多浮筒段缓波型立管向量有限元分析

Analysis of a Lazy-Wave Riser with Multi-Buoy Sections Based on VFIFE

单浮筒段的缓波型柔性立管存在着局部张力或者弯矩过大的情况,并且有着位型拱起过高等问题.针对单浮筒段的缓波型柔性立管存在的这些问题,对多浮筒段的缓波型柔性立管进行研究,基于Fortran通过向量式有限元(VFIFE)法建立了缓波型柔性立管的数学模型,并且通过改变浮筒段的数量、浮筒段的间距、浮筒段的单位浮力、部分浮筒段的浮力损失、海流的速度、浮筒段的位置对多浮筒段的缓波型立管进行静力计算,分析上述条件的改变对静力平衡状态下的缓波型立管的影响;并在实际海况下模拟出悬挂点垂荡激振,对悬挂点垂荡激振下的多浮筒段缓波型立管开展响应特性研究,分析了管段中部的最大弯矩、悬挂点处的最大有效张力以及速度分量的整体动态分布变化.发现在不改变浮筒段单位浮力的情况下,仅通过调整浮筒段数量、间距或者位置是无法同时降低立管顶部的最大有效张力与立管中部的最大弯矩的.除此之外,立管的整体构型也需要进行考虑.只有兼顾浮筒段数量、间距以及位置这三者对立管中部的最大弯矩、悬挂点处的最大有效张力以及立管的整体构型的影响才能获得缓波型立管的最优布局;同时还发现,随着浮筒段数量的增加,多浮筒段缓波型立管能够更好地限制立管的纵向运动,这对限制立管的疲劳损伤有一定的现实意义.

A lazy-wave riser with a single-buoy section has problems.For example,its tension or bending moment is too large in some places and the axch of riser is too high.To solve these problems,the vector form intrinsic finite element(VFIFE)method is adopted to build a mathematical model to analyze a lazy-wave riser with multi-buoy sectionsusing Fortran. We changed the number and unit buoyancy of the buoy sections,the distance between buoy sections,the current speed,and the position of the buoy sections and simulate the loss of the buoy sections. Then,weconducted static analysis. We also determined the hang-off point of vertical harmonic motion to simulate the real seaenvironment. Then,we analyzed the maximum bending moment and effective tension of the riser. Finally,we analyzedthe velocity component of the entire riser. Results showed that it is impossible to reduce the maximum effectivetension at the top of the riser and the maximum bending moment in the middle of the riser by adjusting the number,distance,or position of the buoy sections without changing the unit buoyancy of the buoy sections. The overall configurationof the riser also needs to be considered. We should consider the influence of the number,distance,andposition of the buoy sections on the maximum bending moment,maximum effective tension,and overall configurationof the riser to obtain the optimal lazy-wave riser layout. The results also showed that,with the increase in thenumber of buoy sections,the lazy-wave riser with multi-buoy sections can better limit the vertical movement of theriser,which has a certain practical significance for limiting the fatigue damage of the riser.