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Färm, A., Boij, S., Glav, R. & Dazel, O. (2016). Absorption of sound at a surface exposed to flow and temperature gradients. Applied Acoustics, 110, 33-42
Open this publication in new window or tab >>Absorption of sound at a surface exposed to flow and temperature gradients
2016 (English)In: Applied Acoustics, ISSN 0003-682x, Vol. 110, p. 33-42Article in journal (Other academic) Published
Abstract [en]

In noise abatement using porous or fibrous materials, accurate determination of the surface impedance representing the absorber is decisive for simulation quality. The presence of grazing flow and non-homogeneous ambient temperature influence the reaction of the absorber and may suitably be included in a modified “effective” surface impedance. In this paper, this approach is applied to a generic case representative for the engine bay of a heavy truck, where porous shields suppress the radiated noise, e.g. during a pass-by noise test. The change in the absorption is determined numerically by solving the wave propagation through a layer of varying temperature and flow adjacent to the impedance surface for different angles of incidence. The study shows significant impact of both flow and temperature, especially for materials with low absorption. The diffuse field absorption coefficient is also derived and although the effect is less pronounced in this case, it is still important in lower frequencies and in the frequency range typical for IC engine noise. The proposed numerical method is shown to be accurate and efficient for determination of the effective impedance and moreover not limited to thin boundary layers.

Place, publisher, year, edition, pages
Elsevier, 2016
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-183440 (URN)10.1016/j.apacoust.2016.03.017 (DOI)000377232500005 ()2-s2.0-84977634166 (Scopus ID)
Note

QC 20160407

Available from: 2016-03-11 Created: 2016-03-11 Last updated: 2017-11-30Bibliographically approved
Lund, K. & Glav, R. (2015). Strategies for managing micro-level contextual ambidexterity: Combining exploration and exploitation in R&D. In: Proceedings of the 15th annual CINet conference: . Paper presented at 15th annual CINet conference, 7-9 September, 2014, Budapest, Hungary.
Open this publication in new window or tab >>Strategies for managing micro-level contextual ambidexterity: Combining exploration and exploitation in R&D
2015 (English)In: Proceedings of the 15th annual CINet conference, 2015Conference paper, Published paper (Refereed)
Abstract [en]

In this paper we study the achievement of contextual ambidexterity at the individual level, i.e. the micro-level. We explore how employees in four different teams in an automotive company use different strategies to prioritise time between, on the one hand exploration such as pre-development activities and research and, on the other hand exploitation such as realising set concepts in the later phases of the product development process. Based on our findings we argue that the status of exploratory activities must be elevated to equal levels with exploitation activities if ambidexterity is to achieved without using separation as the main strategy. We propose that clear goal setting, stricter follow-up of exploratory activities, and high levels of endurance among managers in change initiatives are ways to achieve a contextually ambidextrous organisation.

Keywords
Contextual ambidexterity, exploration, exploitation
National Category
Work Sciences Production Engineering, Human Work Science and Ergonomics
Identifiers
urn:nbn:se:kth:diva-160628 (URN)
Conference
15th annual CINet conference, 7-9 September, 2014, Budapest, Hungary
Note

QC 20150225. NV 20160129

Available from: 2015-02-25 Created: 2015-02-25 Last updated: 2016-01-29Bibliographically approved
Färm, A., Boij, S. & Glav, R. (2015). The influence of finite sample size on surface impedance determination of materials with low sound absorpsion at low frequencies. In: : . Paper presented at Euronoise 2015, the 10th European Congress and Exposition on Noise Control Engineering, Maastricht, Netherlands, 2015-06-01.
Open this publication in new window or tab >>The influence of finite sample size on surface impedance determination of materials with low sound absorpsion at low frequencies
2015 (English)Conference paper, Published paper (Refereed)
Abstract [en]

