| 1. |
|
|
| 2. |
- Gaborit, Mathieu, et al.
(författare)
-
A simplified model for thin acoustic screens
- 2018
-
Ingår i: Journal of the Acoustical Society of America. - : Acoustical Society of America (ASA). - 0001-4966 .- 1520-8524. ; 144:1, s. EL76-EL81
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
(författare)
-
Controlled anisotropy materials and 3D printing: experimentations and analyses
- 2022
-
Ingår i: Proceedings of ISMA 2022 - International Conference on Noise and Vibration Engineering and USD 2022 - International Conference on Uncertainty in Structural Dynamics. - : KU Leuven, Departement Werktuigkunde. ; , s. 477-481
-
Konferensbidrag (refereegranskat)abstract
- Novel computational tools and optimisation strategies offer an unprecedented framework to explore large design spaces within a short time frame. In the scope of material design, these new possibilities have completely revolutionized the research horizon, leading amongst other things to controlled anisotropy media with a finer granularity than ever seen before. However, a question arises regarding the manufacturability of such media which most of the time relies on 3D printing and the agreement between modelled and printed geometry. In the recent years, the authors published several articles on the properties of Kelvin Cell packings and the possibility to control their anisotropy. In the last few months, an effort towards printing the designed media has been made in search for experimental validation of the numerical results. This contribution describes the printing process for kelvin cell packing samples with controlled anisotropy and analyses their agreement with the model both from a geometric and from a physical response standpoint. Depending on the advances of current research, information on the dynamic behaviour of such systems will be discussed.
|
|
| 4. |
- Gaborit, Mathieu, et al.
(författare)
-
Coupling of Finite-Element and Plane Waves Discontinuous Galerkin methods for time-harmonic problems
- 2018
-
Ingår i: International Journal for Numerical Methods in Engineering. - : John Wiley & Sons. - 0029-5981 .- 1097-0207. ; 116:7, s. 487-503
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 5. |
- Gaborit, Mathieu, et al.
(författare)
-
Erratum: A simplified model for thin acoustic screens [J. Acoust. Soc. Am. 144(1), EL76–EL81 (2018)]
- 2019
-
Ingår i: Journal of the Acoustical Society of America. - : Acoustical Society of America (ASA). - 0001-4966 .- 1520-8524. ; 146:2, s. 1382-1383
-
Tidskriftsartikel (refereegranskat)abstract
- The present erratum reports an error impacting the figures of a contribution published in 2018 about a simplified model for thin acoustic screens in a transfer matrix context [Gaborit, Dazel, and Göransson (2018). J. Acoust. Soc. Am. 144(1), EL76–EL81]. A mistake in the implementation of the rigid termination condition for the systems under study is identified and a correct version is proposed along with the corrected figures. It is shown that this error does not impact the conclusions of the original contribution and that the model proposed therein keeps its advantages as the approximation error remains very similar to the previously reported values.
|
|
| 6. |
- Gaborit, Mathieu, et al.
(författare)
-
Generation of uncertainty envelopes for thin acoustic screens with uncertain parameters
- 2020
-
Ingår i: Acta Acustica. - : EDP Sciences. - 2681-4617. ; 4:3
-
Tidskriftsartikel (refereegranskat)abstract
- The properties of the materials used for building sound proofing systems are known to exhibit large variations. These may lead to significant differences in the acoustic responses within a given material batch, particularly when resistive screens are used as a surface component for a multi-layered absorbing panel. In such thin films, it is mostly the thickness and the flow resistivity, but in some cases also the porosity, that are difficult to control in the production process. All these potential variations influence the acoustic response of the complete panel. In the present contribution, a method to isolate and evaluate the effect of uncertainties in a film is proposed. Using a transmission line approach, it is shown to be possible to predict the modification of the response induced by the uncertainties. The proposed technique is then adapted to determine uncertainty envelopes of the absorption coefficient, for experimentally acquired responses, that are closer to measured envelopes as compared to those generated using Monte Carlo simulations or simplified approaches. The method is tested both on numerical and experimental cases and shows, in both cases, a very good agreement with the reference solutions. Unlike Monte Carlo approaches, the proposed method does not require a massive computational effort which makes it suitable for real life applications.
|
|
| 7. |
- Gaborit, Mathieu, et al.
(författare)
-
Influence of uncertain parameters on the acoustic behaviour of sound proofing laminates
- 2019
-
Ingår i: INTER-NOISE 2019 MADRID - 48th International Congress and Exhibition on Noise Control Engineering. - : SOCIEDAD ESPANOLA DE ACUSTICA - Spanish Acoustical Society, SEA.
