Study On Hydrodynamic Performance Of A Point Absorber Wave Energy Converter With SPH Method

Renewable energy receives much attention in the past decades because of energy crisis and environmental pollution.Wave energy is an abundant and dense form of ocean renewable energy.It is widely distributed in coastal areas around the world and has greater energy density compared with wind and solar energy.Many research teams in different countries,including China,have contributed to the study of wave energy converter(WEC).But in general,wave energy conversion technology is still not mature currently.There is no universal technology or devices and only a few products in some specific areas can be commercialized.Two key problems that need to be settled are the structural strength reliability under extreme conditions and energy conversion efficiency of the devices.In this thesis,the hydrodynamic performance of a point absorber wave energy converter is analyzed with Smoothed Particle Hydrodynamics method.The hydrodynamic performance under extreme conditions and energy conversion efficiency of the device are researched.The main contents of this paper are as follows:Firstly,applicability and accuracy of SPH method for strongly nonlinear water surface problem are verified by two-dimension wedge water entry problem.Wedge's motion,slamming forces and pressure distributions are calculated by SPH method and the influence of deadrise angle and entry velocity for impact forces are also analyzed.The results are compared with others' researches to verify the accuracy of SPH method.Then wedge water entry experiments are carried out,clear free surface profiles during water entry are obtained,which are compared with results from SPH method.These ensure that SPH method can be used to deal with problems about strong interaction between WEC and water surface.Secondly,hydrodynamic performance of a single Wave Star device on mild and extreme conditions is studied with SPH method.Performance in mild waves is calculated to ensure that motion and force of device can be obtained well with SPH method.For strongly nonlinear problems between WEC and water surface,it is proved that slamming force on device can be predict reasonably by SPH method when it is release into water surface.The device's motion on extreme wave condition is also given.It is indicated that the slamming force on the bottom is the key of structural failure,which can help the structural design of the device.Finally,energy conversion efficiency is discussed with damping system enabled.The efficiency with different damping coefficient is obtain using SPH method,which indicates there is the optimal damping coefficient for a fixed wave period.Then efficiency for different wave heights and wave period is discussed to analyze the device's energy conversion on different wave conditions.Results show that energy conversion efficiency grows with the increase of wave heights and there are different optimal wave periods for different damping coefficient.