| 1. |
- Cuenca, Jacques, et al.
(författare)
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Inverse estimation of the elastic and anelastic properties of anisotropic foams : study of the static/dynamic separation.
- 2015
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Ingår i: EURONOISE 2015.
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Konferensbidrag (refereegranskat)abstract
- This paper investigates the modelling and characterisation of the porous frame of anisotropic open-cell foams. The main objective is to nd a suitable model for describing the elastic and anelasticproperties of the material by making as few assumptions as possible. The proposed model is basedon a fractional di erential equation, taking into account the deformation memory of the materialin a versatile and compact manner. In the frequency domain, this results in an augmented Hooke'slaw, where the sti ness matrix of the porous frame consists of a superposition of a fully-relaxed,frequency-independent elastic part, and a dynamic, frequency-dependent anelastic part. In order toestimate the properties of the material and to determine if the elastic and anelastic parts sharethe same material symmetry, two separate experiments are performed. A static photometry setup isdesigned, where a cubic sample of material is compressed along each of the three directions of spacewhile the deformation is recorded on the four exposed faces. Furthermore, a dynamic measurementof a set of transfer functions between each pair of opposed faces of the sample is performed. Thecharacterisation methodology consists of an inverse estimation of the parameters of the model. Thisis acheved by replicating each experiment as a nite element simulation and tting the model byusing an optimisation algorithm. The static and dynamic observations serve as a basis for discussingthe independence of the elastic and anelastic properties of the material.
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| 2. |
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| 3. |
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| 4. |
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| 5. |
- Göransson, Peter, 1959-, et al.
(författare)
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Parameter estimation in modelling frequency response of coupled systems using a stepwise approach
- 2019
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Ingår i: Mechanical systems and signal processing. - : Elsevier BV. - 0888-3270 .- 1096-1216. ; 126, s. 161-175
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Tidskriftsartikel (refereegranskat)abstract
- This paper studies the problem of parameter estimation in resonant, acoustic fluid-structure interaction problems over a wide frequency range. Problems with multiple resonances are known to be subjected to local minima, which represents a major challenge in the field of parameter identification. We propose a stepwise approach consisting in subdividing the frequency spectrum such that the solution to a low-frequency subproblem serves as the starting point for the immediately higher frequency range. In the current work, two different inversion frameworks are used. The first approach is a gradient-based deterministic procedure that seeks the model parameters by minimising a cost function in the least squares sense and the second approach is a Bayesian inversion framework. The latter provides a potential way to assess the validity of the least squares estimate. In addition, it presents several advantages by providing invaluable information on the uncertainty and correlation between the estimated parameters. The methodology is illustrated on synthetic measurements with known design variables and controlled noise levels. The model problem is deliberately kept simple to allow for extensive numerical experiments to be conducted in order to investigate the nature of the local minima in full spectrum analyses and to assess the potential of the proposed method to overcome these. Numerical experiments suggest that the proposed methods may present an efficient approach to find material parameters and their uncertainty estimates with acceptable accuracy.
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| 6. |
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| 7. |
- Manzari, Luca, et al.
(författare)
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A fully automated high-speed optical rig for in vacuo, full field, non-contact vibration measurements for viscoelastic, anisotropic materials
- 2018
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Ingår i: Proceedings of NOVEM 2018 Noise and vibration emerging methods. ; , s. 91-102
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Konferensbidrag (refereegranskat)abstract
- In this paper, a setup for measuring the three-dimensional displacement field of a test object un-dergoing controlled dynamic excitation in a vacuum chamber is presented. The setup has beendesigned with porous materials in mind, yet is suitable for the measurement of anisotropic vis-coelastic solids in general. To achieve non-contact data acquisition, a stereo high-speed camerasystem measures the displacement of the foundation and of the test object. A laser Doppler vi-brometer is used before the actual measurement to choose an excitation level that maximizes thesignal-to-noise ratio while allowing to ensure that the test object is fully relaxed and stable at thebeginning of every measurement. The setup, comprising both commercial and in-house hardwareand software solutions, addresses the challenges of measuring in vacuum with non-contact tech-niques. All these aspects are discussed in the current paper, and preliminary results are presented.The ultimate objective is to estimate the dynamic properties of a material using inverse methodsand the data obtained.
