Study On Static And Dynamic Contact Effect Of Mooring Line And Seabed

With the rapid development of economy,China has speeded up the utilization of energy.In the development of floating photovoltaic power stations,floating fans,and oil and gas exploration in the deep sea,it is necessary to use mooring lines to connect the floating body with anchor for mooring and positioning.The interaction between the mooring line and the soil affects the load transfer mechanism of the mooring line and affects the stable operation of the mooring system.In the preliminary design of the project or in a good natural environment,quasi-static analysis methods can be used to simplify the calculation.However,in the deep sea where the natural environment is complex,the inertia force of mooring line,the development of trench around the touchdown zone,and the cyclic weakening of the soil may cause the mooring line to become loose,rendering the anchor ineffective and threatening the safety of the mooring system.Therefore,it is necessary to study the dynamic contact effect between the mooring line and the seabed.The following work is carried out based on those problems:(1)The quasi-static analysis model of mooring line and seabed is introduced first.Then,In view of the design method of mooring line of floating photovoltaic power station,the shape of anchor chain under high and low water level is analyzed by considering Ultimate wind force and the water level.The maximum length of anchor chain is calculated under low water level and the length is checked on high water level.Some strategies are put forward,such as mounted chain device,the use of this method is introduced in this paper.(2)A numerical model is developed by using finite element software in accordance with the characteristics of the tension change of anchor chain under dynamic conditions and the correctness of the numerical model is verified by tensioning the mooring line slowly.The tension change of mooring line is studied from the two aspects of motion cycle and soil strength.The effect of tangential soil resistance and inertial force of mooring lines on the tension changes of the mooring lines and the general rule of maximum tension change at the mooring line fairleads are found under dynamic conditions.(3)The formation and development characteristics of trench around the touchdown zone of mooring line is studied by considering different pretension?strength of soil and period.Then the effect of missing soil around touch down zone on load transfer and trench development is studied.(4)A numerical model considering the contact effect between mooring line and soil is developed based on the nonlinear hysteretic model,and it is verified through single point verification and numerical model verification.Then the change of tension and the development of trench is studied from different pretension and soil strength.