A study of fully nonlinear free surface flows.

摘要

A systematic methodology is presented here for the study of the numerical properties of the mixed Eulerian-Lagrangian schemes for the numerical simulation of nonlinear free-surface flows. The present work provides theoretical foundations and applications for the numerical stability analysis theory. Computations based on two different numerical schemes, i.e. a source-doublet panel method and a desingularized method using Rankine ring sources, are presented and compared. An extensive experimental study on flare slamming and deck wetness is also described, as well as explorative numerical simulations of nonlinear free-surface flows, including sloshing waves, flare-slamming flows, green water on deck, free-fall body entry, and planing-hull hydrodynamic problems.; The matrix stability method is developed to obtain the spectral radii and normal modes associated with free-surface discretization. These are then used in establishing the stability criteria, as well as evaluating the effects of the desingularized distance and the artificial absorption device, thus expounding the role stability analysis played in the success of the numerical method, remedying its shortcomings and extending its applicability. Some examples illustrate the usefulness of this stability analysis. In addition, different numerical techniques involving artificial damping are evaluated to improve the numerical procedure for long-time simulations of nonlinear free-surface flows. Numerical experiments are designed to demonstrate the ranges of applicability of the source-doublet panel method (e.g. USAERO/FSP{dollar}copyright{dollar}) and the desingularized boundary element method. Both the source-doublet method and the desingularized method are shown to be efficient and robust time-stepping schemes for fully nonlinear free-surface problems.; An experimental investigation on large-amplitude oscillations of an axisymmetric flared body in a free surface was also conducted; the goal being to generate sets of quality experimental data, e.g. time-history measurements, for the study of flare-slamming flows and green water on deck, as well as comparison with the time-domain numerical codes. The measured time histories of the prescribed displacements, the wave elevations, and the resultant forces have been used to compare with their fully three-dimensional time-domain numerical simulation.