Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004.Includes bibliographical references (p. 178-182).Vibration and noise are an ever-present problem in the majority of mechanical systems, from consumer products to precision manufacturing systems. But most approaches for vibration suppression are expensive and invasive, so only a small subset of the techniques developed in research labs are widely used. In this thesis, we present a novel wave-based damping approach for the suppression of vibration in machines and structures. Our studies show that significant broad-band damping can be attained with little added mass via dynamic interaction between a structure and a low-density, low-wave-speed medium (such as a foam or powder). This damping phenomenon has great promise for many applications because it is robust (that is, not tuned), does not introduce significant creep into a structure, can accommodate large strains, and can be realized using materials that are light weight, low cost, durable, insensitive to temperature, and easy to package. We report on several experiments in which flexural and longitudinal vibration are attenuated using this approach. Experiments on flexural vibration of structures filled with low-density powder show that high damping is obtained (with loss factors as high as 12 percent for a powder fill whose mass is 2.3 percent of that of the beam) over a broad frequency range. Somewhat surprisingly, the response is found to be linear over a wide range of amplitudes. We propose that the powder can be modeled as a fluid in which pressure waves can propagate and find that such a model matches the experiments well. These findings suggest that any moderately lossy medium in which the speed of wave propagation is sufficiently low can be used to obtain similar responses.(cont.) We find that low-density foams coupled to structures exhibit com- parable attenuations over a somewhat broader frequency range, and that the responses can be accurately predicted if dilatation and shear waves are included in the model. We develop simplified models for these phenomena, and thence obtain guidelines for design of structures incorporating low-wave-speed media. The approach is compared to other damping techniques, and applications to belt- driven positioning systems and precision flexure assemblies are described. .by Kripa K. Varanasi.Ph.D
