Modeling of acoustic propagation in a duct with absorbing treatment is considered. The surface impedance of the treatment is sought in the form of a rational fraction. The numerical model is based on a resolution of the linearized Euler equations by finite difference time domain for the calculation of the acoustic propagation under a grazing flow. Sensitivity analysis of the considered numerical model is performed. The uncertainty of the physical parameters is taken into account to determine the most influential input parameters. The robustness of the solution vis-a-vis changes of the flow characteristics and the propagation medium is studied.
Abstract. When fatigue tests are carried out using a shaker, dynamic phenomena often appear and lead to a non-linear behaviour in the experiment. In this paper, the dynamic response of the specimen is studied in order to evaluate the impact on the results. The experiment consists in a notched beam fixed on the armature of an electro-dynamic shaker. The transfer function between the center of the armature and the tip of the beam is obtained with a swept sine near the first resonance frequency of the specimen. The drive is a constant acceleration amplitude. An evolution in the transfer function of the beam is observed when the drive is modified: the resonance frequency decreases and the damping increases. This non-linearity is investigated by studying the movement of the shaker, the fixture and the beam. The results show that the beam close to its resonance disrupt the imposed movement. An experimental setup correcting those defects is proposed.
This paper deals with shape optimization issues under vibroacoustic criteria. The aim of the conducted research is to minimize the energy density in the cavity by changing its geometry parameters. The energy density is obtained through an energy method called simplified energy method (MES). The optimization method is based on a transformation function mapping 3D cavity surface on a 2D domain. The optimization process directly relies on this function and thus avoids remeshing of the geometry. The proposed method allows to describe the geometry through Bezier, Bspline and NURBS parametrization. To illustrate the method, we process a shape optimization on a simple acoustic cavity.
Reducing the noise level in the acoustic cavities is the important problem when treating inflight conditions of commercial planes or boats. Shape optimization of the acoustic cavity that will take into account the geometrical and material uncertainties, arising during the manufacturing process, is presented in this paper. The noise level is controlled by minimizing the energy density in the cavity, obtained through an energy method called Simplified Energy Method. Such formulation is based on our previous published work where transformation function mapping 3D cavity surface on a 2D domain was proposed. The optimization process directly relies on this function and thus avoids remeshing of the geometry. Robust optimization is performed using the nondominated sorting genetic algorithm (NSGA-II) together with the Kriging surrogate model. Influence of geometrical and material characteristics on the optimal solution is identified.Keywords: Simplified energy method; shape optimization; Kriging; genetic algorithm. 1650006-1 J. Comp. Acous. Downloaded from www.worldscientific.com by UNIVERSITY OF CALIFORNIA @ SAN DIEGO on 03/26/16. For personal use only. R. Troian et al. 1650006-2 J. Comp. Acous. Downloaded from www.worldscientific.com by UNIVERSITY OF CALIFORNIA @ SAN DIEGO on 03/26/16. For personal use only. 1650006-4 J. Comp. Acous. Downloaded from www.worldscientific.com by UNIVERSITY OF CALIFORNIA @ SAN DIEGO on 03/26/16. For personal use only. 1650006-8 J. Comp. Acous. Downloaded from www.worldscientific.com by UNIVERSITY OF CALIFORNIA @ SAN DIEGO on 03/26/16. For personal use only.
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