Modal Analysis Of Suspended Span Oil And Gas Pipeline Considering Boundary And Pipe-soil Coupling

As energy development moves toward marine oil and gas resources,the acquisition of marine resources becomes more and more important,and submarine oil and gas pipelines play a vital role in the transportation of marine oil and gas resources.Therefore,it is necessary to target oil and gas pipelines under the seabed research.Submarine pipelines often exist in the form of suspended pipelines under the combined influence of various environmental conditions on the seabed plane,while the suspended pipelines generate periodic vibrations under the action of currents,which is the main cause of the fatigue life of pipelines.Therefore,it is necessary to further study the vibration characteristics of this suspended pipeline.The main research contents of this paper mainly include the following aspects:(1)The research status of submarine suspended pipelines was investigated,and the causes and mechanisms of the formation of suspended pipelines were found and analyzed.The existing forms of suspended pipelines and the post-processing methods of suspended pipelines were introduced in detail.The research status of pipeline research and the research status of pipeline soil contact determine the research content and research direction of this paper.(2)The vibration mechanism of the suspended pipeline under the joint action of soil and sea current is analyzed.The empirical formulas of various soil models are introduced.By combining the soil empirical model with the vibration of the suspended pipeline,the theoretical model of pipeline vibration is established.The simulation study provides a theoretical basis.(3)Through the 3D modeling software,a continuous three-span soil model is established,and the 3D soil model is introduced into the ABAQUS finite element software.The soil has initial stress through the balance of ground stress,and the soil and the 3D soil model are used to analyze the soil and The nonlinear relationship of the pipeline is extracted,and the displacement resistance curves of the soil and the pipeline are extracted.Finally,the influence of the elastic modulus,friction coefficient and cohesion of the soil on the displacement resistance curve is analyzed.(4)Introduce the DNV specification empirical formula to the first-order frequency evaluation criteria under different boundary conditions,and solve the first-order natural frequency of the 30m-40m pipeline under the fixed,simple-supported and elastic boundary conditions of the single-span pipeline specified by the empirical formula through matlab.At the same time,the first-order natural frequency of 30m-40m pipeline is calculated by ABAQUS finite element software.The accuracy of the model is verified by comparison of results.Secondly,the single-span pipeline is under different boundary conditions.The effect of deflection and axial force.(5)The ABAQUS simulation software is used to calculate the natural vibration characteristics of the three-span pipeline.The nonlinear relationship between the soil and the pipeline is used as the nonlinear boundary condition of the three-span pipeline.The length,adjacent span length and wall thickness of the three-span pipeline mid-span are studied.The effects of the initial static deflection and natural frequency of the pipeline are selected from 10 different lengths of the mid-span soil,and the static displacement of the three-span pipeline under different spans of the soil length is studied.At the same time,select 10 different lengths of adjacent spans,analyze the maximum displacement of three-span pipelines under different adjacent span lengths,and study the influence of different adjacent span lengths on the maximum displacement of three-span pipelines;select 5 different wall thicknesses The pipelines are studied for the influence of different wall thicknesses on their maximum displacement and the natural frequency of the pipeline while maintaining other constants.Finally,the static analysis and natural frequencies and mode shapes of single-span,two-span and three-span pipelines are compared and analyzed.The difference is discussed in the vibration characteristics of three-span pipelines with fixed ends,simply supported ends,linear springs and nonlinear boundary conditions.