Abstract
In this presentation, I will discuss the numerical performance modeling of a small-scale (2 m diameter) point absorber wave energy converter (WEC) with inflation geometry control that expands the absorber’s water plane area. WECs of this size can be used for ocean observing, disaster relief, and autonomous underwater vehicle (AUV) charging, applications which could all benefit from a WEC with easier installation and higher average capacity factor. Inflatable section geometry control could bring to life some of these improvements, with inflation in low wave height sea states to increase capacity factor and power production, and deflation during device transport and high sea states to reduce experienced loads. The modeled WEC consists of a 2 m diameter rigid core structure containing the power take-off (PTO) system, energy storage, and pump required to inflate and deflate the inflatable parts of the absorber. Performance is evaluated for irregular waves in the time domain using the open source software WEC-Sim within MATLAB/SIMULINK. Sea states are defined with the two-parameter Pierson-Moskowitz spectrum ranging from 1.5 - 20.5 s energy periods and 0.25 to 8.25 m significant wave heights. The power-take off (PTO) system is first considered as a linear damper for passive control and a spring-damper for reactive control, with PTO coefficients optimized in the spectral domain for power absorption. PTO force constraints are added to the control coefficient optimization to simulate realistic PTO component limits and evaluate which sea states the inflatable parts of the absorber should be deflated. The effect of inflatable size on performance and experienced loads is determined for three sizes ranging from water plane areas of roughly 1.5 - 3 times that of the rigid core. For this analysis, it is assumed that the inflatables are pressurized high enough to prevent deformation (shown to be a good assumption from a previous small-scale inflatable structure WEC modeling study). Finally the practical implementation of an inflation control system like the one modeled here will be discussed. It is thought that using inflation control for point absorber WECs of this size could make WEC deployment easier, increase persistence for ocean observing and AUV charging applications, and increase capacity factor while reducing design loads.