1. |
Opiela K.C., Zieliński T.G., Attenborough K.^{♦}, Manufacturing, modeling, and experimental verification of slitted sound absorbers,
ISMA2020 / USD2020, International Conference on Noise and Vibration Engineering / International Conference on Uncertainty in Structural Dynamics, 2020-09-07/09-09, Leuven (BE), pp.409-420, 2020Streszczenie: Designs with uniformly distributed slits normal or inclined to the incident surface exhibit a great potential because of their simplicity and good acoustical performance. However, production of materials of this sort is challenging as the required fabrication precision is very high. This paper deals with additive manufacturing, modeling, and impedance tube testing of a few slitted geometries and their variations, including cases where the dividing walls between slits are perforated. They were designed to be producible with current 3D printing technology and provide reliable measurements using standardized equipment. The normal incidence sound absorption curves predicted analytically and numerically were verified experimentally. It is observed that such simple configurations may lead to absorption properties comparable to porous acoustic treatments with more complex microstructure. The good agreement between the predictions and measurements supports the validity of the multi-scale modeling employed. Afiliacje autorów:
Opiela K.C. | - | IPPT PAN | Zieliński T.G. | - | IPPT PAN | Attenborough K. | - | The Open University (GB) |
| | 20p. |
2. |
Meissner M., Zieliński T.G., Low-frequency prediction of steady-state room response for different configurations of designed absorbing materials on room walls,
ISMA2020 / USD2020, International Conference on Noise and Vibration Engineering / International Conference on Uncertainty in Structural Dynamics, 2020-09-07/09-09, Leuven (BE), pp.463-477, 2020Streszczenie: A technique commonly used for improving room acoustics consists in increasing a total sound damping in a room. This objective can be achieved by using different configurations of a porous material for acoustical treatment of a room. In this work, that problem is analyzed theoretically by exploiting a modal representation of the impulse response (IR) function for steady-state sound field predictions. A formula for the IR function was obtained by solving a wave equation for an enclosure with complex-valued boundary conditions of walls. On the walls where the acoustic treatment is applied, these boundary conditions are related to the characteristic impedance, effective speed of sound and thickness of the porous material used for padding. Two different porous materials were considered in the analyses of the room with acoustic treatment, and to this end, the required effective properties were calculated for a rigid foam with a designed periodic microstructure, as well as for a poroelastic foam with specific visco-elastic properties of the skeleton. Afiliacje autorów:
Meissner M. | - | IPPT PAN | Zieliński T.G. | - | IPPT PAN |
| | 20p. |
3. |
Zieliński T.G., Venegas R.^{♦}, A multi-scale calculation method for sound absorbing structures with localised micro-porosity,
ISMA2020 / USD2020, International Conference on Noise and Vibration Engineering / International Conference on Uncertainty in Structural Dynamics, 2020-09-07/09-09, Leuven (BE), pp.395-407, 2020Streszczenie: This work presents a three-scale approach to modelling sound absorbing structures with non-uniform porosity, consisting of meso-patterns of localised micro-porosity. It can also be used for structures in which voids in a solid frame are filled with micro-fibres. The method involves double-scale, i.e. micro- and meso-scale, calculations of the effective properties of an equivalent homogenised medium, as well as macro-scale calculations of sound propagation and absorption in this medium, which at the macroscopic level can replace the entire absorbing structure of complex micro-geometry. The basic idea can be explained as follows: the mesoscale areas with localised micro-porosity are treated as homogenised meso-pores saturated with an equivalent visco-thermal fluid replacing the actual gas-saturated micro-porous medium, so that the macroscopic effective properties are finally calculated based on a simplified meso-scale geometry with homogenised mesopores. Afiliacje autorów:
Zieliński T.G. | - | IPPT PAN | Venegas R. | - | inna afiliacja |
| | 20p. |
4. |
Ahsani S.^{♦}, Boukadia R.F.^{♦}, Droz C.^{♦}, Zieliński T.G., Jankowski Ł., Claeys C.^{♦}, Desmet W.^{♦}, Deckers E.^{♦}, On the potential of meta-poro-elastic systems with small mass inclusions to achieve broad band a near-perfect absorption coefficient,
ISMA2020 / USD2020, International Conference on Noise and Vibration Engineering / International Conference on Uncertainty in Structural Dynamics, 2020-09-07/09-09, Leuven (BE), pp.2463-2472, 2020Streszczenie: This paper discusses the potential of meta-poro-elastic systems with small mass inclusions to create broadband sound absorption performance under the quarter-wavelength limit. A first feasibility study is done to evaluate whether embedding small mass inclusions in specific types of foam can lead to near-perfect absorption at tuned frequencies. This paper includes an optimization routine to find the material properties that maximize the losses due to the mass inclusion such that a near-perfect/perfect absorption coefficient can be achieved at specified frequencies. The near-perfect absorption is due to the mass-spring effect, which leads to an increase in the viscous loss. Therefore, it is efficient in the viscous regime. The well-known critical frequency, which depends on the porosity and flow resistivity of the material, is commonly used as a criteria to distinguish the viscous regime from the inertial regime. However, for the types of foam of interest to this work, the value of critical frequency is below the mass-spring resonance frequency. Hence, the inverse quality factor is used to provides a more accurate estimation on the frequency at which the transition from the viscous regime to the inertial regime. Afiliacje autorów:
Ahsani S. | - | Katholieke Universiteit Leuven (BE) | Boukadia R.F. | - | inna afiliacja | Droz C. | - | inna afiliacja | Zieliński T.G. | - | IPPT PAN | Jankowski Ł. | - | IPPT PAN | Claeys C. | - | Katholieke Universiteit Leuven (BE) | Desmet W. | - | Katholieke Universiteit Leuven (BE) | Deckers E. | - | Katholieke Universiteit Leuven (BE) |
