Numerical And Experimental Investigation Of Second Order Wave Force And Motion Response Of FDPSO

The second order wave force may excite large amplitude low frequency horizontal motion of moored vessels,which directly affects the time-domain coupled response of offshore platforms.Due to the drilling system,FDPSO requires a higher ability of mooring positioning,and the wave force and motion response of FDPSO platform should be more accurately predicted during the design stage.The second-order wave force and motion response of FDPSO platform are systematically investigated in this thesis,experiments are also carried out to validate this numerical method.The main contents of this dissertation are as follows:Firstly,the hydrodynamic theory which forms the basis for computations of the second order wave force on floating platform is derived;based on which,a computation module for calculating the second order wave force is developed.In order to verify the solution,the numerical results are compared with analytical solutions and also those obtained with commercial software.Secondly,a model test of the second order mean wave drift force is conducted for an FDPSO.In order to more accuracy measure the mean wave drift force acting on the model,a new measuring system is devised and employed.Experimental results for the first order oscillatory motion and the mean second order wave force on the FDPSO’s main hull in regular waves are used to validate the numerical methods.Subquently,based on an indirect time domain theory,the frequency domain hydro-dynamic parameters are converted into time domain.A nonlinear finite element method is adopted to solve the time domain response of mooring rope.Based on this,coupling equations of floating platform and mooring rope is established and a time domain coupled code is developed.The time domain code is verified by comparing its results with the frequency domain results.Finally,a hybrid model test of FDPSO is conducted.Based on the model test results,numerical reconstruction is carried out with the developed time domain code,and the numerical and experimental results are also compared and analyzed.In addition,a numerical extrapolation is carried out to obtain the full depth results,and the effect of mooring line pretension on FDPSO’s motion is investigated.