Modeling of fully nonlinear wave interactions with moving submerged structures

The purpose of this work is to develop advanced numerical tools for modeling two-way fully nonlinear interactions of ocean surface waves (irregular waves in the general situation) with a submerged structure undergoing large amplitude motion. The final aim is to apply these models to simulating the behavior of a point-absorber-type Wave Energy Converter (WEC). In our modeling approach, an existing two-dimensional Numerical Wave Tank (NWT), based on potential flow theory, is extended to include a submerged horizontal cylinder of arbitrary cross-section. The mathematical problem and related numerical solution are first introduced. Then we present two applications, first for the prescribed motion of a submerged body in a wave field (including the case of a fixed cylinder, such as in Chaplin's (1984) experiments), and then for a freely-moving body in waves. In the first application, we consider the forced oscillations of a circular cylinder, either in the vertical direction or in a circular motion (with comparison to the theoretical results of Wu (1993)). In the second application, dynamical equations describing the body motion are solved simultaneously with the hydrodynamic problem, which requires correctly representing the coupling forces between both mechanical and hydrodynamic problems. This is illustrated by preliminary simulations for the free motion in periodic waves of an idealized WEC; these results are favorably compared to a linear model.