海洋钢悬链线立管振动响应与疲劳预测

Vibration Response and Fatigue Prediction of Marine Steel Catenary Risers

涡激振动是引发立管疲劳损伤的关键诱因之一。基于Van Der Pol尾流振子方程,研究了不同长度两端铰接的钢悬链线立管在相同来流流量不同剖面剪切来流作用下的涡激振动响应。采用二阶中心差分法对时域和空间域的耦合方程组进行了求解,并采用雨流计数法对立管的疲劳寿命进行了预测。结果表明,立管振动沿轴向传播呈驻波和行波的混合模式,随立管长度的增加,振动响应由驻波主导转变为行波主导。受剪切来流剖面的影响,立管振动响应呈现多频特性,行波自立管的顶部向底部传播,且其传播速率随来流剪切程度及立管长度而变化。随剪切程度的增强,立管从流体中获得的能量减少,能耗增加,振动位移减少。相同来流剖面时,随着水深的增加,立管疲劳损伤增加;而水深相同时,随来流剪切程度的增加,疲劳损伤逐渐增大。

Vortex-induced vibration(VIV)is a main factor contributing to the fatigue damage of marine risers.With the aid of Van Der Pol wake oscillator model,the present paper investigates the VIV of pinned-pinned steel catenary risers of different lengths subjected to different shear-flow profiles with the same flow rate.The second-order central difference method is employed to solve the coupled equations in both time and space domain,and the rain flow counting method is used to predict the fatigue life.The vibration presents a blended pattern of standing wave and traveling wave for the response propagation along the span.The vibration shifts from the standing-wave dominated response to the traveling-wave dominated one with the increase of the riser length.The riser experiences multi-frequency oscillation due to the influence of shear flow,and the traveling wave propagates from the riser top to its bottom.Furthermore,the propagation rate of traveling wave varies with the shear degree of flow profile and the riser length.The riser extracts less energy from ambient flow as the shear degree increases,while the energy consumption grows,resulting in the reduction of response amplitude.The fatigue damage is aggravated with the water depth at the same incoming flow profile.The same result is observed as the shear degree of flow profile increases at the same water depth.