| | 20p. |
5. |
Opiela K.C., Zieliński T.G., Dvorák T.^{♦}, Kúdela Jr S.^{♦}, Perforated closed-cell metal foam for acoustic applications,
e-FA2020, e-FORUM ACUSTICUM 2020, 2020-12-07/12-11, Lyon (FR), DOI: 10.48465/fa.2020.0925, pp.2879-2886, 2020Streszczenie: Despite very good mechanical and physical properties such as lightness, rigidity and high thermal conductivity, closed-porosity metal foams alone are usually poor acoustic treatments. However, relatively low production cost weighs them in many applications in favour of their open-cell equivalents. In the present paper, this attractive and popular material is subject to consideration from the point of view of the improvement of its sound absorption characteristics. A classic method of perforation is proposed to open the porous interior of the medium to the penetration of acoustic waves and therefore enhance the dissipation of their energy. The interaction between the perforation diameter and closed-cell microstructure as well as its impact on the overall sound absorption of a similar foam were already studied in 2010 by Chevillotte, Perrot and Panneton, so these topics are not discussed much in this work. On the other hand, the objective here is to investigate if one can efficiently approximate the wave propagation phenomenon in real perforated heterogeneous materials with closed porosity of irregular shape by means of their simplified three-dimensional representation at the micro-level. The applied multi-scale modelling of sound absorption was confronted with measurements performed in an impedance tube. Moreover, as expected, numerical and experimental comparisons with relevant perforated solid samples show great benefit coming from the presence of a porous structure in the foam, although it was initially closed. Afiliacje autorów:
Opiela K.C. | - | IPPT PAN | Zieliński T.G. | - | IPPT PAN | Dvorák T. | - | Institute of Materials and Machine Mechanics, Slovak Academy of Sciences (SK) | Kúdela Jr S. | - | Institute of Materials and Machine Mechanics, Slovak Academy of Sciences (SK) |
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6. |
Zieliński T.G., Galland M.-A.^{♦}, Analysis of wave propagation and absorption at normal and oblique incidence in poroelastic layers with active periodic inclusions,
e-FA2020, e-FORUM ACUSTICUM 2020, 2020-12-07/12-11, Lyon (FR), DOI: 10.48465/fa.2020.0541, pp.2825-2831, 2020Streszczenie: The paper presents numerical studies of wave propagation under normal and oblique incidence in sound-absorbing layers of poroelastic composites with active and passive inclusions embedded periodically along the composite layer surface. The purpose of active inclusions is to increase the mass-spring effect of passive inclusions attached to the viscoelastic skeleton of the poroelastic matrix of the composite in order to increase the dissipation of the energy of acoustic waves penetrating into such a layer of poroelastic composite. Finite element modelling is applied which includes the coupled models of Biot-Allard poroelasticity (for the poroelastic matrix), piezoelectricity and elastodynamics (for the active and passive inclusions, respectively), as well as the Helmholtz equation for the adjacent layer of air. The formulation based on the Floquet-Bloch theory is applied to allow for modelling of wave propagation at oblique incidence to the surface of the periodic composite layer. The actively exited piezoelectric inclusions may become additional (though secondary) sources for wave propagation. Therefore, a background pressure field in a wide adjacent air layer is used to simulate plane waves propagating from the specified direction, oblique or normal, onto the poroelastic layer surface, and a nonreflecting condition is applied on the external boundary of the air layer. Afiliacje autorów:
Zieliński T.G. | - | IPPT PAN | Galland M.-A. | - | École Centrale de Lyon (FR) |
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7. |
Opiela K.C., Zieliński T.G., Adaptation of the equivalent-fluid model to the additively manufactured acoustic porous materials,
ICA 2019, 23rd International Congress on Acoustics integrating 4th EAA Euroregio 2019, 2019-09-09/09-13, Aachen (DE), DOI: 10.18154/RWTH-CONV-239799, pp.1216-1223, 2019Streszczenie: Recent investigations show that the normal incidence sound absorption in 3D-printed rigid porous materials is eminently underestimated by numerical calculations using standard models. In this paper a universal amendment to the existing mathematical description of thermal dispersion and fluid flow inside rigid foams is proposed which takes account of the impact of the additive manufacturing technology on the acoustic properties of produced samples. The porous material with a motionless skeleton is conceptually substituted by an equivalent fluid with effective properties evaluated from the Johnson-Champoux-Allard-Pride-Lafarge model. The required macroscopic transport parameters are computed from the microstructural solutions using the hybrid approach. A cross-functional examination of the quality (shape consistency, representative surface roughness, etc.) of two periodic specimens obtained from additive manufacturing processes is additionally performed in order to link it to the results of the multiscale acoustic modelling. Based on this study, some of the transport parameters are changed depending on certain quantities reflecting the actual quality of a fabricated material. The developed correction has a considerable influence on the predicted value of the sound absorption coefficient such that the original discrepancies between experimental and numerical curves are significantly diminished. Słowa kluczowe: Rigid porous material, Additive manufacturing, Sound absorption Afiliacje autorów:
Opiela K.C. | - | IPPT PAN | Zieliński T.G. | - | IPPT PAN |
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8. |
Zieliński T.G., Opiela K.C., Pawłowski P., Dauchez N.^{♦}, Boutin T.^{♦}, Kennedy J.^{♦}, Trimble D.^{♦}, Rice H.^{♦}, Differences in sound absorption of samples with periodic porosity produced using various Additive Manufacturing Technologies,
