerically examined various
challenges of both types.
a) Floating typeThe floating type offshore wind farm is further classified into four types:
barge, semi-submersible, spar, and tension leg platform types.
A feasibility study was conducted on spar type floaters for a 15 MW wind
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Fig. 1. Proposed spar for 15MW turbine(from Kuroiwa and Chen, 2021)

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turbine, which is the largest turbine proposed to date. In this study, two floaters made of concrete and steel were studied.
Targets for inclination were set to be smaller than 3 and 5 degrees for the static and dynamic inclinations, respectively.
Also, a target for natural period was set to be larger than 20 s, to reduce inclination of the spar in waves. Structural
strength was evaluated against bending moment of the spar and pressure of sea water. The evaluations of the inclination,
natural period and strength were made by analytical methods or numerical simulations. For both types of floaters,
suitable structural dimensions which fulfill the targets and the strength were found (Fig. 1).
One of the two conditions that International Electrotechnical Commission (IEC) Technical Specification (TS) requires for
not necessarily taking into account the damage stability of an unmanned floating offshore wind turbine, is that “The joint
probability of loss of stability and subsequent total loss of the structure does not exceed the probability of failure
corresponding to the safety level used for assessing the structural integrity of the structure.” As the joint probability,
MPAT proposed the product of the probability of collision with cruising ships around a floating offshore wind turbine andthat of structural total loss due to the ship collision. As trial calculations, the former value was obtained using Automatic
Identification System (AIS) data, and the latter was estimated using an FEM model and multi-body dynamics analysis.
80b) Bottom-fixed typeThe bottom-fixed type offshore wind farm is classified into four types:
gravity, monopile, tripod, and jacket types.

The diameters of monopiles for offshore wind turbines are generally
much larger than those for other infrastructures, and thecharacteristics of the lateral resistance of such large diameter piles
are not well understood. In order to estimate the lateral capacity ofsuch piles, it is necessary to accurately predict the grounddeformation caused by pile driving. Hence, MPAT simulated the
behavior of an open-ended pile penetrating the ground quasistatically and the stress induced by the pile penetration usingmaterial point method (MPM). For this simulation, the frictional
contact algorithm in which a rigid body is incorporated in MPM was
newly developed. The pile was treated as a rigid body, and the groundwas discretized by the particles of the MPM. One of the simulation
results successfully represents the soil plugging as shown in Fig. 3,
which is an important phenomenon in pile driving. In the next step,
the effect of pile diameter on the lateral resistance will be
investigated.

460

Coupled
Combined

40

Height above MSL (m)To examine the seismic stability of a monopile type wind turbine, asimulation program for coupled analysis of wind and earthquake
loads was developed. The developed program is based on finite
element analysis (FEA) and models a wind turbine as the combinationof beams and nonlinear Winkler springs. In a simulation, first, theseismic response of ground during an earthquake is estimated by an
external program that is able to reproduce the details of soilliquefaction. Second, the estimated response of ground is transferredthrough the soil-structure interaction springs to the next calculation
for the structure, in which its displacement and bending moment are
estimated. Some of the simulation results for a 2 MW wind turbine
showed that the estimated bending moments of the pile were smaller
than those obtained by combining the values separately estimatedusing the wind and earthquake loads (Fig. 2). This result indicates thatthe wind suppressed the movements of the wind turbine caused byseismic motion and hence suggests that the accurate simulation leads
to more economical design of pile. The estimated bending moments
were also smaller than those estimated by not considering theliquefaction. The liquefaction-induced flow in a sloping stratum
caused a non-negligible force acting on the pile.

Hub height

20
0
-20

MSL
Sea bed
As1

Liquefied

As2
Dc1

-40
Pile tip-60

0

100000Ds1

200000Nonliquefied

300000Max. bending moment (kN⋅m)

Fig. 2. Comparison of maximum bending
moment.

