Kyushu University Academic Staff Educational and Research Activities Database
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Yingyi Liu Last modified date:2023.09.20

Graduate School
大学院総合理工学府  総合理工学専攻 (Ⅲ類)機械・システム理工学メジャー
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Interdisciplinary Graduate School of Engineering Sciences (IGSES) .
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Academic Degree
Doctor of Engineering, Master of Engineering, Bachelor of Engineering
Country of degree conferring institution (Overseas)
Yes Bachelor Master
Field of Specialization
Ocean Renewable Energy, Computational Offshore Hydrodynamics
ORCID(Open Researcher and Contributor ID)
Total Priod of education and research career in the foreign country
Outline Activities
(1) Research: Floating wind turbine dynamic analysis, wind turbine aerodynamics, floating body hydrodynamics, etc.
(2) Education: Interdisciplinary Graduate School of Engineering and Science (IGSES)・Department of Earth System Science and Technology (ESST)・Nonlinear Fluid Engineering Laboratory (NLFE)
Research Interests
  • Wake effect on the loading and performance of downstream wind turbines and the optimal layout of a wind farm
    keyword : analytical modeling, wake effect, wind farm
  • Numerical modeling of wave energy converters in isolation or arrays
    keyword : Ocean wave energy, wave farm, numerical modeling
  • Dynamic analysis of floating offshore wind turbines and the tower aerodynamics on the wind turbine performance
    keyword : floating type, tower aerodynamics
  • Water wave interaction with marine structures in frequency domain and time domain
    Development of high-efficiency computational codes in offshore hydrodynamics
    keyword : Offshore Hydrodynamics, Ocean Engineering
Academic Activities
1. Emre Uzunoglu, Yingyi Liu, Carlos Guedes Soares, Chapter: “Performance of the open-source potential flow solver HAMS in estimating the hydrodynamic properties of a floating wind turbine”. (In C. Guedes Soares eds., "Trends in Renewable Energies Offshore". ISBN: 9781003360773, 968pp.) , CRC Press, 10.1201/9781003360773-70, 2022.10, [URL].
2. Yingyi Liu, Chapter 8: “Large-scale computation of wave energy converter arrays”. (In Dezhi Ning and Boyin Ding eds., "Modelling and Optimization of Wave Energy Converters". ISBN: 9781003198956, 424pp.), CRC Press, 10.1201/9781003198956, p.261-280, 2022.08, [URL].
3. Malin Göteman, Robert Mayon, Yingyi Liu, Siming Zheng, Rongquan Wang, Chapter 2: “Fluid dynamics and wave-structure interactions”. (In Dezhi Ning and Boyin Ding eds., "Modelling and Optimization of Wave Energy Converters". ISBN: 9781003198956, 424pp.), CRC Press, 10.1201/9781003198956, p.281-308, 2022.08, [URL].
1. Wei Shi, Chaojun Yan, Zhengru Ren, Zhiming Yuan, Yingyi Liu, Siming Zheng, Xin Li, Xu Han, Review on the development of marine floating photovoltaic systems, Ocean Engineering, 10.1016/j.oceaneng.2023.115560, 286(1), 115560, 2023.09, [URL].
1. Yingyi Liu, Siming Zheng, Hui Liang, Peiwen Cong, Wave interaction and energy absorption from arrays of complex-shaped point absorbers, Physics of Fluids,, 34, 9, 2022.09, [URL], Water wave interactions with arrays of wave energy converters are numerically investigated based on the interaction theory. The converter is a heaving point absorber that can harness ocean wave energy through up-and-down movements. A semi-analytical hybrid method is developed that combines the boundary element method and the interaction theory. The developed numerical method is verified against theoretical solutions for arrays of truncated vertical circular cylinders. Three different array layouts are studied in detail. It is found that trapped waves exist at critical wave numbers just below the cutoff values, and the peak load on the middle device increases with the number of devices in head waves. With the increase in the complexity of the array layout, significant wave force enhancement is observed, leading to a broader range of magnitude and stronger variations over the frequency band in beam waves. Moreover, variations of the q-factor show that there are some remarkable “bright spot” regions, indicating that the wave energy absorption there is locally optimized against wave conditions. By arranging the layout in a more randomized way, the optimal conditions for maximized power output can be hard to achieve, but the maximum power output can increase to a higher level..
