Une méthode d'analyse des problèmes acoustiques externes et internes en aéronautique. Illustrations dans le cas du véhicule spatial Hermes

To solve aeronautical and aerospace industrial vibro-acoustic problems (cabin noise, panel radiation, vibration environment, ...) Dassault Aviation has developed an attractive computation strategy. Actually, in the so-called 'Coupling Finite Element and Singularity method' (CFES), each field (structure dynamics, interior acoustics, exterior acoustics) is calculated independently from one another with the best suitable methods. As there is no reason to have coincidence between these optimized subsystems, elasto-acoustic couplings are performed via an original technique based upon the introduction of interfacing models both independent of structure and acoustic approximations. The effectiveness of this approach is fully illustrated through the studies undertaken for Hermes spacecraft project. Severe acoustic loadings were identified (engines noise at launch, take off transonic aeronoise, phases of maximum dynamic pressure during atmospheric reentry) which may have caused damage to the 'nose' of this glider. Thus, taking profit on our computational organisation, numerical simulations were done considering a mechanical model (of the nose) coupled with the inside acoustic cavity. This made possible numerous sensitivity analyses from the study of correlation length effect to the determination of equivalent loads for shaker tests on a scaled-down model

Application Of The Active Sound Intensity Control In The Control Of The Sound Transmitted Through Panels

The aim of this work is to compare the transmission loss of a smart panel using optimal solutions that minimize either the pressure or the sound intensity. The investigated configuration consists of a double-wall panel filled with glass wool. A point force is introduced in the outer plate to simulate the incident acoustic field while a moment is located in the inner plate to simulate the control actuation. It is shown that the performance of the intensity control is not superior to the performance of the pressure control, and the latter has the advantage of a simpler implementation.210361043Donadon, L.V., Arruda, J.R.F., Active noise control of free-field radiation using near field error sensing by active sound intensity control (2000) 1st Conference on Noise & Vibration Pre-design and Characterization Using Energy Methods (NOVEM), , LyonFuller, C.R., Jones, J.D., Experiments on reduction of propeller induced interior noise by active control of cylinder vibration (1987) Journal o Sound and Vibration, 112, pp. 389-395Elliott, S.J., Nelson, P.A., (1992) Active Control of Sound, , Academic PressDonadon, L.V., Arruda, J.R.F., Experimental energetic analyzes of an actively controlled one-dimensional acoustic waveguide (2005) Journal of the Sound and Vibration, 280 (1-2), pp. 159-179Fahy, F.J., (1995) Sound Intensity, , 2a ed., E & FN SponBatoz, J.-L., Dhatt, H.G., (1990) Modélisation des Structures par Eléments Finis, 2. , ISBN 2-86601-259-3Tanneau, O., (2004) Modélisation de Panneaux D'isolation Aéronautiques, , Doctorate Thesis, Université de Paris VI, Jun

Vibration And Acoustics In Porous Insulating Materials - The Help Of Fe Numerical Simulations For The Analysis Of Experiments In Rooms And Tubes

To illustrate our purpose we first recall the results of a 4 years study, carried out at the ISMEP, of trimmed fuselage panels of aircraft and multilayered insulating systems. We underline the complementarities of real tests in transmissibility rooms with a set of FE and analytical methods we have developed. Two major difficulties exist i) high performance panel tests rapidly reach the limit of the experimental device, ii) short wave length in poroelastic material do not allow us direct 3D finite element calculations in all the frequency band [0 ; 6,000 Hz] of interest. Therefore, 3D models are completed with 2D models and an analytical method. We show that all this numerical tools are needed to understand the tests and to investigate some particular points as the mounting of the panel in the acoustic room. An other problematic question with poro-elastic materials is that the characterization of the material itself, which is of prior importance for inputting data in numerical models, is highly difficult to carry out. This second point motivates present research at UNICAMP based on the use of FE numerical calculations to determine the absorption and the transmissibility of porous samples in tubes. The construction of modified tubes are also envisaged for a better control of the boundary conditions during tests while the FE model will allow us to recover some fundamental characteristics by inverse calculation. We learned from our first simulations that high precisions calculations are needed to substitute the real device with a numerical one. We list at the end of the paper, new research involving virtual and real tests: curved panels, active control, noise inside a simplified aircraft cabin. From sub-structures to samples of materials, FE calculation proves itself of most practical benefits to exploit tests involving porous materials.429032912Tanneau, O., (2004) Modélisation de Panneaux d'Isolation Aéronautique - Couplages Poro-élastiques, Élastodynamiques et Acoustiques Par Méthodes Analytiques, FEM et BEM, , PhD thesis, University of Pierre et Marie Curie, Paris VILamary, P., Aircraft friendly cabin environment -Enhancement acoustic and vibro-acoustic numerical methods for trimmed fuselage models Proceedings of the XI DINAME, 28th February-4th March, 2005 - Ouro Preto, Brazil, 2005Lamary, P., Casimir, J.-B., Tanneau, O., Pompéi, M., Noise control inside aircraft - Virtual transmissibility tests using CAVOK FE solver Proceedings EuroNoise, Naples 2003Dauchez, N., (1999) Etude Vibro-acoutic des Matériaux Poreux Par Élé ments Finis, , PhD thesis, University of Le Mans, University of SherbrookeSong, B.H., Bolton, J.S., Investigation of the vibration modes of edge-constrained fibrous samples placed in a standing wave tube (2003) JASA, (113), p. 1833Valetim Donadon, L., Lamary, P., Camino, J., De França Arruda, J.R., Application of Active Sound Intensity Control of Sound Transmitted through Panels 12th ICSV Congress, Lisbon 2005Lamary, P., (2005) Final Report of Activity, FAPESP Processo 2003/09812

X-ray tomographic image post-processing and a new 2D LBM simulation for the determination of the porosity and the static airflow resistivity of an acoustic fibrous material

A set of X-ray tomographic images of a highly porous material composed of air-saturated coconut fibers isconsidered and used to estimate intrinsic characteristics of the material. Two physical properties are ofinterest: porosity and static airflow resistivity. For the porosity, two-dimensional gray-scale tomographyimages are obtained and post-processed to produce approximative black and white ones, unambiguouslyattributing distinct regions to fibers and air locations. The porosity is then directly deduced counting theblack and white pixels. Several image processing algorithms are compared and associated porositiesrange from 0:76 to 0:97, depending on the method employed, while it is estimated to be 0:86 from ouranalysis. For the airflow resistivity, the idea followed here is to use the pattern of the post-processedimages as the lattice in a Lattice Boltzmann Method (LBM) fluid dynamics computation. To our knowl-edge, the LBM has not been used in this context before. A new 2D implementation of the method is there-fore developed and studied. After tuning computational parameters, we have estimated the airflowresistivity using ten images of our sample to be 1382#12 Pa:s=m2. Both porosity and resistivity resultsare fully consistent with measurements obtained from a porosity-meter and a resistivity-meter, demon-strating the pertinence of X-ray tomography and the associated proposed methods169