Theoretical Buckling Analysis Of Externally Pressurized Subsea Pipelines And Its Buckle Propagation Analysis

Subsea pipelines are essential equipment in oceanic engineering.Recently the resource exploitation activity has reached deep sea zones.The subsea piplines carry large external pressure and have the risk of instability failure.Especially the geometric imperfection would reduce the collapse pressure,increase the occurrence probability of local buckling and buckle propagation.Under this circumstance,this thesis presents detailed analysis on local buckling of imperfection pipelines and buckle propagation.The main contents and results of this dissertation are listed hereinafter:(1)This thesis presents the controlling differential equations of corroded elastic rings under external pressure based on curved beam model.Introducing the mid-surface inextensible condition,the governing equations are solved with results in good agreement with the FEA results.Moreover the influence of corrosion depth,corrosion angle and initial ovality on the bifurcation pressure is studied.The research shows that the corrosion depth has significant effect on the buckling modes and the buckling modes include the symmetric and anti-symmetric modes.(2)This thesis presents the analytical formulas for bifurcation and static deformation of corroded elastic-plastic tubes under external pressure.Moreover,the interaction effect of two corrosion regions is analyzed and it is proven that when the corrosion depth is extremely large,if the corrosion angle is?/4,then the bifurcation pressure is decreasing with the increase of relative distance of two regions.This research shows that for thick-walled pipelines,the material plasticity significantly influences the collapse pressure,and the pre-buckled configuration has already experienced the plastic deformation.(3)By using the homotopy analysis method,this thesis solves the collapse problem of non-linearly elastic rings under external pressure.Using the analytical results,the effect of softening material parameter is considered.Then the relationship between the homotopy analysis method and linearized harmonic balance method is identified by which the convergence control parameter is introduced to the linearized harmonic balance and the modified linearized harmonic balance method is proposed.Finally by using the analytical method,the rings' collapse with arbitrary thickness distribution under external pressure is solved and it is revealed that if the bending rigidity and the thickness is varying as a cosine function,the bifurcation pressure resulting from the homotopy analysis method may be the same.(4)The dynamic buckle propagation problem is investigated in detail.A non-linearly supported pretensioned string model is proposed and the characteristic properties of dynamic buckle propagation of the string under uniform external pressure are obtained considering the fluid-structure interaction effect.This research reveals the effect of external acoustic fluid on the buckle propagation,identifies the correlation between the governing equation and the reaction-diffusion equation in mathematics.By using some results on the reaction-diffusion equation,this research would enhance the understanding of the dynamic buckle propagation phenomenon.Moreover the indentation process under external pressure is studied analytically.Two cases including the indentation of string model and the realistic pipelines under some denting forces are investigated.This study reveals the different essence of internal pressure and external pressure in this problem.(5)This research proposed an algorithm on the steady dynamic buckle propagation,by using the ABAQUS user defined element,a Fortran code is developed to study the dynamic buckle propagation of shallow panel,deeply buried pipelines and elastic-plastic pipelines.The FSI by acoustic fluid is considered and a pump based on buckle propagation phenomenon is designed in principle.