Vibroacoustic modelling of aircraft double-walls with structural links

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    Submitted on 28 Sep 2012

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    Vibroacoustic modelling of aircraft double-walls withstructural links using Statistical Energy Analysis (SEA)

    Bruno Campolina

    To cite this version:Bruno Campolina. Vibroacoustic modelling of aircraft double-walls with structural links using Statis-tical Energy Analysis (SEA). Acoustics [physics.class-ph]. Universit de Sherbrooke; Universit Pierreet Marie Curie - Paris VI, 2012. English.

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  • UNIVERSIT DE SHERBROOKEFacult de gnie

    Dpartement de gnie mcaniqueSherbrooke (Qubec) CanadaSpcialit : gnie mcanique

    UNIVERSIT PIERRE ET MARIE CURIEcole doctorale SMAER (ED 391)

    Sciences mcaniques, acoustique, lectronique & robotique de ParisParis, France

    Spcialit : acoustique

    MODLISATION VIBROACOUSTIQUE DEDOUBLE-PAROIS ARONAUTIQUESAVEC LIENS MCANIQUES PAR LA

    MTHODE DE LANALYSE STATISTIQUENERGTIQUE

    VIBRO-ACOUSTIC MODELLING OF AIRCRAFTDOUBLE-WALLS WITH STRUCTURAL LINKS USING

    STATISTICAL ENERGY ANALYSIS

    Thse de doctorat (cotutelle)

    Bruno L. CAMPOLINA

    Jury: Nicolas DAUCHEZ, SUPMECA Co-directeurNoureddine ATALLA, U. de Sherbrooke Co-directeurPascale NEPLE, Airbus Operations SAS Co-encadranteJean-Louis GUYADER, INSA Lyon RapporteurAlain BERRY, U. de Sherbrooke RapporteurVincent MARTIN, CNRS/UPMC PrsidentJos R. F. ARRUDA, UNICAMP ExaminateurMarshall DOWNING, LORD Corporation Examinateur

    Juillet 2012

  • RSUM

    La prdiction du bruit intrieur des avions ncessite la modlisation vibroacoustique delensemble fuselage et traitements acoustiques. Cet ensemble est compos dun panneauraidi mtallique ou composite, sur lequel est pos un traitement thermo-acoustique (lainede verre) et connect par des liens anti-vibratiles un panneau dhabillage de type sand-wich nid dabeille. Lobjectif de ce travail consiste optimiser les traitements acoustiquesen prenant en compte les contraintes de design telles que la masse et les dimensions. A cepropos, une double-paroi reprsentative davion est modlise par la mthode de lanalysestatistique nergtique (SEA). Des excitations acadmiques telles que le champ diffus etla force ponctuelle sont utilises et des tendances sont donnes pour des applications sousexcitation arodynamique, du type couche limite turbulente.

    Une premire partie porte sur leffet de compression dune couche poreuse. Pour des ap-plications aronautiques, la compression de ce type de matriaux peut se produire lorsde linstallation dquipements et cbles. Elle est tudie, de manire analytique et ex-primentale, pour une simple-paroi recouverte par une couche de matriau fibreux. Lematriau est comprim sur toute sa surface. Une rduction de la perte par transmission(TL) jusqu 5 dB est observe principalement en moyennes frquences (autour de 800 Hz)lorsque lpaisseur du poreux est comprim de 50%. Cependant pour des cas plus ralistes,cet effet est suppos moins important pour une compression locale et plus faible.

    Dans une seconde partie, la transmission par les connections structurales entre panneauxest tudie par une approche quadripolaire qui relie la paire force-vitesse de chaque ctdu lien mcanique. La modlisation intgre la raideur dynamique mesure par un bancdessai ddi. La transmission structurale est par la suite valide avec des essais et intgreau modle de double-paroi comme un facteur de couplage entre panneaux. Comme lesstructures sont non-courbes, seule la transmission axiale est considre.

    Enfin, les voies de transmission dominantes sont identifies dans la gamme de frquencesentre 100 Hz et 10 kHz pour des double-parois sous champ diffus et sous excitation struc-turale ponctuelle. La transmission non-rsonante est plus importante en basses frquences(jusqu 1 kHz) alors que les parties structurale et arienne dominent respectivement enmoyennes et hautes frquences. Une validation avec des rsultats exprimentaux montreque le modle est capable de prdire les changements au niveau de la transmission, causspar les diffrents couplages structuraux (couplage rigide, couplage via liens anti-vibratileset dcouplage structural). Des diffrentes solutions en termes de traitement acoustique,comme par exemple labsorption, lamortissement et le dcouplage structural, peuvent parla suite tre drives.

