Vibration absorption with nearly irreversible energy sinks

This thesis presents a new energy absorption technique, called here Linear Energy Sinks, as an alternative to conventional methods of vibration absorption in mechanical systems. Linear energy sinks do not rely on dissipation of energy in the form of heat. Instead they are undamped linear substructures, which can be attached to, or an integral part of, a vibrating structure (primary structure). This study shows that even though energy recurrence is a general characteristic of undamped linear systems, a set of linear oscillators attached to a primary structure absorbs and retains most of the vibratory energy without the need of a dissipative mechanism when oscillators have a particular frequency distribution. Two classes of energy sinks are examined.;The first class of linear energy sinks consists of a set of linear oscillators whose total mass is small relative to the primary mass; less than one-tenth of the primary mass. The oscillators that make up an energy sink absorb vibratory energy from a structure and retain it in their phase space when the oscillators have a particular frequency distribution. The flow of energy from the primary structure to attached oscillators appears to the primary structure as damping. Transferred energy is not dissipated as heat; rather, it stays in the phase space of the oscillators with near irreversibility. The particular frequency distribution that enables such absorption is obtained from an optimization that minimizes the energy retained by the primary structure over a time period. Optimization generated particular frequencies are clustered in the vicinity of natural frequency of the primary structure.;The second class of linear energy sinks is realized by attaching a linear undamped continuous structure, which behaves like a set of oscillators. When the natural frequency of such a light continuous structure is properly tuned, the continuous structure absorbs the vibratory energy of the primary structure and retains it for long durations of time.;Linear energy sinks function not only under transient excitations but also under harmonic and random noise excitations. Thus, they find broad range of applications. Absorbing transient vibrations of a large structure (naval vessels, airplanes and skyscrapers) and harmonic vibration of a micro beam are examples of this behavior.;Experimental results demonstrate the viability of linear energy sinks. Different physical realizations of energy sinks show the significance of frequency distributions as well as the ability of energy sinks to reduce vibration amplitude of the primary structure. Simulations are validated by experimental results.