Discrete non-local absorbing boundary condition for ship-wave problems

D'ELÍA, JORGE; STORTI, MARIO; IDELSHON, SERGIO

Buenos Aires

Congreso; WCCM IV (IV World Congress on Computational Mechanics, XIX Congreso Ibero-Latinoamericano sobre Métodos Computacionales); 1998

Asociación Argentina de Mecánica Computacional (AMCA), Sociedad Española de Métodos Numéricos en Ingeniería (SEMNI)

A Discrete Non-Local and non-reflecting boundary condition (DNL) for the wave-resistance problem in ships is presented, and it is implemented in two ways: a finite element model and a boundary element model. In contrast to the Dawson-like methods, the DNL condition avoids the use of numerical viscosities in the discretization, so that a centered scheme can be used for the free surface operator. This boundary condition is completely absorbing in the sense that the solution is independent of the position of the downstream boundary. It is nonlocal in the sense that it represents full matrices connecting all the unknowns at two consecutive layers at the inlet and outlet planes. The finite element model is derived form straightforward analysis of the resulting constant-coefficients difference equations, assuming that the mesh is 1D-structured (in the longitudinal direction). The use of a centered scheme for the free surface operator allows a full element discretization, and the drag is then computed by a momentum flux balance which is more accurate and guarantees positive resistances, whereas the boundary element model is coupled with a finite Fourier-decomposition over an artificial downstream boundary. In this case the drag is computed by a classical pressure integration over the static wetted hull, and the wave-heights in downstream free surface of the artificial boundary is obtained as a post-processing procedure.