| 1. |
- Cameron, Christopher, et al.
(författare)
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Balancing structural and acoustic performance of sandwich panels for vehicle applications with topology, property, and size optimization
- 2010
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Ingår i: 7th Asian-Australasian Conference on Composite Materials 2010, ACCM 2010. - : ACCM-7 Organizing Committee. - 9781632660756 ; , s. 835-838
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Konferensbidrag (refereegranskat)abstract
- Within this paper, a process for the design of a multifunctional sandwich body panel for vehicle applications is proposed. The method, presented with a case study, attempts to achieve a balance between structural and acoustic performance using numerical tools for topology optimization and combined size and property optimization. The goal of the work is to achieve an optimal distribution of traditional sandwich foam material and light weight acoustic foam within the core of the panel. The significance of the coupling between the panels inner face sheet and the acoustic foam is examined and proves to be a critical parameter in the design. An adaptation to existing topology optimization schemes is proposed to deal with the presence or absence of such a coupling. The results show promise in simplifying construction, reducing weight, and streamlining the assembly process.
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| 2. |
- Cuenca, Jacques, et al.
(författare)
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A general methodology for inverse estimation of the elastic and anelastic properties of anisotropic open-cell porous materials-with application to a melamine foam
- 2014
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 115:8, s. 084904-
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Tidskriftsartikel (refereegranskat)abstract
- This paper proposes an inverse estimation method for the characterisation of the elastic and anelastic properties of the frame of anisotropic open-cell foams used for sound absorption. A model of viscoelasticity based on a fractional differential constitutive equation is used, leading to an augmented Hooke's law in the frequency domain, where the elastic and anelastic phenomena appear as distinctive terms in the stiffness matrix. The parameters of the model are nine orthotropic elastic moduli, three angles of orientation of the material principal directions and three parameters governing the anelastic frequency dependence. The inverse estimation consists in numerically fitting the model on a set of transfer functions extracted from a sample of material. The setup uses a seismic-mass measurement repeated in the three directions of space and is placed in a vacuum chamber in order to remove the air from the pores of the sample. The method allows to reconstruct the full frequency-dependent complex stiffness matrix of the frame of an anisotropic open-cell foam and in particular it provides the frequency of maximum energy dissipation by viscoelastic effects. The characterisation of a melamine foam sample is performed and the relation between the fractional-derivative model and other types of parameterisations of the augmented Hooke's law is discussed.
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| 6. |
- Dovstam, Krister, et al.
(författare)
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Is damping additive? : On the accumulated effect of interface damping and material damping
- 2010
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Traditionally the structural loss factor of a vibrating structure at resonance is defined by the half power bandwidth which then incorporates all mechanisms, e. g. material damping, interface damping, added viscoelastic damping, acoustic damping and damping in joints, contributing to the total damping. Damping measures based on vibration response data and vibration energy dissipated locally at interfaces and in material volumes may be computed in post processing finite element computations. Appropriately defined measures may then localize the damping to interfaces and material volumes where the dissipation actually occurs. It is also possible to separate and quantify the damping contributions from different damping sources. The interaction and combined effect of mixed material and interface damping is studied for a simple, three dimensional, build-up structure containing overlapping contact interfaces and internal regions with material damping. Results are presented based on damping measures which separate damping contributions from different contact interfaces and internal material volumes. By comparison of the total structural damping with partial contributions, from the specific damping sources occurring in each case, the combined, accumulated, effect of the different sources is investigated. The question whether different kinds of damping is additive or not is finally addressed.
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| 7. |
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| 8. |
- Gao, Kun, et al.
