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Material selection for soft particle dampers
Abstract
A particle damper can be defined as a container partially filled with particles (eg sand, beads), which is attached to or within a vibrating structure. There is a need for a methodology to design and to qualify a "soft" damping particle adapted to space applications. The aim of this work is to make 'space useable' damping particles without degrading their performances. It induces the elaboration of a methodology in order to select a material with high damping properties and in considering environmental specifications (like vacuum and high temperatures) and sphere manufacturing constraints. The proposed paper presents the dedicated and original methodology that has been developed and which is based on a multiscale approach. This detailed semi-empirical approach offers the advantage to highlight at small scale the influence of parameters such as the particles characteristics (material, size) or the excitation level on the damping properties of the specimens. With this method, we intend to increase the chance to qualify for space missions new particles dampers by taking into account at the same time their damping properties, outgassing behavior and manufacturing cycle.
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We investigate collective dissipative properties of vibrated granular materials by means of molecular dynamics simulations. Rates of energy losses indicate three different regimes or "phases"in the amplitude-frequency plane of the external forcing, namely, solid, convective, and gas-like regimes. The behavior of effective damping decrement in the solid regime is glassy. Practical applications are dicussed. Comment: 5 pages, 4 figures
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 characteristics 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.
The paper presents measuring methods and measurement results of vibration damping of shot-filled containers with some empty volume as the shot damper clearance. The energy dissipation by shot depends on two phenomena: the internal and the external (container walls) impacts of shot particles associated usually with their internal and external friction. This is the working principle of the single-/multi-mass impact dampers and the shot vibration damper as well. It is shown in the paper that the additional loss factor introduced by the shot moving in the properly shaped container is on the order of half of shot mass reduced to the primary system modal mass. It may be even twice more if the energy dissipation by shot friction will be fully utilized. This depends mainly on the motion condition of shot inside a container. It was shown in the paper also that loose shot or better shot tightly packed in a plastic bag or mesh can fulfill this condition. Shot dampers can work efficiently in a broad range of acceleration and frequency and need not be maintained. Due to this it may be very convenient to apply them to structural vibration problems.
This paper describes an experimental investigation of a particle damping method for a beam and a plate. Tungsten carbide particles are embedded within longitudinal (and latitudinal) holes drilled in the structure, as a simple and passive means for vibration suppression. Unlike in traditional damping materials, mechanisms of energy dissipation of particle damping are highly nonlinear and primarily related to friction and impact phenomena. Experiments are conducted with a number of arrangements of the packed particles including different particle sizes and volumetric packing ratios. The results show that the particle damping is remarkably effective and that strong attenuations are achieved within a broad frequency range. The effects of the system parameters including particle size, packing ratio and particle material are studied by broadband and narrow-band random excitations. The experimental results confirm a numerical prediction that shear friction in the longitudinal (and the latitudinal) directions is effective as the major contributing mechanism of damping in the case. Another unique feature of linear decay in free vibrations is also observed in this case of particle damping.
Multi-unit particle dampers are passive damping devices involving granular particles in some cavities of a primary system. The principle behind particle damping is the removal of vibratory energy through losses that occur during impact of granular particles. This paper presents the results of experimental and analytical studies of the performance of a multi-unit particle damper in a horizontally vibrating system. An analytical solution based on the discrete element method is presented. Comparison between the experimental and analytical results shows that accurate estimates of the rms response of a primary system can be obtained. It is shown that the response of the primary system depends on the number of cavities and cavity dimensions.
Particle impact damping (PID) is a means for achieving high structural damping by the use of a particle-filled enclosure attached to the structure in a region of high displacements. The particles absorb kinetic energy of the structure and convert it into heat through inelastic collisions between the particles and the enclosure, and amongst the particles. In this work, PID is measured for a cantilevered aluminium beam with the damping enclosure attached to its free end; lead particles are used in this study. The effect of acceleration amplitude and clearance inside the enclosure on PID is studied. PID is found to be highly non-linear. Perhaps the most useful observation is that for a very small weight penalty (about 6%), the maximum specific damping capacity (SDC) is about 50%, which is more than one order of magnitude higher than the intrinsic material damping of a majority of structural metals (O(1%)). Driven by the experimental observations, an elementary analytical model of PID is constructed. A satisfactory comparison between the theory and the experiment is observed. An encouraging result is that in spite of its simplicity, the model captures the essential physics of PID.
This paper presents initial work on developing models for predicting particle dampers (PDs) 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 PDs 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 PD via a DEM simulation. The results were compared with that of an experiment.
Particle dampers are enclosures partially filled with metallic or glass small spheres, attached to the vibrating structure. This paper deals with replacing hard classical particles by soft hollow ones to maximize damping and mass ratio. Hence, one aspect of this damping method is obtained by mixing the kinetic energy conversion of the structure into heat(frictional losses and collisions) and the elastic energy conversion into heat (visco-elastic deformation). This study is oriented toward experimental and theoretical investigations in order to distinguish the dissipation phenomena. The experimental approach first relies on identification and, then, on validation applied on composite aluminum honeycomb plates. Indeed, equivalent viscous damping is identified on small honeycomb samples; then cantilever honeycomb beams are filled with particles and studied. Theoretically, beyond the nonlinear dissipation by impact and friction, these particles add a visco-elastic behavior. The shapes of the hysteretic loops highlight that this behavior is predominant. Hence, oscillators are added in the FE model and permit to consider the effect of the particles. These kinds of particle dampers are highly nonlinear as a function of excitation frequency and amplitudes. The aim of this study is to provide a structural damping solution for space applications which require high pointing stability to enhance mission performances. In this perspective, damping of micro-vibrations was thought as a possible application; nevertheless it is shown that best efficiency is achieved in high frequency range.
Thesis (M.S.)--Pennsylvania State University, 2004. Library holds archival microfiches negative and service copy.
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