Analytical Calculation Method For Global Buckling And Structural Vibration Of Submarine Pipelines

The development of petroleum resources has brought unprecedented prosperity to the society.With the gradual depletion of terrestrial petroleum resources,people have turned their perspectives to the ocean.With the development of science and the advancement of society,the offshore oil exploration area has continued to expand,forming a deep-sea development trend.However,due to the complexity and variability of the marine environment,it has brought huge impacts on the safe operation of submarine pipelines,such as global buckling caused by high temperature and pressure,the vibration of conveying fluid pipelines during operation,and the response of suspended pipelines under the action of external fluids in the marine environment.These problems are either linear or non-linear,which seriously threaten the safe operation of submarine pipelines.In this paper,the global buckling of submarine pipelines,vibration of conveying fluid pipelines and suspended pipelines will be solved by analytical or approximate analysis methods,and the effects of various sensitive parameters on subsea pipelines will be analyzed.In this paper,the global buckling of subsea pipelines is studied by analytical methods.When the property of the foundation is linear elastic,based on Winkel's assumption,considering the weight of the pipeline and overlying soil,the differential equation is strictly derived through the differential element method.The relationship between the soil stiffness coefficient and the axial force is fully taken into account.Analytical solutions for upheaval buckling of linear elastic seabed subsea pipelines are given for three cases.Then consider the submarine pipeline with initial defects,and give the analytical solutions of upheaval buckling of elastic seabed subsea pipelines with initial defects in the same three cases.The study found that the axial force has a severe effect on the buckling of the pipeline.Controlling the axial force is an effective method to control the global buckling of the pipeline.At the same time,the existence of initial defects makes the pipeline more prone to global buckling.The buckling modal of an intact pipeline is more fierce than the buckling modal of the pipeline with initial defects.So initial defects can alleviate the harm of global buckling to a certain extent.In this paper,the free vibration of conveying fluid pipeline is studied by homotopy analysis method.Studies have shown that the volume fraction index has a small effect on the vibration frequency of the pipeline system,but with the continuous increase of the volume fraction index,the vibration frequency of the pipeline system gradually decreases.The inclination angle of the conveying fluid pipeline has little effect on the critical flow velocity.As the inclination angle becomes larger,the critical flow velocity of conveying fluid pipeline also increases.The increasing speed first increases and then decreases,and the increasing speed is the largest in the horizontal pipeline.When the length of conveying fluid pipeline is small,the influence of the inclination angle on the vibration frequency is minimal.The change of the inclination angle has little effect on the vibration frequency of the conveying fluid pipeline.However,as the length of the transfer pipe continues to increase,the influence of the inclination angle on the vibration frequency is getting larger and larger,which indicates that the increase of the length of the transfer pipe can promote the influence of the inclination angle on the vibration frequency.In this paper,the relationship between the critical flow velocity and the volume fraction index and the relationship between the critical flow velocity and the inclination angle of the pipeline are given.Based on the image,it can be intuitively determined whether the pipeline is in an unstable state.In this paper,the forced vibration of suspended pipeline is studied by the homotopy analysis method.Studies have shown that the shorter the suspended length is,the higher the vibration frequency of suspended pipeline will be,and the longer the suspended length is,the lower the vibration frequency of suspended pipeline will be.Soil stiffness has a very important influence on the vibration frequency and modal of suspended pipeline.At the same time,soil stiffness is affected by the suspended length.When the suspended length is small,the influence of the soil stiffness on the frequency of suspended pipeline is quite significant.After the suspended length exceeds forty meters,under the boundary conditions of pinned-pinned and clamped-clamped,the stiffness of the soil has little effect on the vibration frequency of suspended pipeline.The higher the current velocity,the smaller the vibration frequency of suspended pipeline.Under the condition of elastic soil,the change of ocean current velocity has little effect on the vibration frequency of suspended pipeline when the suspended length is small.But it is more significant when the suspended length is long.It is necessary to fully consider the effect of ocean current velocity.Under rigid soil conditions,the current velocity gradually decreases with the increase of the suspended length,and the variation range under the pinned-pinned boundary condition is higher than the clamped-clamped boundary conditions.