2. Yingyi Liu, Hui Liang, Masashi Kashiwagi, Peiwen Cong, Alternative approaches of evaluating diffraction transfer matrix and radiation characteristics using the hybrid source-dipole formulation, Applied Ocean Research, 10.1016/j.apor.2021.102769, 114, 102769, 2021.09, [URL], The interaction theory presented by Kagemoto and Yue (1986) significantly reduces the computational burden in the wave interaction problem of multiple surface-piercing bodies, particularly arrays of wave energy converters in recent years. Two essential operators of the theory are the so-called Diffraction Transfer Matrix and Radiation Characteristics. Many subsequent researchers (Goo and Yoshida, 1990; Flavià et al., 2018) have implemented the theory using the source distribution method in evaluating the two linear operators of a single unique geometry. However, nowadays, a great majority of boundary element method codes have been written by virtue of the hybrid source-dipole distribution method on account of its high accuracy. In this regard, the present work aims to introduce a full set of mathematical formulations, as well as a complete derivation process of evaluating the two operators based on the hybrid source-dipole distribution method. The proposed formulations are then applied to two benchmark geometries, as given by McNatt et al. (2015) and Flavià et al. (2018). Good agreement is found between the present results and those from the literature. Moreover, two alternative approaches to solve the diffraction problem have been compared to assess both their accuracy and efficiency. It is found that the two methods present similar levels of accuracy but very different computational burden..
3. Yingyi Liu, Changhong Hu, Makoto Sueyoshi, Shigeo Yoshida, Hidetsugu Iwashita, Masashi Kashiwagi, Motion Response Characteristics of a Kyushu-University Semi-Submersible Floating Wind Turbine with Trussed Slender Structures: Experiment vs. Numerical Simulation, Ocean Engineering, 10.1016/j.oceaneng.2021.109078, 232, 109078, 2021.07, [URL], Understanding the dynamics of an FWT (Floating Wind Turbine) is essential for its design and operation. Since a truss structure can reduce the wave load/resistance on the floating foundation, it becomes more popular in industrial applications. In this regard, knowing the effect of slender members of the truss structure on the motion response characteristics of such an FWT is vital. The present work develops a time-domain method for modeling the dynamics of a floating truss-structure wind turbine with multiple rotors on the deck of the platform. A hybrid panel-stick model is built up incorporating the potential flow theory to calculate the wave inertia force and a Morison strip method to calculate the wave drag force. A systematic methodology, and the corresponding efficient tool, have been developed to deal with the floating trussed structure consisting of a set of slender cylindrical members in arbitrary lengths, diameters, orientations, and locations. The Morison dynamic solver is incorporated into the time-domain solver for the FWT dynamics. The proposed model is validated against a model experiment of a semi-submersible FWT with a triangular-shaped truss-structured platform, which was carried out in RIAM (Research Institute for Applied Mechanics), Kyushu University. Good agreements between the simulation results and the experimental data confirm the validity of the developed method. Further numerical simulations are performed in a set of wind and wave conditions to investigate the effect of wave drag force on the FWT dynamics. It is found that without the fluid viscosity, resonant responses are excited in the platform motions at frequencies that are close to the natural frequencies of the FWT system. Via a comparison between the parked conditions and operating conditions of the FWT, it is found that in the presence of steady wind, the translational surge or sway motion is significantly excited at its resonance frequency. This may be attributed to the work done by the wind to the FWT, which enhances remarkably the total kinetic energy of the platform and consequently increases the translational surge or sway velocity of the platform at the equilibrium position. Applying a hybrid panel-stick model will be effective in reducing all these non-realistic large resonant responses..
