基于整体分析的钢悬链线立管触地点动力响应分析

DYNAMIC RESPONSE OF A STEEL CATENARY RISER AT THE TOUCHDOWN POINT BASED ON INTEGRATED ANALYSIS

  • 摘要: 在立管动力平衡系统的力学模型中考虑浮式平台的惯性作用和管-土相互作用,研究在不同参数激励下钢悬链线立管触地点动力响应。基于大挠度柔性索理论,分别采用具有弯曲刚度的大挠度细长梁、弹性地基梁模拟立管的悬垂段和流线段,考虑触地点处的大曲率,建立了立管的三维有限元模型,利用Galerkin方法对运动方程离散为一组非线性二阶常微分方程,运用Newmark-β法求解离散方程。通过在立管的动力方程中引入δ函数来体现浮式平台对立管的惯性和水动力影响,将悬链线立管与浮式平台作为一个整体进行动力分析,以工程中实际使用的1800m水深的钢悬链线立管为例,通过对立管顶部进行谐波激励,分别就水动力系数、管内流体密度和海床土体刚度对立管特征点动力分析的影响进行分析,研究表明:水动力系数的改变对立管触地点的动力响应的影响较为显著,主要体现在弯矩和张力幅值的增加;管内流体密度不同,触地点位置不同,表明立管在输送不同液体或气体可能发生疲劳破坏的位置也不同;而海床土刚度对立管触地点区域的弯曲应力影响较大,对轴向应力则影响不大,其结果对SCR设计具有重要的指导意义。

     

    Abstract: This research’s purpose is to quantify the effect of different parameters on the dynamics of a SCR (Steel Catenary Riser) by incorporating floating-body inertia and the soil reaction force into the theoretical model of the dynamic equilibrium system. The dynamic response simulation of a SCR under oceanic environmental loads was carried out. The simulating method through which the riser-soil interaction is studied is based on an extensible curved beam with a large curvature and a beam on an elastic foundation. The sag-bend and the flow-line sections of the SCR are modeled by the extensible curve beam with a large curvature and the beam on an elastic foundation, respectively. Galerkin’s method was used to discretize the dynamic equations in space, resulting in a set of nonlinear 2nd-order ordinary differential equations in the time domain. Newmark method was employed for time-domain integration of the discretized equations. The hydrodynamic and inertial forces of the floating-body can be added to the dynamic equations by introducing a δ function. A 1800m floating-body and riser system of engineering is analyzed. Several test cases of top end harmonic excitations were performed, aiming to investigate the effect of the various dynamic parameters on the dynamic analysis at the key zone, such as hydrodynamic coefficient, internal fluid density, and seabed stiffness, etc. The results indicated that changing the hydrodynamic coefficient has an obvious effect on the amplitude of tension and bending moment at the TDP (Touchdown point), different internal densities will change the position of the TDP, and the changing soil stiffness has a great impact on the maximum variation of bending stress and on fatigue life. Fatigue damage at the TDP is mainly induced by bending stress rather than axial stress. Hence results have significance as a guideline for the design of SCR.

     

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