Numerical Research On Unsteady Ship Wave-making Problems In Time-domain

Resistance performance is one of the fundamental hydrodynamic performances of ships. Ship resistance is composed of viscous resistance and wave-making resistance, whereas wave-making resistance is sensitive to the changing of the ship shape. The wave-making resistance can be remarkably reduced by properly amending the ship form. Therefore, to design the optimal ship form by investigating the mechanism of the wave-making phenomena and predicting the ship wave-making resistance is the focus of ship hydrodynamics at all times.Compared with the theoretical and experimental methods, numerical method has some merits in predicting ship hydrodynamic performances. Since 1960's, with the development of computer technology, many breakthroughs have been obtained on the Computational Fluid Dynamics (CFD). CFD being applied in resolving ship hydrodynamic problems results in a new branch in ship hydrodynamics - ship CFD. During the last 20 years, a great deal of efforts has been devoted to ship CFD research and great success has been achieved in this aspect. The most remarkable success of CFD in ship hydrodynamics is the numerical solution of wave-making problems.In the recent years, more and more attention has been paid to unsteady problems. There are large numbers of literatures describing the study of ship motion in waves, including the large amplitude oscillation motion with linearized free surface boundary condition. There are also some researches on unsteady wave-making problems. During the recent 10 years, some new unsteady wave-making problems appeared when developing high speed ships, including the unsteady wave-making of a high speed craft in the starting phase. These problems are encountered by modern high speed ships or conventional ships moving at unusual conditions. The mechanism of these unsteady wave-making phenomena is far from being understood. Therefore, it is necessary for researchers to pay more attention to unsteady wave-making problems. In fact, associated with the development of ship CFD, solving the unsteady wave-making problems will be one of the important research subjects of ship CFD.As ship CFD is more and more widely used in engineering problems, accurately and rapidly solution of ship hydrodynamic problems by potential theory method becomes more and more important. One of the focuses of recent researches is to solve the ship hydrodynamic problems using high-order panel method. In recent years, many high-order panel methods have been proposed, among them the high-orderpanel method based on the Non-uniform Rational B-splines (NURBS) is most promising due to its special merits that it can be combined with the Computer Aided Design (CAD) to be conveniently used in design of the optimal ship shape from the point of view of ship hydrodynamic performances.This thesis deals with the numerical solution of linearized unsteady wave-making problems in time domain. A time-domain Kelvin source high-order panel method based on NURBS is developed and applied to solve the unsteady wave-making problems caused by a ship moves forward with non-uniform speed.In Chapter 2, the mathematical formulation of the unsteady wave-making problems is described. The source distribution model of the Kelvin source panel method applied to solve the unsteady wave-making problems in a time-marching procedure is presented. Since rapid and accurate calculation of the time-domain Green function is essential to the time-marching procedure, in Chapter 3 a new method for calculating the time-domain Green function and it's derivatives is proposed based on the work of other researchers. The results presented in this chapter have shown the efficiency of the method.In Chapter 4, some fundamental theories and technologies about NURBS which will be adopted in the subsequent calculation are introduced. Adopting the format of NURBS some curves and surfaces of ship hull are generated. The vertexes generating these curves and surfaces are directly used by the subsequent numerical calculation, which avoids the miscellaneous work of data inputting and proc...