A VARIABLE STIFFNESS VIBRATION ABSORBER FOR MINIMIZATION OF TRANSIENT VIBRATIONS

An adaptable vibration absorber has been designed and investigated. The objectives of the absorber are to: (a) minimize transient vibrations of rotating machines during start-up and shut-down conditions, and (b) to adapt to changes in steady state operating speeds such as might occur in engines and pumps when load conditions vary. The model on which the design was based is a single-degree-of-freedom main system consisting of constant mass, stiffness and damping ratio, and an absorber consisting of constant mass and damping ratio but a variable stiffness. The excitation investigated is a rotating unbalance which undergoes a period of constant acceleration and then transitions to a steady operating frequency. The system response was found by means of numerical integration. Improvements in root mean squared displacement of 47% and peak displacement of 53% were found with the adjustable absorber tuned to the angular velocity of the unbalance. An optimization of the time-varying-stiffness yielded improvements of 66% and 67% in r.m.s. (root mean square) and peak displacements, respectively. A variable stiffness spring design is investigated, and is shown to provide a sufficient range of stiffness variation to yield the previously mentioned improvements. © 1992.