ICA 2019, 23rd International Congress on Acoustics integrating 4th EAA Euroregio 2019, 2019-09-09/09-13, Aachen (DE), DOI: 10.18154/RWTH-CONV-239456, pp.4505-4512, 2019Streszczenie: With a rapid development of modern Additive Manufacturing Technologies it seems inevitable that they will sooner or later serve for production of specific porous and meta-porous acoustic treatments. Moreover, these new technologies are already being used to manufacture original micro-geometric designs of sound absorbing media in order to test microstructure-based effects, models and hypothesis. In the view of these statements, this work reports differences in acoustic absorption measured for porous specimens which were produced from the same CAD-geometry model using several additive manufacturing technologies and 3D-printers. A specific periodic unit cell of open porosity was designed for the purpose. The samples were measured acoustically in the impedance tube and also subjected to a thorough microscopic survey in order to check their quality and look for the discrepancy reasons. Słowa kluczowe: Sound absorption, Additive Manufacturing Technologies Afiliacje autorów:
Zieliński T.G. | - | IPPT PAN | Opiela K.C. | - | IPPT PAN | Pawłowski P. | - | IPPT PAN | Dauchez N. | - | Sorbonne University Alliance (FR) | Boutin T. | - | Sorbonne University Alliance (FR) | Kennedy J. | - | Trinity College (IE) | Trimble D. | - | Trinity College (IE) | Rice H. | - | Trinity College (IE) |
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9. |
Zieliński T.G., Červenka M.^{♦}, On a relative shift in the periodic micro-geometry and other causes for discrepancy in the microstructure-based modelling of 3D-printed porous media,
INTER-NOISE 2019, INTER-NOISE 2019 - 48th International Congress and Exhibition on Noise Control Engineering, 2019-06-16/06-19, Madrid (ES), No.1695, pp.1-10, 2019Streszczenie: Samples with periodic microstructures, designed for good sound absorption, have been manufactured by 3D printing. Typically, however, the acoustical properties of the resulting samples differ from those predicted. Two causes of the discrepancies are (1) inaccuracies related to the 3D-printing resolution and (2) imperfections resulting from micro-fibres, micro-pores, and pore surface roughness, created during manufacture. Discrepancies due to the first cause can be addressed, post hoc, by updating the idealised periodic geometric model used for creating the codes for fabrication on the basis of a survey using a scanning microscope, or through computerised micro-tomography scans. Reducing the discrepancies due to the second cause requires a relatively significant further modelling effort. Another cause for small discrepancies is when two layers of the same periodic porous material and thickness differ only by a relative shift of the internal geometry of the periodic Representative Volume Element (RVE). This causes the absorption peaks to be shifted in frequency. A modelling procedure is proposed to take this into account. Słowa kluczowe: Sound absorption, Periodic porous media, Additive manufacturing Afiliacje autorów:
Zieliński T.G. | - | IPPT PAN | Červenka M. | - | Czech Technical University in Prague (CZ) |
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10. |
Ahsani S.^{♦}, Deckers E.^{♦}, Zieliński T.G., Jankowski Ł., Claeys C.^{♦}, Desmet W.^{♦}, Absorption enhancement in poro-elastic materials by mass inclusion, exploiting the mass-spring effect,
SMART 2019, 9th ECCOMAS Thematic Conference on Smart Structures and Materials, 2019-07-08/07-11, Paris (FR), pp.1076-1084, 2019Streszczenie: In this paper the possibility of enhancing the absorption coefficient of a poro-elastic material using small, elastic mass inclusions in frequencies lower than the quarter-wavelength resonance of the porous material is discussed. We show that absorption peaks can be achieved not only by what is known in literature as the trapped mode effect, but also by the resonance of small elastic inclusions at low frequencies, which can be interpreted as a mass-spring effect. In this work, the inclusion and the porous skeleton is considered elastic and fully coupled to each other, therefore accounting for all types of energy dissipation i.e. viscous, thermal, and structural losses and energy dissipated due to the relative motion of the fluid phase and the frame excited by the resonating inclusion. Additionally, the inclusions are also modeled as motionless and rigid to distinguish between the trapped mode and/or the modified frame mode effect and the mass-spring effect. Moreover, the distinction between these two effects are explained in more detail by comparing the dissipated energy by each mechanism (viscous, thermal and structural effect). Słowa kluczowe: Meta-porous material, Biot-Allard poroelastic model, Mass-spring effect Afiliacje autorów:
Ahsani S. | - | Katholieke Universiteit Leuven (BE) | Deckers E. | - | Katholieke Universiteit Leuven (BE) | Zieliński T.G. | - | IPPT PAN | Jankowski Ł. | - | IPPT PAN | Claeys C. | - | Katholieke Universiteit Leuven (BE) | Desmet W. | - | Katholieke Universiteit Leuven (BE) |
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11. |
Zieliński T.G., Galland M.-A.^{♦}, Deckers E.^{♦}, Influencing the wave-attenuating coupling of solid and fluid phases in poroelastic layers using piezoelectric inclusions and locally added masses,
ISMA 2018 / USD 2018, International Conference on Noise and Vibration Engineering / International Conference on Uncertainty in Structural Dynamics, 2018-09-17/09-19, Leuven (BE), pp.1195-1207, 2018Streszczenie: When airborne acoustic waves penetrate porous media their carrier becomes the air in pores, but also the solid skeleton - provided that it is sufficiently soft. Then, there is a coupled propagation of fluid-borne and solid-borne waves in a poroelastic medium. The coupling of fluid and solid phases of such media can be responsible for significantly better or weaker sound absorption in medium and lower frequency ranges. It has been observed that adding some well-localised small mass inclusions inside a poroelastic layer may improve its acoustic absorption in some medium frequency range, however, at the same time the absorption is usually decreased at some slightly higher frequencies. This situation can be improved by applying additionally an active approach using small piezoelectric inclusions which actively influence the vibrations of the solid skeleton with added masses, so that the interaction between the solid-borne and fluid-borne waves is always directed for a better mutual energy dissipation of the both types of waves. Afiliacje autorów:
