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International audienceParticle dampers are passive devices allowing strong damping of structures vibrating in harsh environment. We investigate the energy dissipation in a rigid enclosure attached to a shaker and partially filled with particles. Our experiments match an analytical description, which we corroborate then with discrete element method simulations. We show that the loss factor does not depend on the material of the particles or their number, but heavily relies on the total mass of the embedded grains and on the driving magnitude only. Our measurements reveal the contribution of the viscous flow of air surrounding the grains to the overall loss factor of the dampers

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The development of materials both rigid and light with high damping effect and acoustic insulation is possible by using a multilayer panel with viscoelastic material. The rigidity of a multilayer panel is provided by its elastic layers, and damping is provided by viscoelastic layers. Prediction of the behavior of such systems in the conception phase is very important to determine the most important parameters in a multilayer panel in the aim to maximize insulation and to properly design this panel for several applications. In this work we have developed a model based on transfer matrix method, which is an analytic method to predict behavior of infinite layer subjected to a plane wave with an oblique incidence.

This paper presents a novel meta-heuristic approach based on the crow search algorithm (CSA) for solving the optimal reactive power dispatch (ORPD) problem. The ORPD is formulated as a nonlinear optimization problem designed to minimize power losses while satisfying the required constraints. The CSA is a recent efficient approach that depends on the intelligent behavior of crows. Nowadays, it has been used to solve many complex engineering optimization problems where it has proven its power and effectiveness. Motivated by the high ability in solving complex optimization problems and faster convergence of CSA, this paper proposes a novel approach to solve the ORPD problem. Furthermore, the settings of control variables such as generator terminal voltage, tap changer positions, and capacitor banks are determined to achieve the minimum total power loss while satisfying a set of nonlinear constraints. The accuracy and the performance of the proposed algorithm were performed and compared to other meta-heuristic algorithms reported in the literature. Several tests are applied on two standard test systems, including IEEE 14-bus and IEEE 30-bus as well as on the large-scale Tunisian 86-bus system. In addition, a sensitivity analysis has been performed to valid the performance of the CSA in solving the ORPD problem. We demonstrate that the proposed CSA provides a supremacy results and statistically significant in solving ORPD problems (for IEEE-14 bus p < 0.0006 , for IEEE-30 bus p < 0.006 , and for Tunisian 86-bus p < 0.0000001 ).