Study On Hydrodynamic Performances Of FPSO And Its Offloading System

In recent years,with the progress of society and industrial development,land oil and gas resources have been unable to meet human demand for energy.People’s exploration and development of marine oil and gas resources has gradually moved from shallow sea to deep sea and even deep sea.FPSO(Floating Production Storage and Offloading Unit)is a large-scale offshore oil production equipment integrating living facilities and production facilities.It has the advantages of strong wind and wave resistance,wide water depth range,large capacity for oil storage and unloading,and good economics.At present,FPSO has been widely used in marine oil and gas development.Therefore,the research on hydrodynamic performance of FPSO has become one of the research hotspots in the field of ocean engineering.Based on the three-dimensional potential flow theory,this paper establishes the FPSO hull hydrodynamic analysis model and numerically predicts the hydrodynamic performance of FPSO in the frequency domain.A three-stage combined mooring system is designed for FPSO.Based on Cummings theory,the time-frequency coupling method is used to analyze the time domain coupling of FPSO hull and mooring system.Based on the coupled dynamic analysis method,the hydrodynamic characteristics of the multi-floating system under the tandem offloading mode are studied.Finally,Based on the basic theory of SCR layout and the lumped mass method,the layout of the riser applied to the FPSO production system is designed.Considering the shape deformation and suction effect of the seabed soil,based on the formula of the soil stiffness of the hyperbolic secant,the soil is considered.The weakened nonlinear hysteresis model is used to study the interaction process of soil and soil.The full coupling model of FPSO hull,mooring system,riser and nonlinear seabed is established to study the nonlinear dynamic response of SCR.The research results show that: the second-order drift force variation of the FPSO in each direction of freedom reflects the nonlinear characteristics.The FPSO surge,sway and yaw motion exhibit low frequency characteristics,which easily resonate with the second-order wave drift force with lower frequency;the heave,roll and pitch are wave frequency motions,which easily resonate with the first-order wave force.The effective tension and stress maximum of SCR appear in the top suspension,and a large stress peak is generated near touch down point,which easily leads to fatigue failure;the vertical velocity and vertical acceleration of the riser change rapidly near TDP,causing a sharp increase in the inertial compressive load,and the resulting compressive load will cause local dynamic buckling;the nonlinear hysteretic soil model accurately simulates the plastic deformation of the soil and the process of pipe-soil interaction.The change of tube movement is very significant and rapid.At first,due to the power cycle,the soil weakens,which leads to the deepening of the sea bottom groove.After the soil strength and stiffness are gradually stabilized,the pipe movement reaches equilibrium and the seafloor groove changes weakly.The two-body hydrodynamic interaction has little effect on the motion response of the FPSO.Under the environmental load,the motion response of the tanker is significantly larger than that of the FPSO.The FPSO exhibits better stability than the tanker.