Study On Particle Damping And Its Control With Applications

Particle damping technology is new vibration passive control approach. It can make use of the structural pre-existing voids or enclosures attached to structure to partially fill with particles. When the structure moves, the particles collide with each other and with the enclosure causing damping through inelastic of nearly collisions, and convert kinetic energy into heat or sound energy. At same time, the momentum conversion between particles and structure can also suppress the dynamic response of primary system. It enjoys a lot of advantages such as: it can be used in a wide range of environment, the structures are modified hardly, additional mass to the system is minimum, and the effect of vibration absorption is notable etc. all of them make it to be used widely in the future.At present, the researches on particle damping are falling to doing, and the theories are not far away from satisfactory. In this paper, some theoretical model and experiments are introduced to study the dynamic characteristics of particle damping, and some technique are used to control and improve the performance of particle damper. The dissertation includes:1. Based on the predecessors'studies, the properties of granular matter are systematically discussed. Presupposing the granular as continuous material, the stress state of particle is analysised with Mohr stress circle under harmonic excitation, and obtains the acceleration theoretics value at which the granular matter is on utmost stress state. The value is very important for particle damping because it can tell us when the granular friction effectiveness act.2. The dissipated energy by the particle damper is analysised on the cases ofΓ<1 andΓ>1, hereΓis the dimensionless reduced acceleration of damper. WhenΓ>1, the model of completely inelastic boucing ball is used to derive the formula of total dissipated energy of particle damper.3. The dynamic characteristics of particle damper are experimentally investigated for thorough understanding its behaviors. It is observed that the impact force between granular bed and container bottom, controlled by the dimensionless reduced vibration acceleration of container, undergoes a series of period doubling bifurcations. Derive a same expression for all of impact forces with different period bifurcations. The Statistical Energy Analysis(SEA)technique is used to estimate the dissipated energy and the dynamic mass of damper. As a result, there is a critical acceleration at which the dissipated energy and the dynamic mass can change suddenly. Below the critical value, the damper can't dissipate the energy and the additional mass of particles does not change distinctly. Over the point, the dissipated power increases with excitation level and takes some regularity depended on velocity amplitude. However the equivalent mass of damper falls with acceleration amplitude increasing, and is not relative with the vibration frequency. The 3-dimemension contours of loss factor on velocity and frequency is a better way to describe the particle damping performance, by which we can confirm and estimate the best working area of damper.4. Based on the conventional restoring force surface (RFS) method, the paper puts forward a new arithmetic to identify the parameters of particle damping single degree of freedom system by the way of adding acceleration terms into the restoring force equation. And utilize the new method to estimate the equivalent damping ratio and equivalent mass of particle damping system on the cases of different vibration level, different particle sizes and different particle filling ratio under the narrowband random excitation. The results resemble with the case of harmonic excitation.5. The effect of direct current electromagnetic field on ferromagnetic particle damping is theoretically anlysised and experimently investigated for low level vibration case. As a result, the electromagnetic field can significantly increases the momentum conversion between particles and structure, at same time it can also enlarge the contact and friction force between ferromagnetic particles, therefore enhancing its vibration suppression ability. This result suggests that the electromagnetic field could be used to control the energy dissipation performance of a particle damping system in a semi-active way.