Zieliński T.G. | - | IPPT PAN | Galland M.-A. | - | École Centrale de Lyon (FR) | Deckers E. | - | Katholieke Universiteit Leuven (BE) |
| | 20p. |
12. |
Opiela K.C., Rak M.^{♦}, Zieliński T.G., A concept demonstrator of adaptive sound absorber/insulator involving microstructure-based modelling and 3D-printing,
ISMA 2018 / USD 2018, International Conference on Noise and Vibration Engineering / International Conference on Uncertainty in Structural Dynamics, 2018-09-17/09-19, Leuven (BE), pp.1091-1103, 2018Streszczenie: The purpose of this work is to present and investigate the concept of adaptive sound absorbers, that is, periodic porous media with modifiable micro-geometry, so that their ability of sound absorption or insulation can be changed in various frequency ranges. To demonstrate this concept, a simple periodic porous micro-geometry with small bearing balls inside pores is proposed. By a simple positioning of the periodic porous sample the gravity force is used for the small balls to close some of the windows linking the pores, changing in that way the flow path inside pores, which entails significant modifications of the relevant parameters of permeability and tortuosity. Also the viscous characteristic length is changed, while the porosity as well as the thermal characteristic length remain unchanged. Nevertheless, such significant changes of some crucial transport parameters strongly affect the overall acoustic wave propagation in the porous medium. All this is studied using an advanced dual-scale modelling as well as experimental testing of 3D-printed specimens. Afiliacje autorów:
Opiela K.C. | - | IPPT PAN | Rak M. | - | inna afiliacja | Zieliński T.G. | - | IPPT PAN |
| | 20p. |
13. |
Červenka M.^{♦}, Bednařík M.^{♦}, Zieliński T.G., Direct numerical simulation of sound absorption in porous media,
Euronoise 2018 - 11th European Congress and Exposition on Noise Control Engineering, 2018-05-27/05-31, Hersonissos (GR), pp.59-54, 2018Streszczenie: Numerical simulation of absorption of sound in porous media is an important part of the design of the treatments for the environmental noise reduction. In the porous media, the mechanical energy carried by sound is dissipated by thermo-viscous interactions with the solid surface of the media frame, which usually has complicated geometry at the microscopic (sub-millimetre) scale. In order to be able to absorb the acoustic energy at the low frequencies of interest, a layer of porous material must be rather thick (at the order of centimetres). This is why direct numerical simulation (DNS) of the sound absorption in porous media is a rather computationally challenging task because small geometrical details must be properly resolved in a large computational domain. In order to avoid these difficulties, simplified semi-phenomenological models introducing so called effective fluid have been proposed. For example, the Johnson-Champoux-Allard-Pride-Lafarge (JCAPL) model is based on eight parameters which can be measured or calculated based on the media micro-structural geometry. Within this work, we compare the numerical results obtained by the 3D DNS with the prediction of the JCAPL model in case of several porous media represented by closely-packed spheres. The DNS calculations are performed using the linearised Navier-Stokes equations for layers of spheres of different thicknesses, the parameters for the JCAPL model are calculated subsequently using Laplace, Poisson, and Stokes flow analyses on a representative volume element of the media. Very good agreement between the results has been found. Afiliacje autorów:
Červenka M. | - | Czech Technical University in Prague (CZ) | Bednařík M. | - | Czech Technical University in Prague (CZ) | Zieliński T.G. | - | IPPT PAN |
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14. |
Zieliński T.G., Pore-size effects in sound absorbing foams with periodic microstructure: modelling and experimental verification using 3D printed specimens,
ISMA 2016 / USD 2016, International Conference on Noise and Vibration Engineering / International Conference on Uncertainty in Structural Dynamics, 2016-09-19/09-21, Leuven (BE), pp.95-104, 2016Streszczenie: Microstructure-based modelling of sound absorbing porous media has been recently successfully applied for various materials, however, still some questions concerning the reliability and accuracy of such predictions are open. These issues are investigated here for periodic foams with open porosity. First, a geometry of foam microstructure is generated using an algorithm which ensures periodic arrangements of pores in a cube. Then, the cube is appropriately scaled to various sizes and for each size case finite-element analyses are performed on the periodic fluid domain to calculate the so-called transport parameters. Finally, the effective speed of sound and density are determined for the so-called equivalent fluid, macroscopically suitable to describe wave propagation in such an open rigid foam filled with air. All this allows to estimate the sound absorption for periodic foam layers of various pore-sizes and thicknesses. This parametric study is confronted with some impedance-tube measurements carried out for a few foam samples produced using 3D-printing technology. Słowa kluczowe: Sound absorbing foams, Microstructure, Micro-macro modelling, Acoustic testing, 3D printing Afiliacje autorów:
Zieliński T.G. | - | IPPT PAN |
| | 15p. |
15. |
Zieliński T.G., On representativeness of the representative cells for the microstructure-based predictions of sound absorption in fibrous and porous media,
