Study On Motion Performance Of Single Point Moored FPSO With Viscous Correction

The hydrodynamic performance of the floating structures is the most important target to predict whether the floating structure can work in a fixed ocean area safely and stably.The study on hydrodynamic performance of floating structures is usually based on by frequency domain potential flow theory and time domain theory.The motion status of floating structures can be simulated by coupling motion response analysis accurately.To verify the numerical results of wave tank model tests,it is found that those are different with numerical simulation results,because of the side walls and bottom of wave tank.The influence of wave tank side walls should be considered in wave tank model tests of ocean floating structures.This paper is focus on the study of the Single-Point Moored(SPM)of FPSO(Floating,Production,Storage and Offloading).The hydrodynamic performances of SPM FPSO were computed by frequency-domain theory method and time-domain theory method respectively.Based on the 3D elastic slender rod theory,the mooring linear finite element model was built.Then the tension's transformation of mooring line was calculated.The motion displacement and tension transformation at fairlead were updated and transmitted between mooring line and floating structure using asynchronous coupling method.Thereby the analysis of SPM FPSO's nonlinear time-domain coupling dynamic response was completed.Finally,the hydrodynamic performance transmits of SPM FPSO with side wall effect was studied.The following works were introduced in this paper:1?Based on three-dimensional potential flow theory,the hydrodynamic mesh model of SPM FPSO was built.The motion of floating structures with incident wave was solved by the cohesive potential flow theory.The analytical solutions of Green Function with viscous free surface and the fast numerical algorithm were derivated.Then the first-order wave exciting force,second-order wave drift load,hydrodynamic coefficients and first-order motion responses of SPM FPSO were computed respectively.Compared with the commercial numerical software SESAM,the numerical method was validated.The second-order difference frequency and sum frequency wave load and second-order difference and sum frequency motion response Quadratic Transfer Function be calculated by commercial numerical software SESAM.2?Based on point source images method,the analytical solution of wave tank Green Function with partial reflections from side walls and fast numerical algorithm were proposed.The radiation and diffraction problem of SPM FPSO in wave tank were studied.The first-order wave existing force,second-order wave drift load and first-order motion response of SPM FPSO were calculated in this paper.The analysis of SPM FPSO with parallel walls and rectangular section were presented,and with different side walls distance,the numerical results were compared and discussed.3?Based on the 3D elastic slender rod theory,the finite element model was established for the mooring lines.The Adam-Moultion method was employed to solve the dynamic problem.When the dynamic response of mooring lines was calculated,the slender rod theory is more effective than catenary theory and had more accurate results than lumped-mass method.Finally,compared with commercial numerical software,the results show the method can obtain effective results.Meanwhile,the effects of mooring lines were discussed with the different oscillation amplitude and frequency.4?The indirect time-domain method is introduced in this paper.The time-domain hydrodynamic impulse response function of deep-water floating structures is obtained by Fast Fourier Transform from frequency-domain hydrodynamic coefficients and wave load transform with viscous dissipation.Then the results were compared between indirect time-domain method and frequency-domain RAO transform.Finally the SPM FPSO's motion and first-order wave load were computed by indirect time-domain method.The hydrodynamic model of nonlinear time-domain coupled dynamic response had been built for deep-water moored floating structure in the transient position.Asynchronous coupled method is adopted to solve the equations of motion and mooring lines at each optimal time steps.The coupled relationship is(achieved)obtained through the information of the motion and mooring load force at the fairlead position.Then the nonlinear time-domain coupled dynamic response of SPM FPSO was implemented.