Study On Fluid-structure Interaction Response Of The Fluid-conveying Pipe Under Water Hammer

The water pipeline system is spread all over the water conservancy,municipal and other industrial fields,which brings great convenience for people’s daily life and industrial production.However,for the pipeline,the flow pattern of pipeline system often changes and to causes the pipeline vibration because of the working condition of the working part or the external excitation and so on,which is commonly known as the water hammer phenomenon.Pipeline vibration caused by water hammer has great harm.Therefore,it is of great engineering significance and economic value to study the fluid-structure interaction(FSI)response characteristics of the fluid-conveying pipe underwater hammer excitation.According to the vibration response characteristics of the fluid-conveying pipe under water hammer excitation,this paper selects the reservoir-pipeline-valve system as the basic research object.The research contents and related achievements are as follows:(1)The effect of FSI on axial vibration response of elastic water-conveying pipe is studied by using the split-coefficient matrix difference method(SCM-FDM)and implicit Euler method.In comparison with the method of characteristics(MOC),the SCM-FDM can avoid time-consuming calculations of spatial or temporal interpolations.It is easy and efficient since the optimal choices of different difference formulas only can be determined from the directions of wave propagation.The response characteristics of four characteristic parameters,which are fluid velocity,pressure head,pipe axial vibration velocity and wall stress,are given and compared with the classical water hammer theory.The results show that the coupling effect of Poisson and junction on the axial vibration of the pipeline cannot be neglected.Poisson coupling mainly affects the amplitude of the vibration response,while the junction coupling not only affects the vibration amplitude but also the vibration frequency.(2)The characteristic of water hammer considering the viscosity of pipe wall is studied by using the finite difference method and implicit Euler method.The response characteristics of the two parameters of the fluid flow velocity and the pressure head are obtained.Meanwhile,the effect of wall friction on the vibration response characteristics is also studied,and compared the calculation results with the classical theory of water hammer.The results show that the viscoelastic effect not only makes the vibration attenuation,but also causes the vibration delay,which has significant influence on the water hammer response characteristics.But the effect of pipe wall friction is small,it can be ignored.(3)The effect of FSI on the response characteristics of the axial vibration of a viscoelastic water-conveying pipe is studied by using the finite difference method,implicit Euler method and Newton-Raphson method.The response characteristics of four characteristic parameters of fluid flow velocity,pressure head,pipe axial vibration velocity and pipe wall stress with time are given and compared with viscoelastic water hammer.The results show that the coupling effects of Poisson coupling and junction coupling are larger and cannot be neglected,the two coupling will not only affect the amplitude of vibration,but also affect the vibration frequency,and the effect of friction coupling is negligible.In addition,it is found that there are significant differences in the axial vibration characteristics of the elastic pipe and the viscoelastic pipe.For the elastic pipe,the vibration response will not be attenuated with time,and the initial vibration amplitude is larger,the fluctuation curve appears more local mutation,and the vibration is more intense.For the viscoelastic pipe,the vibration response will attenuate rapidly with time.The existence of viscoelastic action has a better viscosity and delay effect on the higher frequency,and the response curve is smoother.