Euro Noise 2015, 10th European Congress and Exposition on Noise Control Engineering, 2015-05-31/06-03, Maastricht (NL), pp.2473-2478, 2015Streszczenie: Realistic microstructure-based calculations have recently become an important tool for a performance prediction of sound absorbing porous media, seemingly suitable also for a design and optimization of novel acoustic materials. However, the accuracy of such calculations strongly depends on a correct choice of the representative microstructural geometry of porous media, and that choice is constrained by some requirements, like, the periodicity, a relative simplicity, and the size small enough to allow for the so-called separation of scales. This paper discusses some issues concerning this important matter of the representativeness of representative geometries (two-dimensional cells or three-dimensional volume elements) for sound absorbing porous and fibrous media with rigid frame. To this end, the accuracy of two- and three-dimensional cells for fibrous materials is compared, and the microstructure-based predictions of sound absorption are validated experimentally in case of a fibrous material made up of a copper wire. Similarly, the numerical predictions of sound absorption obtained from some regular Representative Volume Elements proposed for porous media made up of loosely-packed identical rigid spheres are confronted with the corresponding analytical estimations and experimental results. Finally, a method for controlled random generation of representative microstructural geometries for sound absorbing open foams with spherical pores is briefly presented. Słowa kluczowe: Fibrous materials, Open-cell foams, Representative microstructure, Modelling of sound absorption Afiliacje autorów:
Zieliński T.G. | - | IPPT PAN |
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16. |
Zieliński T.G., A methodology for a robust inverse identification of model parameters for porous sound absorbing materials,
ISMA 2014, International Conference on Noise and Vibration Engineering, 2014-09-15/09-17, Leuven (BE), pp.63-76, 2014Streszczenie: A methodology of inverse identification of parameters for the Johnson-Champoux-Allard-Lafarge model of porous sound absorbing materials (also with Pride and Lafarge enhancements) is advocated. The inverse identification is based on the measurements of surface acoustic impedance of porous samples. For a single sample of porous material set on a rigid backing wall such measurements provide two specific curves in the considered frequency range, namely, the real and imaginary parts of acoustic impedance. More data suitable for inverse identification can be gathered from additional measurements where the surface acoustic impedance is determined for the same sample yet with an air gap between the sample and the backing wall. As matter of fact, such measurements should be carried out for a few cases where the air gap varies in thickness. Eventually, a set of impedance curves is gained suitable for inverse simultaneous identification of model parameters. In the paper analytical solutions are given for both measurement configurations, namely, for a layer of porous material set on the rigid wall, and for the porous layer separated from the rigid wall by an air gap. These solutions are used by the identification procedure which minimises the difference between the experimental curves and the curves computed from the analytical solutions where the porous layer is modelled using some version of the mentioned poro-acoustic model. The minimisation is carried out with respect to the model parameters, however, not directly, since for this purpose the corresponding dimensionless parameters are introduced. Formulas for the dimensionless parameters are given with respect to the model parameters, and then conversely, for the model parameters with respect to the dimensionless ones. In the formulas two normalising frequencies are introduced which can be considered: one - as characteristic for viscous effects, and the other - as typical for thermal effects. It is claimed that they are not additional parameters, and can be set quite arbitrarily, however, reasonable values must be assumed to allow for very fast and robust identification with initial values for all dimensionless parameters set to 1. This feature is quite important in view of the fact that the choice of initial values for the actual model parameters is rather essential and can be often very problematic. The whole procedure is illustrated with a numerical example and by tests based on laboratory measurements of porous ceramic samples. Słowa kluczowe: Sound absorbing porous media, Inverse identification, Acoustic impedance, Acoustic testing Afiliacje autorów:
Zieliński T.G. | - | IPPT PAN |
| | 10p. |
17. |
Zieliński T.G., Sound absorption of porous layers of loosely-packed rigid spheres: multiscale modelling and experimental validation,
FA2014, 7th FORUM ACUSTICUM 2014, 2014-09-07/09-12, Kraków (PL), No.R13K_2, pp.1-6, 2014Streszczenie: Sound absorption in porous media with rigid structure and open porosity is most often modelled using the so-called fluid-equivalent approach, in which a porous medium is substituted by an effective dispersive fluid. There are many models of that kind. Perhaps the most frequently used and efficient one is the so-called Johnson-Champoux-Allard-Lafrage model, or its variations. This a rather advanced semi-phenomenological model with six to eight parameters; with enhancements by Pride and Lafarge, there are eight parameters, namely: the total open porosity, the tortuosity, the (viscous) permeability, the thermal permeability, the viscous and thermal characteristic lengths, and finally, the viscous and thermal tortuosities at low frequency limit (i.e., at 0 Hz). Although, most of these parameters can be measured, it is sometimes very problematic and requires various experimental facilities, which makes the idea of calculation of these parameters from the geometry of microstructure of porous medium very tempting – such multiscale modelling requires, however, some periodic yet sufficiently realistic representation of the actual porous geometry. In this paper such multiscale modelling is presented for the problem of sound absorption in layers composed of loosely-packed rigid spheres. Since the spheres are identical, the packing, although not dense, tends to be semi-regular. Therefore, some regular sphere packings are used to construct periodic Representative Volume Elements for such porous media – they are, however, modified a bit by shifting the spheres in order to fit exactly the actual measured porosity. Basing on such numerical representations of porous microstructure, all the necessary parameters are calculated from finite-element solutions of some relevant Boundary-Value Problems and the effective characteristics for equivalent fluid are determined. Then, the acoustic absorption coefficients are computed for a porous layer of specified thickness for some wide frequency range and the results are compared with the experimental curve obtained from the measurements of such layer carried out in the impedance tube using the so-called two-microphone transfer function method. Słowa kluczowe: Granular media, Sound absorption, Multiscale modelling, Acoustic measurements Afiliacje autorów:
