Study On The Coupled Hydrodynamic Performance Of Deepwater FPSO Offloading System

Oil and gas resources are the most important strategy resources for the future development of science and technology.Offshore deepwater even ultra deepwater oil area has become an important field make up the gap between supply and demand of oil and gas.The rapid growth of China's economy is also inseparable from the energy support,and China has been a long time to pay attention to the oil&gas exploitation in the deepwater.It is one of the most significant strategies for China to participate in oil&gas exploitation overseas.Under this background,this paper has completely finished a series analysis of the FPSO(Floating,Production,Storage and Offloading)offloading system,which has been served in the West Africa.Theoretic analyses,numerical calculations and model tests are conducted to investigate the hydrodynamic performance of FPSO offloading system in the special environment condition.The FPSO offloading system involves four main components,such as FPSO,CALM(Catenary Anchor Leg Mooring)buoy,mooring system and oil offloading lines(OOL).These components could have mutual coupling effections between each other under the external forces,and how to solve the coupling effections is the key technology to accurately forecast the dynamic performance of the offloading system.Three-dimensional potential flow theory is used to solve the floating body motion equation and lumped mass method is used to calculate the mooring line/OOL tension.This paper use the way of force transfer to deal with the coupling effect between floating body and lines,the program algorithm is implemented by the FORTRAN language.And then through the comparision of numerical simulation and model test results to verify the reasonable and reliability of the algorithm.Based on the above research,the dynamic response of FPSO offloading system is also studied in the irregular waves,swells,squall and current load in the West Africa area.Investigation on the hydrodynamics of FPSO offloading system is conducted by model test,which has been compelet in the basin of Harbin Engineering University.The law of FPSO offloading system motion has been discussed in this paper.And the characteristic of mooring/OOL line tension has also been inductived.Besides,the dynamic response of the offloading system is studied in different wave heights,wave approach angles and spectrum peak periods.The law of floating body motion and line tension could be provided for the further engineering practice.In addition,vortex-induced vibrations(VIVs)may occur when the oil offloading lines are subiective to the effects of currents and cause unacceptable fatigue damage in the pipeline.The viv phenomenon of pipeline and the coupled motion equation are integrated to study the motion law of offloading system.Different wave heights,wave approach angles and spectrum peak periods are considered to the analysis the dynamic response of the system,through the dynamic results of systm to analysis the influence of viv phenomenon.The results indicate that the viv phenomenon has a huge effect on its own fatigue life,but has smaller effect on body motion and line tension.At last,in the view of into/out problem between OOL and free surface,this paper considered the different way of calculating the pipeline tension respectively.The offloading system is calculated in the wind,wave and current loads.Through the comparision of the two results,it says that considering the relationship of OOL and free surface is helpful to improve the calculation accuracy of OOL tension.