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。%The submarine pipeline from offshore petroleum fields must frequently pass over une-ven seafloor areas.In such cases,the pipeline may have free spans when crossing depressions.If dy-namic 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 vibra-tion (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 vibra-tions in a free-span pipeline are a highly complex phenomenon in which the fluid-pipeline-soil cou-pling 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 pipe-line under asymmetric boundary conditions is analyzed.The submarine pipeline was modeled by u-sing 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 in-troduced.The model parameters were estimated according to experimental data.The coupling e-quations 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 re-sponse amplitude.
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