Absorbing Boundary Conditions for the Ship Wave problem. FEM and Panel Methods

MARIO STORTI; JORGE D'ELÍA; SERGIO IDELSOHN

Athens, Greece.

Congreso; Fourth European Computational Fluid Dynamics Conference; 1998

European Community on Computational Methods in Applied Sciences

An absorbing boundary condition for the ship wave resistance problem is presented. In contrast to the Dawson-like methods, it avoids the use of numericai viscosities in the discretization, so that a centred scheme can be used for the free surface operator. The absorbing boundary condition is completely absorbing, in thesense that the solution is independent of the position of the downstream boundary and is derived from straight foward analysis of the resulting system of ODE´s which is obtained after semidiscretization in the transversal and nomral directions. The eigen-decomposition of a matrix that is one dimension lower than the system matrix is required. The use of a centered scheme for the free surface operator allows a full finite element discretization. The drag is computed by a momentum flux balance. This method is more accurate and guarantees positive resistances. On the other hand, a low order panel method has been developed by means of coupling it with a finite Fourier-decomposition for the asymptotic wave-perturbation potential which is imposed over a verticaldownstream wall. The wave-resistance is then computed by a pressure integration over the static wetted hull and the wave-heights downstream of the artificial wail are obtained as a post-processing procedure.