AN INVESTIGATION OF THE DAMPED DYNAMIC VIBRATION ABSORBERS INCORPORATING MEANS FOR TUNING OPTIMIZATION

Abstract

Typically, a damped dynamic vibration absorber is designed for a given main system, with a fixed absorber-tuning properly related to the natural frequency of the main system.. If the main system is such that its vibratory characteristics change during operation, then the damper will, in general,: be less effective because of the corresponding deviation in relative damper tuning. In view of above it becomes desirable to employ a device in which the auxiliary system is adjustable with respect to its tuning. This thesis deals with the study of a new design of a variable tuning damper. It consists of an overhupg mass the posi-tion of which can be varied, thus changing its moment of inertia. This change in inertia of the damper is the means for matching its tuning with respect to the main system. Single and two degrees of freedom vibration dampers of the variable inertia type have been studied on a single degree of freedom main system. Digital computer analysis has been used to obtain the optimum response of the main system and the correspon-ding damper parameters. It has been found that, for the optimum magnification, the damper parameters are such that the complete system behaves like a classical system, but with a reduced effective damper mass, the effectiveness depending upon the location of the damper mass along its axis. The damper characteristics have been investigated for the various parameters involved for translational and angular excitations of the main system and the results explained with particular reference to the classical system. Regions are deter-mined in which the damper is most effective with respect to tuning capability and amplitude reduction. The effectiveness of the damper with optimum tuning is also indicated for the main system with variable natural frequency. Further, a self optimizing control circuit has been designed and tested on a variable inertia vibration damper for the purpose of tuning it autcmatically to the varying operating conditions of the main system. The control circuit consists of a sensing device, a logic circuit and a mechanism for varying the position of the adjustable damper mass by means of a motor. The system .has been tested under different operating conditions and it has been found that it is capable of locating the optimum tuning corresponding to the least respohse at a given exciting frequency. There have been, however, found to be certain limitations of the device, but on the whole, the performance of the control system has been more than satisfactory.