Nonlinear Dynamics Research Of Mooring Rope Of Offshore Platform

With putting forward the strategy of sea power, our country has being investing in the field of ocean more and more. As one of the main equipment of the development and utilization of marine resources, offshore platforms’ scale of building and using expands unceasingly. For each type of offshore platforms, all need positioning system to help them to locate. Now the mooring system is one of the positioning systems which is used more extensive. Using of the mooring system for positioning, the deep ocean marine platform can produce and operate smoothly. In the process of developing offshore floating structures, grasping its various nonlinear dynamic characteristics of mooring system accurately is a very important work. One of the key issues to offshore platform’s stability and reliability is to study the nonlinear dynamic behavior of the offshore mooring rope, Such as the stability equilibrium point of the motorial mooring rope,the period-doubling、chaos and bifurcation phenomena of vibratory mooring rope. Making comprehensive analysis to nonlinear dynamic characteristics of mooring rope can provide reliable technical advice and project references when design and manufacture mooring systems, thus better able to withstand the negative impact of various complex harsh marine environment loads to the offshore platform, so ensure that offshore platform can produce stesdily and reliably in some area for a long time.Based on the offshore mooring system simplified mechanical model as the research object in this paper, exploring the dynamic characteristics of mooring rope under longitudinal excitation. The specific research contents as follows:(1) Establish the mooring cable dynamics modelChoosing tension leg platform(TLP) mooring system as the research and analysis of objects in all types of offshore platforms. Because of the tension leg platform mooring system is almost based on the sea bottom in the way of vertical anchorage, this kind of situation provides convenient for later analysis and model simplified. Using the Hamilton principle to establish dynamic equation and variational calculation, the equilibrium equations are listed after analyzing the micro section of cable force.(2) List the dynamics equations of mooring rope and dimensionless equations on dynamicsEstablish the dynamics equation under the longitudinal excitation response through the above calculation, it is concluded that expression of unknown quantities after the simplified analysis. In order to analyze the dynamic characteristics of cable in each direction, the equations are dimensionless processed through introducing the dimensionless parameters.(3) Analyze the nonlinear dynamic characteristics of mooring ropeThrough the method of numerical calculation, the influence of the mooring cable dynamics are researched under different amplitudes of vibration force、different initial phase angles、different vibration frequencies、different pretensions in cable and different initial conditions.