Numerical Simulation Of Submarine Pipeline Self-buried Mechanism

With less and less oil reserves on land, people began to set their sights on the use and exploitation of undersea oil. Submarine pipelines as an important means of transportation, has many merits, such as continuously deliver, large conveying capacity, and convenience management and so on, so they have been used extensively in ocean engineering currently. Normally because of the severe conditions in marine environment, the pipelines will be suspended and lose its stability caused by wave and tide, so it is generally to embed the pipe during the laying of the pipeline. The traditional method is relaying on mechanical means to realize embedment, but the prices of various types of machinery and equipment are very high, in order to find a cost-effective way, people placed a kind of spoiler device which is similar to the fish fin above the pipe to achieve the self-burial of pipelines. In this paper, basing on the self-buried technology in Hangzhou Bay's laying of submarine pipelines, apply the method of numerical simulation to compare two kinds of conditions of having spoilers or not on pipelines under the scouring of current. By comparing, it illustrate that the spoiler's role of promoting in pipelines' self-burial.Firstly, the sea-bed is assumed to be solid wall, to simulate the scour around the pipeline of having spoilers or not. Through the comparative analysis of pressure coefficient and lift coefficient on the surface of pipe as well as seabed shear stress, it is explain that spoilers are able to cause the changes of flow around the pipeline, so that the pressure above the pipe increase, lift coefficients reduce, flow velocity under the pipe greaten and flush the seabed, finally cause the increasing of seabed shear stress. All of them play an important role in the self-burial of pipelines.Then, simulate that seabed scouring around the pipeline, to study the scour pit pattern below the pipeline and to export the distribution of surface pressure coefficient from the pipeline. Meanwhile, we contrasted the flow velocity below the pipeline. It can be seen that the surface pressure of pipelines adding spoiler device is an obvious left-right asymmetry.Because of the countercheck by spoiler device, it causes the top pressure of pipelines' meeting flow surface increasing obviously, it will also cause the lift coefficient of pipeline decrease and the scour below the scour intensifies. For the form of scouring pit, spoiler device makes the scouring pit deepen, the pipe will sink rapidly by gravity, so as to realize the self- burial.Simulate the process of pipe sinking, we can see that the process of pipeline self-burial firstly is sediment erosion beneath the pipe, forming the scour hole. Due to the pipe itself exsists gravity, so it will sink slowly under the action of gravity. The sediment washed will be accumulating behind the pipe.With the pipe down, rear sediment will slowly backfill, the pipe then will be buried under the seabed. This is the actual process of pipeline self-burial.