Coupling Dynamic Analysis Of Manifold Installation In Deep Water

Vertical lifting method is widely used in the installation of marine structures,but the deep movement of the installation ship on the sea surface will have a great influence on the movement of underwater structures during the installation operation,and with the increase of wave height,wave cycle and sea water velocity,this effect becomes more obvious,which makes the installation work more difficult.In this paper,the manifold is taken as the installation object.Through dynamic analysis and OrcaFlex simulation,the vertical displacement,velocity,horizontal direction and maximum tension of the cable during the vertical lifting process are studied.The specific contents are as follows:In the two-dimensional vertical plane,the longitudinal motion equation of the installation ship is established based on the slice theory,and the dynamic equation of the cable is established by the finite difference method.The dynamic equation of the manifold is established on the basis of the simplified form of the six degree of freedom equation of underwater structure.The end point of the cable is the same as the speed of the installation ship,and the end point of the cable is the same as the manifold velocity as the boundary condition.Three equations are combined to get the dynamic model of the ship cable manifold coupling system.Using the UDF technology and dynamic mesh model in Fluent,the resistance to uniform motion and accelerated motion is calculated.By means of the force equation,the hydrodynamic coefficients of the manifold are obtained.Compared with the DNV specification,the error is less than 3%,which proves the reliability of the calculation method and lays the foundation for the accurate calculation of the motion response of the manifold.With the calculation of the calculated hydrodynamic coefficient,the OrcaFlex is used to simulate the vertical lifting process.In view of the dangerous entry stage and the deep water stage,the water slamming force,the maximum tension of the cable,the vertical amplitude of the pipe sink and the horizontal offset with the wave height and the period are studied.The change law of the velocity of the current and the weight of the pipe.The influence of different parameters was determined by orthogonal test.Finally,according to the analysis results,suggestions for actual installation are put forward.