Numerical Investigation Of The Hydrodynamic Characteristics Of Multi-degree-of-freedom Cylindrical Oscillating Water Column Devices

Wave energy is an important part of marine renewable energy,which has the advantages of large reserves and wide distribution,and has a good application prospect.Oscillating water column device(OWC)is one of the most widely used wave energy development devices.The principle of oscillating water column power generation device is relatively simple.Under the action of incident waves,the water body inside the device moves up and down,and motivates the air flow through the duct,which in turn drives the turbine to generate power.At present,the technology of stationary oscillating water column power generation devices is mature,and has been applied in the practical engineering.With the development of offshore engineering moving forward gradually,the stationary oscillating water column device cannot meet the actual engineering needs,and the floating device will gradually become the dominant equipment of wave energy development.Based on the above research background,this paper focuses on the interaction between water waves and floating OWC devices,and studies the motion response and wave energy capture of multi-degree-of-freedom moving OWC devices under wave action.Firstly,the wave diffraction and radiation problems of OWC device were analyzed under the framework of potential flow theory,and the modified inner surface dynamics boundary conditions were established considering the influence of pneumatic pressure.The boundary integral equation was established by introducing Green’s function,and the boundary integral equation was solved by using the higher-order boundary element method.After the velocity potential is obtained,the added mass,radiation damping,wave force transfer function and other hydrodynamic parameters are calculated.The motion of the air column in the chamber is generalized as the seventh degree of freedom for the system.Based on the coupling relationship between the air column motion and body motion,a set of extended motion equations have been established for the system.By solving the motion equation,the device’s movement and the dynamic air pressure are determined.Then,the eigenfunction expansion matching method is used to develop the analytical model for a typical hollow column OWC device,and the numerical model is verified based on the obtained analytical numerical model.The main objective is to establish an effective analytical tool for the floating oscillating water column device.Thirdly,based on the established numerical model,the performance of the hollow column OWC was analyzed,and its dimensions and parameters were mainly analyzed under the specified working conditions.The wave energy capture was improved by optimizing the pneumatic damping parameters and structural sizes,and the motion response of the system under the action of regular waves was obtained.Then,the structure optimization of hollow column OWCs is carried out,and the performance of the device is improved by attaching arcshaped plates to the structure,and the wave energy capture and motion response of the device after installing arc-shaped plates are analyzed.The calculation shows that the device with the attached curved plate has higher wave energy capture in a wider frequency range,and the motion response of the device also increases due to the presence of the curved plate.The submersible caisson at the bottom of the device is also considered to form a rear curved tube wave energy platform.The calculation results show that the structure movement of the backbend device drives the fluid movement significantly in the gas chamber,thus significantly enhancing the wave energy capture.Finally,the motion response and wave energy capture under irregular wave action are analyzed.Firstly,the optimal performance parameters of the turbine under the action of irregular waves are determined,and the performance of the turbine is evaluated from three aspects: pressure standard deviation,gas volume flux standard deviation and wave energy capture.The effects of incident wave direction,additional arc-shaped shaped plate,submerged caisson size and different working conditions on the device performance are considered.The calculation results show that OWC device still has good energy capture under the action of irregular waves.