Motion Response Analysis Of Floating Platform Under The Action Of Asymmetric Mooring System

With the social development increasingly in our country,energy demand is more and more enormous.However,the energy on land is diminishing,exploitation of oil and gas resources turn to the ocean,which is of great significance to develop and utilize the rich oil and gas resources.The oil and gas resources in the deep sea are widely distributed on the continental shelf with gentle slope and the continental slope with steeper slope liking step.When exploiting the oil and gas resources on continental slope,the seabed topography of the floating platform may have a large slope,which an asymmetric mooring system is required,and the motion of the floating platform is relatively complicated.The thesis is based on a Deep Draft Multi-Spar proposed by our research group before,and three sets of asymmetric mooring systems are designed.The motion responses of platform and the dynamic characteristics of mooring system are studied and analyzed.At first,the geometric model of platform based on the ANSYS software is established and the suitable meshing platform surface is divided.The parameters of platform model are imported in AQWA software,and also the parameters such as center of gravity and moment of inertia a hydrodynamic model of the platform is changed.Then,the mooring material parameters by using semi-tensioned moorings are chosen.With keeping the depth of mooring anchorage points on one side of the platform invariability and the depth of mooring anchorage points on the other side is changed,the asymmetric mooring system based on the original symmetric mooring system is designed.The adjustment mooring line length is optimized by MATLAB program.Finally,the asymmetric mooring parameters are inputted into the AQWA module to establish the time domain coupling model.The free decay test and motion responses under regular wave are conducted.And then the motion response of platform is compared under different combinations of wind,wave and current.The study shows that the surge,sway and pitch response amplitudes of platform adopting the asymmetric mooring system under both regular wave and irregular wave and the combined action of wind and current meets the requirements of the engineering.Comparing with the symmetric mooring system,the horizontal stiffness of asymmetric mooring system is larger,which can provide larger horizontal restoring force,effectively reduce the horizontal displacement of platform,and improve the platform motion performance.For the tension of mooring rope in the process of platform movement,the mooring depth of shallow water side is lower,the mooring tension is greater,which require the strength of mooring materials is also higher.