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  • 1.
    Gaborit, Mathieu
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. LAUM UMR CNRS 6613, Le Mans Université, Le Mans, France.
    Modelling of thin and imperfect interfaces: Tools and preliminary study2018Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    For quite some time, the strive for more efficient acoustic absorbers keepsincreasing, driven by a number of psycho-physiological studies on health re-lated dangers of noise exposure. As the global wealth increases and with itthe global expectation of quieter living and working environments, manifestedin both politics and research, an important market for sound absorbing andnoise control systems develops in all industrialised countries. In the acousticcommunity, the main endeavours of the two last decades have been orientedtowards a better understanding of the dissipation phenomena in absorbers(and especially in poroelastic media) as well as proposing new topologies andstructures for these elements. These efforts have resulted in an abundant lit-erature and numerous improvements of the characterisation, modelling anddesign methodologies for a wide range of media and many different systems.The chosen research direction for the present thesis slightly deviates fromthis usual path of modelling absorbing materials as bulk media. Here theaim is to investigate the interfaces between the different components of typ-ical absorbers. Indeed, these interface regions are known to be difficult tocharacterise and controlling their properties is challenging for a number ofreasons. Interfaces in sound packages for instance are inherently by-productsof the assembly process and, even if they surely have an important impact onthe acoustic performance, they remain mostly overlooked in the establishedmodelling practices. Therefore, the overall objective of the current doctoralproject is to identify strategies and methods to simulate the effect(s) of un-certainties on the interface physical or geometrical parameters.The present licentiate thesis compiles three works which together form adiscussion about techniques and tools designed in an attempt to efficientlymodel thin layers and small details in rather large systems. As part of thework a section of physical model simplifications is discussed which will laythe ground for the next stages of the research. Two publications on the firsttopic are included, presenting Finite-Element-based hybrid methods that al-low for coating elements in meta-poroelastic systems to be taken into accountand reduce the computational cost of modelling small geometric features em-bedded in large domains. The third included contribution is an anticipation,to a certain extent, of the remainder of the doctoral project, discussing theuse of physical heuristics to simplify porous thin film models. Here a steptowards the modelling of interface zones is taken, departing from numericalsimulations and reflecting instead on the physical description and modellingof thin poroelastic layers.

  • 2.
    Gaborit, Mathieu
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. Le Mans Univ, Lab Acoust, CNRS, UMR 6613,Univ Mans, F-72000 Le Mans, France.
    Dazel, Olivier
    Le Mans Univ, Lab Acoust, CNRS, UMR 6613,Univ Mans, F-72000 Le Mans, France..
    Göransson, Peter
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    A simplified model for thin acoustic screens2018Inngår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 144, nr 1, s. EL76-EL81Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A generalization of the commonly used pressure jump modeling of thin porous layers is proposed. The starting point is a transfer matrix model of the layer derived using matrix exponentials. First order expansions of the propagating terms lead to a linear approximation of the associated phenomena and the resulting matrix is further simplified based on physical assumptions. As a consequence, the equivalent fluid parameters used in the model may be reduced to simpler expressions and the transfer matrix rendered sparser. The proposed model is validated for different backing conditions, from normal to grazing incidence and for a wide range of thin films. In the paper, the physical hypotheses are discussed, together with the origin of the field jumps.

  • 3.
    Gaborit, Mathieu
    et al.
    University of Le Mans.
    Dazel, Olivier
    Université du Maine, Le Mans France.
    Göransson, Peter
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. Centre for ECO2 Vehicle Design.
    Gabard, Gwenael
    University of Le Mans.
    Coupling of finite element and plane waves discontinuous Galerkin methods for time-harmonic problems2018Inngår i: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 116, nr 7, s. 487-503Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A coupling approach is presented to combine a wave-based method to the standard finite element method. This coupling methodology is presented here for the Helmholtz equation but it can be applied to a wide range of wave propagation problems. While wave-based methods can significantly reduce the computational cost, especially at high frequencies, their efficiency is hampered by the need to use small elements to resolve complex geometric features. This can be alleviated by using a standard finite element model close to the surfaces to model geometric details and create large, simply-shaped areas to model with a wave-based method. This strategy is formulated and validated in this paper for the wave-based discontinuous Galerkin method together with the standard finite element method. The coupling is formulated without using Lagrange multipliers and results demonstrate that the coupling is optimal in that the convergence rates of the individual methods are maintained.

  • 4.
    Gaborit, Mathieu
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. Université du Maine, Le Mans France.
    Göransson, Peter
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Numerisk akustik. KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design. Centre for ECO2 Vehicle Design.
    Dazel, Olivier
    Université du Maine, Le Mans France.
    Simplification of the transfer matrix model for acoustic screens2018Konferansepaper (Fagfellevurdert)
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