Numerical Simulation Of Scour By Underwater Jet

With the exploitation and transportation of oil and gas resources in recent years,the laying of submarine pipelines with low difficulty is the most efficient and economical offshore oil and gas transportation method.In order to ensure the safety of submarine pipelines,trenching and burying are usually adopted.In trenching and burying projects,post-trenching technology is the most common.As the depth of operation and the diameter of pipelines continue to increase,the requirements for the depth of trenching continue to increase.In this regard,it is necessary to study the influence of different factors on the underwater scouring effect and to optimize the design of the actual underwater jet trenching system.In this paper,three-dimensional numerical simulations are used to study the factors that affect the scouring effect.Base on the previous research work,a numerical model of scour was established using FLOW-3D sediment scour model,and combined with the scale parameters of the trenching equipment,the underwater jet scour simulation was performed.Firstly,the sediment scour model was verified and calculated,and the reliability of the model on the scour of underwater jets was determined.Then simulate the jet scouring of the fixed double nozzle,analyze the flushing process from the aspects of flow velocity and pressure distribution,suspended sediment concentration,and the change of the scour cross section,and study the self-similarity of the scour profile and the effects of scour under different jet velocities,and the results show that the larger the jet velocity,the larger the size of the scour pool,and the self-similarity of the scouring profile at different jet velocities.Finally,the simulation of the jet scouring of the moving double nozzles was carried out.The effect of different moving speeds,jet velocities,and the size of sand grains on scour was analyzed.The problems of secondary flushing and pipeline pre-embedding were also studied.The calculation results show that in the calculated operating conditions,the smaller the moving speed,the greater the jet velocity,the smaller the size of the sand grains,the larger the size of the scour pool;in the flushing trenching project,the secondary scouring enhances the flushing effect,in order to increase the trenching efficiency,the pipeline embedded should be avoided.