-
Konferensbidrag (refereegranskat)abstract
- The protection against excessive noise has gathered a lot of attention along the years. Tailored solutions for specific types of noise conditions emerged and many communications on the subject are published every year. Although designing sound proofing systems is a well developed topic, building the proposed systems is still subject to many uncertainties. For instance, the very nature of the foams used in many broadband absorbers implies a degree of uncertainty on some of the most important parameters (e.g. the airflow resistivity). This phenomenon is even more noticeable in modern sound absorbing laminates in which every interface implies a barely controllable change in the continuity conditions. This effect being rarely accounted for and the interfaces' properties hard to quantify, it adds uncertainties that are widely neglected even though having a potentially strong impact. In this contribution, the effect of randomly distributed parameters on the overall acoustic response of multi-layer systems is considered. The influence of choosing specific acoustic models for each layer is emphasized and the resulting response envelope is studied.
|
|
| 8. |
- Gaborit, Mathieu Maël, et al.
(författare)
-
Coupling FEM, bloch waves and TMM in meta poroelastic laminates
- 2018
-
Ingår i: Acta Acoustica united with Acustica. - : S. Hirzel Verlag GmbH. - 1610-1928 .- 1861-9959. ; 104:2, s. 220-227
-
Tidskriftsartikel (refereegranskat)abstract
- The propagation of airborne plane waves in the presence of a meta poroelastic laminate, that is a poroelastic matrix coated with thin elastic layers at its facings and periodically-embedded with inclusions, is studied. Using the Finite Element Method (FEM) only would result in a drastic increase of the degrees of freedom due to the fine mesh required to account for the very thin coatings. Here, the approach relies on: The Bloch wave expansion of the fields in air; the modal Transfer Matrix Method to account for the coatings; and the coupling with the FEM model of the poroelastic matrix and the resonant inclusions. The model is developed for reflection and transmission problems and it can account for coatings with multiple layers. The procedure induces the addition of the Bloch coefficients in the FEM's linear system at a negligible additional computational cost. It is applied to the meta poroelastic laminates with poroelastic inclusions and rubber shell inclusions. The results are compared with those from the Multiple Scattering Theory and an excellent agreement between the methods is found. The approach offers a numerically-efficient way to account for coatings applied to meta poroelastic layers, and finds applications in industrial prototypes where coatings are widely used.
|
|
| 9. |
- Gaborit, Mathieu
(författare)
-
Modelling of thin and imperfect interfaces : Tools and preliminary study
- 2018
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
|
|
| 10. |
- Gaborit, Mathieu
(författare)
-
Modelling strategies for thin imperfect interfaces and layers
- 2019
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The global trend towards quieter environments has been one of the key topics of acoustics research for years. The recent tightening of the regulations on noise exposure as well as the many reports on the impact of noise on human health confirm this situation and stress ever more the need for innovative mitigation strategies. Numerous efforts from many teams allowed to refine existing solutions and explore new approaches towards a lower noise level ultimately leading to a number of promising concepts. Central to this field, the use of poroelastic media and the development of realistic meta-materials are paving the way to tackle the problem. In the meantime, a great part of the most widely adopted systems to mitigate noise, such as acoustics panels for instance, resort to thin resistive screens placed on the surface to protect the bulk and control the properties. Despite often being one of the thinnest components of the systems, they have a non-negligible impact on the overall response and are subject to a number of uncertainties.The approach chosen in this thesis differs from the global trend of designing new solutions and conversely relies on investigating the effect of uncertainties inherent to all these sound proofing systems. More precisely, the work performed focuses on modelling the impact of uncertain interfaces and uncertain parameters in the thin layers used as protective, tuning or aesthetic elements. These acoustic films, and to a certain extent the thin interface zones resulting from the assembly process, are notably challenging to characterise with precision. The main goal of this thesis is then to propose strategies to account for uncertainties on the parameters of the films and interfaces and predict their impact on the overall response of the systems.Three different scientific contributions are presented in this thesis. Together they discuss modelling aspects related to the films, propose possible simplifications and demonstrate the effect of parameter uncertainties. Finally they introduce numerical strategies to efficiently account for uncertainties in computations within the context of poroelastic and meta-poroelastic media.
|
|
| 11. |
- Gaborit, Mathieu, et al.
