Damping of plates with attached fluid or elastic layers

Abstract

The thesis is in three parts. The first is a theoretical and experimental investigation of squeeze-film damping on plates separated by gas, for example. air. For this study a thick excited plate was attached to an auxiliary plate parallel to the surface, thereby trapping a thin layer of air. Relative vibration of these two plates pumps this air at high velocities, resulting in energy loss due to air viscosity. The theory employs an impedance approach to predict the loss factor of the coupled plates. Below the excited plate critical frequency the damping is controlled by gas pumping, while above the critical frequency the plate couplings are the controlling factor. Theoretical predictions were compared with experimental measurements. A brief examination of the bolting effect on the loss factor was also conducted. The second part is a theoretical and experimental investigation of squeeze-film damping on plates separated by heavy fluid, for example, oil. The attached plate can be either perforated or unperforated. The ratio of fluid dynamic viscosity to density controls the losses. Viscosity was artificially increased by inserting porous materials into the oil layer. The properties of the porous materials were obtained from macroscopic flow resistance measurements. Theoretical modelling of the loss factor of these layered configurations with oil alone and with oil impregnated porous material were conducted using the impedance approach and compared with experimental measurements. The third part is a theoretical and experimental investigation of granular infill damping treatments on plates. Sand was used in the experiments and the bulk and shear elastic constants were measured when the sand was subjected to varying hydrostatic pressures. Both the dilatational and rotational motions in the granular layer were considered and the loss factor predictions were compared with measured results.

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