Fast accurate seakeeping predictions

ABSTRACT Accurate predictions of ship motions and loads in a steep seaway require to include contributions depending non-linearly on wave amplitude. CFD methods do that routinely, but they require very high computing effort. Previous potential methods neglect either all or at least some nonlinear effects. The present method includes all substantial nonlinear effects amenable to potential flow. Using approximations for effects of flow separation at the aft end of hull and rudder, an accuracy comparable to that of good model experiments and CFD calculations is attained. That is demonstrated for motions and loads in cross sections of a containership sailing in head and quartering waves of large amplitude. Compared are results of model experiments, CFD calculations, a linear and the new nonlinear potential flow method. Another comparison is made for motions and added resistance of a second containership in head waves, where, apparently, an exceptional accuracy of experiments and calculations has been attained. A number of new ideas which were necessary to obtain a robust and accurate, fully nonlinear procedure are described. In typical cases, the method may take only one or a few percent of the computing effort of a comparable CFD computation.