(författare)
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Microstructure-based numerical modeling of the solid-fluid coupling interaction in acoustic foams
- 2013
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Ingår i: Poromechanics V - Proceedings of the 5th Biot Conference on Poromechanics. - Reston, VA : American Society of Civil Engineers. ; , s. 2123-2130
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Konferensbidrag (refereegranskat)abstract
- In this paper, based on a representative volume element (RVE) and Slattery’s averaging theorem, parameters of Biot’s poroelastic equations for homogenous isotropic porous materials are obtained. According to Slattery’s averaging theorem, the coupling terms, which describe the inertial effects and the viscous effects, are represented by an integral of the solid-fluid interaction force. This relation provides a new approach to obtain the parameters required in Biot’s equations through a direct numerical simulation of the RVE. An example of a 2D RVE is given and simulations of sound propagation in an impedance tube with a foam are conducted using Biot’s equations. It is shown that the numerical coupling mass obtained from this new approach behaves qualitatively the same as an associated phenomenological model.
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| 9. |
- Gao, Kun, et al.
(författare)
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Microstructure-based numerical modelling of foams for acoustic shielding
- 2014
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Ingår i: 21st International Congress on Sound and Vibration 2014, ICSV 2014. - : International Institute of Acoustics and Vibrations. - 9781634392389 ; , s. 881-887
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Konferensbidrag (refereegranskat)abstract
- In this paper, a numerical homogenization approach is proposed to obtain isotropic Biot's parameters based on the microstructure of an porous material. It is assumed that a macroscopic point can be represented by a microscopic Representative Volume Element (RVE) consisting of the solid and the fluid. The macroscopic properties are controlled by Biot's equations and the RVE is governed by linearized balance equations for momentum and linear constitutive laws. With suitable boundary conditions, the micro-macro relation is formulated based on consistency of energy. Then, Biot's parameters are calculated through the response of the RVE. By following this new homogenization approach, examples with simple microstructures are given and simulations of two sound absorption experiments are conducted by using Biot's equations. The results are compared with Direct Numerical Simulations and it shows a favourable performance of this new approach compared to the alternative Transfer Matrix Method.
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| 16. |
- Göransson, Peter, 1959-, et al.
(författare)
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Vibro-acoustic energy propagation in anisotropic, anelastic porous materials
- 2014
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Ingår i: Proceedings of the 9th International Conference on Structural Dynamics, EURODYN 2014. - 9789727521654 ; , s. 83-90
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Konferensbidrag (refereegranskat)abstract
- Historically, the modelling of the acoustics of poro-elastic materials (APEMs) has assumed the materials to be isotropic in both their elastic as well as their acoustic properties including the dissipative mechanisms related to viscous, inertialand thermal interactions. While this is a reasonable approximation when the absorption of sound is of interest, it fails to provide meaningful results for most foamed materials in general and for certain sets of boundary conditions involving elastic contact with solids or other APEMs in particular. A general modelling of fully anisotropic APEMs will be reviewed and taken as a starting point for a series of numerical experiments focussing on aspects of propagation of vibro-acoustic energy, in a homogeneous layer as well as in multiple layer arrangements. From previous works it is known that the influence of anisotropy may be quite significant, in particular for structure-borne vibro-acoustic energy. In addition, it is known that the alignment of principal directions may have substantial influence on the transmission of vibro-acoustic energy. These findings will be recalled in order to prepare for a discussion on the aspects of the directional dependence of the anelastic moduli which will be the core of the presentation at the conference. Real material tensors may be constructed from a superposition of these anisotropic contributions, in the most general case, not necessarily sharing the same principal directions. Starting from these fully anisotropic constitutive tensors with general symmetry properties, studies of optimal alignment between conservative and dissipative tensors, as well as between different materials in various configurations of interest, will be illustrated in the lecture.
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| 17. |
- Göransson, Peter, 1959-, et al.
(författare)
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Vibro-acoustic modelling of anisotropic porous elastic materials: A preliminary study of the influence of anisotropy on the predicted performancein a multi-layer arrangement.
