Hydrodynamic Characteristics Of Wave Energy Device Based On FMM-BEM

With the change of climate and environment,the global demand for energy is increasing,and the development and utilization of marine renewable energy has been raised to a strategic position.Wave energy has been paid more and more attention by many countries because of its wide distribution and high energy density.In the process of efficient utilization and technology development of wave energy,energy conversion of wave energy conversion system is an important research content.The oscillating float type wave energy generation device converts wave energy into electric energy through the reciprocating motion of the float under the action of waves.The hydrodynamic calculation and analysis of the floater is the most important step in the research of wave energy conversion system.The boundary element method(BEM)is a commonly used hydrodynamic calculation method.By establishing boundary integral equation,BEM has the advantages of dimensionality reduction and high accuracy.However,BEM needs to solve linear equations whose coefficient matrix is a dense matrix.When solving large-scale potential flow problems,the number of unknown quantities increases sharply,and the amount of calculation and storage increases significantly.First of all,in order to solve the above problems,this paper uses the fast multipole technique to divide the calculation domain into near-field and far-field parts.The near-field part is directly calculated by boundary element method,and the far-field part is calculated by fast multipole method,thus reducing the amount of calculation.According to the theoretical derivation,the calculation and storage of the fast multipole boundary element method are both less than that of the traditional boundary element method.Numerical results show that the fast multipole boundary element method is more efficient than the traditional boundary element method.Secondly,this paper establishes the hydrodynamic mathematical model and energy conversion mathematical model of the oscillating float wave energy device.Hydrodynamic numerical calculations are carried out on cylindrical floats,cone-bottomed cylindrical floats and spherical-bottomed cylindrical floats with the same geometric parameters.The influence of different geometric configurations of the float on the energy conversion performance of the wave energy device is analyzed.The results show that the hydrodynamic performance of the cone-bottomed cylindrical float is better than the other two types of floats.On this basis,further analysis of other factors affecting the hydrodynamic force of the cone-bottomed cylindrical float is carried out.The experimental results show that the cone angle coefficient and mass of the cone-bottom cylindrical float have a significant influence on the hydrodynamic performance of the wave energy device.The research results of this paper show that in the process of hydrodynamic calculation of wave energy devices,the fast multipole boundary element method has higher calculation efficiency and obvious advantages than the traditional boundary element method.Therefore,the fast multipole boundary element method has important application value for the geometric selection and parameter optimization of wave energy-capturing floats.