内输高温高压流体海底悬跨管道的非线性涡激振动响应分析

Nonlinear dynamic response of suspended span pipe conveying high temperature and high pressure flow

海底管道内输的高温高压流体会引起管内较大的轴力,从而诱发管道的整体屈曲。发生屈曲的管道凸出海床表面,出现部分管道悬跨的现象,进而在海流的作用下会形成涡激振动现象。本文研究因热屈曲引起初始竖向变形的海底悬跨管道在内外流耦合作用下的涡激振动响应。首先,采用Euler-Bernoulli梁模型来模拟海底管道,通过对管道单元和内部流体单元进行受力分析,建立悬跨管道运动学平衡方程,确定内输高温流体管道的热屈曲平衡状态。然后,在方程中引入尾流振子模型,建立内输高温高压流体管道在内外流作用下的耦合动力学方程,采用Newmark-β方法对离散的涡激振动响应方程进行逐步求解,得到管道时程的振动位移、速度及加速度,确立了有初始变形管道振动的非线性振动时域预报方法。基于该方法进行算例分析,首先对比不同模态下考虑热屈曲和不考虑热屈曲的管道振型,观察热屈曲效应对于不同模态下管道振动形态的影响;通过分析管道振动频率随时间的变化趋势,结合建模过程中刚度矩阵的变化趋势,推导出管道轴力的周期性变化会引起自然频率的周期性变化;改变管道外部流体流速,观察管道振动频率、模态和幅值的变化,分析得出管道从低模态振动转为高阶模态振动时,管道从周期运动变为混沌运动,后随外流速增加又转为周期运动,此过程中管道会出现多模态振动的现象,并且多模态作用对低阶模态的振动影响较大;改变管道内部流体温度和压力,观察管道振动频率和振动幅值的变化,得到管内温度和压力的增加会导致管道振动频率的降低及管道振动幅值的增加。

Internal high temperature and high pressure flow of a subsea pipe will cause high axial force, which could induce global buckling of the pipe. The buckling pipe, which curves out of the seabed, forms a suspended span and vibrates under the action of cross currents. The dynamic response of a subsea pipe with initial vertical deformation caused by thermal buckling under the combined action of internal and external flow was analyzed. Firstly, the Euler Bernoulli beam model is used to simulate the suspended span pipe. Through stress analysis of the pipeline element and internal fluid elements, the kinematic equilibrium equation of the suspended span pipeline is established to determine the thermal buckling equilibrium state of the internal high-temperature fluid pipeline. Then, the wake oscillator model is introduced into the equation to establish the dynamic coupling equation of an internal high temperature and high pressure fluid pipeline under the action of internal and external flow.By using the Newmark--β method the discrete vortex induced vibration response equation is solved step by step, the vibration displacement, velocity and acceleration of the pipeline in time history are obtained, and the nonlinear vibration time domain prediction method of pipeline vibration with initial deformation is established. Firstly, the vibration modes of a pipeline with and without thermal buckling under different modes are compared, and the influence of the thermal buckling effect on the vibration mode of the pipeline under different modes is observed;By analyzing the pipeline vibration frequency change trend with time and combined with the change trend of the stiffness matrix in the modeling process, it is deduced that the periodic change of pipeline’s axial force will cause the periodic change of natural frequency. We changed the external fluid flow velocity of the pipeline, observed the changes of vibration frequency, mode and amplitude of the pipeline, and concluded that when the pipeline changes from low mode vibration to high-order mode vibration, the pipeline changes from periodic motion to chaotic motion,and then changes to periodic motion with the increase of external flow velocity. In this process, the phenomenon of multi-modal vibration will appear in the pipeline, and the multi-modal effect has a great influence on the vibration of low-order modes;We then changed the fluid temperature and pressure inside the pipeline, observed the changes of pipeline vibration frequency and vibration amplitude, and get that the increase of temperature and pressure in the pipeline will lead to a decrease of pipeline vibration frequency and an increase of pipeline vibration amplitude.