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| 8. |
- Manzari, Luca, et al.
(författare)
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Experimental-numerical methods for inverse characterization of the anisotropic-anelastic properties of porous materials, based on dynamic Digital Image Correlation
- 2018
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Ingår i: Proceedings of ISMA 2018 - International Conference on Noise and Vibration Engineering and USD 2018 - International Conference on Uncertainty in Structural Dynamics. - 9789073802995 ; , s. 687-695
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Konferensbidrag (refereegranskat)abstract
- One of the major challenges in accurately modeling poroelastic materials is the choice of the parametersrequired for their modeling, immediately followed by the practical difficulty in obtaining them. The direc-tional dependencies of the physical properties further complicate the task of designing experimental setupscapable of providing the macroscopic properties. In the work presented here, the focus has been set on theacquisition of high quality displacement data by means of two high-speed cameras and 3D Digital ImageCorrelation. The obtained displacement field, is fed into a general inverse formulation which is guided by anoptimization tool that minimizes the difference between the predicted and the measured data. As a minimumis found, the corresponding parameters are interpreted as material properties for a certain physical model.The solutions for each iteration are calculated with numerical prediction tools, in the cases discussed herethe finite element method, where it must be ascertained that the numerical errors are kept to a minimal level
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| 9. |
- Manzari, Luca, et al.
(författare)
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Toward fully anisotropic viscoelastic material models using an automated high-speed optical rig
- 2018
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Ingår i: 13TH INTERNATIONAL CONFERENCE ON VIBRATION MEASUREMENTS BY LASER AND NONCONTACT TECHNIQUES, 2018. - : IOP PUBLISHING LTD.
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Konferensbidrag (refereegranskat)abstract
- This paper describes some of the algorithms that are employed in the post-processing of the data obtained from an automated high-speed optical rig. The setup, entirely designed by some of the authors, is used for measuring the full field displacement in time of anisotropic viscoelastic solids undergoing controlled dynamic excitation. The setup main goal is to provide complex transfer functions relating the three-dimensional sinusoidal displacement on the surface of the sample to the sinusoidal motion of the foundation, suitable for the inverse estimation of the dynamic properties of the material under analysis. The complete automation of the measurement process aims at maximizing repeatability and signal-to-noise ratio. In particular, a stereo high-speed camera system is responsible for the actual measurement, while a laser Doppler vibrometer is used for a preliminary autoranging procedure and for data validation. The camera system does not directly output the high-quality data that is needed for a successful, physically meaningful inverse estimation. Hence, here the algorithms described in this paper come into play. Since digital image correlation (DIC) may fail in some frames or in some regions of the pictures, a mask is applied and calculated for every measurement run to preserve information only where the success rate of the DIC algorithm is higher than a specified threshold. The sample is mounted on a foundation whose sides are flat: random sample consensus (RANSAC) and principal component analysis (PCA) are used to respectively eliminate outliers and find the best fitting plane to the foundation side - the measured displacement field can then be expressed in a local coordinate system, truly relative to the foundation. The transfer functions are now obtained in two steps: first an optimizer is used to fit a cosine to all the measured displacement time-series, then the complex amplitudes representing the motion of the sample faces are divided by the average of the complex amplitudes representing the motion of the foundation.
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| 10. |
- Parra Martinez, Juan Pablo, 1985-, et al.
(författare)
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Acoustic analysis of anisotropic poroelastic multilayered systems
- 2016
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 119:8, s. 084907-
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Tidskriftsartikel (refereegranskat)abstract
- The proposed method allows for an extended analysis of the wave analysis, internal powers, and acoustic performance of anisotropic poroelastic media within semi-infinite multilayered systems under arbitrary excitation. Based on a plane wave expansion, the solution is derived from a first order partial derivative as proposed by Stroh. This allows for an in-depth analysis of the mechanisms controlling the acoustic behaviour in terms of internal powers and wave properties in the media. In particular, the proposed approach is used to highlight the influence of the phenomena intrinsic to anisotropic poroelastic media, such as compression-shear coupling related to the material alignment, the frequency shift of the fundamental resonance, or the appearance of particular geometrical coincidences in multilayered systems with such materials.
