State space model of an array of oscillating water column wave energy converters with inter-body hydrodynamic coupling

Abstract

In this paper we derive a state-space model restricted to heave motion of a full scale array of floating oscillating-water-column (OWC) wave energy converters with nonlinear power take off dynamics, taking hydrodynamic interactions between all bodies into account. The resulting state-space model is intended as a basis for accelerated development of advanced control approaches to maximize power generation. The kinetic and potential energy transferred to the air chamber causes a pressure difference, inducing unidirectional motion of a novel bi-radial turbine. This can be accurately modeled using pressure dependent turbine characteristics, taking into account the nonlinearity of the gas compressibility. The analytical model of the floating OWC is based on linear hydrodynamic coefficients, obtained using the boundary element solver ANSYS Aqwa of an equilateral triangle array of axis-symmetric floating OWCs of the Marmok-A-5 type. Finally, the system’s model time domain equations are simulated in different wave climates and an ideal active controller is applied to maximize energy conversion. For the specific implemented separation distance the resulting cross body interactions are found to be negligible in irregular compared to regular wave scenarios. The turbine rotational speed suggests investigations on discontinues nonlinear control methods before semi-global approaches are used to optimize power generation.