Research On Horizontal Stability Of SPM System

In recent years,with the drying up of onshore petroleum resources,people have been focusing on the offshore resources.Marine exploitation equipment like FPSO,FLNG have been proposed.Single point mooring(SPM)system is the locating device of these marine exploitation equipment.With the weathercock effect,SPM system allows the moored structure rotate around the mooring point to maintain the minimum load position.The author has done research on CALM SPM system and external turret SPM system.Horizontal motion stability of both have been analyzed respectively.Firstly,a hydrodynamic model of SPM hull was built.Comparison between simulation and experiment has been done to validate the correctness of numerical model and numerical method.Afterwards,research on the horizontal stability of CALM system has been done.By discussing the main influencing factor on CALM system using time domain simulation,some conclusions were drawn.An initial angle between hull and environmental load in time domain simulation can improve the rapidity and accuracy of the simulation;length of the mooring line and speed of the current are negative to the stability of CALM system.The increasing of wind speed can reduce the horizontal motion response which is positive to the horizontal stability.Analysis on external turret SPM system under a-hundred-year return period and side by side offloading Inline sea condition has been done.By solving the characteristic polynomial of the sway-yaw differential equations,estimation of the stability of external turret SPM has been made.Consistency of simulation and theoretical derivation has been found that the external turret SPM system was horizontally stable which was contradictory to the result of SJTU pool experiment.Given the potential flow theory,it is necessary to take viscosity into consideration.In order to take viscosity into consideration,CFD simulation of the external turret SPM system hull outflow filed has been done.By simulating the outflow field in different depth,the periodic changing lift moment was obtained.Putting the lift moment into hull by secondary development of the Aqwa software,new horizontal motion response appear which was in good agreement with the result of the SJTU pool experiment.