4. Yingyi Liu, Boyin Ding, Binzhen Zhou, Peiwen Cong, Siming Zheng, Editorial: Advances and Challenges in Ocean Wave Energy Harvesting, Frontiers in Energy Research, 10.3389/fenrg.2020.614904, 8, 614904, 2020.12, [URL].
5. Yingyi Liu, Peiwen Cong, Ying Gou, Shigeo Yoshida, Masashi Kashiwagi, Enhanced Endo's approach for evaluating free-surface Green's function with application to wave-structure interactions, Ocean Engineering, 10.1016/j.oceaneng.2020.107377, 207, 107377, 2020.07, [URL].
6. Yingyi Liu, HAMS: A frequency-domain preprocessor for wave-structure interactions-Theory, development, and application, Journal of Marine Science and Engineering, 10.3390/jmse7030081, 7, 81, 1-19, 2019.03, [URL].
7. Yingyi Liu, Shigeo Yoshida, Hiroshi Yamamoto, Akinori Toyofuku, Guanghua He, Shunhan Yang, Response characteristics of the DeepCwind floating wind turbine moored by a Single-Point Mooring system, Applied Sciences (Switzerland), 10.3390/app8112306, 8, 11, 1-20, 2018.11, [URL].
8. Yingyi Liu, Shigeo Yoshida, Changhong Hu, Makoto Sueyoshi, Liang Sun, Junliang Gao, Peiwen Cong, Guanghua He, A reliable open-source package for performance evaluation of floating renewable energy systems in coastal and offshore regions, Energy Conversion and Management, 10.1016/j.enconman.2018.08.012, 174, 516-536, 2018.10, [URL].
9. Yingyi Liu, Shigeo Yoshida, An extension of the generalized actuator disc theory for aerodynamic analysis of the diffuser-augmented wind turbines, Energy, 10.1016/, 93, 2, 1852-1859, 2015.12, [URL].
10. Yingyi Liu, Changhong Hu, Sueyoshi Makoto, Hidetsugu Iwashita, Masashi Kashiwagi, Motion response prediction by hybrid panel-stick models for a semi-submersible with bracings, Journal of Marine Science and Technology, 10.1007/s00773-016-0390-1, 21, 4, 742-757, 2016.12, [URL].
11. Yingyi Liu, Hidetsugu Iwashita, Changhong Hu, A calculation method for finite depth free-surface green function, International Journal of Naval Architecture and Ocean Engineering, 10.1515/ijnaoe-2015-0026, 7, 2, 375-389, 2015.03, [URL].
12. Yingyi Liu, Bin Teng, Peiwen Cong, Changfeng Liu, Ying Gou, Analytical study of wave diffraction and radiation by a submerged sphere in infinite water depth, Ocean Engineering, 10.1016/j.oceaneng.2012.05.004, 51, 129-141, 2012.07, [URL].
13. Yingyi Liu, Ying Gou, Bin Teng, Shigeo Yoshida, An Extremely Efficient Boundary Element Method for Wave Interaction with Long Cylindrical Structures Based on Free-Surface Green’s Function, Computation, 10.3390/computation4030036, 4, 3, 1-20, 2016.09, [URL].
Works, Software and Database
1. HAMS (abbr. for Hydrodynamic Analysis of Marine Structures) is the world's 2nd open-source BEM code (released after Nemoh by Centrale Nantes, France, 2014) in offshore hydrodynamics. It is based on boundary integral equations of the potential flow theory and implemented in the frequency domain for analysing the wave-structure interaction phenomenon. HAMS is released in the hope that it will contribute to eliminating the inequality (for those who are not able to afford to purchase a costly commercial BEM software) in the continuous research developments related to offshore engineering and ocean renewable energies. HAMS is freely distributed under the Apache License and updated on GitHub.
2. FINGREEN3D is an open-source package for computation of the free-surface Green's function under a finite water depth, which is the core-part of the boundary integral equations in the potential flow theory for analysis of wave-structure interactions. It is currently written in FORTRAN 90. FINGREEN3D is developed in the hope that it can contribute to the continuous development of offshore floating renewable energy systems as well as other ocean/marine engineering applications, regardless of academic or industrial purpose.
