Vibration Absorber

This paper describes the application of a vibration absorber to ameliorate the comfort of motorcycle handles. The concept of dynamical absorber is briefly summarised and a frequency response function is expressed as the ratio of vibration amplitudes (transmissibility). Some practical hints on the tuning strategy are also suggested in order to correctly define the absorber and then achieve the most effective vibration reduction. A specifically designed item is presented, with the peculiar characteristic of taking advantage of the damping properties of viscoelastic material undergoing shear deformations. An experimental verification of the good performances of the absorber is eventually given on the basis of both a modal analysis of a motorbike and the testing of its handle on an electrodynamical shaker.

Vibration dynamic absorber is in use to reduce machinery vibrations. This paper presents a novel idea for using the mass-spring absorber as an energy harvester. The aim is to tune the absorber to cancel the machine vibration and produce maximum vibration of the absorber mass to act as an energy harvester. The main vibrating system is damped and assumed as a SDOF. A new frequency is defined called harvesting frequency at which the amplitude of the absorber mass vibration is maximum. It is shown that his frequency is dependent only on the mass ratio of the absorber and independent of the main system damping ratio. The optimal operation of the proposed system is investigated for damping ratio between 0.1 and 0.4 and mass ratio between 0.05 and 4.5. The absorber succeeds to eliminate completely the main system vibrations at a tuning condition and provides high vibration amplitude at the absorber mass at the new defined harvesting frequency..

Typical turboprop noise spectra exhibit a series of characteristic peaks which are directly related to the product of propeller rpm and number of propeller blades. These blade passage frequencies contribute significantly to the overall sound pressure level both outside and inside the aircraft. Their contribution to cabin noise is usually reduced by appropriately adjusted mass dampers. However, since the engine rpm varies for different flight stages, any fixed eigenfrequency absorber will merely be a sub-optimal compromise. The Tunable Vibration Absorber (TVA) introduced in this article has a variable resonant frequency which enables an adaptation to different flight phases providing largely improved performance. Frequency tuning is achieved through a piezo-electric stack actuator, which applies a pressure force to a pair of leaf springs thus reducing their effective bending stiffness. Among the main advantages of this particular approach are a static control signal and low power consumption. To enable a light-weight construction the components which generate the pressure loading are incorporated into the oscillating mass. The TVA allows to cover a wide frequency range using only a single device. Additionally, it features damping control capability and optional active multi-mode operation. Structural-acoustic simulations have indicated a noise reduction potential of approximately 10 dB. This article gives a short overview of different tuneable vibration absorber concepts, lines out the theoretical background of the proposed approach, discusses the general components layout and describes the experimental verification of a prototype TVA for the Airbus A400M.