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Particle impact dampers are dissipative devices that can easily be coupled to structures in order to reduce vibrations over a wide frequency range and in adverse environmental conditions. In this work, a multiple-sphere chain impact damper is coupled to a cantilever beam in order to attenuate its flexural motions. This simple configuration was chosen to better understand the energy dissipation phenomena by the device when the beam is subjected to random excitations. In addition, a parametric study of the coupled system is conducted in order to assert optimal working conditions of the damper. This study is mostly based on a numerical model of the vibro-impacting system, which was calibrated based on an experimental rig. Firstly, the computational modal basis of the bare beam was experimentally identified, and then theoretically modified taking into account the mass of the container. Secondly, calibration of the impact model was achieved by fitting the parameters of the contact formulation with respect to sphere-dropping experiments. Finally, extensive parametric computations are presented and discussed. The vibratory responses are computed using a frequency banded Gaussian random excitation, for several values of the excitation amplitude, for an increasing number of spheres and for several values of the damper clearance. The numerical results concern the r.m.s. motion of the spheres and the beam, the r.m.s. spheres/beam contact forces, the average mechanical and dissipated energies by the beam modes and the damper, as well as the effective beam modal parameters when fitted with the damper, which are essential results for understanding these damping devices. Finally, the numerical results are reduced into relevant dimensionless parameters, which prove reasonably effective in collapsing the dynamical data from such a highly nonlinear system. The present study thus highlights interesting essential features on the dynamics of structures coupled to multiple particle vibro-impact dampers under random excitation. [ABSTRACT FROM AUTHOR]

This research examines a Progressive Damage Model for laminated composites using a wave-based technique. Using conventional numerical methodologies, such studies may require a significant amount of CPU time. Compared to standard techniques, the approach proposed can provide a quick and cost-effective evaluation. This work presents a numerical approach for dealing with periodic media subjected to an impact load that can provide damage initiate and evolution. The proposed model is based on a hybrid formulation for the wave-damage interaction that describes wave scatterings, as well as a stress analysis of a composite structure subjected to an impact force. The failure analysis is carried out by identifying the damage location and then describing the modification of the material properties of the damaged elements using Hashin's failure criteria and material property degradation rules. A comparison of stress distribution with results from the conventional finite element approach was performed in order to confirm the hybrid WFE/FE method, and good agreement was noted. Finally, an impact on a composite beam was studied. The evolution of the structural failure is presented. This article takes into consideration material degradation over time. [ABSTRACT FROM AUTHOR]

This paper presents a numerical research of the influence of baffle plates integration inside a horizontal storage tank on the solar water storage tank efficiency. In this work, the baffle plates are integrated inside the tank with different locations and different distances between them to study their effects and also to determine the optimum position in order to enhance the thermal storage system (TSS) performance. The CFD comparison between all proposed designs was carried out and different methods of evaluating mixing and stratification such as temperature evolution, outlet temperature, Richardson number, and full efficiency were calculated to quantify the degree of stratification. Results show that the TSS performance depends on the baffle locations and distance between them. Therefore, a superior thermal performance was achieved for baffles with superior distance between them which are maintained in top of the water storage tank (WST). [ABSTRACT FROM AUTHOR]

Byline: F. Bouchoucha, M. Akrout, T. Fakhfakh, M.N. Ichchou, M. Haddar In this paper, we present an inexpensive and robust tool for the vibratory monitoring of cylindrical pipes. The tool will be based on the analysis of the anomalies which affect the elastic waves travelling in the pipe. We develop a numerical approach to study the guided elastic wave propagation in tubular structures. Wave finite element method (WFEM) based on the characterisation of the elastic waves is introduced to investigate the dispersion and wave scattering in pipes. Dynamic reduction technique is employed to improve the computational efficiency. Through WFEM and using a modal decomposition, we develop the dynamical behaviour of the pipe. We study the detection of some defects which affect the junction between two adjacent pipes. The question of the mode sensitivity to the defect's detection is considered.

The main source of vibration and noise in planetary gear train systems is the parametric instability caused by variable meshing stiffnesses. The operating conditions leading to parametric instability are investigated for planetary gear trains with three and four planets. Perturbation technique is used to study the primary, secondary, and combination instabilities. The effects of mesh stiffness parameters, including stiffness variation amplitudes, contact ratios, and mesh phasing, on these instabilities are identified. A rectangular waveform is used to describe the mesh stiffness variation. The boundaries separating stable and unstable conditions are obtained as simple expressions in terms of mesh parameters. These expressions allow the suppression of particular instabilities by adjusting the contact ratios and mesh phasing. [ABSTRACT FROM AUTHOR]

In this paper, we propose the interval analysis method for the dynamic response of wind turbine gear system with uncertain-but-bounded parameters. We developed a lumped dynamic model with 8dofs. Lagrange formalism is used to formulate the governing equation of motion of the model. The simulation results are obtained by the interval analysis method for dynamic analysis under uncertainty. The interval analysis method results are compared with probabilistic approach results. This kind of results is coincident with the meaning of the probabilistic approach and interval analysis method. [ABSTRACT FROM AUTHOR]