Practical industrial method of increasing structural damping in machinery, II: Squeeze-film damping with liquids

Abstract Machinery panels can be damped by attaching a plate parallel to the surface with the intermediate layer filled with a high-viscosity fluid, for example oil. Relative vibration of the plates pumps the fluid at high velocities, resulting in energy losses due to the viscous shear. The damping with oil alone is found to be very low. The ratio of the fluid dynamic viscosity to its density is the controlling parameter which governs the level of the losses. Loss factors higher than 0·1 can be achieved if the viscosity can be increased by various means. The damping over the whole frequency range above and below the excited plate critical frequency is measured and compared with prediction. The agreement is good. By increasing the viscous shear in the layer by using a foam, the loss factor increases substantially. However, the loss factor is very sensitive to the tortuosity and the size of the cells in the foam.