Time Domain Simulation Of FPSO Motion In Waves

The floating platforms which are often moored at a specified sea area are notlikely to avoid storms, a proper prediction method for platform-wave interaction isessential. The application of frequency domain potential flow theory is prevalencein previous researches and studies. However, in recent times, direct time domainsimulation has received much attention with the eye-dazzling development ofcomputer technology. In this thesis, the time domain simulation method is appliedin the prediction of a FPSO motion in waves. In addition, the overall impacts ofgreen water loads on ship motions are also investigated.High order boundary element method (HOBEM), which is capable of dealingwith complicated surface especially with the large curvature surface, is used in thepresent study. The basic functions of HOBEM and the application of this method insolving three-dimensional boundary integral equation are described. The methodsused in eliminating singularity of G and Gintegral are introduced. One ofthem is triangle coordinate transformation and the other is imposing constantpotential. Further, a program of four and nine nodes high order element are writtenwith Fortran and followed by a verification of its accuracy in solving classicalwave-body interaction problems.In this basis, a time domain Rankine source method is developed. A dampingzone is adopted to represent radiation boundary condition and the corners in domainsurface are dealing with a double-node technique. The numerical simulation ofwave diffraction on a bottom-mounted cylinder, wave radiation of a truncatecylinder, free-floating ship in regular waves and etc. are carried out. Comparisonwith results by other researchers shows the accuracy of the present method.Further, motions of a FPSO in waves are calculated and the green water loadsare added in the motion equation. A simplified shallow water theory is employed tosimulate the flow on deck and its accuracy as well as limitations are discussed. Forthe purposes of investigating green water impacts on ship motions, a comparisonbetween results with and without green water loads is also carried out.Contrasting with the free-surface green function method, the large number of panels and simulation time steps in Rankine source method lead to the increase ofcomputational time. GMRES(m) solver is introduced in solving the boundaryelement integral equation. Comparison with Gauss solver shows that GMRES solveris efficient. The appropriate restart number m for the BE-integral equationgenerated by Rankine source method is investigated. Moreover, the parallelprogram based on Open MP is also built.