Zieliński T.G. | - | IPPT PAN |
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18. |
Zieliński T.G., Representative volume elements, microstructural calculation and macroscopic inverse identification of parameters for modelling sound propagation in rigid porous materials,
ICSV20, 20th International Congress on Sound and Vibration: Recent Developments in Acoustics, Noise and Vibration, 2013-07-07/07-11, Bangkok (TH), pp.2228-2235, 2013Streszczenie: The micro-geometry of porous material is responsible for its sound absorption performance and should be now a design objective. Microstructural calculation of parameters and/or characteristic functions for acoustical models of porous materials with rigid frame requires the so-called Representative Volume Elements, that is, usually cubes which should contain several pores or fibres of typical sizes and distribution. The design of such RVEs, which correctly represent a typical micro-geometry of porous medium, is by no means an easy task since usually the RVE should be also periodic and 'isotropic' (identical with respect to the three mutually-perpendicular directions). The task is simpler in case of two-dimensional microscopic models of some fibrous materials, but such modelling is obviously rather approximative. Designs of periodic RVEs for porous foams and fibrous materials will be presented and used by FE analyses of microstructural problems defined by the application of the Multiscale Asymptotic Method to the problem of sound propagation and absorption in porous media with rigid skeleton. Moreover, a methodology of automatic generation of periodic RVEs with random arrangement of pores based on a simple bubble dynamics will be explained. Among other examples, designs of RVE cubes representative for a corrundum ceramic foam with porosity 90% will be shown and serve for microstructural calculation of some macroscopic parameters used in advanced acoustical modelling of porous media. The curves of acoustic impedance and absorption measured in the frequency range from 500Hz to 6.4kHz for two samples of the corrundum foam will be presented. These measurements will be used for inverse identification of relevant macroscopic parameters, namely: the tortuosity, the viscous and thermal permeabilities, and two characteristic lengths. The concurrence of some results obtained by the RVE-based micro-scale calculation and the measurement-based macro-scale identification will be shown. Słowa kluczowe: Rigid porous media, Microstructure-based calculations, Inverse identification, Sound propagation Afiliacje autorów:
Zieliński T.G. | - | IPPT PAN |
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19. |
Zieliński T.G., Inverse identification and microscopic estimation of parameters for models of sound absorption in porous ceramics,
ISMA 2012 / USD 2012, International Conference on Noise and Vibration Engineering / International Conference on Uncertainty in Structural Dynamics, 2012-09-17/09-19, Leuven (BE), pp.95-107, 2012Streszczenie: Samples of porous ceramics Al2O3, manufactured by a promising technology of gelcasting of cellural foams by using biopolymers as gel-formers, are examined in the impedance tube using the transfer function method. It is shown that the ceramics of total porosity around 90% forms an excellent sound absorbing material in the frequency range from 500 Hz to 6.4 kHz. Experimentally-determined curves of acoustic impedance and absorption are then used for inverse identification of relevant geometric parameters like: tortuosity, viscous and thermal permeability parameters and characteristic lengths. These parameters are required by some advanced models of sound propagation in rigid porous media, developed by Johnson, Koplik and Dashen, Champoux and Allard, with some variations introduced by Pride et al., and Lafarge et al. These models are utilized to produce curves of acoustic impedance and absorption that are used by the identification procedure which minimizes the objective function defined as a squared difference to the appropriate curves obtained experimentally. As a matter of fact, some experimental data are used for the determination of parameters while the other data-obtained for another sample of the same porous ceramics, yet having different thickness-serve for the validation purposes. Moreover, it is observed that the identified characteristic length for thermal effects corresponds very well to the average radius of pores, whereas the characteristic length for viscous forces is similar with the average size of Słowa kluczowe: Sound-absorbing foams, Inverse identification, Micro-scale calculations, Porous ceramics Afiliacje autorów:
Zieliński T.G. | - | IPPT PAN |
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Nowak Ł.J., Zieliński T.G., Determining the optimal locations of piezoelectric transducers for vibroacoustic control of structures with general boundary conditions,
ISMA 2012 / USD 2012, International Conference on Noise and Vibration Engineering / International Conference on Uncertainty in Structural Dynamics, 2012-09-17/09-19, Leuven (BE), pp.369-383, 2012Streszczenie: Vibroacoustic control of thin beam, plate and panelled structures with arbitrary boundary conditions is investigated. The study focuses on determining optimal locations of piezoelectric sensors and actuators on the surfaces of structures under vibroacoustic control. The work consists of three parts. In the first part, the undertaken assumptions and some governing equations are briefly introduced. Then, in the second part of the study, the piezo-transducers' locations which ensure optimal sensing/actuating capabilities for specific vibration modes are determined, basing on the derived analytical formulas and on some results of numerical simulations, as well as on the actuator/sensor equations given in the first part of the study. The relevant modes are selected by taking into account that the main purpose is to minimise the acoustic field generated by the vibrating structure. The third part of the work discusses some experimental investigations aimed for the verification of the results obtained theoretically. Some technical aspects of creating the composite structures for active control systems are briefly described in appendix. Słowa kluczowe: Vibroacoustic panels, Vibroacoustic control, Piezoelectric transducers, Optimal placement Afiliacje autorów:
