Shape Optimization of a Submerged Pressure Differential Wave Energy Converter for Load Reductions

Abstract

The ocean is full of untapped energy, however it is a wild place where harsh conditions can occur that can damage wave energy converters (WEC’s). During high load conditions, many WEC’s must go into survival mode to prevent damage or are overdesigned to continue operating in high sea states, which can increase capital costs. The authors propose a different approach, where geometry control is used to change to an absorber shape that experiences minimal hydrodynamic loads during high sea states. This could allow for a decrease in capital costs while increasing the operating range of WEC’s. This paper seeks an optimal geometry of a submerged planar pressure differential WEC that minimizes heave excitation force or motion magnitudes without using the power take-off system. Simple elliptical and circular absorbers as well as optimized absorbers are compared to quantify heave load reductions. Optimized absorbers are generated using a summation of Fourier terms with controllable weights and phases that are optimized with a genetic algorithm for two regular wave conditions. Heave load reductions are found to depend on wave frequency, orientation angle, and elongation. It is shown that peak loads can be reduced by up to 60% when comparing to a circular absorber.