Numerical Investigation Of Local Scour Around Submarine Pipeline Based On Secondary Development Of Fluent

Submarine pipeline transportation is an efficient,Practical and economical transport method that guarantees the safe transportation of oil and natural gas resources.The submarine pipelines are served in complex hydrodynamic environments such as currents and waves.The sediment on the surrounding seabed is prone to starting scour,causing local scouring pits to form below the submarine pipelines,causing suspended phenomena,and inducing structural failure.The failure of submarine pipelines will lead to oil and gas leakage,which will seriously threaten the environment and cause huge economic losses.Therefore,it is very important to carry out the prediction of the local scour process around of the submarine pipeline.This thesis is aimed at the problem of local scour around submarine pipeline.Based on computational fluid dynamics and sediment motion mechanics,the flow field model is constructed,the secondary development of fluent by UDF is used to establish a scour model.The dynamic mesh technology is used to realize the deformation of the seabed surface,and establish a numerical simulation model of sediment scour.The numerical simulation of the local scour around the submarine single pipeline,the two submarine pipelines in tandem,and the submarine piggyback pipeline are carried out.The specific research contents are as follows:Comparative analysis of the flow field around the cylindrical pipeline under the Standard k-?,RNG k-? and Realizable k-? turbulence models,select a reasonable k-? turbulence model to establish the flow field model.By considering the flow field simulation around the wall-mounted cylindrical pipeline,the accuracy of the flow field model will be verified.Considering the mass transfer of bed-load,UDF is used for secondary development of fluent to construct the socur model,combined with dynamic mesh technology to achieve seabed surface deformation and a numerical simulation model of sediment scour was constructed.Based on the numerical simulation model of sediment scour,the establishment of geometric model,mesh division and selection of simulation scheme were carried out to simulate the local scour process of submarine single pipeline.The numerical simulation of seabed surface morphology and scour process were compared with the scour test results to verify the feasibility of the numerical simulation model of sediment scour.In view of the form of two submarine pipelines in tandem,a numerical simulation study of local scour was carried out.By analyzing the process of scour pit extension and the change of flow field during scour process,the influence of the relative distance between two pipelines on the local scour behavior of upstream pipeline and downstream pipeline were revealed.According to the form of submarine piggyback pipelines,keep the diameter ratio of the large pipeline and small pipeline unchanged.By changing the relative distance between the large pipeline and small pipeline and the relative position between the bottom of submarine piggyback pipelines and the seabed surface,the influence of relative clearance and relative void on the local scour behavior of the piggyback pipelines were studied.Provide reference for the laying and research of submarine pipelines.