(författare)
-
Off-line envelope estimation for acoustic screens with uncertain properties
- 2019
-
Ingår i: Proceedings of the International Congress on Acoustics. - : International Commission for Acoustics (ICA). - 9783939296157 ; , s. 1992-1999
-
Konferensbidrag (refereegranskat)abstract
- The development of new solutions to reduce impact of noise receives constant attention both from the research and engineering communities. Even though the proposed systems tend to diversify, multi-layered absorbers based on foams remain the most common. Such structures feature one or several thick slabs of foam and are completed by protective or tuning layers of small thickness inserted between slabs or on the free surface. These layers (acoustics screens or films) bring a number of challenges. Firstly, their thickness makes them hard to characterise and some parameters are uncertain. Secondly, the bonding to the surrounding system alter the effective properties. Given the strong influence the films have on the system's response, it appears important to account for these uncertainties from the design phase on. The present contribution introduces a new technique to efficiently account for uncertainty linked to the screens. More precisely, the proposed approach is based on separating the average film influence from the deviation due to uncertainties. This allows to estimate the response envelope using a pre-computed average response and the properties. The results computed for a range of typical and challenging configurations are promising and validate the robustness of the method at any angle of incidence.
|
|
| 12. |
- Gaborit, Mathieu, et al.
(författare)
-
Reinforcement Learning to Refine FEM Meshes for Acoustic Problems
- 2022
-
Ingår i: Proceedings Of The 4Th International Conference On Numerical Modelling In Engineering. - Singapore : Springer Nature. ; , s. 209-215
-
Konferensbidrag (refereegranskat)abstract
- Numerical methods are central to modern engineering and the Finite Element Method (FEM) specifically is used in a variety of domains and for countless applications. One of the main challenges of using FEM lies in the choice of parameters to generate the mesh. This is particularly the case in acoustics. Indeed, for the phenomena to be correctly modelled, the mesh parameters must be chosen in concordance with the frequency range of interest. So far, the choices regarding the mesh are mostly guided by past experience or widely accepted guidelines (for instance 7-10 points per wavelength when using quadratic elements). In this contribution, we explore the use of reinforcement learning to construct and refine a FEM mesh. This technique implies that the machine is learning how to complete a given task based solely on the so-called state of the environment (including a measure of the error on the result). The key aspect of this research is to challenge the traditional guidelines used for acoustic problems by letting a machine explore and converge without human intervention. The overall strategy will be introduced and demonstrated on simple problems, the results compared with pre-existing recommendations and the challenges ahead will be briefly presented.
|
|
| 13. |
|
|
| 14. |
|
|
| 15. |
- Gaborit, Mathieu, et al.
(författare)
-
Towards fully controlled anisotropy in cellular porous media : An overview
- 2021
-
Ingår i: Proceedings of INTER-NOISE 2021 - 2021 International Congress and Exposition of Noise Control Engineering. - : Institute of Noise Control Engineering (INCE). ; , s. 5253-5259
-
Konferensbidrag (refereegranskat)abstract
- In the recent years, our team has been working to identify key aspects of anisotropy in porous media. More than just characterising their anisotropic properties, we're interested in generating cellular media with completely designed anisotropic properties. The results of these studies have partly been published and more are to come. In this presentation, we'll present an overview of this work and how it ultimately ties to acoustics. We will introduce the key findings,discussed specific results that can be achieved and provide context and details related to the strategy developed to address the tasks.
|
|
| 16. |
- Lundberg, Eva, 1964-, et al.
(författare)
-
Tuning sound transmission loss for multi-layer panels with anisotropic foams
- 2022
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Multilayer panels consisting of a load carrying structure, a porous material for thermal and acoustic insulation and an interior trim panel is a very common type of design for vehicles. Weight as well as total build height are usually limiting constraints on the design. The idea of using an anisotropic porous material instead of an isotropic one to improve the sound transmission loss without adding a lot of weight or thickness is explored in the paper. By using a state space formulation of the transfer matrix method transmission loss it is possible to include anisotropic material properties in the calculation. The anisotropic material is modelled by a combination of a simplified analytical model for the acoustic losses and inverse estimation of the 21 independent elastic constants of the Hooke’s tensor. The porous material, which has typical dimensions possible to 3D print, is based on a Kelvin cell micro model that has a controlled degree of anisotropy.
|
|
| 17. |
- Mao, Huina, et al.
