Investigation On Self-burial Effect Of Submarine Pipeline With Spoiler Under Wave Or Current Action

Offshore pipelines have been used extensively in the oil and gas industry to transport hydrocarbons from sub-sea well-heads to onshore plants.It plays an important role in the developing of offshore oil and gas engineering.To protect the pipelines from possible damage caused by excessive hydrodynamic forces of waves and currents or the human activities of anchor dropping/dragging,it is customary to bury pipelines to a certain depth below the seabed.However,because of soil erosion and interaction of currents with the pipeline on the moveable seabed,the processes of local scouring and,sometimes,self-burial of pipelines take place.It is helpful to realize self-burial of pipeline if we can make rational use of local scour.During that process,we choose a new technology-spoiler.The cost of mechanical trenching and refilling is high especially in a low price of crude oil today.So we come to an economical way: self-burial of pipelines.If the self-burial process could be exploited,the potential cost savings in the pipeline industry could be considerable.In this paper,a vertical two-dimensional numerical model has been established to study the flow and scour around offshore pipelines.Simulations were carried out for cases of a pipe with different height of spoilers,different current velocity,different gaps,and various orientations of spoilers under the effect of current.The influences of these factors on pressure distribution,lift coefficient,drag coefficient,shear stress on the wall,as well as velocity profile are investigated.It is indicated that the coefficients for Drag are increased with the application of the spoiler.The lift coefficient is reversed with the application of the spoiler,which may enhance the self-burial of the pipeline.Then I use the Euler-Euler method to simulate the real scour and self-burial of pipelines.Simulate the self-burial process of pipeline through dynamic mesh method.After the fully analysis of the influence of current,simulation was made to study the flow around submarine pipelines under the effect of waves.A wave making module was developed.Then,the two-phase model was used to simulate the wave-induced scour beneath the pipeline laid on a plane erodible bed,and study the impact of wave on scour and 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.Scouring sediment piled up behind the pipeline.Because of equipped with spoiler,the flow velocity below the pipeline is faster and scouring process developed quickly.The pipe suffers a downward force.Due to the pipe itself exists gravity,so it will sink slowly under the action of gravity.With the pipe down,rear sediment will slowly backfill,the pipe then will be buried under the seabed.