| The concept of utilizing hydrodynamics to improve the ships'performance first appeared on the planing vessle. Compared with the ordinary displacement vessels, the hydrodynamics of planing is much more complex. One of the most important differences is that while the planing hull moving with a high speed, the majority weight of vessel is supported by the hydrodynamic lift. As a result, the whole vessel would be raised, and the draft decrease much compared with the static floating. The hydrodynamics will produce a slide trim angle, make the bow up. In addition, most hull design includes the hard chine and transom stern. The flow separation induced by the chine and transom stern, would greatly influence the load distribution on the hull.When operating in the seaway, the wet surface and water line of high-speed planing hulls have significant change. The hulls exhibit strong nonlinearities. The wave impact will induce severe turbulence. Sometimes the hull can jump out of the free surface, from one peak to another. These phenomenons are complex. So, the conventional motion predication is not applicable.In this paper, we combined theoretical formula and empirical formula to find a new applicable theoretical method, for the motion predication of the prismatic planing hulls in regular waves. We design the theoretical model and do many numerical calculations. Then Verify the reliability of the traditional empirical formula. On this basis, we discuss the calculation of the restoring force (moment) coefficient, which is the main nonlinearity and also is the main influence to the coupled motion, to ensure that the hydrodynamic lift is considered in the theoretical model. Also we use other methods to get the damping and added mass. Then establish the coupled motion equations of heave and pitch in frequency domain and time domain respectively. The results will be compared to the experimental data to analyze the nonlinear factors, for the further research on the motions in irregular waves. |
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