Research On Vibration Response Characteristics Of Vertical Pipe String Under Water Flow Impact

Vertical pipe strings in water areas are widely used in oil and gas production and transportation.The action of internal and external fluids can cause the problem of pipe string vibration,which will mainly cause the fatigue failure of underwater pipe strings,and that failure will bring a series of economic,safety and environmental protection problems.Based on these,there is great theoretical significance and application value on rationally arranging underwater pipe strings and preventing pipe string fatigue failure.In this paper,the common single,double and multi-pipe strings in underwater oil production are taken as the research objects,the internal and external flow and the coupling effect of the pipe string are considered,and the experimental research and numerical simulation of the vibration response characteristics of the vertical pipe string under the impact of water flow are carried out.The main research work is as follows :Based on vortex-induced vibration theory,the researcher will conduct numerical analysis of underwater vertical pipe string fluid-structure coupling by using computational fluid dynamics and structural mechanics.The fluid domain analysis adopts the finite volume method and the structural domain analysis adopts the finite element method,and a three-dimensional fluid-structure coupling motion numerical analysis model is established which considers the interaction between the inner and outer fluids and the deformation and vibration of the pipe string.To accurately characterize the instantaneous load on the column surface,the model adopts a fully coupled time-advance algorithm for subdomain solution,which ensures the synchronization and accuracy of the solution.The numerical model and calculation method are provided for the calculation of the vibration response of the string under the joint action of internal and external flow.The resercher has built an experimental platform for the vibration response of water sagging straight pipe string composed of internal and external circulation systems and data acquisition and processing systems in the fluid machinery laboratory,which is to deepen the understanding of the physical process and mechanism of the vibration response of the pipe string under the impact of water flow,to verify the correctness of the numerical simulation calculation results,meanwhile to carry out the physical model experiment of vortex induced vibration of vertical pipe string with similar ratio,to conduct the experimental research on the vibration response factors of single pipe string and series double pipe string,to test the vibration influence of vertical pipe string from internal,external flow and spacing ratio,hence to formulate the variation rules of displacement vibration response,natural frequency,mode and other parameters of different test points along the length direction of pipe string under different factors.The experimental results show that both the internal and external flow velocities affect the natural vibration frequency and vibration amplitude of the string,and the increase of the external flow velocity causes the phenomenon of multi-order control of the string.The dynamic response characteristics of the tandem double string are significantly different from that of the single string under the influence of the spacing ratio,and the vibration of the string is significantly suppressed when the spacing ratio is less than 4.By adpoting the three-dimensional numerical model developed in this paper,the hydrodynamic characteristics of single,double and multi-string flow fields under typical flow rates are deeply studied.Through the numerical example of the flow field,the researcher analyzed the relationship between the flow field around the pipe string and the form of vortex shedding under different factors in detail,and finally reveal the influence of the flow field change on the force of the pipe string and the suppression mechanism of the auxiliary pipe string on the vortex-induced vibration of the pipe string.The flow field analysis of a single string shows that: there are three different forms of vortex shedding in the flow field between the double-pipe strings in series under different spacing ratios,there is a sudden change in the lift resistance coefficient between front and rear string.The incoming flow angle has a significant effect on the lift and drag of the double-pipe-strings with equal diameters,and the drag coefficient is in the incoming flow angle.There is a breakpoint when θ=40°,and there is a breakpoint in the lift coefficient when the inflow angle θ=10°.The analytical results of the multi-string flow field show that within the two spacing ratio ranges studied in this paper,the multi-string system with six auxiliary strings has significantly smaller lift and drag coefficients than a single string,and the vibration of the main string is significantly reduced and suppressed,meanwhile the diameter ratio has less influence on the force of the main string.The paper also studies the vibration response characteristics of the pipe string structure in the fluid-structure interaction vibration process and discusses the frequency locking phenomenon of the pipe string vibration and the nonlinear behavior of the vibration response,which is based on the numerical simulation calculation of the fluid-structure interaction of the underwater vertical pipe string.The ratio,spacing ratio and incoming flow angle are analyzed in detail,and generate the relevant conclusions.The research results show that the larger the mass ratio,the smaller the vibration response of the string.With the increase of the outflow velocity,the string with several mass ratios participates in the vibration.The vibration response analysis of the double-string structure shows that the force of the double-string with different arrangements is related to the spacing ratio,and the vibration amplitude is much larger than that of the single string when the flow rate is high,which indicates that the double-string arrangement It is more sensitive to the incoming flow angle and spacing ratio,and the change of the incoming flow angle may aggravate the vibration of the pipe string.The analysis of the vibration response of the multi-string structure with six auxiliary pipe strings shows that the amplitude of the vibration response of the main string is significantly reduced in the two spacing ratio ranges studied in this paper,and the adaptability to the incoming flow angle is good.The vibration response amplitude of the main column at the flow angle is reduced by about 50%.Through the research of this paper,a set of experimental testing technology for underwater vertical pipe string vibration response is established,and a set of numerical simulation analysis method of underwater vertical pipe string fluid-structure coupling is generated,which is the fluid-structure coupling analysis method of pipe string system under the action of fluid.This research can provide effective methods and means for the fluid structure coupling analysis of the pipe string system under the action of fluid,and also a reference for the layouts and vibration suppression methods of the underwater pipe string such as the riser system of the offshore drilling platform and the drilling riser system.