A Time Domain Model for Wave Induced Motions Coupled to Energy Extraction.

The focus of this research is numerical modeling and experimental validation of the coupled dynamics of water wave induced motions and energy extraction of a free floating body. Of interest is extraction of wave energy as a means to augment the powering requirements of a data buoy. A physics based simulation is developed for the purpose of exploring the design space for such a device. In contrast to conventional seakeeping analysis, the parameter range of interest does not constrain wave amplitude or wavelength by the characteristic body length scale. A potential flow panel code is developed that is designed to capture the nonlinearities associated with the problem of a body that has characteristic length that is an order of magnitude smaller than the amplitude of ambient waves. The Weak Scatterer nonlinear free surface boundary conditions are instituted in order to satisfy the demands of this paramter range. The hydrodynamic problem is solved using a desingularized boundary integral method. The body exact instantaneous wetted surface is determined by consideration of the time dependent position and orientation of the body relative to an ambient wave field. The specific application of a planar pendulum contained within a floating hull and coupled to an energy extraction device is suggested for the purpose of validation. A simplified model of the application is developed to gage reasonability of the application. The fully nonlinear coupled equations of motion for the seven degree of freedom system are explicitly written and implemented into the panel code. Experiments are performed that measure the response of the system to regular wave excitation. An infra-red vision system is used to characterize the free surface flows and to track rigid body motions in waves. The free surface characterization experiments agree well with Stokes second order drift. Experimental results for rigid body motions demonstrate large amplitude pitch as well as a nonlinear drift. Chaotic behavior of the pendulum is indicated by experimental results for the buoy with energy extraction. The numerical computations agree well with the nonlinear drift phenomenon and demonstrate similar chaotic behavior.Ph.D.Naval Architecture & Marine EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/62195/1/jimbretl_1.pd