Nowak Ł.J. | - | IPPT PAN | Zieliński T.G. | - | IPPT PAN |
| | 10p. |
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Zieliński T.G., Finite-element modelling of fully-coupled active systems involving poroelasticity, piezoelectricity, elasticity, and acoustics,
CMM 2011, 19th International Conference on Computer Methods in Mechanics, 2011-05-09/05-12, Warszawa (PL), pp.218-1-8, 2011Streszczenie: The paper discusses some issues concerning fully-coupled finite-element modelling of active-passive systems for vibroacoustic attenuation, involving porous, piezoelectric, and elastic materials, as well as 'acoustic' (inviscid) fluids. For porous materials, the advanced, bi-phasic model of poroelasticity is used, which allows to consider elastic vibrations of solid skeleton important at lower frequencies and for porous composites with active inclusions. A discrete finite-element model suitable for analysis of such multiphysics problems is briefly explained. The model is derived (using the Galerkin method) from the variational formulation of coupled problems of poroelasticity, piezoelectricity, elasticity, and acoustics. Finally, some relevant results obtained from a numerical analysis of a disk of active sandwich panel with poroelastic core, fitted into an acoustic waveguide, are presented. Słowa kluczowe: Acoustics, Porous media, Smart materials, Vibrations, Coupled fields, Finite element methods, Numerical analysis, Elasticity Afiliacje autorów:
Zieliński T.G. | - | IPPT PAN |
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Nowak Ł.J., Zieliński T.G., Wybrane aspekty aktywnej kontroli wibroakustycznej na przykładzie struktury płytowej,
58 Otwarte Seminarium z Akustyki, 2011-08-13/08-16, Jurata (PL), Vol.2, pp.129-138, 2011Streszczenie: W artykule przedstawiono wyniki badań nad aktywną redukcją transmisji wibroakustycznej przez strukturę płytową. Zakres przedstawionych w pracy zagadnień obejmuje zarówno opis teoretyczny rozpatrywanych zjawisk i układów, jak i rezultaty symulacji numerycznych oraz badań doświadczalnych. Rozważanym obiektem jest płyta aluminiowa o grubości 2mm z przyklejonymi na jednej z jej powierzchni elementami piezoelektrycznymi. Część tych elementów pełni funkcję sensorów, pozostałe zaś stanowią aktywatory, za pomocą których realizowane jest sterowanie aktywne. Kontroler pracuje w układzie sprzężenia zwrotnego, na jego wejście podawany jest wzmocniony i odwrócony w fazie sygnał napięciowy z sensorów, będący jednocześnie sygnałem błędu. Algorytm sterowania realizowany jest w oparciu o klasyczny regulator proporcjonalno-całkująco-różniczkujący (PID), dla różnych konfiguracji połączeń poszczególnych członów. Fizyczna realizacja kontrolera wykonana została w formie układu analogowego bazującego na niskoszumnych wzmacniaczach operacyjnych. Słowa kluczowe: Aktywna kontrola wibroakustyczna, Regulator PID, Aktywna redukcja drgań Afiliacje autorów:
Nowak Ł.J. | - | IPPT PAN | Zieliński T.G. | - | IPPT PAN |
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Zieliński T.G., Multiphysics modelling and experimental verification of active and passive reduction of structural noise,
ICA 2010, 20th International Congress on Acoustics, 2010-08-23/08-27, Sydney (AU), pp.1-5, 2010Streszczenie: A fully-coupled multiphysics modelling is applied for the problem of simultaneous active and passive reduction of noise generated by a thin panel under forced vibration providing many relevant results of various type (noise and vibration levels, necessary voltage for control signals, efficiency of the approach) which are validated experimentally. The panel is excited in order to generate a noise consisting of significant lower and higher frequency contributions. Then the low-frequency noisy modes are reduced by actuators in the form of piezoelectric patches glued with epoxy resin in locations chosen optimally thanks to the multiphysics analysis, whereas the emission of higher frequency noise is attenuated by well-chosen thin layers of porous materials. To this end, a fully-coupled finite element system relevant for the problem is derived. Such multiphysics approach is accurate: advanced models of porous media are used for the porous layers, the piezoelectric patches are modelled according to the fully-coupled electro-mechanical theory of piezoelectricity, the layers of epoxy resin are thoroughly considered, finally, the acoustic-structure interaction involves modelling of a surrounding sphere of air with the non-reflective boundary conditions applied in order to simulate the conditions found in anechoic chamber. The FE simulation is compared with many experimental results. The sound pressure levels computed in points at different distances from the panel agree excellently with the noise measured in these points. Similarly, the computed voltage amplitudes of controlling signal turn out to be very estimations. Słowa kluczowe: Structural acoustics and vibration, Active noise reduction, Poroelasticity, Sandwich panels Afiliacje autorów:
Zieliński T.G. | - | IPPT PAN |
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Motylewski J., Pawłowski P., Rak M.^{♦}, Zieliński T.G., Identyfikacja źródeł aktywności wibroakustycznej maszyn metodą kształtowania wiązki sygnału (beamforming),
XXXVII Ogólnopolskie Sympozjum Diagnostyka Maszyn, 2010-03-08/03-13, Wisła (PL), pp.1-8, 2010Streszczenie: W zagadnieniach identyfikacji i lokalizacji źródeł aktywności wibroakustycznej maszyn, istotnym problemem jest wizualizacja pól rozkładu wielkości akustycznych na wybranych powierzchniach oraz określenie udziału poszczególnych źródeł w bilansie energetycznym sygnału wibroakustycznego maszyny.