(författare)
-
Dynamic behaviour of low- to high-density anisotropic cellular materials
- 2022
-
Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 536
-
Tidskriftsartikel (refereegranskat)abstract
- The dynamic behaviour of a novel anisotropic cellular micro-structural geometry derived from the basic symmetric Kelvin cell is discussed for varying relative density. The cells are arranged in a cubic array and the dynamic response is studied in a classical seismic mass setup using beam elements to represent the ligaments of the cell. The eigenfrequencies and the eigenmodes of the cellular array are computed together with forced response simulations where a proportional damping model of the Young's modulus for the cell ligaments is assumed. The frequency dependence of the damping is based on a fractional derivative representation. Using a recently developed inversion method, equivalent, homogenised solid material models of the cellular array are discussed with the associated equivalent elastic properties given in terms of the 21 elastic constants of the Hooke's tensor. For the equivalent solid material models, the eigenfrequencies and eigenmodes are computed, and forced response simulations are performed assuming the same type of proportionality in the damping as the cellular array, for the same seismic mass setup. The correlation, between the eigenfrequencies and the eigenmodes, shows an overall interesting agreement between the cellular and the equivalent solid model for the quite complex deformation shapes observed. The forced response results indicate that the equivalent solid modelling accurately represents the global dynamics of the anisotropic cellular array, but needs to be further refined when local shearing deformation within the individual cells starts to be dominating.
|
|
| 18. |
- Mao, Huina, et al.
(författare)
-
Twist, tilt and stretch: From isometric Kelvin cells to anisotropic cellular materials
- 2020
-
Ingår i: Materials & design. - : Elsevier BV. - 0264-1275 .- 1873-4197. ; 193
-
Tidskriftsartikel (refereegranskat)abstract
- Simple geometric distortions applied to the isometric Kelvin cell structures, (the tetrakaidecahedron), are shown to result in equivalent materials with anisotropic Hooke's tensors. The equivalent material models are estimated using a recently published inversion method where the 21 independent elastic constants of the Hooke's tensor are identified. In these cell geometries, some of the faces of the Kelvin cell have been twisted and/or tilted. Numerical experiments suggest that the equivalent material models of the distorted cells exhibit variations in compression, shearing, shear-compression and shear-shear coupling moduli, which are shown to be continuous functions of the degree of twist and tilt applied. When twist and tilt are combined, it is demonstrated that full anisotropy in the elastic properties may be generated. A rotational symmetry without symmetry planes, but having either a tetragonal or a monoclinic elastic symmetry is discussed. Four cell geometries, one isometric and three distorted, were manufactured using masked stereolithography 3D printing technology and measured in a laboratory compression set-up. Results from numerical simulations are compared to the experimental in terms of the compressive modulus.
|
|
| 19. |
- Mao, Huina, et al.
(författare)
-
Vibro-acoustic behaviour of low- to high-density anisotropic cellular foams
- 2020
-
Ingår i: PROCEEDINGS OF INTERNATIONAL CONFERENCE ON NOISE AND VIBRATION ENGINEERING (ISMA2020) / INTERNATIONAL CONFERENCE ON UNCERTAINTY IN STRUCTURAL DYNAMICS (USD2020). - : KATHOLIEKE UNIV LEUVEN, DEPT WERKTUIGKUNDE. ; , s. 451-461
-
Konferensbidrag (refereegranskat)abstract
- The paper discusses the vibro-acoustic behaviour of a recently proposed novel anisotropic cellular foam geometry derived from the basic symmetric Kelvin cell geometry. The associated equivalent elastic material properties are estimated based on a recently developed inversion method, in terms of the 21 elastic constants of the Hooke's tensor. The dynamic behaviour of the cellular material configuration and its homogeneous model by applying the equivalent material properties are studied under arbitrary excitation. The correlation between the vibro-acoustic behaviour, foam density, and material anisotropy is studied based on finite element simulations. High correlations of eigenfrequency and eigenmode shapes between the target cellular foam model and the equivalent solid model are found. A set of empirical relations are proposed, linking the micro-structure in low to high relative density for the anisotropic cellular geometries investigated. Potential applications in vibro-acoustic of the proposed anisotropic foam are discussed
|
|
| 20. |
- Zieliński, Tomasz G., et al.
(författare)
-
Reproducibility of sound-absorbing periodic porous materials using additive manufacturing technologies : Round robin study
- 2020
-
Ingår i: Additive Manufacturing. - : Elsevier B.V.. - 2214-8604 .- 2214-7810. ; 36
-
Tidskriftsartikel (refereegranskat)abstract
- The purpose of this work is to check if additive manufacturing technologies are suitable for reproducing porous samples designed for sound absorption. The work is an inter-laboratory test, in which the production of samples and their acoustic measurements are carried out independently by different laboratories, sharing only the same geometry codes describing agreed periodic cellular designs. Different additive manufacturing technologies and equipment are used to make samples. Although most of the results obtained from measurements performed on samples with the same cellular design are very close, it is shown that some discrepancies are due to shape and surface imperfections, or microporosity, induced by the manufacturing process. The proposed periodic cellular designs can be easily reproduced and are suitable for further benchmarking of additive manufacturing techniques for rapid prototyping of acoustic materials and metamaterials.
|
|
