On the Sensitivity of Optimal Wave Energy Device Geometry to the Energy Maximizing Control System

Abstract

Wave energy converters (WECs) are traditionally designed independently of control systems. This usually involves matching the device frequency response to the predominant sea spectrum of a specific site. Energy maximizing control systems are subsequently employed to improve the energy conversion of the device for sea states other than the design sea state. It is well known that some control techniques have the ability to change the characteristics of a wave energy device, allowing it to improve the power absorption for frequencies other than the device natural frequency. However, while the controllers do their best to broaden the device frequency response, they can be limited in their capability to produce an overall optimal system. A different approach is studied in this paper, where iteration is performed between geometry optimization and control design. The aim is to investigate the implications of geometry optimization in the absence of control and the ultimate effect of incorporating the control design at the geometry optimization stage. Unconstrained control strategies are considered, namely, latching, declutching, and a model predictive control-like algorithm. It is shown that different optimal WEC geometries can be obtained depending on whether the device is controlled or not and the type of controller employed. The differences in overall power absorption characteristics of the optimized geometries are presented.