桁架式Spar平台与系泊/立管系统的全时域非线性耦合动态分析

开发了对浮式平台系统进行耦合动态分析的全时域程序。采用二阶时域方法计算水动力荷载,在此方法中,对物面边界条件和自由水面边界条件进行泰勒级数展开,利用Stokes摄动展开分别建立相应的一阶、二阶边值问题,而且此边值问题的计算域不随时间变化。采用高阶边界元方法计算每一时刻流场中的速度势,利用四阶预报校正法对二阶自由水面边界条件进行数值积分。在自由表面加入一个人工阻尼层来避免波浪的反射。对于系泊缆索/立管/张力腿的动力分析,在一个总体坐标系中对控制方程进行描述,采用基于细长杆理论的有限元方法进行求解。在耦合动态分析中,采用Newmark方法对平台和系泊缆索/立管/张力腿的运动方程同时进行求解。利用开发的耦合分析程序对一个桁架式Spar平台的运动响应进行了数值模拟,给出了平台的位移和系泊缆索/立管上端点的张力,并得到了一些重要结论。

Full time-domain nonlinear coupled dynamic analysis of Truss Spar and mooring/riser system

A full time-domain program is developed for the coupled dynamic analysis of floating platform systems. For the hydrodynamic loads, a time domain second order method is developed. In this approach, Taylor series expansions are applied to the body surface and free-surface boundary conditions, and Stokes perturbation procedure is used to establish corresponding first-order and second-order boundary value problems with time-independent boundaries. A higher-order boundary element method (HOBEM) is devel-oped to calculate the velocity potential of the resulting flow field at each time step. The free-surface bound-ary condition is satisfied to the second order by 4th order Adams-Bashforth-Moultn method. An artificialdamping layer is adopted on the free surface to avoid the wave reflection. The mooring-line/tendon/riser dy-namics are based on a rod theory and finite element method (FEM), with the governing equations described in a global coordinate system. In the coupled dynamic analysis, the motion equation for the hull and dy-namic equations for mooring-lines/tendons/risers are solved simultaneously using Newmark method. The coupled analysis program is applied for a Truss Spar motion response simulation. Numerical results includ-ing hull motions and tensions at the top of mooring-lines/risers are presented, and some significant conclu-sions are derived.