- 2010
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Ingår i: Acta Acoustica united with Acustica. - 1610-1928 .- 1861-9959. ; 96, s. 258-265
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Tidskriftsartikel (refereegranskat)abstract
- During the recent years considerable efforts have been spent on developing numerical models and performing the necessary characterisation of elastic, dynamic and acoustic properties of porous materials. Originally having been considered to be isotropic, such materials have lately also been studied in terms of their anisotropic properties. In this paper, the influence of anisotropy on the vibroacoustic performance is illustrated and evaluated for a multi-layer configuration with varying boundary conditions between the porous material and a solid plate. The paper starts with a brief review of a recently published anisotropic, mixed displacement pressure weak formulation with a particular emphasis on the anisotropic properties. Using the material properties for a hypothetical porous foam model, the predicted response is evaluated. The influence of anisotropy is found to be significant in terms of response amplitude and apparent damping. For some boundary conditions the predicted response is an order of magnitude lower for the anisotropic material model, in particular for frequency ranges where the dynamics of the foam are significant.
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| 18. |
- Krank, Benjamin, et al.
(författare)
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Tuning spot weld models for vehicle body structural dynamics
- 2012
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Ingår i: Proceedings Of International Conference On Noise And Vibration Engineering (ISMA2012) / International Conference On Uncertainty In Structural Dynamics (USD2012). - : Katholieke Universiteit Leuven. - 9789073802896 ; , s. 3915-3926
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Konferensbidrag (refereegranskat)abstract
- Efforts focussing on modelling of spot welds in typical automotive structures have been spent during the last decades resulting in a number of different modelling techniques. One of the crucial aspects common to all these approaches is the difficulties related to the local complexity of the modelling of the actual connections. In order to handle this complexity, spot weld models are often dependent on parameters tuning their characteristics. This paper discusses the tuning of two different spot weld models with respect to certain parameters; the RBE3-Hexa-RBE3 model (also known as the ACM 2) and the Spider2 model available in the pre-processor Ansa. With the current trend towards increasingly refined finite element model meshes, current guide lines need to be updated and elaborated further in order to identify the best performing models. In this paper, model studies are discussed targeting tuning of spot weld parameters together with a new proposal for an exact method for updating the Young's modulus and density of isotropic shell structures analytically using an initial FE calculation.
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| 19. |
- Lundberg, Eva, et al.
(författare)
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Sensitivity of macroscopic properties of a multi-layer panel including porous material on the micro-level parameters of an open cell porous material
- 2014
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Ingår i: PROCEEDINGS OF INTERNATIONAL CONFERENCE ON NOISE AND VIBRATION ENGINEERING (ISMA2014) AND INTERNATIONAL CONFERENCE ON UNCERTAINTY IN STRUCTURAL DYNAMICS (USD2014). - 9789073802919 ; , s. 2135-2149
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Konferensbidrag (refereegranskat)abstract
- The micro-structure of an open cell porous material is modelled as an idealized, periodic structure, allowing anisotropic properties to form on the micro-scale. Using simple analytic descriptions of acoustic and elastic properties calculated from micro-structure geometry, the microstructural properties can be linked to averaged macroscopic elasto-acoustic properties, which can be measured and observed. These macro level properties may be deduced from measurements on a sample of a porous material which is at least a few centimetres across. The most common of the acoustic properties are the flow resistivity or the (dynamic) permeability, the porosity and the viscous and thermal characteristic lengths, together with the tortuosity. For the elasticity, the moduli of the Hooke's law are the most important. The underlying motivation for the current work is that the quantities are interdependent since they all depend on the micro geometry. Thus, to design the macro level acoustic properties for a required performance, physically relevant models linking these to the micro structure would be necessary. In this paper, a set of such models are proposed and utilising these, the influence of the anisotropy on acoustic properties of the foam as well as the transmission loss of a multi-layer plate is investigated. Typical macro level acoustic properties of open cell poro-elastic materials calculated from micro structure parameters are found to give results of the same order of magnitude as measured data found in the literature. Further, the model is applied to evaluate transmission loss of roof constructions with isotropic and anisotropic foam. It is shown that the sound reduction can be improved without changing the overall surface weight of the structure by making use of the anisotropy of the foam. The results Underline the importance of anisotropy and in addition provide guidance for further research.
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| 20. |
- Nadampalli, Ravi Varma, et al.
