Prof. Dezhi Ning got his PhD degree major in Port, Coastal and Offshore Engineering at Dalian University of Technology (DUT) in 2005. Then he worked in the University of Oxford as a Postdoctoral Researcher from 2005 to 2007. Now, he is the professor in the field of coastal and ocean engineering at Dalian University of Technology. He currently serves as the Head of the Offshore Renewable Energy Research Centre at DUT, Vice Dean of the Faculty of Infrastructure Engineering and the Associate Director of the State Key Laboratory of Coastal and Offshore Engineering, leading one of the top research groups in China on wave hydrodynamics and wave energy conversion (WEC). He is the Principal Investigator for five major projects sponsored by the National Science Foundation of China (NSFC), and he is supported by the highly-competitive Excellent Young Scientist programme in China. He also leads a Royal Academy of Engineering Project under Newton Fund for the integration of WECs and floating breakwaters. He has published over 200 peer-reviewed journal/conference papers and selected as one of the Most Cited Chinese Scholars in 2020 and 2021. He chaired several international conferences on water waves and marine renewable energies such as IWWWFB, PACOMS and CoastLab etc. He serves as the editorial board members of the international journals of Ocean Engineering, Journal of Hydrodynamics, Journal of Marine Science and Application, Proceedings of the Institution of Civil Engineering-Marine Engineering etc.
Numerical and experimental investigation on an Offshore Cylindrical Oscillating Water Column Wave Energy Converter
Among all the wave energy converters, the oscillating water column (OWC)-type wave energy converter (WEC) is the most attractive and extensive one due to its simple structure and reliable technology. However, most researches on OWC device are focused on the bottom-standing ones constructed on the shoreline. The development of floating WEC devices has been in the urgent stage since the offshore wave energy exploitation attracted the world attention. In the present study, the hydrodynamic performance of a floating OWC WEC was investigated experimentally and numerically. The physical experiment was carried out at a nonlinear wave flume at Dalian University of Technology. The floating cylindrical OWC device is constrained by the spring and only moves in the heave mode. A second-order time-domain higher-order boundary element method (HOBEM) based on the perturbation expansion technique is applied to simulate the nonlinear wave interaction with the floating OWC device. The nonlinear terms of pneumatic and viscous damping are introduced on the free surface boundary conditions inside the OWC chamber. The comparisons between experimental data and numerical results for the air pressure and surface elevation in the chamber, the hydrodynamic efficiency and the vertical displacement of the OWC device were performed. The effects of the opening ratio, wave steepness, mooring stiffness, chamber number and chamber draft on the hydrodynamic performance were investigated. It was found that the mooring stiffness has a great influence on the hydrodynamics, i.e., the hydrodynamic efficiency and the effective frequency bandwidth increasing with the mooring stiffness. Compare to the fixed OWC device, the hydrodynamic efficiency increases due to the vertical moment in the high frequency domain. The hydrodynamic efficiency of the dual-chamber OWC device increases by comparison with the single-chamber one. A coupled resonant effect between the inner- and outer chambers was observed for the dual-chamber OWC, which leads to the difference between the resonant frequencies and broadens the effective frequency bandwidth. For the proposed floating OWC device, a shorter chamber draft can lead to a wider effective frequency bandwidth, though the resonant efficiency and frequency decrease. The present HOBEM model can enable the structural design of the floating OWC device.