Modeling and Analysis of a Multi Degree of Freedom Point Absorber Wave Energy Converter

This paper illustrates an approach to the modeling of a point absorbing Wave Energy Converter (WEC) with the intent of analyzing the sensitivity of the system response to variation in the model parameters. Using first principles, the nonlinear equations of motion are formed to describe the heave motion of a 3 body system. A linearized model is developed and used to simulate the system in both the time and frequency domains. The input to the model is a time series displacement and a time series velocity that describes the incident waves. A sensitivity analysis is then performed on the system parameters to show how the characteristics of the heave plate, the component masses, and the mass of the entrained fluid affect the performance of the system. The model is validated by numerically modeling a generation 1 device produced by Oscilla Power Inc., which is compared against experimental data from a field test on Lake Washington. The WEC is designed to provide tension along a series of tethers with connected power take off units. The wave input is specified using frequency spectra measured with a nearby Datawell Waverider MK III buoy during the field testing, from which time domain waves are reconstructed.