Vibration analysis of viscoelastic composite panels of engine cowling in propeller aircraft using analytical & numerical methods

In this work the vibration analysis of viscoelastic composite panels of engine in propeller aircraft has been carried out. Both analytical and numerical (Finite Element) analysis has been carried out. Engine Panels are similar to plates. So, analytical formulation of the plate has been carried out to find out the vibrational response for specially orthotropic composite panel. As the solution of equilibrium equations for general laminates with any stacking sequence cannot be obtained analytically. Therefore, numerical method technique (Finite Element Analysis) is then employed to find out the vibrational characteristics of the panel. By carrying out modal analysis it is found out that the natural frequencies of the composite panel became higher by the inclusion of viscoelastic layers. So, increase in the natural frequencies will be advantageous in engine cowling panels. It is also observed that for panels with and without viscoelastic laminas, the deflection patterns are quite similar. However, as the natural frequencies of the panel without viscous effects are lower, so therefore deflection of the central node occurred earlier. Furthermore, a very small decrease in the transverse deflection of the node is seen for viscoelastic panel. A phase shift is also observed. Transient analysis revealed that all composite panels exhibit damping characteristics to an impulse force. However, damping effect is prominent in panels with viscoelastic laminas.