| 1. |
- 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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| 2. |
- 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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| 3. |
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| 4. |
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| 5. |
- Cuenca, Jacques, et al.
(författare)
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Inverse estimation of the elastic and anelastic properties of the porous frame of anisotropic open-cell foams
- 2012
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Ingår i: Journal of the Acoustical Society of America. - : Acoustical Society of America (ASA). - 0001-4966 .- 1520-8524. ; 132:2, s. 621-629
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a method for simultaneously identifying both the elastic and anelastic properties of the porous frame of anisotropic open-cell foams. The approach is based on an inverse estimation procedure of the complex stiffness matrix of the frame by performing a model fit of a set of transfer functions of a sample of material subjected to compression excitation in vacuo. The material elastic properties are assumed to have orthotropic symmetry and the anelastic properties are described using a fractional-derivative model within the framework of an augmented Hooke's law. The inverse estimation problem is formulated as a numerical optimization procedure and solved using the globally convergent method of moving asymptotes. To show the feasibility of the approach a numerically generated target material is used here as a benchmark. It is shown that the method provides the full frequency-dependent orthotropic complex stiffness matrix within a reasonable degree of accuracy.
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| 6. |
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| 7. |
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| 8. |
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| 9. |
- 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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| 10. |
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| 11. |
- Lundin, Oscar, et al.
(författare)
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Prediction of eigenfrequencies in non-rectangular rooms with machine learning
- 2022
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Ingår i: Proceedings of the 24th International Congress on Acoustics. ; , s. 1-5
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Knowing the eigenfrequencies of a space is important for designing its acoustic performance at low frequencies. The eigenfrequencies can be analytically calculated for a limited set of room shapes, while for more complex domains it is common to use Finite Element methods (FEM). This paper investigates the use of Convolutional Neural Networks (CNN) to predict the eigenfrequencies based on a digital image of a 2D room shape. FEM software is used to create a training set of pseudorandom room shapes and identify their eigenfrequencies. In this study, only rooms with rigid walls are studied, and the CNN is used to predict the first ten eigenfrequencies for rooms with normalized surface area. The rooms have three to sixteen walls, including slanted walls and non-convex geometries, as well as corridor rooms. The accuracy of this approach is compared to the FEM solutions, as well as to analytical solutions for room shapes with solutions available.
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| 12. |
- 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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| 13. |
- Manzari, Luca, et al.
(författare)
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A method for the observation of the anelastic behaviour of anisotropic porous materials using digital image correlation
- 2020
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Ingår i: Journal of Sound and Vibration. - : ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD. - 0022-460X .- 1095-8568. ; 474
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Tidskriftsartikel (refereegranskat)abstract
- This paper proposes an experimental method for observing the anelastic anisotropic behaviour of poroelastic media. The setup relies on three-dimensional digital image correlation, enabling the acquisition of full-field displacement data from the visible faces of a vibrating cubic material sample. The latter is placed in a vacuum chamber, loaded with a seismic mass and excited uniaxially. The observability and relevance of the three-dimensional displacement field is assessed by means of a numerical simulation. A homogenised fully anisotropic model is used, implemented using the finite element method. Thus, a set of material properties obtained using single-point data is considered as the reference configuration for the numerical method. Selected experimental and numerical results are presented, highlighting the importance and the advantages that full-field observations yield over single-point measurements.
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| 14. |
- 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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| 15. |
- Manzari, Luca, et al.
(författare)
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Full-field harmonic deformation measurement using short-time stereo high-speed imaging — with application to anisotropic viscoelastic porous media
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- This paper proposes a method for the measurement of full-field three-dimensional displacement transfer functions using short-time harmonic high-speed imaging. The methodology makes use of stereo digital image correlation and enables high-precision harmonic observations, for instance when stationary conditions are unavailable. An optimization algorithm is used as a search procedure for the point-wise amplitude, phase and frequency of the full-field motion, thus avoiding the intrinsic limitations of a Fourier-based approach for short acquisitions. In addition, the proposed approach enables the identification of mechanical non-linearities within the sample of interest and is robust to momentary data loss. Furthermore, an adaptive framework for extracting the coordinate system of the setup is proposed, thus allowing for the measured displacement field to be expressed therein. The method is demonstrated on a sample of sound-absorbing melamine foam, which poses a number of challenges, including the observability of its motion due to its high porosity and the inaccessibility of true stationary conditions due to relaxation processes. Selected results are presented and discussed, with a particular focus on computational costs and advantages with respect to existent techniques in terms of resolving power and amount of information retrieved.
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| 16. |
- Manzari, Luca
(författare)
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High-speed stereo imaging for the characterization of anisotropic viscoelastic media
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis proposes an experimental method for observing and characterizing the viscoelastic properties of anisotropic media using high-speed white light stereo imaging. The method uses short-time video recordings of a specimen undergoing forced harmonic motion.The three-dimensional displacement field of the specimen is then resolved using digital image correlation.Measuring for a short time has multiple advantages: it minimizes the conditioning of the specimen, and gives meaningful results when true stationary conditions are inaccessible (e.g. because of relaxation processes, or changes in the environmental conditions that cannot be accounted for).Moreover, it enables a reduction of the data storage needs and the computational costs associated with the image acquisition and processing.To overcome the intrinsic limitations of a Fourier-based approach for short time records, an optimization algorithm is used to determine the point-wise amplitude, phase and frequency of the full-field harmonic motion.This approach maximizes signal-to-noise ratio, is suitable for the identification of non-linear behaviors and tolerates data records that are non-uniformly spaced in time (e.g. because of momentary data losses and failure of the image matching algorithms).The measurement accuracy is increased by proposing a method to extract the frame of reference of the specimen on a per-frame bases, and express the measured displacement field therein.A cube of melamine foam and a pantographic sheet have been observed using the proposed method, and the measured data compared with the outcome of linear viscoelastic numerical models.The added information obtained about the melamine is believed to improve the accuracy of the characterization of its viscoelastic behavior, and the observation of the pantographic sheet represents and absolute first in the experimental studies of its dynamics.
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| 17. |
- 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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| 18. |
- 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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| 19. |
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| 20. |
- Parra Martinez, Juan Pablo, 1985-, et al.
(författare)
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Analysis of the frequency response behaviour of anisotropic multilayered structures and potential acoustic performance optimizations
- 2014
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Ingår i: Proceedings of ISMA 2014 - International Conference on Noise and Vibration Engineering and USD 2014 - International Conference on Uncertainty in Structural Dynamics. - Leuven, Belgium : KU Leuven. - 9789073802919 ; , s. 4279-4290
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Konferensbidrag (refereegranskat)abstract
- Anisotropy of elastic and acoustic properties increases the potential for performance tailoring of multilayered structures including poroelastic materials. An intrinsic part of such a design optimization is to understand the frequency response behaviour of such configurations in general and those including anisotropic porous layers in particular. In this work a plane wave method for anisotropic multilayered structures has been used to study the response sensitivity for anisotropic porous materials as a function of their material coordinate orientation. It is shown that, depending on the frequency range of interest, the sensitivity to the orientation of the anisotropic porous material varies.
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| 21. |
- 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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| 22. |
- 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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| 23. |
- 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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| 24. |
- 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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| 25. |
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