The effect of functional loads on free spanning pipeline’s VIV response

During the operation and installation of offshore pipelines, high axial forces and pressures are experienced, and their effects cannot be neglected. In this article, the effect of internal flow velocity and functional loads on vortex-induced vibration (VIV) response is investigated. On the basis of the Hamilton principle, a differential equation was derived to describe the motion of a pinned-pinned tensioned spanning pipeline conveying fluid. The VIV response was calculated according to DNV-RP-F105 under different functional loads. The results showed that functional loads influence free spanning pipeline VIV response by changing the natural frequency. Internal flow velocity was found less important for VIV response than other functional load factors, such as effective axial force, because the speed in reality is not high enough to be significant. The research may provide a reference for sensitivity studies of the effect of functional loads on allowable free span lengths.摘 要在海底悬跨管道安装和操作过程中会产生的高轴向力和高压力, 功能载荷对管道涡激振动的影响不可忽略。 本文首先基于Hamilton 原理, 推导并求解了简单支撑的输液张力管道自由运动方程, 在此基础上利用DNV-RP105 规范评估悬跨涡激振动响应, 对悬跨管道受不同功能载荷(特别是有效轴向力和内流流速)进行计算。 结果显示功能载荷通过改变管道的固有频率来影响涡激振动响应, 而且由于实际内流流速一般不高, 其影响较有效轴向力要弱。 结果可以为悬跨管道的许用长度选取提供参考。