Computational Modeling of Rolling Wave Energy Converters in a Viscous Fluid1

Abstract

The performance of an asymmetrical rolling cam as an oceanwave energy extractor was studied experimentally and theoretically in the 70s. Previous inviscidfluid theory indicated that energyabsorbing efficiency could approach 100% in the absence of realfluid effects. The way viscosity alters the performance is examined in this paper for two distinctive rollingcam shapes: a smooth “Eyeball Cam (EC)â€‌ with a simple mathematical form and a “Keeled Cam (KC)â€‌ with a single sharpedged keel. Frequencydomain solutions in an inviscid fluid were first sought for as baseline performance metrics. As expected, without viscosity, both shapes, despite their differences, perform exceedingly well in terms of extraction efficiency. The hydrodynamic properties of the two shapes were then examined in a real fluid, using the solution methodology called the freesurface randomvortex method (FSRVM). The added inertia and radiation damping were changed, especially for the KC. With the powertakeoff (PTO) damping present, nonlinear timedomain solutions were developed to predict the rolling motion, the effects of PTO damping, and the effects of the cam shapes. For the EC, the coupled motion of sway, heave and roll in waves was investigated to understand how energy extraction was affected.