IMPROVEMENT AND THE EFFECT OF THE EXTRAPOLATION METHODS FOR FREE SURFACE BOUNDARY VELOCITIES IN CADMAS-SURF3D

Abstract

 CADMAS-SURF (CS) is a computational fluid dynamics model for the analysis of incompressible single layer fluid. CS uses the VOF method to represent the free surface and the free surface boundary velocities are extrapolated from the fluid interior. In CS, linear extrapolation is the standard method, but causes numerical instability under strong velocity gradients. On the other hand, zero-gradient extrapolation, which has relatively high numerical stability, causes the wave damping and the inaccuracy of wave breaking. Therefore, in this study, “variable gradient extrapolation” was implemented, which compensates for the disadvantages of conventional methods. Variable gradient extrapolation improves numerical instablity under strong velocity gradients, reduces the damping of wave height and also represents wave breaking on uniform gradient slopes, good agreement with Goda (1970). Variable gradient extrapolation could be expected to be utilised as a method that is superior to the conventional extrapolation methods.