This paper presents initial work on developing models for predicting particle dampers behaviour using the Discrete Element Method (DEM). In the DEM approach, individual particles are typically represented as elements with mass and rotational inertia. Contacts between particles and with walls are represented using springs, dampers and sliding friction interfaces. In order to use DEM to predict damper behaviour adequately, it is important to identify representative models of the contact conditions. It is particularly important to get the appropriate trade-off between accuracy and computational efficiency as particle dampers ave so many individual elements. In order to understand appropriate models, experimental work w s carri d out to understand interactions between the typically small (~ 1.5-3 mm diameter) particles used. Measurements were made of coefficient of restitution and interface friction. These were used to give an indication of the level of uncertainty that the simplest (linear) models might assume.These data were used to predict energy dissipation in a particle damper via a DEM simulation. The results were compared with that of an experiment. Keywords: particle damping, energy dissipationThis paper presents initial work on developing models for predicting particle dampers behaviour using the Discrete Element Method (DEM). In the DEM approach, individual particles are typically represented as elements with mass and rotational inertia. Contacts between particles and with walls are represented using springs, dampers and sliding friction interfaces. In order to use DEM to predict damper behaviour adequately, it is important to identify representative models of the contact conditions. It is particularly important to get the appropriate trade-off between accuracy and computational efficiency as particle dampers have so many individual elements. In order to understand appropriate models, experimental work was carried out to understand interactions between the typically small (~ 1.5-3 mm diameter) particles used. Measurements were made of coefficient of restitution and interface friction. These were used to give an indication of the level of uncertainty that the simplest (linear) models might assume. These data were used to predict energy dissipation in a particle damper via a DEM simulation. The results were compared with that of an experiment.

Particle dampers (PDs) have the advantages of being simple in geometry, small in volume and applicable in extreme temperature environments. Experimental studies have shown that PDs can offer considerable potential for suppressing structural resonant conditions over a wide frequency range. In this paper, the nonlinear characters of PDs are studied experimentally in a series of response-level-controlled tests. The effect of the geometry is studied and a method is developed to model the nonlinear damping of PDs as equivalent viscous dampers that can be applied directly to engineering structures at the design stage.

No abstract

We perform finite element analysis of the mechanical response of random RVEs representing the microstructure of a unidirectional (UD) fibre composite, predicting its anisotropic stiffness and damping properties and their sensitivity to temperature and frequency, using as inputs only the measured response of the constituents. The simulations are validated by DMTA measurements on a UD composite; then, the numerical predictions are compared to those of previously published theoretical models. New equations are proposed to predict the viscoelastic constants, providing better accuracy than existing models. The accuracy of these new equations is tested, over wide ranges of fibre volume fractions and stiffness ratios of the constituents, against the numerical predictions

In this paper the authors discuss the progress that has been made over the past decade in active constrained-layer damping (ACLD). ACLD treatments combine the best features of passive and active control of structural vibrations. By way of introduction the paper describes well-established techniques for passive control of structural vibrations and noise. A concise discussion of the development of so-called 'smart' (or 'intelligent') actuators and sensors and the emergence of suitable control algorithms show how passive techniques were extended to produce ACLD. A comprehensive literature review follows. It is shown how the passive and active components of ACLD complement each other to enable control of both high and low frequency modes of vibration. The active elements allow structures to adapt to suit a changing environment while the passive elements provide a fail-safe mechanism. Because of the available technology, these bene ts are available without signi cant penalties in terms of cost, weight and complexity.

The energy leakage is an inherent deficiency of Discrete WaveletTransform (DWT) which is often ignored by researchers and practitioners. In this paper, a systematic investigation into the energy leakage is reported. The DWT is briefly introduced first, and then the energy leakage phenomenon is described using a numerical example as an illustration and its effect on the DWT results is discussed.Focusing on the Daubechies wavelet functions, the band overlap between the quadrature mirror analysis filters was studied and the results reveal that there is an unavoidable tradeoff between the band overlap degree and the time resolution for the DWT. The dependency of the energy leakage to the wavelet function order was studied by using a criterion defined to evaluate the severity of the energy leakage. In addition, a method based on resampling technique was proposed to relieve the effects of the energy leakage. The effectiveness of the proposed method has been validated by numerical simulation study and experimental study.

It has been shown that significant reductions in structural vibration levels can be achieved using a hybrid system involving constrained layer damping and active control with piezoceramics. In this paper, mathematical models based on the Rayleigh Ritz approach, are developed to describe the longitudinal and flexural vibration behaviour of a cantilevered beam when excited using piezoceramic patches bonded to a constrained layer damping treatment. Predictions of static and steady state dynamic behaviour, obtained using the models are validated by comparison with results from finite element analysis and laboratory experiments. The models are then used in open loop and closed loop velocity feedback control simulations to demonstrate the improvements in stability and performance achieved using this method over that achieved using conventional active control.

The hysteresis behaviour of metal rubber particles has been characterised. A quasi-static experiment was conducted to measure the damping behaviour of metal rubber particles. The effects of imposed displacement and filling density were examined. A mathematic model has been established to characterise the damping behaviour of metal rubber particles. A single-helix spring model was used to represent the microelement of the metal rubber material. This was composed of three contact states: open, slipping and sticking. The stiffness properties for the three cases were derived. The arrangement and spatial distribution of the microsprings were assumed to be uniform and periodic inside the metal rubber particles component. The test results were compared with the simulation results which showed a good correspondence.