Computation Method Of Floating Body Motions And Wave Loads Based On Higher-order Panel Method

According to potential theory, by use of the boundary element method based on non-uniform rational B-spline (NURBS), the linear and second-order motion responses and wave loads of ship and ocean structure are calculated in frequency domain. By combining the calculating method of the nonlinear responses for floating structures and that for mooring lines, the coupled analysis method of floating body/mooring system is made in time domain:At first, the boundary element method based on NURBS is made. After developed in several aspects, NURBS technology is applied to construct complex ocean floating body and generate the wetted surface mesh, and the calculating results show that by the developing NURBS method, high quality mesh and floating body constructure can be obtained efficiently. Based on the above method for mesh, the further modifying method for mesh is applied for removing the irregular frequencies by the expanding boundary integral method.According to 3 dimension potential theory, by use of the boundary element method based on NURBS, the theory model for calculating motion response and wave loads of floating body is built and the irregular frequencies are removed by the expanding boundary integral method, In frequency domain, the linear motion response and wave loads are calculated and the results are compared with that from experiment. According to the comparison, it can be seen that the boundary element method based on NURBS is a new type of numerical method with high efficiency and accuracy.The boundary conditions are expanded by talor series, and then by perturbation expanding and separating series, the second order boundary value problems are built and the calculating domain for these problems does not change with the increasing time. Free surface integral term exists in the second order problem and by order analysis, it is analyzed that whether the term can be neglected or not and it's influence on the calculating difficulty and the accuracy of the results. In frequency domain, by the boundary element method based on NURBS, the second order motion response and wave loads of floating body are calculated and the spectrum analysis method is applied to calculate the slow drift motion of floating body which is compared with the results from the similar calculation in literatures, and from the comparison, it can be drawn that the calculating methods for second order problem are reliable in this text.By the 3 dimension elastic beam theory, the calculating model for mooring lines is obtained and then the motion equations of the mooring lines are solved by nonlinear finite element method, so the displacement and tension response of the mooring lines are obtained in static and dynamic problem. The comparison between the results and that from literatures shows that the calculating method used in this text for mooring lines is highly efficient.In time domain analysis of the coupled floating body/mooring system, a coupled analysis technology is developed for the forecasting of nonlinear motion responses and wave loads of floating body and mooring system. Considering the nonlinear factors resulting from considering the changing of transient body wetted surface, the nonlinear motion equations are built and solved in time domain. The incident wave force and hydrostatic restoring are calculated in transient body surface condition, while the diffraction force and radiation forces are calculated on the assume that the floating body oscillates around the balance situation which is the transient body wetted surface. Based on 3 dimension elastic beam theory, the calculation is carried out for mooring lines by the nonlinear finite element method. Combining the analysis method for floating body and that for mooring lines, the coupled calculating method of nonlinear motion responses and mooring line tension for floating body and mooring lines is made. For the mooring floating body, all kinds of calculations are carried out, such as the natural periods, large amplitude nonlinear motion in all kinds of sea condition, mooring lines tension and so on, and at the same time comparisons among the results show that the analysis methods in this text are fit not only for small amplitude motion but also large amplitude motion in time domain.