Research On Vibration Suppression Mechanism Of Particle Dampers With Obstacle Grid And Its Application In Structural Vibration Reduction

The mechanical noise generated by the power unit is the main noise source of the underwater vehicle in the low-speed navigation state,and its damping characteristics have a large impact on the overall acoustic index of the underwater vehicle.Through viscoelastic damping materials,power absorption and raft damping technology and other means can play a significant damping effect,but the damping properties of viscoelastic damping materials are unusually sensitive to temperature,power absorption technology has the problem of narrow damping frequency band,and raft damping technology for low frequency damping effect is limited.Particle damping technology is a kind of broadband damping means applicable to harsh working conditions,and has good prospects for application in the field of naval vibration and noise reduction.The damping mechanism of particle damping is still unclear,as well as the deficiency of particle dampers with extremely low energy dissipation under certain vibration conditions.In this thesis,we propose a built-in obstacle grid structure to enhance the energy dissipation of particle dampers,and the following research work is carried out for the energy dissipation mechanism of obstacle grid particle dampers and their application on plate and beam structures:To study and analyze the damping characteristics of particle dampers directly without attaching them to the vibrating structure.In this thesis,the loss factor of the particle dampers is determined by the loss factor experiments of the particle dampers to determine the loss factor of the obstacle grid particle dampers and its corresponding conventional particle dampers under different excitation conditions and filling ratios.The loss factors of two kinds of particle dampers are compared to obtain a preliminary understanding of the respective damping characteristics and the applicable range of vibration conditions of obstacle grid particle dampers and conventional particle dampers.The influence of the change of filling ratio on the loss factor under different excitation frequencies and amplitudes is studied.The loss factor experimental results of the particle dampers provide some reference for the application of particle dampers on plate and beam structures.Based on the mastery of the damping characteristics of the two particle dampers,in order to reveal the energy dissipation mechanism of the particle dampers with obstacle grid.The numerical models of the two particle dampers were developed using the discrete element method and the accuracy of the models was verified by loss factor experiments One typical working condition is selected for each of the two vibration amplitude periods,respectively,in which the obstacle grid attenuates and enhances energy dissipation.The mechanism of energy dissipation by the obstacle grid on the particle dampers is discussed from various perspectives,including the energy spectrum analysis,energy migration and spatial energy dissipation distribution of the simulation results,in combination with the particle motion states observed in the experiments and simulations.The obstacle grid particle dampers were applied to the cantilever beam structure.The effects of filling ratio,particle size,particle material and excitation amplitude of the obstacle grid particle dampers on the vibration characteristics of cantilever beams were investigated experimentally and compared with conventional particle dampers for vibration damping effects.The experimental results show that the vibration acceleration response of the obstacle grid particle dampers decreases by 10.4 d B compared to the conventional particle dampers at 90% filling ratio.For the wide frequency damping characteristics of the obstacle grid particle damper.Mass blocks,conventional particle dampers and obstacle network particle dampers are attached to vertically and horizontally clamped cantilever plates,respectively.The experimental results show that both particle dampers have good broadband vibration control compared to the additional mass block.At the first order resonance peak of 31 Hz,the damping effect of the obstacle grid particle dampers is inferior to that of the conventional particle dampers.The effect of obstacle grid enhanced energy dissipation is shown in the frequency band of 50 Hz to 2000 Hz.The vibration attenuation of the obstacle grid particle damper is 3～6 d B based on the conventional particle damper.The energy dissipation characteristics of the obstacle grid particle damper at 31 Hz,206 Hz and 1606 Hz with and without the obstacle grid particle damper are analyzed by discrete element simulation at low,medium and high frequencies.