海洋立管内流流动分析及疲劳寿命预测

涡激振动是立管发生疲劳破坏的关键因素之一。为了更加准确预测其疲劳寿命,基于Van Der Pol尾流振子模型,考虑内外流共同作用对立管的涡激振动影响及横向和顺流向的耦合作用,建立了立管涡激振动方程,用Hermit插值函数和Newmark-β法对方程求解,进一步采用P-M准则对立管疲劳寿命进行分析。并且通过设计试验对模型进行验证,最后研究管内流速对位移响应和疲劳寿命的影响。结果表明:立管振动位移随内流流速的增加而增加,造成立管疲劳寿命降低;通过增大顶张力可以有效消除内流的影响;立管两自由度涡激振动疲劳寿命大体相等,因此双向耦合作用在立管振动分析中应给予足够重视。

Internal fluid analysis and fatigue life prediction of marine riser

Vortex induced vibration (VIV) is one of the main causes of fatigue damage of marine riser. In order to predict the fatigue life more accurately, effects of internal flow and the coupled in line and axial motion are taken into account, a fluid solid coupled model of VIV in risers is established based on the Van Der Pol wake oscillator model. Then the method of Hermit interpolation function and Newmark β are used to solve the equation. The fatigue life of the marine riser is analyzed by using the P-M criterion. And a VIV experiment is conducted to verify the prediction model. Finally, the effect of the internal flow velocity on displacement response of VIV and the fatigue life of the riser are analyzed. The results show that the vibration displacement of the riser increases with the increase of the flow velocity, and its fatigue life is reduced at the same time. By increasing the top tension, the influence of internal flow can be effectively eliminated; the fatigue life of the two degree of freedom vortex induced vibration of the riser is roughly equal. The two way coupling should be given sufficient attention in the vibration analysis of the riser.