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| 11. |
- Parra Martinez, Juan Pablo, 1985-, et al.
(författare)
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Calculation of internal powers for anisotropic porous materials within multilayered structures based on plane wave approximation
- 2015
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper presents a method for calculating internal powers of multilayered configurations with anisotropic porous materials. The methodology takes a plane wave solution for anisotropic multilayered structures as a mathematical base for the derivation of the corresponding integral expressions. Different physical phenomena within the assessed structure can be then studied in detail as a whole or in terms of partial contributions to the total power balance. In the paper, an analysis of the dissipation in an anisotropic porous material as a function of its material coordinate orientation is performed.
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| 12. |
- Parra Martinez, Juan Pablo, 1985-, et al.
(författare)
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Derivation of the state matrix for dynamic analysis of linear homogeneous media
- 2016
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Ingår i: Journal of the Acoustical Society of America. - : Acoustical Society of America (ASA). - 0001-4966 .- 1520-8524. ; 140:2, s. EL218-EL220
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Tidskriftsartikel (refereegranskat)abstract
- A method to obtain the state matrix of an arbitrary linear homogeneous medium excited by a plane wave is proposed. The approach is based on projections on the eigenspace of the governing equations matrix. It is an alternative to manually obtaining a linearly independent set of equations by combining the governing equations. The resulting matrix has been validated against previously published derivations for an anisotropic poroelastic medium.
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| 13. |
- Parra Martinez, Juan Pablo, 1985-
(författare)
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On multilayered system dynamics and waves in anisotropic poroelastic media
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The mechanical and acoustic anisotropy of media is a governing factor in the behaviour of multilayered systems including such media. The understanding of the mechanisms conditioning the dynamic behaviour of multilayered systems is of paramount importance. In particular, the intrinsic anisotropy of poroelastic media presents a potential for the optimal design of systems for multifunctional performances. Indeed, these multilayered systems are bound by stiffness, thermal and acoustic performance constraints in simultaneously. A plane wave method is presented to study the influence of material orientation in the dynamic behaviour of multilayered systems composed of anisotropic poroelastic media. The method is applied to a system composed of an anisotropic open-celled melamine foam core in between two metal sheets. This particular multilayered configuration allows to shed light on phenomena intrinsic to layers composed of anisotropic poroelastic materials, such as the frequency shift of the fundamental resonance of the panel, or the compression-shear coupling effects taking place in the poroelastic core layers. The latter phenomena is of particular importance, as it is evidenced on the unconventional polarisation of waves in anisotropic poroelastic media. Finally, the method is adapted to the optimisation of multilayered systems for acoustic performance. the design variables are consequently the core material orientations with respect to the global coordinate system. The solutions to the optimisation problem are analysed in terms of dynamic behaviour, thus allowing to correlate acoustic performance of the overall structure, and the response of each individual layer.
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| 14. |
- Parra Martinez, Juan Pablo, 1985-
(författare)
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On the ECO2 multifunctional design paradigm and tools for acoustic tailoring
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nowadays vehicle design paradigm influences not only the effectiveness of the different means of transport, but also the environment and economy in a critical way. The assessment of the consequences that design choices have on society at large are necessary to understand the limits of the methods and techniques currently employed. One of the mechanisms set in motion is the planned obsolescence of products and services. This has affected vehicle design paradigm in such a way that the variety in the market has shadowed the primary function of vehicle systems: the transport of persons and goods. Amongst the consequences of the expansion of such market is the exponential rise on combustion emissions to the atmosphere, which has become a great hindrance for humans health and survival of ecosystems. The development of evaluation tools for such consequences and their piloting mechanisms is needed so as to implement an ECO2 (Ecological and Economical) vehicle design paradigm. Moreover, the multifunctional design paradigm that drives aeronautical and vehicle engineering is an ever-growing demand of smart materials and structures, able to fulfil multiple requirements in an effective way. The understanding of certain phenomena intrinsic to the introduction of novel materials has found certain limits due to the complexity of the models needed. This work presents as a first step an assessment of the causes and consequences of the vehicle exponential market growth based on the analysis of the planned obsolescence within. Furthermore, a method for the acoustic response analysis of multilayered structures including anisotropic poroelastic materials is introduced. The methodology consists in a plane wave approach as a base for introducing the complex mechanic and acoustic equations governing anisotropic homogeneous media, e.g. open-celled foams, into an alternative mathematical tool manipulating physical wave amplitudes propagation within the studied media. In addition, this method is coupled to a power partitioning and energetic assessment tool so as to understand the phenomena present in complex multilayered designs.