    Mots-cls : Analyse statistique nergetique, Lien anti-vibratile, Double-paroi, Analysede chemins de transfert, Perte par transmission.

    i

  • ABSTRACT

    The prediction of aircraft interior noise involves the vibroacoustic modelling of the fuse-lage with noise control treatments. This structure is composed of a stiffened metallic orcomposite panel, lined with a thermal and acoustic insulation layer (glass wool), and struc-turally connected via vibration isolators to a commercial lining panel (trim). The goal ofthis work aims at tailoring the noise control treatments taking design constraints such asweight and space optimization into account. For this purpose, a representative aircraftdouble-wall is modelled using the Statistical Energy Analysis (SEA) method. Laboratoryexcitations such as diffuse acoustic field and point force are addressed and trends arederived for applications under in-flight conditions, considering turbulent boundary layerexcitation.

    The effect of the porous layer compression is firstly addressed. In aeronautical applica-tions, compression can result from the installation of equipment and cables. It is studiedanalytically and experimentally, using a single panel and a fibrous uniformly compressedover 100% of its surface. When compression increases, a degradation of the transmissionloss up to 5 dB for a 50% compression of the porous thickness is observed mainly in themid-frequency range (around 800 Hz). However, for realistic cases, the effect should bereduced since the compression rate is lower and compression occurs locally.

    Then the transmission through structural connections between panels is addressed usinga four-pole approach that links the force-velocity pair at each side of the connection. Themodelling integrates experimental dynamic stiffness of isolators, derived using an adaptedtest rig. The structural transmission is then experimentally validated and included in thedouble-wall SEA model as an equivalent coupling loss factor (CLF) between panels. Thetested structures being flat, only axial transmission is addressed.

    Finally, the dominant sound transmission paths are identified in the 100 Hz to 10 kHz fre-quency range for double-walls under diffuse acoustic field and under point-force excitations.Non-resonant transmission is higher at low frequencies (frequencies lower than 1 kHz) whilethe structure-borne and the airborne paths dominate at mid- and high-frequencies, around1 kHz and higher, respectively. An experimental validation on double-walls shows thatthe model is able to predict changes in the overall transmission caused by different struc-tural couplings (rigid coupling, coupling via isolators and structurally uncoupled). Noisereduction means adapted to each transmission path, such as absorption, dissipation andstructural decoupling, may be then derived.

    Keywords: Statistical energy analysis, Vibration isolator, Double-wall, Transfer pathanalysis, Transmission Loss.

    iii

  • ACKNOWLEDGEMENTS

    I thank M. Armand Malagoli, ex-responsible for the Airbus Acoustics & Environmentdepartment for accepting my application to integrate the Near-field & Interior noise teamand start the present PhD thesis in collaboration with the University of Sherbrooke, theInstitut Suprieur de Mcanique de Paris (Supmca), the University Pierre and MarieCurie (UPMC), and the Association nationale de la recherche et de la technologie (ANRT).

    I would like to express my sincere gratitude to my thesis supervisors Pascale Neple, Near-field & Interior Noise research coordinator at Airbus; Nicolas Dauchez, professor at Sup-mca and Noureddine Atalla, professor at the University of Sherbrooke. Their valuableadvices and attentive supervision were major contributors to the achievement of my ob-jectives. I appreciate their availability, insightful discussions and expertise shared. I thankthem also for encouraging my participation to several international conferences.

    I address my acknowledgements to all the members of the thesis defence board for theirparticipation as well as for the interest and time dispensed to this work. Special thanksgo to Alain Berry and Jean-Louis Guyader for their detailed reports. Sren Callsen isacknowledged for his participation in the defence board during the defence presentation.Stphane Moreau is also acknowledged for his advices during the pre-PhD examination.

    Thanks to all my colleagues of the Acoustics & Environment department at Airbus, spe-cially the Near-field & Interior noise team at Toulouse and Hamburg for all the technicaldiscussions and good time spent together. Fabien Vieuille, from the numerical simulationsgroup, is also acknowledged for the technical assistance related to Actran FEM modelling.I would also like to acknowledge Rdiger Thomas, Sylvain Miklaszewiski, Pierre Lem-pereur, Klaus Renger, Christophe Ligu and Hugues Rmy for their support, confidence inthis work and for the feedback on research