横向有限应变对张力腿平台空间涡激振动响应的影响

Influence of Transverse Finite Strains on Spatial Vortex Induced Vibration of Tension Leg Platform

为研究张力腿平台的动力响应问题,基于Hamilton原理,根据克希霍夫假设以及拉格朗日函数,得到张力腿海洋平台空间运动的运动方程和边界条件,运用有限差分法对运动方程和边界条件进行离散,最终采用吉尔法求解微分方程组。采用半经验Morison公式模拟流体力的作用,在不同水流流速作用和涡旋脱落载荷共同作用下,比较了横向有限应变对空间涡激振动响应的影响。计算结果表明:当涡旋脱落频率接近结构的固有频率时,横向有限应变对涡旋脱落载荷作用方向的横向位移响应将产生较明显的影响,可产生超过30%的偏差。然而,即使在涡旋脱落频率不靠近结构的固有频率时,横向有限应变对水流作用方向的横向位移响应和轴向位移响应都有很大的影响,可产生100%以上的偏差。

In order to research the dynamic response of the tension leg platform, the equations of motion and boundary conditions of the tension leg platform in three dimensions are derived from the Hamilton＇s principle, the Kirehhoff＇s hypothesis and the Lagrange functions. The motion equations and the boundary.conditions are diseretized in time and space by using the finite difference method. The differential equations are solved numerically by the Gear＇s method. The semi-empirical Morison equation is applied to the fluid force simulation. The influence of the transverse finite strains on the spatial vortex induced vibration is compared under the interaction of variable current velocity water flow and vortex-shedding load. The calculation result shows： when the vortex-shedding load frequency approaches the natural frequency of the platform, the transverse finite strains influence the transverse displacement response obviously, and the deviation is more than 30%. The transverse finite strains influence the transverse and vertical displacement response greatly, and the deviation is more than 100%, even when the vortex-shedding load frequency is rather away from the natural frequency of the platform.