Substitute for the Impact Damper

Abstract

A barrier to the widespread use of the impact damper is its noisy operation. Described in this paper is work related to the development of a substitute for the impact damper combining effective vibration reduction and low noise while preserving simplicity and light weight. The device is a vibration-driven, free-piston pump which dissipates energy by forcing air through throttling valves at either end of its container during operation. Equations of motion are developed for a single-degree-of-freedom oscillator and attached free-piston damper. The thermodynamic cycle assumed for the damper involves polytropic compression, expulsion at constant pressure, polytropic expansion, and intake at constant volume. The resulting nonlinear formulation is analyzed approximately using the method described by Kryloff and Bogoliuboff. Ranges of system parameters providing nonimpacting steady symmetric operation are developed, and stability is explored. A digital model is formulated to investigate transient response and to establish the ranges of stable operation possible when the system is started from rest. It is established by comparing approximate and simulated results that when steady symmetric operation without impact is achieved, the approximate analysis provides a good prediction of system response amplitude. The relative efficacy of an impact damper and a free-piston damper of comparable weight is examined, and it is established that the free-piston damper may prove a suitable substitute for particular applications.