瞬時波形中船體水下網格建立技術之研發

The present research applies the surface-to-surface intersection method to decide the instantaneous approximated waterline for the ship moving in waves. Having the instantaneous waterline, we could obtain the ship underwater hull shape and its NURBS parameters. Incorporated with hyper tangent functions, we can build up the mesh on the wetted hull surface very fast and save much time on the mesh generation. We can also define the ship wetted surface under the instantaneous wave form to correct the changes of the pressure and normal vector on the hull surface in three dimensional analysis which can improve the accuracy of the calculations of the hydrodynamic coefficients and offer the better basis in the future time-domain analysis. In the research, we firstly use the similar way of finding the waterline to cut a sphere quarterly to investigate the accuracy of the mesh generation method developed here through the calculations of the sphere wetted surface area and volume. The calculation results of the ship hull wetted surface are also compared with those obtained from the commercial CAD software Rihno based on the cases in calm water and in sinuous waves with different wave headings. The general results show that the technique developed in the present study can indeed obtain quite good results either in hydrostatic or in hydrodynamic calculations except some special region, e.g. bulbous bow, which needs further study in the future.