Vibration Characteristics And Responses Of Long-distance Buried Oil-conveying Pipelines By(Semi) Analytical Methods

Buried oil-conveying pipeline plays a very important role in engineering,like oil and gas industry and oil transportation.In this dissertation,the vibration characteristics and responses of long-distance buried oil-conveying pipelines are systematically studied via(semi)analytical methods,with the effects of environmental parameters,flow velocity,crack and structural parameters being discussed.Up to three kinds of different pipelines are studied,pipelines on the Pasternak foundation,pipelines on the Winkler foundation and with combined factors,and long-distance pipelines with multiple discontinuous points on the Pasternak foundation.For the forced vibration of a single span fluid-conveying pipeline on the Pasternak foundation,the analytical solution under generalized boundary is obtained by using Green's function,then the dynamic responses and stability characteristics are analyzed.Parametric results show that: under different stiffness of boundary spring,the first three natural frequencies firstly decrease and then change complicated with the increase of the flow velocity;different forms of boundary spring have different effects on the critical velocity;two foundation parameters have different effects on the natural frequency and critical velocity;the increase of length-to-diameter ratio will reduce the natural frequency and critical velocity,while the increase of thickness-to-diameter ratio will improve the critical velocity.Then,the vibration characteristics of a multi-span fluid-conveying pipeline with nonuniform cross-section on the Winkler foundation are studied.Based on the traditional Transfer Matrix Method,a modified Transfer Matrix Method is proposed to deal with the two difficulties of elastic foundation and non-zero flow velocity of the system.The proposed method enables us to use a uniform frequency equation for all kinds of boundary conditions.Parametric results are as follows: when many factors act on the pipeline at the same time,the maximum amplitude of the mode shapes is more likely to appear in the suspension-span section of the pipeline;the additional concentrated mass has obvious effect on the higher mode shape,and the moment of inertia sometimes has obvious effect on the mode shapes;generally,the mode shape does not change significantly with the increase of flow velocity,but in some cases,the change of the stiffness of the Winkler foundation also causes mode shapes to change significantly with the increase of flow velocity.Based on Laplace transform,continuity condition and generalized boundary condition,a general analytical solution of the vibrations of pipelines with multiple discontinuity points and arbitrary discontinuities on the Pasternak foundation is derived.The effects of crack parameters,support spring stiffness,flow velocity,foundation parameters and structural parameters on the natural frequency of a double-span and double-crack elastic-support pipe are discussed,and the results show that: the effect of crack location on the natural frequency is symmetrical,the closer the crack is to the nearest node of a certain mode shape,the less effect on the natural frequency of corresponding order;the depth of crack has different effects on the different order natural frequencies;the position of support spring changes the effect of crack on the natural frequency by affecting positions of structural nodes;transverse and rotational support spring stiffness have different effects on cracks;the first two natural frequency reductions increase with the increase of the Winkler foundation parameter and decreases with the increase of shear layer parameter;the first three natural frequency reductions decrease sharply with the increase of thickness-to-diameter ratio,especially the second order.Finally,the current work of this dissertation is summarized,and the future work is discussed.