| Since the beginning of the 21st century,the pace of offshore oil and gas exploration and development has been significantly accelerated,but our country’s offshore oil and gas development is still in the early and mid-stage,with great industrial potential,which is the strategic focus of my country’s energy industry development in the future.In the development of offshore oil and gas resources,submarine pipelines have always been an important part of marine infrastructure.Subsea pipelines are usually laid flat or shallowly buried on the seabed.Under the action of waves and currents,the surrounding subsea pipelines will be scoured,causing the pipelines to hang in the air,resulting in fatigue damage.Vortex-induced vibration and fatigue damage.The oil and gas transported by submarine pipelines are hazardous substances,and once leakage or rupture occurs,it will have serious consequences for the surrounding environment and personnel.Compared with the scour around a single pipeline under other similar water flow and seabed conditions,the sediment transportation and scour around the piggyback pipeline are more complicated.Therefore,the numerical simulation method is used to study the water flow characteristics and the scour of the piggyback pipeline.wash out charact’’eristics.FLO W-3D is used to establish the numerical scour model of the piggyback pipeline,and the scour results of the piggyback pipeline with a parent pipe diameter of 0.1 m are studied.Calculate,explore the influence of the position angle of the sub-pipe relative to the parent pipe and the diameter of the sub-pipe on the scour result and the flow field around the pipe,and finally draw the following conclusions:(1)When the position angle of the sub-pipe is α=90°,the piggyback water-facing area is the largest,and the depth of the scour pit on the bed surface reaches the maximum value.This setting should be avoided in practical engineering.When a is between 0°～40° and 150°～180°,the maximum scouring depth of the piggyback bed is less than that of a single pipe.When the position angle α of the sub-pipe is between 40° and 150°,the maximum scouring depth of the bed below the piggyback is greater than the maximum scouring depth of the bed below the single pipe.When the position angle α of the sub-pipe is between 0°～40° and 150°～180°,the scouring depth of the piggyback is smaller than that of the single pipe,and the sub-pipe has an inhibitory effect on the scouring under the piggyback.,at this time,the force on the parent pipe is the smallest,and it is most reasonable to adopt this type of setting in the project.(2)When the sub-pipe is placed on the water-facing side or the back-water side,the maximum depth of the sand bed scour pit increases with the increase of the diameter of the subpipe.When the diameter of the sub-pipe/the diameter of the parent pipe is less than 1/2,the shape of the scour pit under the piggyback is similar to that of the single pipe.When the diameter of the sub-pipe/the diameter of the main pipe is greater than 1/2,the sub-pipe has a promoting effect on the scouring under the sub-pipe.In practical engineering,the side-by-side arrangement of piggybacks with similar pipe diameters should be avoided to reduce the influence of the vortexinduced vibration caused by the increased depth of the scour pit.(3)When the diameter of the sub-pipe/the diameter of the parent pipe is less than 1/2,the lift and drag force acting on the sub-pipe are very small,and have little effect on the flow field around the piggyback and the depth of the scour pit below the piggyback.,so when the diameter of the sub-pipe/the diameter of the parent pipe is less than 1/2,the lift and drag force on the subpipe can be ignored.This kind of setting is the most reasonable in practical engineering. |
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