Wave-Current-Body Interaction By a Tune-D0main High-Order Boundary Element Method

The effects of uniform steady currents (or small forward velocity) on the interaction of a large three-dimensional body with waves are investigated by a time-domain higher order boundary element method (THOBEM). Using regular perturbation with two small parameters є and δ associated with wave slope and current velocity, respectively, the boundary value problem is decomposed into the zeroth-order steady double-body-flow problem at 0(δ) with a rigid-wall free-surface condition and the first order unsay wave problem with the modified free-surface and body-boundary conditions ended up to O(єδ). Higher-order boundary integral equation methods are then used to solve the respective problems with the Rankine sources distributed over the entire boundary. The free surface is integrated at each time step. The Sommerfeld/Orlanski radiation condition is numerically implemented to absorb all the wave energy at the open boundary. Using the developed numerical method, wave forces, wave field and run-up, mean drift forces and wave drift damping are calculated. Introduction Reliable predictions of wave forces and run-up on large offshore structures in combined waves and currents are of practical importance in the design and operation of these structures in the actual sea conditions. Recently, several numerical methods to solve the wave-current-body interaction problem have been developed mostly in the frequency domain (e.g. Zhao et al, 1988; Wu & Eatock-Taylor, 1990; Emmerhoff & Sclavounus, 1992; Nossen et al, 1991; Teng & Eatock Taylor; 1995). The frequency-domain analysis is in general mathematically complicated and cannot easily be extended to fully nonlinear problems. Isaacson & Cheung (1992) and Prins (1995) recently employed alternative timedomain analyses to solve the same problem using constant panel methods. In addition to simplifying the mathematical treatment, the time-domain approach can also include transient responses.