UC Berkeley

The aim of this research is to study the operational and survivability modes of asymmetric wave-energy converters (AWEC). “The Berkeley Wedge” (TBW), a one-degree-of-freedom, asymmetrical, energy-capturing, floating breakwater, which is relatively free from viscosity effects, is used as a canonical problem of study.

For the operational mode, the focus of the analysis is to optimize the power-to-load ratio of TBW. Linear hydrodynamic theory was used to calculate bounds on the expected time-averaged power (TAP), the corresponding surge restraining force, pitch restraining torque, and power take-off (PTO) control force. This thesis formulates the optimal control problem to incorporate metrics that provide a measure of the surge restraining force, pitch restraining torque, and PTO control force. The controller handles an objective function with competing terms, so as to maximize power capture while minimizing structural and actuator loads. In achieving these goals, a per-unit gain in TAP would not lead to a greater per-unit demand in structural strength, hence yielding a favorable benefit-to-cost ratio. Demonstrative results in the form of TAP, reactive TAP, and the amplitudes of the surge restraining force, pitch restraining torque, and PTO control force are shown for TBW example.

To provide guidance for improving the survivability of the AWECs, analysis of the extreme forces they experience in deep-water breaking waves was conducted. The forces were obtained by computation using the Weakly Compressible Smoothed Particle Hydrodynamics (WCSPH) method and also by model-scaled experiments (conducted at the RFS Model Testing Facility of the University of California at Berkeley). Breaking waves were first generated for both physical and computational modeling by developing appropriate time histories of the wavemaker, using potential-flow theory. Plunging breakers and wave forces at two target locations by computations were verified by experiments. The effects of different drafts of TBW on the force reduction were studied. To increase the survivability while maintaining the operational draft of the TBW, pressure-relief channel (PRC), a new scheme that allows water to flow through TBW was implemented. The PRC effectiveness in reducing the extreme wave forces was demonstrated computationally. With guidance from these computations, a design is proposed to illustrate an effective way to install and operate the PRCs so as to increase the survivability of TBW and similar devices in extreme sea states.