1. Yingyi Liu, Siming Zheng, Hui Liang, Peiwen Cong, Wave energy absorption amongst arrays of point absorbers with a non-regular geometry, Proc. of the 37th International Workshop on Water Waves and Floating Bodies (IWWWFB37), 2022.04, [URL].
2. Yingyi Liu, Introduction of the Open-Source Boundary Element Method Solver HAMS to the Ocean Renewable Energy Community, Proc. of the 14th European Wave and Tidal Energy Conference (EWTEC2021), 2021.09.
3. Yingyi Liu, Hui Liang, Masashi Kashiwagi, Peiwen Cong, Computational accuracy and efficiency for Diffraction Transfer Matrix using hybrid source-dipole formulations, Proc. of the 36th International Workshop on Water Waves and Floating Bodies (IWWWFB36), 2021.04, [URL].
4. Yingyi Liu, Changhong Hu, Shigeo Yoshida, Time-Domain Response of a Semi-Submersible Floating Wind Turbine with Trussed Slender Structures, Proc. of the 14th ISOPE Pacific-Asia Offshore Mechanics Symposium (PACOMS 2020), 2020.11, [URL].
5. Yingyi Liu, Shigeo Yoshida, Hiroshi Yamamoto, Akinori Toyofuku, Changhong Hu, Makoto Sueyoshi, Hongzhong Zhu, Release of a reliable open-source package for performance evaluation of ocean renewable energy devices, Proc. of the 4th Asian Wave and Tidal Energy Conference (AWTEC 2018), 2018.09, Marine renewable energy (MRE) devices, such as offshore wind turbines, wave energy converters and tidal energy converters, are usually in the form of floating types and anchored by mooring systems. To analyze the feasibility of these floating systems in an efficient manner with respect to a wide band of frequency, frequency domain methods are good options to choose. In the present work, we developed an efficient software package for evaluating the performance of floating renewable energy systems in the coastal and offshore regions. It aims to contribute an open-source effort to numerical simulations for ocean energy converters. The interface and structure of the software package are introduced in detail so as to let it be well understood by the readers. Computations of a benchmark geometry and two practical applications of floating wind turbine are conducted and compared with theoretical results, experimental data and results from commercial software Hydrostar, justifying the effectiveness of the developed software package..
6. Yingyi Liu, Yoshida Shigeo, Development of an open-source package for computing free-surface Green’s function in constant-depth ocean Topography: FinGreen3D, International Symposium on Ocean Science and Technology, 2017.11.
7. Yingyi Liu, Changhong Hu, Sueyoshi Makoto, Hidetsugu Iwashita, Hydrodynamic analysis of a semi-submersible FOWT by hybrid panel-stick models, Proc. of the 25th International Ocean and Polar Engineering Conference (ISOPE2015), 2015.06, [URL].
8. Yingyi Liu, Changhong Hu, Sueyoshi Makoto, Shigeo Yoshida, Yuichiro Honda, Yuji Ohya, Time domain simulation of a semi-submersible type floating wind turbine, Proc. of the 24th International Ocean and Polar Engineering Conference (ISOPE2014), 2014.06, [URL].
Membership in Academic Society
  • IEEE Power & Energy Society (IEEE-PE)
  • IEEE Oceanic Engineering Society (IEEE-OE)
  • Institute of Electrical and Electronics Engineers (IEEE)
  • International Society of Offshore and Polar Engineers (ISOPE)
  • The Japan Society of Naval Architects and Ocean Engineers (JASNAOE)
  • International Network on Offshore Renewable Energy (INORE)
Educational Activities
I'm affiliated to the Department of Earth System Science & Technology, the Graduate School of Science and Engineering of Kyushu University.

I'm engaged in the research work of graduate students and provide guidance on daily technical solutions and Q&A to the graduate students.

Assist guidance on preparing Master theses by the graduate students.