(författare)
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Finite element formulation and implementation of poroelastic materials in an unbonded case
- 2012
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Ingår i: International Conference on Noise and Vibration Engineering 2012, ISMA 2012, including USD 2012: International Conference on Uncertainty in Structure Dynamics. - : Katholieke Universiteit Leuven. - 9781622768257 ; , s. 1815-1825
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Konferensbidrag (refereegranskat)abstract
- Porous material modelling in the automotive industry is gaining more importance due to the ever increasing need for reducing the weight of the car body. This trend towards weight reduction makes it all the more important to optimize acoustic treatments. Extensive research has been done on understanding the physical behaviour of porous materials and their applications. However, when it comes to design, efficient predictive tools are needed in order to allow industrial applications to be performed at a reasonable costs, i.e. time and computation resources. During the product development cycle for the computations with trim body, a good correlation can be found between the measurements and the simulations in the low frequency region. But there is more effort needed in understanding the physical behaviour of trim components when coupled with structural parts, to improve prediction accuracy in the mid frequency region. Finite element techniques are widely used in computing trimmed vehicle bodies but modelling of poroelastic materials frequently requires refined meshes. This implies an increased amount of resources needed to solve the problem, both in terms of computational time and memory allocation. As a consequence, the computational costs increase substantially when a fully trimmed car body is analysed and compared to a body-in-white structure. This paper discusses one particular aspect in the modelling of trimmed vehicle bodies, namely the coupling conditions along the surfaces where the trim and the sheet metal are interfacing. These conditions are known to vary for a number of reasons, mostly production related, and bring in sources of variation among similar car bodies leading to a higher degree of uncertainty in the NVH behaviour, potentially affecting the possibilities of optimizing the overall system performance. In this paper, an investigation of the interfacial boundary conditions in general and the partially bonded and partially un-bonded coupling conditions in particular, will be discussed. The sensitivity to variations in the contact, both area and location will be illustrated, in order to increase the level of understanding in the modelling of the trim components, when compared by numerical simulations on a CAE model and a simplified test set-up.
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| 23. |
- Rumpler, Romain, 1983-, et al.
(författare)
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A finite element solution strategy based on Padé approximants for fast multiple frequency sweeps of coupled elastic, poroelastic, and internal acoustic problems
- 2013
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Ingår i: Journal of the Acoustical Society of America. - : Acoustical Society of America (ASA). - 0001-4966 .- 1520-8524. ; 133:5, s. 3241-3241
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Tidskriftsartikel (refereegranskat)abstract
- Analyses involving structural-acoustic finite element models including three-dimensional modeling of porous media are, in general, computationally costly. While being the most commonly used predictive tool in the context of noise and vibrations reduction, efficient solution strategies enabling the handling of large-size multiphysics industrial problems are still lacking, particularly in the context where multiple frequency response estimations are required, e.g., for topology optimization, multiple load cases analysis, etc. In this work, an original solution strategy is presented for the solution of multi-frequency structural-acoustic problems including poroelastic damping. Based on the use of Padé approximants, very accurate interpolations of multiple frequency sweeps are performed, allowing for substantial improvements in terms of computational resources, i.e., time and memory allocation. The method is validated and demonstrated for its potential on 3D applications involving coupled elastic, poroelastic, and internal acoustic domains.
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| 24. |
- Rumpler, Romain, et al.
(författare)
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A Padé approximant reconstruction scheme for fast resolution of structural-acoustic finite element models including porous materials.
- 2012
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Konferensbidrag (refereegranskat)abstract
- In this work, an efficient solution strategy is investigated for the resolution of multi-frequency structural-acoustic problems including 3D modelling of poroelastic materials. The finite element method is used, together with a combination of a modal-based reduction of the poroelastic domain and a Pad´e-based reconstruction approach. It thus takes advantage of the reduced-size of the problem while further improving the computational efficiency by limiting the number of frequency resolutions of the original problem. An adaptive procedure is proposed for the discretization of the frequency range into frequency intervals of reconstructed solution. The validation is presented on a 3D poro-acoustic example.
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| 25. |
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