Research On Damage Of Submarine Pipeline Based On Dynamic Simulation Of Ship's Anchoring

The oil and gas pipelines laid on the seabed play a very important role in the process of transporting oil and gas resources.The submarine pipelines have the characteristics of large transportation,safety and fast speed,which makes the submarine pipelines widely used in the oil and gas transportation projects all over the world.In recent years,with the growing demand for oil and natural gas in China,the laying mileage of submarine pipelines is increasing gradually.As the "lifeline" of marine oil and gas production system,once any damage or leakage occurred in the submarine pipelines,not only will the oil and gas companies pay a huge economic price,it will also cause serious pollution to the ecological environment around the pipelines,and leads to adverse social impacts.Because the costs of burying submarine pipeline is high,and the submarine pipelines are easily damaged by the unintended ship's anchoring.In this context,it has very important significance to study the dynamic simulation of the ship's anchor,so as to determine the damage degree of pipelines under a certain depth caused by the anchor.Therefore it can not only protecting the pipeline from the damage of anchor but also can save the laying cost.In this paper,a physical model test of an anchor drops into the water and a finite element model for the entire process of an anchor drops into the water until it penetrates the seabed based on ANSYS/LS-DYNA finite element software is designed.Through combining the theoretical calculation and the numerical simulation to determine the extent of damage to the submarine pipeline under the impact load because of accidental anchoring of ships.The specific work of this paper is as follows:Firstly,design and carry out the physical model test of hall anchor in a free-fall manner,in order to study the impact of the anchorage height and the mass of the anchor on the velocity of the anchor in the water,then the fluid resistance coefficient of the hall anchor is obtained by using the results of the mold test.Based on the same shape has the same fluid resistance coefficient,this coefficient can be used to calculate the speed of the uniform motion of the hall anchor in the water with different weights.Then the calculated results and the results of the numerical simulation can be mutual authentication.Secondly,the finite element simulation model of hall anchor from air to water is established.Analyze the hall anchor's movement in the water based on ANSYS/LS-DYNA software,by changing the anchorage height and the mass of the anchor and the depth of the water to explore the influence of various factors on the speed of anchor.The speed of the simulation experiment is compared with the velocity obtained through the physical model test,when the difference between the two is small,it can be proved that the modeling and calculation of simulation test are reliable.So as to lay the foundation for the next simulation experiment.Finally,the finite element simulation model of hall anchor penetrates the seabed is established.Establish the finite element model of anchor-sea-seabed-pipeline based on ANSYS/LS-DYNA software,and simulate the whole dynamic process of the anchor penetrates into the seabed,analyze the stress change of the pipeline during the process,and design many groups of simulation test to explore the influence of different factors on the pipeline damage degree.Thus,the minimum safety depth of the submarine pipeline from anchor damage is determined.The research results of this paper can provide scientific theoretical basis for the laying of pipelines in practical engineering and determining the minimum safe burial depth of pipelines in special working condition.