The Normal Impact Of Debris Flow On Submarine Pipelines

In recent years,the number and types of Marine engineering are increasing,especially the submarine pipeline has become an important tool for Marine transportation.The subsea pipeline is the"conveyor belt"for offshore oil and gas resources development,which effectively integrates the well platform,single point and onshore oil depot.With the development of offshore oil and gas resources,more and more subsea pipelines are needed.However,the laying environment and terrain limitations,the laying difficulty and use conditions of submarine pipelines are greatly different from those on land,and the repair is extremely difficult.Therefore,it is necessary to ensure the safety of the pipelines in the design process.In order to ensure the safe and efficient operation of Marine engineering,it is of great significance to study the impact of submarine landslide on pipeline.The first part of the paper is the centrifugal model test of landslide impacting pipeline in normal direction with different overburden thickness.By changing the initial burial depth of the pipeline,the normal impact of sliding bodies with different overburden thicknesses on the pipeline was simulated,and six centrifugal model tests were carried out in total with the initial burial depth of 0.5,1.0,1.5,2.0,2.5 and 3.0 times the diameter of the pipeline.Through the analysis of the experimental data and the comparison with the results of other scholars,a more applicable computational model is given.The second part of the paper ANSYS CFX calculation software and four power-law rheological models proposed in the existing literature are used to calculate the normal impact of the sliding body with Reynolds number in the range of 10^-4-10² on the suspended span pipeline.By using the methods of fluid mechanics,soil mechanics and mixed method,the calculation results of pipeline impact from the landslide body are compared with the results of the existing flume test and centrifugal model test,and the fitting equation of the numerical calculation results is obtained.Based on the analysis of the applicable scope of the four P-L models in the literature,the calculation results of the four P-L models are analyzed separately.It is found that the soil mechanics method can more accurately reflect the impact force of the pipeline when the Reynolds number of the landslide is smaller,and the fluid mechanics method can more accurately describe the working condition when the Reynolds number is larger.In view of the hybrid method analysis of P-L model?and P-L model?problems of applicability is not strong,and combined with the applicability of the method of soil mechanics and fluid mechanics method,the hybrid method is improved,and the results show that the revised hybrid method can better describe the range of Reynolds number Re is small landslide impact conditions.