Stosowane w wibroakustyce metody formowania wiązki (beamforming) polegają na przestrzenno-czasowym przetwarzaniu sygnału rejestrowanego przez matrycę mikrofonową. Identyfikacja źródła odbywa się poprzez analizę zależności amplitudowo-fazowych sygnałów akustycznych padających na poszczególne przetworniki matrycy. Ponieważ z metodologicznego punktu widzenia interesujące jest określenie możliwości zastosowania metody kształtowania wiązki w przypadku złożonych urządzeń posiadających źródła o małej aktywności wibroakustycznej, obiektem wstępnych prac był zasilacz hydrauliczny typu Silentflo firmy MTS. Rezultaty otrzymane w wyniku przeprowadzonych badań w pełni potwierdzają zalety metody beamformingu w określeniu lokalizacji i identyfikacji źródeł aktywności wibroakustycznej maszyn. Słowa kluczowe: Wibroakustyka, Lokalizacja źródeł akustycznych, Beamforming Afiliacje autorów:
Motylewski J. | - | IPPT PAN | Pawłowski P. | - | IPPT PAN | Rak M. | - | inna afiliacja | Zieliński T.G. | - | IPPT PAN |
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Zieliński T.G., Active porous composites for wide frequency-range noise absorption,
ISMA 2008, International Conference on Noise and Vibration Engineering, 2008-09-15/09-17, Louvain (BE), Vol.1, pp.89-103, 2008Streszczenie: The paper presents a design, accurate multiphysics modeling and analysis of active porous-composite sound absorbers. Such absorbers are made up of a layer of poroelastic material (a porous foam) with embedded elastic implants having active (piezoelectric) elements. The purpose of such active composite material is to significantly absorb the energy of acoustic waves in a wide frequency range, particularly, in low frequencies. At the same time the total thickness of composites should be very moderate. The active parts of composites are used to adapt the absorbing properties of porous layers to different noise conditions by affecting the so-called solid-borne wave (originating mainly from the vibrations of elastic skeleton of porous medium) to counteract the fluid-borne wave (resulting mainly from the vibrations of air in the pores); the both waves are strongly coupled, especially, in lower frequencies. Passive and active performance of the absorbers is analysed to test the feasibility of this approach. Słowa kluczowe: Poroelasticity, Piezoelectricity, Weak formulation, Acoustic insulation, Active-passive approach Afiliacje autorów:
Zieliński T.G. | - | IPPT PAN |
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Zieliński T.G., Modelling of poroelastic layers with mass implants improving acoustic absorption,
19th International Congress on Acoustics, 2007-09-02/09-07, Madrid (ES), pp.1-8, 2007Streszczenie: The paper presents the modelling and frequency analysis of poroelastic layers with heavy solid implants where an improvement of acoustic absorption at lower frequencies is observed. To model the porous material the Biot’s theory of poroelasticity is used while the solid implants are modelled in two ways: first, as small subdomains of elastic material (steel) situated inside the porouslayer, and for the second time, in a more virtual manner (mathematically equivalent to the presence of masses in the given points), as some adequate inertial terms added directly to the weak (variational) formulation of the problem. Since the solid implants are very small the both ways give similar results. Obviously, the second approach is much more efficient to carry out numerical tests where the influence of the distribution of masses for the acoustic absorption of layers can be analysed. It seems that the improvement by distributed masses (implants) may be greater than the one due to the mass effect alone. Słowa kluczowe: Poroelasticity, Weak formulation, Acoustic absorption Afiliacje autorów:
Zieliński T.G. | - | IPPT PAN |
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Zieliński T.G., Galland M.A.^{♦}, Ichchou M.N.^{♦}, Further modeling and new results of active noise reduction using elasto-poroelastic panels,
ISMA 2006, International Conference on Noise and Vibration Engineering, 2006-09-18/09-20, Louvain (BE), Vol.1, pp.309-319, 2006Streszczenie: The paper presents further development in modeling of active elasto-poroelastic sandwich panels. In fact, a new design of a demi-sandwich panel is proposed and analysed. A numerical model of panel is implemented in COMSOL Multiphysics environment using the most fundamental but very flexible Weak Form PDE Mode. Various physical problems are modeled using Finite Element Method: the wave propagation in acoustic and poroelastic medium, the vibrations of elastic plate, the piezoelectric behavior of actuator. All these problems interact. in the examined application of active panel. The presented results of FE analysis and some analytical solutions prove the necessity of modeling the panel's interaction with an acoustic medium. Again, confirmed is the fact that an active control is necessary for lower resonances while for the higher frequencies the passive reduction of vibroacoustic transmission performed by a well-designed poroelastic layer is sufficient. Słowa kluczowe: Active sandiwch panels, Poroelasticity, Piezoelectricity, Vibroacoustics Afiliacje autorów:
Zieliński T.G. | - | IPPT PAN | Galland M.A. | - | École Centrale de Lyon (FR) | Ichchou M.N. | - | École Centrale de Lyon (FR) |
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Zieliński T.G.^{♦}, Galland M.A.^{♦}, Ichchou M.^{♦}, Active reduction of vibroacoustic transmission using elasto-poroelastic sandwich panels and piezoelectric materials,
SAPEM'2005, Symposium on the Acoustics of Poro-Elastic Materials, 2005-12-07/12-09, Lyon (FR), pp.1-8, 2005Streszczenie: The paper addresses the issue of an active sandwich panel made of elastic faceplates and a poroelastic core. The panel is supposed to be active thanks to piezoelectric patches glued to the one of elastic layers. This piezoelectric actuator is used to excite the panel vibrations in the low frequency range with the aim to reduce the transmitted wave. A complete description of the sandwich behaviour is obtained using a finite element model implemented in FEMLAB environment. The poroelastic material is modeled using a recent formulation (by Atalla et al.) valid for harmonic oscillations, but the classical Biot formulation is also implemented. Coupling occurring between poroelastic material and plates, and between elastic plate and piezoelectric patches is fully considered. The achieved numerical model allows prediction of transmission coefficient for plane waves under normal incidence. Hence, some numerical experiments can be offered for multiple assembly configurations whose ultimate goal is to determine the best assembly and the best control strategy for reducing the transmission over a wide frequency range. Słowa kluczowe: Poroelacticity, Piezoelectricity, Active vibroacoustic panles Afiliacje autorów:
Zieliński T.G. | - | inna afiliacja | Galland M.A. | - | École Centrale de Lyon (FR) | Ichchou M. | - | École Centrale de Lyon (FR) |
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