Proceedings of the ASME 2014 33rd International Conference on Ocean, Offshore and Arctic Engineering OMAE2014 June 8-13, 2014, San Francisco, USA OMAE2014-23475 MODELING AND ANALYSIS OF A MULTI DEGREE OF FREEDOM POINT ABSORBER WAVE ENERGY CONVERTER Andrew F. Davis Department of Mechanical Engineering University of Washington Seattle, Washington 98195 Email: afdavis@uw.edu Jim Thomson Applied Physics Laboratory University of Washington Seattle, Washington, 98195 Email: jthomson@apl.washington.edu Tim R. Mundon Oscilla Power Inc. Seattle, Washington, 98103 Email: mundon@oscillapower.com Brian C. Fabien Department of Mechanical Engineering University of Washington Seattle, Washington, 98195 Email: fabien@uw.edu ABSTRACT This paper illustrates an approach to the modeling of a point absorbing Wave Energy Converter (WEC) with the intent of an- alyzing the sensitivity of the system response to variation in the model parameters. Using first principles, the nonlinear equa- tions of motion are formed to describe the heave motion of a 3 body system. A linearized model is developed and used to sim- ulate 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 analy- sis 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 sys- tem. The model is validated by numerically modeling a genera- tion 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 speci- fied using frequency spectra measured with a nearby Datawell Waverider MK III buoy during the field testing, from which time domain waves are reconstructed. INTRODUCTION Wave energy has strong potential for being a component of the solution to the problems presented by an increasing energy demand. While the idea of harvesting energy from waves is not new, there has been increasing research in this area. Wave en- ergy converters (WECs) have significant potential in the marine renewable energy field, and pre-commercial prototypes of ma- rine energy devices are being developed and implemented in test situations. However, significant research is still required to de- velop wave energy into a feasible renewable energy source for coastal regions [1]. The mooring and installation of a wave energy converter is a significant factor in the cost of produced energy. In shallow wa- ters (i.e., depth less than 30 meters) it may be cost effective to use a rigid foundation, such as a monopile or jacketed pile. However at greater depths or when the wave energy converter must re- spond dynamically to the water surface (as in the case of point absorbing wave energy converters), compliant moorings are nec- essary. Work has been done to model the dynamics of compli- ant and even slack mooring lines [2]. However, this must be combined with an effective model of WEC dynamics and power 1 Copyright c  2014 by ASME