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| 15. |
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| 16. |
- Parra Martinez, Juan Pablo, 1985-, et al.
(författare)
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Wave analysis of intrinsic phenomena related to anisotropic poroelastic materials in multilayered systems
- 2016
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Konferensbidrag (refereegranskat)abstract
- An analysis of intrinsic dynamic phenomena in anisotropic poroelastic media is presented, based on a plane wave formulation. The latter is derived from the Stroh formalism on the state variables governing the beha- viour of such media. A particular interest is given to the compression-shear coupling related to the material alignment of the anisotropic poroelastic core. This coupling motion can be directly correlated to the ma- terial mechanical parameters and affects the response of the overall structure in specific frequency ranges. Furthermore, the effect of the anisotropic poroelastic material coordinate orientation on the the acoustic and elastical response of multilayered systems with such material cores is investigated under diffuse field excita- tion conditions (i.e. only a part the mechanics which doesnt include maximum stress at rupture). An insight into other effects of anisotropy is provided, such as the frequency shift of the fundamental resonance related to the core material alignment and the appearance of particular geometrical coincidences in the acoustic behaviour of the system.
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| 17. |
- Van der Kelen, Christophe, 1986-, et al.
(författare)
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A method for characterisation of the static elastic properties of the porous frame of orthotropic open-cell foams
- 2015
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Ingår i: International Journal of Engineering Science. - : Elsevier BV. - 0020-7225 .- 1879-2197. ; 86, s. 44-59
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Tidskriftsartikel (refereegranskat)abstract
- This paper proposes a method to identify the static, fully relaxed elastic Hooke's matrix of a porous open-cell material. The moduli are estimated through an inverse estimation method, by performing a fit of a numerical model on the measured displacements on the faces of the porous material. These displacements are obtained from a static compression along each of the three coordinate axes. The material is modelled as an orthotropic equivalent solid, of which the principal directions are not necessarily aligned with the orthonormal coordinate system in which the experiments are conducted. The angles of relative orientation accounting for the misalignment are among the properties to be estimated. The focus in this paper is on the methodology itself, and its validity is verified by applying the method to four artificial materials with different levels of anisotropy. In addition, the robustness of the method to perturbations on the input data is investigated.
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| 18. |
- Van Der Kelen, Christophe, et al.
(författare)
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A method for the inverse estimation of the static elastic compressional moduli of anisotropic poroelastic foams-With application to a melamine foam
- 2015
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Ingår i: Polymer testing. - : Elsevier BV. - 0142-9418 .- 1873-2348. ; 43, s. 123-130
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents the application of a method for the characterisation of the static, fully relaxed elastic properties of poroelastic materials. The approach is based on full field measurements of the 3D displacements in a number of points on the faces of the compressed material sample. These are used as targets in an inverse estimation to fit a model of the material to the experimental data. The material is modelled as an orthotropic equivalent solid, whose principal directions are not necessarily aligned with the coordinate system in which the experiments are conducted. The angles of relative orientation accounting for the potential misalignment are estimated, together with the elastic moduli of the material. In addition, the proposed model considers the region of reduced stiffness close to material discontinuities, which has been identified in previous investigations. The method is applied to a melamine foam, which is found to have its lowest stiffness in the direction parallel to the rise direction of the material.
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