Numerical Simulation Research Of Submarine Pipeline Depth Against Emergency Anchor Loading

With the development of the offshore oil industry,offshore pipeline has been widely used in the transportation of offshore oil and gas.The submarine pipelines which cross the channel are easily to be damaged due to the third-party human activities such as fishing,transport of goods and anchoring and so on in the process of installation and transportation.If the dropped objects impacted the pipelines,it will cause the damage of pipelines,even lead to serious leak accidents.Once the leak accidents occurred,it not only affect the normal mining and industrial production,but also cause pollution of the marine environment and huge economic losses,the consequences could be disastrous.Throughout the pipeline damage accidents occurred at home and abroad in recent years,we can see that most of them are caused by emergency anchor of the ships.In order to ensure the safety and smoothness of the oil and gas transportation by submarine pipeline,and the sustainable development of the marine environment,it is necessary to analyze and assess the damage risk caused by emergency anchor,and then propose appropriate protection measures.The usual protection is that make the pipelines buried or covered with a protective layer of rockfill above them.This paper mainly analyze the extent of damage of pipelines impacted by emergency anchor in the comparative cases that if the pipelines are buried.It's proved that the buried protection is necessary.It simulated the process of the anchor penetration in the seabed based on finite element analysis program ANSYS / LS-DYNA,and analyzed the factors that affect the penetration depth such as anchor weight,anchor height,water depth and soil material of seabed,in which way to determine safe buried depth of the pipelines under the influence of anchor impact ultimately.The main work is as follows:(1)Establish motion model of anchor in various stages of the movement process.Use mathematical physics model to solute the velocity of anchor when it arrives the surface of the seabed.The velocity is useful for the numerical simulation of penetration process of the anchor.(2)Analyze the extent of injury and risk of the unburied pipeline impacted by an anchor based on the finite element method.Then point out the necessity to bury the pipelines under seabed.(3)Establish finite element model of anchor-seabed-pipeline,simulated the process of anchor penetration into the seabed above pipelines.Analyze dynamic response of pipeline in the whole process,and compared with dynamic response of unburied pipeline impacted by anchor,indicating that the protection is effective.(4)A numerical method for calculating the depth of the pipeline was proposed based on the numerical simulation.And the factors affect the burial depth were analyzed,such as anchor weight,impact velocity,seabed soil cohesion,internal friction angle and so on.Contents and results of this study has reference value for laying and buried depth design in practice.