Motion Responses Analysis of Moored Spar Platform in Irregular Waves in Deepwater

The depth of South China Sea is usually between 500 meters and 2000 meters,which belongs to deep water,while Spar platform is suitable for economic development platforms in deep water with the depth between 500 meters and 3000 meters.An numerical simulation for motion response and the tension of cable in irregular waves of Classic Spar platform moored at the depth of 2000m undersea is performed in this paper.First of all,the wave force,added mass and radiation damping are gotten through the method of frequency domain,and then the fast Fourier transform is applied to transfer the results from frequency domain to time domain.The tension of mooring rope is calculated based on the total Lagrangian formulation and two-node isoparametric cable unit as well as Geometric nonlinear finite element method and Newmark method.Motion response and cable tension are gotten with the help of Runge Kutta method of fourth order equation of motion in time domain.Irregular wave surface is obtained by JONSWAP wave spectrum,and impact of overshoot parameter is taken into account.The effects on the mooing system of second order drifting force,pretension and elastic stiffness of mooring lines have been analyzed.