A fully nonlinear potential flow method for threedimensional body motions

Paper i proceeding, 2012

A large variety of numerical tools with different levels of sophistication for the prediction of wave induced loads and motions have been developed over the last decades and are being applied today. With the current trend of larger, more advanced and optimized designs, e.g. large container ships and focus turning more and more towards safety and energy efficiency, nonlinear phenomena are becoming more important and many of the traditional methods fail to capture some of the physics induced by such hull shapes and involved in large amplitude wave induced loads and motions. The purpose of this paper is to present the work done on a numerical method for the three-dimensional fully nonlinear potential flow (FNPF) problem. The aim of the development is the prediction of large amplitude wave induced loads and motions with actual forward speed, taking into account implicitly all kinds of nonlinearities, i.e. higher and lower order frequency components, hull shape above the calm water level (exact body approach) and self interaction between the forward speed flow field and the radiated/diffracted waves. The body boundary conditions are imposed on the instantaneous wetted surface and the fully nonlinear free surface boundary conditions are updated using the common mixed Euler-Lagrange (MEL) method. Free surface panels are raised a distance above the surface while the boundary conditions are imposed on markers tracing the free surface. The computational domain moves forward in time consistently with the time integral scheme and the evolution of the free surface marker elevation and velocity potential to include the actual effect of forward speed. Incident waves can be prescribed either from standard perturbation solutions or from fully nonlinear numerical solutions. In addition to a description of the overall methodology, the paper presents numerical results and a systematic comparison with experimental data from the literature.