Physical principles governing the damping of structural vibrations by modification of the environment and by addition of appendages

Abstract

This paper discusses how vibrations can be damped by the external environment or by addition of external appendages. The topic is an old one and goes back to Stokes (1845) who considered the damping of pendulums by a surrounding viscous fluid. Damping can also occur because of the radiation of sound into the fluid. In more recent years various authors have considered the possibility of attaching something on the surface of the body, where, by some mechanism, vibrational energy is absorbed within in the appendage. Several widely used concepts are reviewed: the dynamic vibration absorber, constrained layer damping, attachment of fuzzy structures, and attachment of piezoelectric strips. A principal (weak damping) approximation is that the vibrations of the environment and the appendage are the same as if the surface vibrations were unaffected. If energy is held in the vicinity of the surface, then there must be some mechanism by which the energy is dissipated in the appendage, and this dissipation should be higher than in the structure proper. The relevant physical principles vary and must be identified if meaningful estimates of damping are to be made. In some cases, generally because of resonance, the energy density in the appendage is considerably higher than in the structure. Given that the governing equations are linear, the damping is invariably frequency dependent. Paper attempts to succinctly summarize the physical principles and give quantitative guidelines for estimating the damping. [Work supported in part by ONR.]This paper discusses how vibrations can be damped by the external environment or by addition of external appendages. The topic is an old one and goes back to Stokes (1845) who considered the damping of pendulums by a surrounding viscous fluid. Damping can also occur because of the radiation of sound into the fluid. In more recent years various authors have considered the possibility of attaching something on the surface of the body, where, by some mechanism, vibrational energy is absorbed within in the appendage. Several widely used concepts are reviewed: the dynamic vibration absorber, constrained layer damping, attachment of fuzzy structures, and attachment of piezoelectric strips. A principal (weak damping) approximation is that the vibrations of the environment and the appendage are the same as if the surface vibrations were unaffected. If energy is held in the vicinity of the surface, then there must be some mechanism by which the energy is dissipated in the appendage, and this dissipation should be ...