Study On Resistance Coefficient Of Submarine Pipelines Under Debris Flow Based On CFD Method

In marine exploration of oil and gas,submarine pipelines can conveniently transport oil and gas resources over long distances,and at the same time they can adapt to the extreme environments of the ocean.Therefore,submarine pipelines are the most economical and effective way of transporting oil and gas resources over long distances.China's submarine pipelines have been developed in the past 30 years.The construction of submarine pipelines has been greatly developed with the continuous improvement of technology of offshore oil and gas exploration.Over the past 30 years,China's submarine pipelines have reached thousands of kilometers in the Bohai Sea,the East China Sea and the South China Sea.As an important part of the offshore petroleum engineering system,submarine pipelines resemble other marine engineering structures.They will be affected by various complex environmental marine factors.These uncertain factors are likely to cause safety hazards such as bareness and suspension on the submarine pipelines.In recent years,with the increase in the quantity of geological disasters caused by extreme weather,the amount of submarine debris flow which leads to the failure of submarine pipelines has increased.Submarine debris flow has become a hot issue in oil and gas pipeline marine projects in recent years.It is of great significance to study the impact of submarine debris flow on submarine pipelines.Based on the research results of the forces under the action of submarine debris flow on submarine pipelines at home and abroad,the computational fluid dynamics(CFD)method is used to establish the submarine pipeline models placed on the surface of the seabed,and the numerical simulations of submarine debris flow impinging submarine pipelines have been carried out.The research contents and results are as follows:(1)Based on the basic theory of fluid mechanics,the different hydrodynamic characteristics of fluids are discussed.The regime and rheological model of submarine debris flow which are suitable for the working conditions are selected in this paper;(2)The model of the submarine pipeline is established,and the normal and axial resistance coefficients of the pipeline are obtained by numerical simulation of the submarine debris flow at different angles.The simulation results of this paper are compared with the results of Zakeri's physical experiments and numerical calculations to verify the reliability of the model established in this paper;(3)The sensitive parameters of the numerical model are divided into two categories.The resistance coefficients of the submarine pipeline are studied from the submarine debris flow parameters and pipeline parameters respectively.The sensitivity of different parameters is analyzed.Next,the calculation formulas of the normal and axial resistance coefficients on the pipeline caused by submarine debris flow at different impact angles are fitted;(4)The CFD-Soil Mechanics comprehensive analysis is used to calculate the normal and axial bearing capacity of the submarine pipeline under the action of submarine debris flow in the Soil Mechanics method.The calculation formulas of normal and axial resistances in the Soil Mechanics method are fitted out;(5)The CFD-Soil Mechanics comprehensive analysis is applied to the working conditions of submarine suspended pipelines,and the prediction formulas of axial and normal resistance coefficients and resistances in CFD method and Soil Mechanics method are obtained respectively,which provide references for the engineering design of submarine pipelines.