Nonlinear Vibration And Passive Control Of Fluid-conveying Cantilevered Pipe

A fluid-conveying pipe acts as a connection device of transport system in aerospace,marine engineering and petrochemical industry.The importance of fluid-conveying pipe is more and more prominent.In practice,external excitations imposed on fluid-conveying pipe are complex and changeable due to the wide applications and variable environment.The common external excitations include impacting constraints,base excitation and external cross flow,etc.In this work,theoretical models of fluid-conveying cantilevered pipe under different external excitations are established,and the nonlinear oscillation behaviors of fluidconveying cantilevered pipe under each condition are studied.Moreover,passive control of fluid-conveying cantilevered pipe is studied.The main research results of the present dissertation are organized as follows:1.The influence of amplitude and frequency of base excitation on the oscillation responses of a fluid-conveying cantilevered pipe is revealed.Firstly,the modal truncation number required for numerical solution convergence of the dynamical system is determined.Secondly,the effect of internal flow velocities on the forced vibration of the pipe system is analyzed for small base excitation amplitude,and the mechanism for the pipe system to occur first-order frequency resonance,jump phenomenon and quenching phenomenon is investigated.Finally,the superharmonic resonance characteristics of the pipe system for large excitation amplitude are analyzed.2.A passive control method for fluid-conveying cantilevered pipe is proposed,and the effects of different physical and geometric parameters of linear dynamic vibration absorber(DVA)on the vibration control of fluid-conveying cantilevered pipes are studied.By considering several different parameters of the DVA,including mass ratio,damping coefficient,stiffness and location of the DVA,the influences of several different parameters on the stability of the fluid-conveying cantilevered pipe are studied by using the orthogonal parameter analysis algorithm.Based on the optimization of each parameter of the DVA,not only the critical velocities of the fluid-conveying cantilevered pipe can be effectively improved,but also the amplitudes of the nonlinear oscillations of the fluid-conveying cantilevered pipe can be well suppressed.3.The effects of asymmetric impacting constraints on the nonlinear oscillation characteristics of a fluid-conveying cantilevered pipe is discussed.The gap offset of the asymmetric impacting constraints is introduced into the smoothened trilinear model to establish the nonlinear governing equation of the fluid-conveying cantilevered pipe.The influences of gap size,stiffness,and gap offset on the bifurcation route of the dynamical system are analyzed,and the mechanism for the dynamical system to generate pitchfork bifurcation,period-doubling,chaotic vibration and sticking behavior are revealed.4.The nonlinear governing equations of the structure and the wake oscillator equations are fully coupled to study the nonplanar vortex-induced vibrations of a fluid-conveying cantilevered pipe subjected to impacting constraints.Firstly,the research method and the accuracy of calculation procedure are verified.Secondly,the dynamic responses of the constrained fluid-conveying cantilevered pipe without cross flow are analyzed.Thirdly,the effects of subcritical and supercritical internal flow velocities on the vortex-induced vibration of the pipe are discussed.Finally,the effect of different locations of impacting constraints on the vortex-induced vibration of the fluid-conveying cantilevered pipe is shown.5.The idea of using pipe-in-pipe structure to suppress vortex-induced vibrations of fluid-conveying cantilevered pipes is proposed,and the stability and vortex-induced vibration mechanism of the fluid-conveying pipe-in-pipe structure are explored through a large number of calculation examples.The interaction between the inner and outer pipe are modeled by using a distributed linear damping and a nonlinear spring.Then the stability of the dynamical system,the nonlinear oscillation responses of the pipe without cross flow,and the effects of subcritical and supercritical internal flow velocities on the nonplanar vortex-induced vibration responses of the pipe are investigated.The results show that the pipe-in-pipe structure can effectively increase the critical value of internal flow velocity for flutter instability and reduce the amplitude of vortex-induced vibrations of the pipe system.