The Application Of Muti-body System Dynamics In The Dynamic Analysis Of Mooring Lines

With the continuous development of marine resources, marine engineering has been great developed. Mooring cable systems plays an important role in the marine engineering system. It is significant to accurately estimate the dynamic characteristics of the cable system for the design, safety and operation of marine engineering systems. Multi-body system dynamics has been widely used in the field of aerospace, vehicles, and so on. With the application of Multi-body dynamics in the analysis of mooring lines, tedious calculation between segments can be automatically eliminated and the tedious differentiation is no longer required.And the method can be used to calculate the large displacements and the motion of slack mooring lines.In this paper,based on the method of muti-body system dynamics, each section of the chain link has been simplified into a cylinder, and the mooring line is considered connected by a series of cylinders,then the dynamic model of the mooring line was stablished. According to the Morison equations, Kane method was employed to obtain the dynamic equations. The dynamic response of the mooring line can be calculated by the fourth-order Runge-Kutta method.For a single chain, multi-body method and the finite element method are employed to obtain the dynamic response of the mooring line. The results are compared with the experiment. The comparison results validate that the multi-body method is available in the dynamic analysis of chains. The method is applied to the dynamic analysis of cables by changing chain-link length and compare the upper end tension of the cable. From the results, it can be found that in the certain range of different ratios of link length to total cable length, the muti-body method can be adopted in the dynamic analysis of cables used in seakeeping. With the appropriate length of the chain link, the effect of current on the tension of the endpoint is studied.Through the calculation,the result show that low-speed flow has little effect on the tension of the cable.