Hongzhong Zhu

RIAM, Kyushu-U

6-1 Kasuga-Koen, Kasuga

Fukuoka, 816-8580, JAPAN

I’m an associate professor for offshore renewable energy at Research Institute for Applied Mechanics(RIAM), Kyushu University. My research of interests are motion control, mathematical optermization, floating offshore wind/wave energy conversion systems, and multi-body dynamics.

My PhD was at the department of electrical engineering and information systems, The University of Tokyo where I worked on high-precision motion control. Prior to this I studied control theory and convex optimization at Kyoto University and physics at Shanghai University of Electric Power.

I love running, playing badminton and basketball. I also prefer to DIY at home and programming.

news

Aug 12, 2023	Attended 1st Symposium on Hydrodynamics and Ocean Engineering @ Shanghai Jiaotong University.
Jul 22, 2023	Started this website.

selected publications

2022

Optimal Semi-Active Control for a Hybrid Wind-Wave Energy System on Motion Reduction

Hongzhong Zhu

IEEE Transactions on Sustainable Energy, 2022

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Integration of wave energy converters and floating wind turbine can potentially reduce the levelized cost of energy. The coupling effects between the wave energy converters and the foundation, however, could amplify the foundation motion so that both the efficiency and the fatigue life of wind turbine would be degraded. In this study, wave energy converters are designed as a controlled suspension system for a novel hybrid wind-wave energy system, and an optimal semi-active control method having predictive ability is proposed for reducing the foundation motion. In the controller design, the physical constraints and the passivity of the wave energy converters are also taken into consideration. A full numerical model taking account of aero-hydro-servo-mooring coupled dynamics is proposed for a comprehensive analysis of the controller under various environmental conditions. Numerical results show that the foundation motion can be reduced by 16% even in very rough sea states with the help of the controller.

2021

A unified seakeeping and maneuvering analysis of multiple linked towing system with triangular Bodies

Hongzhong Zhu, and Changhong Hu

Ocean Engineering, 2021

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Three-legged triangular tension leg platforms (TLPs), which are a kind of compliant-type floating structure, are drawing attention from industrial society. To reduce the transportation cost, a multiple linked ship towing system that the platform and anchor are linked and wet towed is studied. A unified seakeeping and maneuvering method which can take account of the hydrodynamic interaction between the bodies and utilize the experimental results for tuning the damping coefficients is proposed to model the towing system. In the method, a low-pass filter is applied to separate the slowly and fast motion components for the maneuvering and seakeeping calculations. The maneuvering and seakeeping problems can thus be solved simultaneously with a same time scale. SimMechanics™, which provides multi-body simulation environment for mechanical systems, is applied to implement the numerical model for studying the fully coupled six degrees-of-freedom (DOFs) motion of the towing system. Besides, experiments are carried out to demonstrate the feasibility of the system and the effectiveness of the numerical model. A circular motion in irregular waves is studied at the end and the issues of the system are discussed accordingly.
A study on floating overhead power transmission system for offshore energy development: Design and modeling approach

Hongzhong Zhu, and Changhong Hu

Ocean Engineering, 2021

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In this paper, a floating overhead power transmission system (FOPTS), which has the potentiality to lower the electricity transmission cost for offshore renewable energy, is studied. In the design, a sheave mechanism is applied to mount one end of conductor on its supportive tower so that the coupling effects between the conductor and its supportive towers are reduced. Then, a mathematical optimization approach, which can take account of the placement of system’s natural frequencies to avoid first-order wave excitation, is presented to design the properties of the floating foundation and conductor. In the model-ing, the flexibility of the conductor is handled and both the first-and second-order wave loads are considered. The aero-hydro-elastic dynamics of the system would be analyzed by the numerical model. Finally, a moderate FOPTS in a harsh ocean environment with wind speed of 70 m/s and significant wave height of 14 m is studied with emphasis on the wind-wave misalignment. The feasibility and issues of the system are discussed based on fully coupled time-domain simulation.

2019

A study on a floating type shrouded wind turbine: Design, modeling and analysis

Hongzhong Zhu, Makoto Sueyoshi, Changhong Hu, and 1 more author

Renewable Energy, 2019

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This paper addresses a fundamental study of a floating type shrouded wind turbine on the design, mathematical model and motion analysis. Several novel concepts are introduced to the system for cost reduction: a revolute hinge is applied between the tower and the nacelle to maintain the orientation of the nacelle even in a large tower inclination, a swashplate mechanism with cyclic control is employed for blade pitch regulation to improve the system controllability, a novel mooring system with a slewing bearing is utilized to build the passive yawing system, and an advanced spar-type floater is used to obtain high restoring performance with a short spar. Firstly, the design aspects of the main components of the system are given. Then, the numerical model including the structural model, hydrodynamic/aerodynamic model, and the control system is presented. The static and dynamic responses under both the operational situation and survival conditions are finally studied. The paper illustrates the probability of the shrouded wind turbine on floating offshore application, and can provide critical information for the optimization design in next stage.