Study On Dynamic Response Characteristics Of FPSO With Soft Yoke Mooring System

With the increasing operation life of FPSO and mooring systems, there havebeen some accidents in soft yoke mooring system, which had a great impact on safetyin production in oil field. Currently, the cause of accidents in most soft yoke mooringsystems is unclear, which has brought some difficulties in failure recovery, operationaltesting for mooring system. Therefore, there is need to study the influence of differentparameters on the performance of FPSO and mooring system to provide basis forthe design and selection of soft yoke mooring system.Based on multi-body dynamics theory, the multi-body coupling model includingsoft yoke system and FPSO is established. The dynamic response of both FPSO andmooring system is calculated to analyze the influence of loading condition onrestoring stiffness of soft yoke, motion response of FPSO and force in mooringsystem. Through selecting different environmental conditions, such as wind speed,current velocity, significant wave height, spectral peak period and water depth, thesensitivity of force in mooring system to environmental parameters is analyzed;through selecting different design parameters, such as height of single point mooring,length of pendant, height of mooring frame, length of soft yoke and ballast weight, thesensitivity of force in mooring system to design parameters of soft yoke mooringsystem is analyzed.Some main conclusions are as follows：（1）Soft yoke mooring system mainly provides longitudinal restoring stiffnessfor FPSO, which gradually increases with the decrease of draft.（2）When the heading of FPSO and environment forces are not along the sameline, force in mooring system increases first and then decreases with the decrease ofdraft; when the heading of FPSO and environment forces are along the same line,force in mooring system varies little with the decrease of draft.（3）The motion response amplitude of the three horizontal degrees of freedomvary more obviously with the decrease of draft than the three vertical plane degrees offreedom.（4）Sensitivity priority of force in mooring tower to environment parameters areas follows：spectral peak period, significant wave height, current velocity, wind speed; sensitivity priority of force in pendant are as follows：significant wave height, spectralpeak period, current velocity, wind speed.（5）Sensitivity priority of force in mooring tower to design parameters are asfollows：length of soft yoke, length of pendant, height of mooring frame, height ofSPM and ballast weight; sensitivity priority of force in pendant are as follows：lengthof soft yoke, ballast weight, height of mooring frame, height of SPM and length ofpendant.