Dynamic Response of a Wave Energy Converter With Resonant U-Tank

This paper describes the concept design and preliminary dynamic analysis of a pitching wave energy converter (WEC) device, based on a pitching resonant floater, a pitch resonance tuning tank system and Wells turbines in regular head waves. The device has a bow/stern symmetry, which gives an advantage of the U-tank been strongly coupled with the floater in the pitch degree of freedom and both chambers will have their separate pneumatic turbines. The integrated dynamic model coupling the U-tank system as given with the motion of the floating body in regular waves and the power take off (PTO) device is physically and mathematically defined. This coupling effectively creates a multi-body dynamic system and thus alters the motion response amplitude operator of the device in waves creating multiple resonance peaks. The integrated dynamic model is solved in time domain to account for non-linearities. Excitation, radiation and diffraction forces are calculated in frequency domain from a 3D boundary element method (BEM) and corrected by Cummins equation (convolution integral) for memory effects to be used in the time domain solution. The time dependent motion of the free surface creates a pressure difference inside the chamber with respect to the atmosphere which is used by the PTO turbine. The dynamic model of the integrated system is used to predict the maximum extracted power for a given incident wave power. A systematic study, considering a change in PTO damping is performed to search for the maximum extracted power in any given regular wave condition.