Optimisation de la vérification de l'équation vibroacoustique des plaques sur un échantillonnage spatial: application au bruit intérieur des avions

This PhD thesis deals with the use of damping patches on aircraft skins to reduce interior noise. Induced mass penalties are considered high today, hence the interest of damping size and placement optimizations. Three excitations are used by Airbus to assess a damping technology: mechanical (laboratory or ground tests), acoustic (laboratory or ground tests) and aerodynamic (flight tests) excitations. The strategy adopted to study the acoustic benefit of such treatments is chosen analytical so as to cover the large frequency band associated with low computation time. An original approach is first of all proposed to compute sound radiation from locally damped plates. The advantages of this method are twofold: first avoid difficulties of radiation impedances calculation and then handle complex aircraft structures. The scientific outcome in term of modelisation lies in the two following points. First an approach based on the minimization of error on a sample of observation points has been developed to solve vibroacoustic equations. A method handling Dirac delta functions to model heterogeneities at localized damping patch boundaries is then proposed. The analytical model developed is applied to unstiffened finite flat plates where a localized damping treatment, a multilayer plate or a varying thickness can be considered. The principle of the method remains valid for curved or stiffened plates, only the equation of motion must be adapted. All studies presented in this manuscript are led at ambient temperature. Numerical validations for mechanical, acoustic and aerodynamic excitations and an experimental validation for acoustic excitation are led. Results prove a very good accuracy of the method developed: fluid-structure interaction and localized damping are well modeled. The focus is also put on the choice of the aerodynamic excitation model. It is pointed out a strong influence of the model for absolute levels and a low influence for relative levels, in-flight validation appear to be necessary even if such flight tests are challenging. An experimental study led on localized damping patches under acoustic excitation has pointed out some tendencies for damping patch size optimization. Using the method developed, a numerical study has then detailed this analysis and extended it to excitation and damping patch placement influences. Acoustic and aerodynamic excitations play clearly different roles in damping impact assessment. Damping patch size and placement effects are finally analyzed under aerodynamic excitation in realistic conditions. A non-linear behavior of the size versus the added mass is observed allowing definition of an optimum. The placement of the damping treatment is presented to be critical only at low frequencies where modal phenomena dominate. This PhD work gives an accurate prediction tool adapted to the industrial needs of aircraft interior noise control. Extensions are of course necessary to consider more realistic structures but the present method allows already the optimization of damping treatments with regard to mass constraints.Dans le contexte du bruit intérieur des avions, ce travail de thèse étudie l'intérêt acoustique de l'utilisation de patchs viscoélastiques. La masse de ces traitements est aujourd'hui considérée comme pénalisante. Une optimisation en termes de taille et de placement est donc envisagée. La stratégie adoptée est choisie analytique pour couvrir une large gamme de fréquences avec des temps de calcul performants. Ce mémoire de thèse propose une approche originale calculant le rayonnement acoustique de plaques amorties localement. Cette approche présente les intérêts suivants : s'absoudre des difficultés de calcul des impédances de rayonnement et être particulièrement adaptée aux structures complexes de l'avion. L'apport scientifique de cette thèse en terme de modélisation réside d'une part dans une approche de calcul vibroacoustique basée sur la minimisation de l'erreur de vérification de l'équation de mouvement sur un échantillonnage spatial et, d'autre part, dans un formalisme par fonctions Dirac mis en œuvre pour simuler les hétérogénéités aux limites d'un patch amortissant localisé. Ce modèle analytique est appliqué à des plaques planes finies non raidies où un traitement amortissant localisé, une plaque multicouche ou une plaque à épaisseur variable peuvent être considérés. Une validation numérique pour les excitations mécanique, acoustique et aérodynamique ainsi qu'une validation expérimentale sous excitation champ diffus démontrent une très bonne précision du modèle développé : le couplage fluide-structure et l'amortissement localisé sont correctement modélisés. Les effets de taille et de placement du patch sont finalement étudiés sur un cas particulier sous excitation aérodynamique en conditions réalistes. Le comportement non linéaire observé de l'effet de taille par rapport à la masse ajoutée permet de définir un optimum. L'apport scientifique de cette thèse offre un outil prédictif performant et adapté à la problématique du bruit interne des avions

ATLAS

% ATLAS \\ \\ ATLAS is a general-purpose experiment for recording proton-proton collisions at LHC. The ATLAS collaboration consists of 144 participating institutions (June 1998) with more than 1750~physicists and engineers (700 from non-Member States). The detector design has been optimized to cover the largest possible range of LHC physics: searches for Higgs bosons and alternative schemes for the spontaneous symmetry-breaking mechanism; searches for supersymmetric particles, new gauge bosons, leptoquarks, and quark and lepton compositeness indicating extensions to the Standard Model and new physics beyond it; studies of the origin of CP violation via high-precision measurements of CP-violating B-decays; high-precision measurements of the third quark family such as the top-quark mass and decay properties, rare decays of B-hadrons, spectroscopy of rare B-hadrons, and $B ^0 _{s}$-mixing. \\ \\The ATLAS dectector, shown in the Figure includes an inner tracking detector inside a 2~T~solenoid providing an axial field, electromagnetic and hadronic calorimeters outside the solenoid and in the forward regions, and barrel and end-cap air-core-toroid muon spectrometers. The precision measurements for photons, electrons, muons and hadrons, and identification of photons, electrons, muons, $\tau$-leptons and b-quark jets are performed over $| \eta |$ < 2.5. The complete hadronic energy measurement extends over $| \eta |$ < 4.7. \\ \\The inner tracking detector consists of straw drift tubes interleaved with transition radiators for robust pattern recognition and electron identification, and several layers of semiconductor strip and pixel detectors providing high-precision space points. \\ \\The e.m. calorimeter is a lead-Liquid Argon sampling calorimeter with an integrated preshower detector and a presampler layer immediately behind the cryostat wall for energy recovery. The end-cap hadronic calorimeters also use Liquid Argon technology, with copper absorber plates. The end-cap cryostats house the e.m., hadronic and forward calorimeters (tungsten-Liquid Argon sampling). The barrel hadronic calorimeter is an iron-scintillating tile sampling calorimeter with longitudinal tile geometry. \\ \\Air-core toroids are used for the muon spectrometer. Eight superconducting coils with warm voussoirs are used in the barrel region complemented with superconducting end-cap toroids in the forward regions. The toroids will be instrumented with Monitored Drift Tubes (Cathode Strip Chambers at large rapidity where there are high radiation levels). The muon trigger and second coordinate measurement for muon tracks are provide