海底管道受抛锚撞击的数值模拟

海底管道常会因受到抛锚等坠物撞击而发生管道破损、油气泄漏等事故,通常的保护措施是将海底管道埋入海床下一定安全的深度。锚在贯入海床的过程中,与海床相互作用会耗散掉锚的大部分能量,从而使锚对管道的撞击能量减小,继而避免或降低锚对管道的撞击损害。运用非线性有限元软件ANSYS/LS-DYNA建立锚、海床、管道的有限元模型以还原锚贯入海床的过程,选取不同锚重、不同撞击速度及不同海底底质得到锚在贯入海床的过程中与海床的能量变换情况,即锚的速度及位移变化、海底管道的应力应变情况。模拟结果表明,锚的贯穿量随锚重和触底速度增加而增大,随土壤内摩擦角和土体黏聚力增加而减小。

Numerical simulation for the submarine pipelines disturbed by the anchor loading

In order to ensure the safety and smoothness of the oil and gas transportation by submarine pipeline,it is necessary to analyze and assess the damage risk caused by the emergency anchor. By using a nonlinear finite element software known as the ANSYS /LS-DYNA,the present paper has been trying to restore the process of a certain anchor penetrating into the seafloor. To achieve the purpose,we have,first of all,built up a geometric model of the anchor,pipelines and seafloor,then the unit type and the real constant has been defined and then meshed the geometric model so as to work out a finite element model. Secondly, the contact and collision dynamic response between anchor and seabed was analyzed by penetration method,and the velocity change and energy dissipation in the process of anchor injection into the seabed was simulated. Thirdly,energy transformation between the anchor and seabed,the velocity and displacement of the anchor as well as the stress and strain state of submarine pipelines were obtained by selecting different anchor weights,different impact velocities and different seabed sediments. Finally,according to the output file of the LS-PREPOST processing program,the energy change curve,the velocity-time curve and the anchor's displacement curve of the model were obtained,the numerical simulation results can correctly show the energy dissipation and displacement changes of the anchor in the seabed. The results showed that when anchor was penetrating the seabed,the seabed dissipated most of the anchor's energy so that the impact energy of the anchor on the pipelines decreased. The injection energy of the anchor increased almost linearly with the increase of anchor's weight and bottoming speed. Furthermore,the injection energy of the anchor decreased with the increase of internal friction angle and cohesive strength of soil. The research of this paper can provide references for the safety protection of submarine pipelines.