Fig. 3. Mean stress caused by pile penetration
simulated using MPM and its frictional
contact algorithm (from Nakamura et al.,2021)

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The dynamic response of a monopile type offshore windturbine to wind and wave was tested using the numericalsimulation code called FAST (Fatigue, Aerodynamics,
Structures, and Turbulence) developed by National
Renewable Energy Laboratory in USA, which couples wind
and wave forces. The simulation results for a 5 MW windturbine at a water depth of 20 m show that the waveinduced bending moment took place at the sea bottom,
depended on the wave height rather than the wave period,and became large for waves just before breaking in theshallow water region, in which the water-depth-wavelength ratio is below 0.5 (Fig. 4).
c) Influence of blade on electronic navigation system
The positions of airplanes are detected using signals from
VHF omni-directional radio ranges (VORs) and radars. Thosesignals may be disturbed by the blades of an offshore wind
farm. Hence, model experiments for a 2.3 MW wind turbine
at scales of 1/144 and 1/72 were carried out in a large
anechoic chamber (32 m × 6.2 m × 4.2 m, Fig. 5). One of theresults showed that in some conditions, the signals from aradar were scattered by the rotating blades, which indicatesthat the potential scattering should be tested in planning an
offshore wind farm.

Fig. 4. Occurrence of wave-induced bending moment
at a wind speed of 8 m/sd) Vessel movement with suspended load
For construction, operation, and maintenance of an
offshore wind farm project, vessels load, transfer, andunload materials. The vessels containing suspended loads
behave differently from those without the loads, and hence
the movement of a vessel with a suspended load in the air
and in the water were examined in laboratory experiments,
in which the model scale was 1/30 and the displacement
Fig. 5. Measurement setup for radio scattering by
and the immersed load weight were 6129 t and 176 t,
the rotating wind turbine
respectively. One of the results showed that the natural
period became longer and shorter by 10 to 30 % when thesuspended load was in the air and half in the water, respectively (Fig. 6). A numerical simulation confirmed the result andfurther showed that the differences in the natural period increased with the increase in the distance between the vessel
and the suspended load.

Fig. 6. Model experiments (left) and the variation of natural period with suspended loads in the air and half in the water(right). T0 is the natural period without load5Volume 7, Issue 2 June 2022
3.2 Zero-emission ship
The International Maritime Organization (IMO) declared in 2018 that the amount of the emission of CO2 in international
shipping is reduced by 50% by 2050 than the 2008 level. To meet this goal, several methods to reduce the amount of CO2
emission are being examined. One of the methods is to use as fuel a mixture of petroleum fuel and ammonia, NH3, orthat of methane, CH4, and hydrogen, H2.
When NH3 is used, one of the problems is the emission of nitrous oxide, N2O, which has the greenhouse gas (GHG) effectabout 300 times that for CO2. MPAT experimentally showed that the double injection of light fuel oil, in which the oil islightly injected before the main injection, drastically reduced the amount of N2O. The reduction rate of N2O reached 84%
for a mixture of fuel containing 45% NH3 and 55% light fuel oil by lower heating value. As a result, the reduction rate of
GHG became 46%.
Adding H2 into Liquified Natural Gas (LNG), of which about 90% is CH4, reduced the amount of unburned CH4, which has
GHG effect 25 times that for CO2. The unburned CH4 was reduced more by controlling excess air ratio. To confirm thevalidity of those methods, MPAT conducted experiments by using city gas instead of LNG. The reduction rate of CH4 wasabout 50% for a mixture of 20% H2 and 80% city gas at a load factor of 25% and increased to about 80% by controllingthe excess air ratio in addition. As a result, for a mixture of 60% H2 and 40% city gas at a load factor of 25%, the reduction
rate of GHG reached 70%. The emission of NOx, which is also a problem when LNG mixed with H2 is used, was reduced
by water injection.
Another method for the reduction of CO2 emissions is to decrease the frictional resistance of a ship by injecting air
bubbles from the bottom of the ship and make it flow more efficiently. Model experiments conducted in a 400 m towing
tank showed that air bubbles repetitively injected with intervals reduced the frictional force by at most 5% thancontinuously injected bubbles (Fig. 7) and by at most 20% than no air bubbles.

Fig. 7. Resistance test in a 400 m towing tank (left) and reduction effect of frictional force at a towing speed of 8m/s (right)
3.3 Blue Carbon
Blue Carbon is CO2 stored in ocean and coastal ecosystems, which
was firstly used in United Nations Environment Programme(UNEP) in 2009. Thus, Blue Carbon is relatively new research topic,
and MPAT is one of the leading research institutes for the Blue
Carbon research.
CO2 is captured in particular in the shallow water region including
seagrasses, mangroves, and salt marshes as well as seaweeds,
tidal flats, and coral reefs. The amount of CO2 taken by shallow
water ecosystems across the globe was estimated based on thevalues listed in articles and reports. The estimated value was 1.07
billion t C/year (3.92 billion t CO2/year) on the average (Fig. 8).
Then, the value in Japan was estimated using more detailed
parameters according to the Intergovernmental Panel on Climate
Change (IPCC) guidelines. It is 1.32 million t CO2/year on the
average and 4.01 million t CO2/year at most.

