Vibration Mechanism Investigation Of Pipe Network Based On Dual Hydraulic Excitation Sources

Aiming at vibrating machine especially the linear vibrating screen based on inertial excitation, the eccentric block will generate component force of centrifugal pull in the non-vibration direction, consequently which will cause low efficiency and difficult adjustment process of vibration parameters. This dissertation introduces a new hydraulic excitation mechanism that the excitation source is generated by vibration exciter, which is just like the sudden open-close of valve. With continuous rotation of the valve, the flow velocity and the pressure will vary intensively, through which the pipe network will vibrate with multiple-excitation point and multiple-degree of freedom. Then, simulation analysis and experimental investigation about coupling characteristic of fluid and pipe are performed. Through dual excitation sources composed of hydraulic cylinder and vibration exciter, the vibration control of fluid-filled pipe is realized, and a three-dimensional vibrating screen based on the hydraulic excitation is investigated for application.Firstly, mathematical model of hydraulic excitation system is established and computer code based on the method of characteristics (MOC) is developed. The relationship among the excitation force, the frequency of converter and the system pressure are simulated, indicating that the vibration parameters of hydraulic excitation system can be adjusted by the frequency of converter and the system pressure. Then the testing system is established and the data are obtained by pressure transmitter and data acquisition card. The dynamic characteristic of fluid is revealed by time-domain and frequency-domain analysis, thus the controllability of the hydraulic excitation system is presented. A new vibration mechanism of dual excitation sources composed of hydraulic cylinder and vibration exciter is introduced, through the transfer functions, the kinematics characteristic of major components of the hydraulic excitation system are simulated and its dual sources characteristics are revealed.Considering the fluid-structure interaction, the vibration equations are derived, and the pipe is simplified as beam model, which can be analyzed by finite element method (FEM).Then the excitation pressure calculated by MOC is forced upon the corresponding finite element nodes of the pipe. Especially, the nodes of fluid by MOC are assured to coincide with that of the pipe by FEM. Then, using Newmark’s method, the dynamic response at every cross section of the pipe is calculated, the vibration response of the lateral vibration and the axial vibration of pipe are obtained, besides, the amplitude-frequency characteristic curve of pipe is performed by FFT method and which is compared with testing results.Through experimental comparison analyses, the testing system for the pipe network is established, and an optimal experimental scheme is considered. According to the measured data, some regression analysis are carried out and the relationships among the system pressure, the vibration frequency of pipe, the frequency of converter and the displacement amplitude of pipe are revealed, by comparison analyses with the simulation results, indicating a good agreement in amplitude and vibration mode.For the purpose of carrying out the experimental modal parameter identification for the fluid-filled pipe, firstly the Laplace transform for solid-liquid coupling vibration equation is deduced and the transfer function is obtained, consequentally the displacement frequency response function of the vibration equation are presented. Then, the least squares method and the five-point moving average method are used to smooth high-frequency signal, the results show that it can improve the waveform quality significantly. In addition, the normal mode least-squares iterative method is applied to frequency domain identification for modal parameter of the pipe, some experimental modal parameters are obtained. Meanwhile, ITD method and STD method are used to time domain identification, which are also compared with the frequency domain method. So, it can provide some evidence for seeking the optimal vibration frequency of the pipe network.To investigate a three-dimensional vibrating screen based on the fluid-filled pipe, the hydraulic excitation testing system is established, where the screen plate is simplified as the elastic plate. Some regressions analyses are carried out and the relationships among the system pressure, the frequency of converter and the displacement amplitude of the elastic plate are revealled and the controllability of the three-dimensional vibrating screen is presented.Then, the three-dimensional resultant vibrations of the hydraulic excitation system are simulated, and some comparisons of vibration characteristic between two-dimensional and three-dimensional vibrating screen are performed, it shows that the three-dimensional vibrating screen based on the pipe network excitation is multiple-excitation point and multiple-degree of freedom vibration with different displacement amplitudes and vibration frequencies distributed along the screen plate, which can satisfy the motion demands for materials on the vibrating screen, indicating that the three-dimensional vibrating screen based on the hydraulic excitation has higher screening efficiency.In this dissertation, combining the theoretical analysis and experimental study, a new hydraulic excitation mechanism is presented, through which, an active hydraulic wave is applied to the vibration control of pipe, indicating that fluid-filled pipe can be controlled by the hydraulic excitation wave. This investigation is expected to present a new vibration mechanism and serve for the application research of the hydraulic excitation system. Soit has important theoretical and practical significance for deepening the hydraulic vibration theory and vibration utilization engineering.