The Numerical Simulation Of Single Anchor Leg Mooring System

Single Anchor Leg Mooring System (SALMS) is currently under studyand will be put into practice in navy programs. It is mostly designed byempirical formula at present. In this paper, a numerical model in time domainis present to predict the dynamic responses of SALMS subject to wind, waveand current, and the relative dynamic simulation calculation programs isprovided. The model is established under the comprehensive study on theachievements of Single Point Mooring Systems and risers of oil drillingplatform.The nonlinear five-order Stokes wave is employed to predict the waveload of SALMS, and second-order wave drift forces are also considered bytaking into account of the square item in Bernoulli equation. In this program,the directions of wind, wave and current can be different, but it is usuallyassumed that wind, wave and current are all from the same direction at theinitial design. Because of the 'weather vane' characteristic and the dynamicresponses of SALMS would be maximal when the directions of wind, waveand current are consistent, it calculated the dynamic responses of wind, waveand current acting on the same direction that is the long direction of thevessel. The results are reasonable. 3-D concentrated mass method is adoptedto obtain the riser's dynamic response equation. The static method isemployed in calculations of riser tension. For buoy, it ignored the effect ofwind load, and the calculations of wave load and current load are similar tothe methods of risers'. The loads acting on vessel are obtained withexperimental equations, and the movement responses effect on surging andswaying. The static method is also employed in calculations of mooringforce.Based on the Hamilton-type quasi-variation principle, a new method isintroduced in this paper which applying the quintic B-spline function asinterpolation to the time sub domain. And it is used to solve the vessel andriser's dynamical response. The initial values are decided by the initiativeconditions.The dynamic simulation calculating programs serve to two SALMS(LOOP SALMS and Tembungo SALMS), and the calculating results ofseveral cases are compared with design and experimental results, which showfairly good consistency and stability. Then, compared with the Wilson-θapproach, B-spline function method is better at the accuracy and the stability.The research provided the directions in theory for designing andconstructing the SALMS. And it grounded SALMS in next study.