Absorption (acoustics)

Résumé

Acoustic absorption refers to the process by which a material, structure, or object takes in sound energy when sound waves are encountered, as opposed to reflecting the energy. Part of the absorbed energy is transformed into heat and part is transmitted through the absorbing body. The energy transformed into heat is said to have been 'lost'. When sound from a loudspeaker collides with the walls of a room part of the sound's energy is reflected, part is transmitted, and part is absorbed into the walls. Just as the acoustic energy was transmitted through the air as pressure differentials (or deformations), the acoustic energy travels through the material which makes up the wall in the same manner. Deformation causes mechanical losses via conversion of part of the sound energy into heat, resulting in acoustic attenuation, mostly due to the wall's viscosity. Similar attenuation mechanisms apply for the air and any other medium through which sound travels. The fraction of sound absorbed i

Source officielle

https://en.wikipedia.org/wiki/Absorption_(acoustics)

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Ce cours a pour objectif de former les étudiants de section Génie Electrique et Electronique à la conception de systèmes acoustiques, à l'aide d'un formalisme basé sur l'électrotechnique. A la fin du semestre, les étudiants seront capables de dimensionner, entre autres, des filtres acoustiques.

Apply the knowledge acquired in Electroacoustics, Audio Engineering and Propagation of Acoustic Waves lectures.

Réaliser un système d'optique complexe. Comprendre l'interaction de la lumière avec la matière en optique nonlinéaire et optique pulsé. Comprendre les méthodes de génération, d'amplification e de compression des impulsions courtes. Connaitre les techniques de spectroscopies résolues en temps.

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Structural and acoustic behavior of chiral truss-core beams

Alessandro Spadoni

The vibration-reduction and sound-absorption properties of a truss-core sandwich beam are analyzed. The core is composed by the assembly of unit cells across both the length and thickness of the proposed beam. The cells have chiral geometry which features cylinders, or nodes, joined by ligaments, or ribs. The resulting assembly is characterized by a number of interesting properties that can be exploited for the design of alternative honeycomb or cellular topologies to be used in sandwich construction. The vibro-acoustic analysis of the considered beam is performed through a finite element model developed using a commercially available Finite Element package. In the model, the sandwich beam is constrained to a rigid baffle and divides two fluid domains of infinite extent. The dynamic performance of the beam is evaluated through the estimation of the vibration amplitudes of the two constraining layers, while the performance of the beam as an acoustic panel with high insulation characteristics is analyzed through the estimation of the sound transmission loss between the two fluid domains. A sensitivity study to investigate the influence of core configuration and geometry on the beam’s performance is presented. The results indicate the design flexibility offered by the proposed design, which allows modifying and optimizing the structural acoustic performance of the beam through proper selection of the core configuration.

2004

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Conceptual design of the ECH upper launcher system for ITER

Robert Bertizzolo, René Chavan

The challenge of developing the conceptual design of the ECH Upper Launcher system for MHD control in the ITER plasmas has been tackled by team of European Associations together with the European Domestic Agency ("F4E"). The launcher system has to meet the following requirements: (a) a mm-wave system extending from the interface to the transmission line up to the target absorption zone in the plasma and performing as an intelligent antenna; (b) a structural system integrating the mm-wave system and ensuring sufficient thermal and nuclear shielding; (C) port Plug remote handling and testing capability ensuring high Port plug system availability. The paper describes the reference launcher design. The mm-wave system is composed of waveguide and quasi-optical sections with a front steering system. An automated feedback control system is developed as a concept based on an assimilation procedure between predicted and diagnosed absorption location. The structural system consists of the blanket shield module, the port plug frame, and the internal shield for appropriate neutron shielding towards the launcher back-end. The specific advantages of a double walled structure are discussed with respect to adequate baking, to rigidity towards launcher deflection under plasma-generated loads and to removal of thermal loads, including nuclear ones. Basic Studies of remote handling (RH) to validate design development are initiated using a virtual reality simulation backed by experimental validation, for which a launcher handling test facility (LHT) is set LIP as a full scale experimental site allowing furthermore thermohydraulic studies with ITER blanket water parameters. (C) 2008 Elsevier B.V. All rights reserved.

Elsevier2009

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Poloidally asymmetric plasma response with ECH deposition near q=1 in TCV

Timothy Goodman, Jean-Philippe Hogge, Antoine Pochelon, Olivier Sauter

A small component of ECCD exists when heating off-axis with no toroidal injection due to the field helicity. The sign of the ECCD will change depending on the absorption location in a poloidal plane, the beam injection relative to delB(vac), and the direction of the toroidal magnetic field. The importance of the ECCD component can be confirmed by the behavior of the sawteeth when the ECH deposition crosses the q=1 surface. The sawtooth period is very sensitive to the local shear at q=1 and it is shown that difference in sawtooth period when heating above and below the midplane are consistent with the presence of a small ECCD component. Experiments have also shown that the sawtooth period is strongly determined by the absorbed ECH power near the q=1 surface. In particular significant changes in the sawtooth period are observed as the absorption location is varied on a scale smaller than the beam spot size. A narrow region of rapidly changing confinement is shown to exist near the q=1 surface to be located outside the q=1 surface by a factor of 1.3 in radii. The region can be used as a method for measuring the beam deposition width in the plasma. (C) 2001 Elsevier Science B.V. All rights reserved.

2001

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