Vibration Attenuation And Isolation Of Two-dimensional Periodic Composite Thin Plates

Controlling vibrations in structures has been one of the pop research topics in academic and engineering for a long time. In periodic composite structrure, frequencies within certain range are forbidden, which is called band gap. If periodic structure is introduced into their design, engineering structures will exhibit frequency band gaps and attenuate their vibration, which provides a new approach for vibration control.In this dissertation, by using plane wave expansion method and suppercell calculation, combining with finite-element simulation, theoretical investigation of bragg scattering periodic composite thin plate(steel-concrete,steel-epoxy) has been performed,and the following conclusions are obtained:1. Band gap emerge both in steel-concrete and steel-epoxy periodic composite thin plate for in-plane vibration,and it's more wider in the latter one.But band gap does not show up in steel-concrete thin plate. That is to say, the appearance of bengding vibration band gap demand greater difference between scatters and matrix.What's more, finite element simulation results validate the existence of band gap, and the band gaps obtained well meets with the theoretical results on the whole.2. With filling fraction fixed, band gap for in-plane vibration of periodic thin plate is proportional to 1/a; and it's proportional to h/a~2 for bending vibration.3. Filling fraction is very important for the location and width of band gap. Band gap get wider and then get narrower with the accretion of filling fraction, namely the maximum exists.4. When point defect is introduced, several bands will show up within the original band gap, namely defect state. Defect bands are flat lines with zero velocity, indicating vibratin localized within defect without transmission.5. On the whole, with the accretion of defect, defect band emerged from both edge of band gap and move towards the middle for in-plane vibration. However defect band show up from the upper edge of the band gap and move towards the lower for bending vibraion.