非对称管 土边界的海底悬跨管道涡激振动特性

Vortex-induced Vibrations of a Free-span Submarine Pipeline underAsymmetric Pipe-soil Boundary Conditions

摘要:

海底悬跨管道涡激振动问题十分复杂，需考虑流 管-土多场耦合效应。本文将悬跨管线简化为Euler-Bernoulli梁，两端跨肩管-土作用与线弹性弹簧和扭转弹簧近似，采用Van der pol方程描述旋涡脱落的尾迹特性。利用模态正交性对流-耦合控制方程进行解耦，采用龙格-库塔法进行数值求解，重点分析非对称边界对海底管道涡激振动特性的影响。计算结果表明：非对称边界条件对最大响应幅值影响不大；约束条件越强烈，模态激发越难，响应频率越高。

Abstract:

The submarine pipeline from offshore petroleum fields must frequently pass over uneven seafloor areas.In such cases，the pipeline may have free spans when crossing depressions.If dynamic loads occur，the free span may oscillate，and time-varying stresses may create unacceptable fatigue damage.A major source for dynamic stresses in free-span pipelines is vortex-induced vibration （VIV）caused by steady current.This effect is dominant on deep water pipelines because wave-induced velocities and accelerations decay with increasing water depth.Vortex-induced vibrations in a free-span pipeline are a highly complex phenomenon in which the fluid-pipeline-soil coupling should be considered.One challenge for free-span analysis relates to accurate prediction of VIV and design of a pipeline system to mitigate its effects.In this paper，VIV of a free-span pipeline under asymmetric boundary conditions is analyzed.The submarine pipeline was modeled by using an Euler-Bernoulli beam.The two ends were restrained by an extension spring and a twist spring.The wake flow was described by Van der pol equation，and a wake oscillator model was introduced.The model parameters were estimated according to experimental data.The coupling equations were decoupled by the modal principle，and the numerical results were obtained by Runge-Kutta method.It was concluded that stricter asymmetric boundary conditions relate to more difficulty in the high mode and higher response frequency，which had little effect on the response amplitude.