Vibration Characteristics Of Unsteady-fluid-filled Pipe System And Vibration Restrain

Waterflooding is an important measures to improve output of crude oil in oil field. Waterflooding system is a typical fluid-filled pipe syetem, flow in the system is unsteady and high-pressure flow, pressure pulsation of fluid and vibration of pipe wall exist in the system and they interacts each other, which brings about pollution of vibration and noise, and even disaster if the coupled vibration is severe. It is necessary to study the coupled vibration characteristics of unsteady-fluid-filled pipe system and influence factors of the vibration, to predict response of the system, to take some necessary measures to restrain or minish vibration of the system, to lessen the chance of accident or avoid accident, to safeguard the safty of the waterflooding system.Based on the Timoshenko beam theory, coupled nonlinear differential equation, lateral differential equations under periodic loads and corresponding dimensionless expressions of unsteady-fluid-filled straight pipe were developed, and quasilinear equations of the fluid-filled straight pipe with consideration of fluid-structure interaction (FSI) was obtained.Numerical methods to exactly get the vibration response solutions of fluid-filled pipe system with consideration of FSI in time-domain were studied. Method to define the time step, divided number of simple fluid-filled pipe system and method to subdivide the mesh spacing were advanced to better capture the change of waterhammer pressure;"Optimization method of damping-redistribution and pipe-steel"was put forword to establish the optimization model of time step and divided numbers of pipes for complex fluid-filled pipe system, which ensured time steps of all pipes being the same during numerical computing by the method of characteristics (MOC). A complex fluid-filled pipe system was adopted to study with the present method, the results agree with the experimental results from literature very well.MOC-FDM was applied to get fully-coupled nonlinear vibration responses of a complex fluid-filled pipe system, comparison between the numerical results and those of test from literature validates the validity of the method.Influences of junction coupling, Poisson coupling, frictional coupling, thickness of pipe wall, structural damping of pipe and material of pipe on the responses of fluid-filled pipe system were studied, the results show that weak-restriction junction converts some pressure energy of fluid into vibration of pipe wall, meanwhile Poisson coupling converts some kinetic energy of pipe into pressure energy of fluid, Poisson coupling and junction coupling act as energy transformer. Structural damping of pipe has greater peak attenuation of pipe vibration than viscous damping of fluid, but greater damping ration can causes rise of fluid pressure.When pipes'outer diameters are the same, the pipes with thicker wall have less kinetic energy, but increase pressure energy of fluid. The vibration energy of fluid-filled steel pipe and copper pipe system mainly concentrates in fluid, but the vibration energy of fluid-filled PVC pipe and PE pipe system mainly concentrate in pipes. Dynamic response of pipe wall can be reduced effectively with larger relative stiffness of restriction, at the same time, pressure energy of fluid in steel pipe or copper pipe system is strengthened remarkably, however, pressure energy of fluid in PVC pipe or PE pipe system is hardly influenced.Method of modal analysis of fluid-filled pipe system was studied, numerical results show that FSI has graet influence on modal characteristics, natural frequency modes with consideration of FSI is obviously more than that without consideration of FSI in a definite frequency range, and the natural frequency values changed evidently. MOC-FFT was advanced and adopted to get natural frequencies of a fluid-filled pipe system with neglect of structural damping of pipes and frictional damping of fluid, the results agree with the results of transfer matrix method (TMM) and those from literature.Finally, a waterflooding system was adopted to study. Vibration restrain results of adjusting restriction positions and using damping material were obtained by simulation, which show that vibration of pipe can be reduced remarkably by minishing out-length of pipe, but the pressure of fluid rises. Responses of pipe and fluid can be reduced by covering the pipe with appropriate damping material.Unsteady-fluid-filled pipe systems have been widely applied in many engineering realms such as oil transporting, waterpower, biology, spaceflight, drilling, hydraulic system, construction, nuclear industry and so on. researching the coupled vibration characteristics and influence factors of the vibration of the systems are helpful to predict their vibration responses, to take some necessary measures to restrain or minish their vibrations, to lessen the chance of accident or avoid accident, which is very important and necessary for safty of the pipe systems.