PERFORMANCE OF A NEAR SHORE OSCILLATING WAVE SURGE CONVERTER WITH VARIABLE FLAP CONFIGURATIONS

Abstract

Most oscillating wave surge converters (OWSCs) are designed to enter survival mode during energetic wave conditions where they forego the opportunity to extract energy in an attempt to preserve structural integrity. While this is a good tradeoff, it is important that OWSC technology progresses to a point where energy is constantly extracted when waves are present. The OWSC studied here is a variation of a device that was conceptually designed and patented by researchers at the National Renewable Energy Laboratory (NREL) and consists of multiple adjustable vanes that, when opened, allow some of the wave force to pass through the device. Currently, NREL's investigations have been limited to a single OWSC consisting of 4 and 5 adjustable vanes. Therefore, there exists a need to further investigate the performance of this nearshore variable geometry OWSC in various arrangements and configurations. This research analyzes the hydrodynamic response of a 2-vane OWSC, a 4-vane OWSC, and an array of OWSCs in a frequency-domain code, a 2-vane OWSC's power generation capabilities in a wide range of sea states in a time-domain wave energy converter simulation tool, and a fluid flow analysis of the 2-vane OWSC in standard and energetic sea states using computational fluid dynamics (CFD). It was hypothesized that opening the vane angles would significantly and consistently reduce the OWSC's hydrodynamic response to various wave frequencies, its power production capabilities, its oscillatory motions, and the potential for wave slamming. The frequency- and time-domain results indicated that most configurations had consistent and predictable responses, while other configurations were more sensitive to the vane angle changes. The CFD results indicated that opening the vanes led to a reduction in wave slamming. However, the fluid flow became highly unpredictable as the vane angles changed, resulting in incident wave damping, inconsistent OWSC oscillations, and hydraulic jump formation.