Studies Onvibration Response And Bifurcation Behavior Of Inclined Cantilervered And Hinged-Hinged Fluid-Conveying Pipes

In modern industries, such as aerospace, marine, nuclear and chemical industry, fluid-conveying pipes are widely used, and their stability and reliability will directly affect the entire system’s operating status. In large pipeline systems, most pipes are horizontally or vertically supported, but some pipes inevitably erected at inclined angles due to some restrictions, and in a strict sense, all the pipes are inclined to some extent. Hence, it is essential to perform the analysis of the dynamical characteristics of inclined fluid-conveying pipes, which can provide a theoretical reference for engineering applications. In this thesis, the vibration response characteristics and bifurcation behavior of the inclined cantilevered and hinged-hinged pipes conveying fluid are analyzed based on the nonlinear oscillation theory and the stochastically nonlinear dynamical theory. The main contents are listed as follows:1) Based on the force balance analysis of infinitesimal pipe element and fluid element, the differential equations of motions of the cantilevered and the hinged-hinged pipes under inclined support conditions are established, where random excitations are also taken into account.2) Two-parameter coupling influence on the system are discussed on the basis of single parameter case, the vibration response surfaces of the system are displayed for a cantilevered pipe, from which the vibration response characteristics are discussed in detail and the stable regions of the system are then presented.3) From the phase portraits, the Poincare maps and the bifurcation diagrams of the vibration responses of the system, the coupling effect of the supported angle and the gravity on the system are analyzed and the bifurcation phenomenon of the vibration response will arise with the support angle. It is also shown that, the influences of other parameters on the vibration responses are different with other under various fixed support angles, and there exist obviously differences between the vibration responses of the inclined, horizontal and vertical fluid-conveying pipes.4) Based on the analysis of the vibration response characteristics of the fluid-conveying pipe under the distributed and concentrated random excitations, the effects of the central frequencies, spectrum widths and action positions of the random excitations on the vibration response characteristics of the system are discussed, and the action mechanisms of these parameters are also presented.5) The vibration modes of the pipes with various pipe wall thickness and length-diameter ratio are investigated by comparing the numerical results from the mathematical model with the experimental ones, and the influence rule of both the parameters are also concluded. Then, the effect of two-phase fluid excitation on the pipe vibration is discussed from the experimental data, and the spectral characteristics of the vibration responses under different random excitations from the two-phase fluids are compared with each other.