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Fig. 8. Global carbon cycling (from Kuwae andCrooks 2021)

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In the CO2 sequestration in the shallow region, the storage of organic carbon, Corg, is one of the vital processes. The Corg
accumulation rate and the controlling factors for 8,000 years in two lagoons in Japan were investigated using isotopic andelemental signatures. The results showed that the Corg accumulation rate was larger in salt marshes than in seagrasses
and that it increased as the sediment accumulation rate increased during the period of the relative sea level rise (Fig. 9).

Fig. 9. Corg accumulation rates increased in response to relative sea-level rise (from Watanabe et al. 2019)
3.4 Fixed Flight-Path Angle (Fixed-FPA) Descent for efficient aircraft arrival operations
Aircraft generally follows a descent profile (altitude and speed) calculated by the onboard Flight Management System
which is adjusted according to Air Traffic Control (ATC) instructions for safe separation with surrounding traffic.
Continuous Descent Operation (CDO) is a potential aircraft operating technique for reducing CO2 emissions which enables
a descent profile optimized to the operating capability of the aircraft as a continuously descending path with idle-thrust.
However, CDO can disperse significantly depending on the aircraft making trajectory prediction a daunting challenge forATC. This leads to relatively long intervals between aircraft to maintain safe separation. As a result, CDO is not preferrable
during high-traffic conditions. As a solution, MPAT proposed fixed flight-path angle (Fixed-FPA) descent in which an aircraftcontinuously descends at a fixed flight-path angle with near-idle thrust. Fig. 10 depicts the proposed concept design.
Fixed-FPA descent consumes slightly more fuel compared to CDO but significantly increases the trajectory prediction
accuracy which is vital for reducing low-efficient level-off / holding procedures at high-traffic environment. Various fasttime and full-flight simulations were conducted at the Kansai International Airport for procedure validation.

Fig. 10. Fixed-FPA Descent concept design

4. Future development

In this article, I introduced some of our research projects towards carbon neutrality. Our institute, MPAT, has scientists
and engineers in a relatively wide range of fields in transportation engineering such as shipbuilding, ocean development,
marine and coastal environment, ports and airports, and air traffic management. To contribute to the achievement of thegovernment’s challenging target in 2050, discussion and interaction across various research groups in our institute areimportant. However, not only those actions but also cooperation and collaboration with industry, universities and otherresearch institutes are crucial. By promoting such joint activities, we will expand and develop our research for the futurecarbon-free world.

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References[1] Kuroiwa, T. and Chen, X.: Feasible study on spar type floater for 15MW wind turbine, The 43rd Wind Energy
Symposium, Japan Wind Energy Association, 2021.
[2] Nakamura, K., Matsumura, S. and Mizutani, T.: Particle-to-surface frictional contact algorithm for material point
method using weighted least squares. Computers and Geotechnics, 134, 104069, 2021.
[3] Kuwae, T. and Crooks, S.: Linking climate change mitigation and adaptation through coastal green-gray infrastructure:a perspective. Coastal Engineering Journal, 63, 188-199, 2021. https://www.tandfonline.com/doi/full/10.1080/21664250.
2021.1935581.
[4] Watanabe, K., Seike, K., Kajihara, R., Montani, S. and Kuwae, T.: Relative sea-level change regulates organic carbon
accumulation in coastal habitats. Global Change Biology, 25(3), 1063–1077, 2019. https://doi.org/10.1111/gcb.14558.

◆ A brief CV of Dr. Yoshiaki Kuriyama
Yoshiaki Kuriyama is the President of the National Institute of Maritime, Port and Aviation
Technology (MPAT) in Japan. He graduated from the Department of Civil Engineering, Tokyo
Institute of Technology, and joined the Port and Harbour Research Institute (PHRI), Ministry ofTransport, in 1983. Since then, he has been conducting the research work on waves, currents, andsediment transport in the nearshore zone. He was appointed as the Director General of the Portand Airport Research Institute (PARI), the successor of PHRI, in 2016 and as the President of MPATin 2020.

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