A Mesh Dependency Study for the Mean Drift Forces by Pressure Integration

The convergence of drift force computation on a LNGC in shallow water is studied. It is found that the convergence of the result, especially for the pressure integration method, is largely dependent on the mesh quality. Furthermore, the irregular frequencies degenerate the results in the high frequency region. The LNGC analysis has numerical challenges related to the geometry and water depth. We also wanted to see if the convergence properties are due to this or if they are of more general nature. To investigate this, an additional analysis was done for a Wigley ship in deep water. The convergence properties were found to be even poorer in this case. This shows that the convergence problem seems to be quite general. It is also found that the vertical components, which have to be evaluated by pressure integration, converge much better than the horizontal components. Hence all six components can be found using a moderately dense mesh by using the far field integration for the horizontal components and only the vertical components from the pressure integration.