Investigation On Semi-analytical Solution Of Dynamic Characteristics Of An Anti-pitching Generating WEC (AGWEC)

This paper combines the floating hinged platform and wave energy conversion device,constructs Anti-pitching Generating WEC(AGWEC),installs wave energy device between the articulated floating platforms,reduces the relative pitch between the platforms through Power Take-Off(PTO)damping,and at the same time,the PTO system generates electric energy,achieving the purpose of complementary advantages and self-sufficiency between the two.For this device,the semi analytical solution of dynamic characteristics of the potential flow theory with viscous dissipation effect is developed,which reveals the complex principle of coupled motion between waves and multi floating bodies,and enriches the hydrodynamic calculation method of floating bodies based on real fluid to a certain extent.In this paper,the overall structure scheme of the AGWEC is introduced,and according to the structure scheme,the diffraction and radiation of the AGWEC in the potential flow are studied by using the Eigenfunction Expansion Matching(EEM)method.On this basis,the semi analytical expressions of the excitation moment and the hydrodynamic coefficients(Added Mass and Radiation Damping)are obtained.At the same time,the influence of different axis spacing of the floating body on the pitching diffraction excitation moment and the hydrodynamic coefficient of pitching radiation of the device is analyzed.A two-degree of freedom frequency-domain motion control equations is constructed based on the wave excitation moment and the radiated hydrodynamic coefficient of the AGWEC with the linear PTO spring damping system.The analytical solutions of the motion response,the average output power and the average capture width ratio of the AGWEC in the frequency-domain analysis are obtained;Through the analysis and optimization of the PTO system,the mechanism of efficient energy capture of the device is revealed.The frequency-domain dynamic characteristics of the AGWEC under different wave conditions and PTO damping coefficient are analyzed.Based on the Impulse Response Function(IRF)method,the frequency-domain analytical expression is transformed into the time-domain semi analytical expression.At the same time,based on the nonlinear PTO system,the time-domain motion control equations are constructed,and the numerical solution of time-domain motion response and instantaneous output power of the AGWEC under regular wave is solved by the Runge-Kutta Methods with fixed step size.Based on the irregular wave theory,the ISSC wave spectrum is selected to study the time-domain dynamic characteristics of the AGWEC under the irregular wave.The CFD method based on STAR-CCM+ is applied to simulate the motion characteristics of the AGWEC,and the viscous dissipation effect is introduced into the potential flow theory.The semi-analytical solutions with viscous dissipation term of the excitation moment of the pitching diffraction wave and the hydrodynamic coefficient of pitching radiation are obtained.At the same time,the potential flow results considering the viscous effect are compared with the CFD method to obtain relatively accurate correction coefficient of viscous dissipation.Meanwhile,the influence of different axial spacing of floating body on the correction coefficient of viscous dissipation is discussed.In this paper,the research of the AGWEC improves the energy capture efficiency of the wave energy conversion system,and effectively improves the overall performance of the combined system.At the same time,the development and optimization of marine energy utilization devices in this paper can effectively reduce the pressure of energy supply in coastal areas,which has a wide application prospect and practical significance.