The most common noise reducing measure is to add sound absorbing material on the domain boundaries. The boundaries covered by the material may in sumilations be represented by the surface impedance of the material. The impedance can either be modeled or determined experimentally. The experimental determination can be done by the well known standing wave tube method or by a free field method. These free field methods enable impedance determination at any angle of incidence for bulk reacting materials, as opposed to the standing wave tube method that is restricted to normal incidence or locally reacting materials. The method prescribes a point source above the surface and measurements in two points close to the sample surface. From this, the surface impedance can be deduced through the known sound field formulation. Among other things, the impact on the accuracy of the method from the field formulation, signal conditioning and sensor type have been studied in previous work. One major concern is the finite size of the material sample, and its influence on the measurement accuracy. This has previously been investigated for highly absorbing materials and it was shown to be a low frequency problem. Therefore, we focus on the impact of the finite sample in frequencies below 2 kHz. In particular, we relate the magnitude of the impact to the properties of the tested material. Also, the influence of the mounting of the material is analyzed. The study is made through analyzing numerical simulations of the experiment for a variety of setups and materials. Theoretical discussion is provided for deeper understanding of the results. The impact of the finite sample is seen to depend on the material properties, not only the setup as previously shown. Materials with high absorption are shown to be more sensitive to these errors.

National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-181690 (URN)
Conference
Euronoise 2015, the 10th European Congress and Exposition on Noise Control Engineering, Maastricht, Netherlands, 2015-06-01
Note

QC 20160225

Available from: 2016-02-02 Created: 2016-02-02 Last updated: 2016-02-25Bibliographically approved
Glav, R. & Färm, A. (2013). Analysis of a cylindrical micro-perforated resistive silencer. In: 42nd International Congress and Exposition on Noise Control Engineering 2013, INTER-NOISE 2013: Noise Control for Quality of Life. Paper presented at 42nd International Congress and Exposition on Noise Control Engineering 2013: Noise Control for Quality of Life, INTER-NOISE 2013, 15 September 2013 through 18 September 2013, Innsbruck, Austria (pp. 5867-5876). OAL-Osterreichischer Arbeitsring fur Larmbekampfung
Open this publication in new window or tab >>Analysis of a cylindrical micro-perforated resistive silencer
2013 (English)In: 42nd International Congress and Exposition on Noise Control Engineering 2013, INTER-NOISE 2013: Noise Control for Quality of Life, OAL-Osterreichischer Arbeitsring fur Larmbekampfung , 2013, p. 5867-5876Conference paper, Published paper (Refereed)
Abstract [en]

This paper presents an analytical wave decomposition model for predicting the transmission loss a cylindrical silencer with both annular and baffled micro-perforated screens. Numerical simulation shows the fundamental characteristics as well as the potential to achieve large attenuation using micro-perforations. The numerical model is verified by measurements using the 2-microphone technique and shown to be a useful tool in practical design. Clear from the analysis is the sensitivity of the micro-perforated silencer to changes in both porosity and overall layout.

Place, publisher, year, edition, pages
OAL-Osterreichischer Arbeitsring fur Larmbekampfung, 2013
Keywords
Numerical models, Fundamental characteristics, Micro-perforations, Transmission loss, Wave decomposition, Acoustic variables control
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-151079 (URN)2-s2.0-84904498254 (Scopus ID)978-163266267-5 (ISBN)
Conference
42nd International Congress and Exposition on Noise Control Engineering 2013: Noise Control for Quality of Life, INTER-NOISE 2013, 15 September 2013 through 18 September 2013, Innsbruck, Austria
Note

QC 20160122

Available from: 2014-09-15 Created: 2014-09-15 Last updated: 2016-01-22Bibliographically approved
Färm, A., Boij, S., Göransson, P. & Glav, R. (2013). On internal mean flow in porous absorbers and its effect on attenuation properties. In: Proceedings of Meetings on Acoustics: Volume 19, 2013. Paper presented at 21st International Congress on Acoustics, ICA 2013 - 165th Meeting of the Acoustical Society of America; Montreal, QC; Canada; 2 June 2013 through 7 June 2013 (pp. 1-6). Acoustical Society of America (ASA), 19
Open this publication in new window or tab >>On internal mean flow in porous absorbers and its effect on attenuation properties
2013 (English)In: Proceedings of Meetings on Acoustics: Volume 19, 2013, Acoustical Society of America (ASA), 2013, Vol. 19, p. 1-6Conference paper, Published paper (Other academic)
Abstract [en]

In vehicle applications, absorbing materials are often used to attenuate sound. In, for example, exhaust systems and on noise encapsulations, the absorber is exposed to flow. This creates a boundary layer above the absorber, which affects the impedance of the surface, and hence alters the absorption properties. In addition to this effect, the flow itself may enter the absorbent material due to high pressure and forced flow paths. An investigation of the effects that internal flow in the absorber imposes on the acoustic properties is presented. One way to describe the effect is by a change in flow resistivity. The effect is investigated for typical absorbers used in noise encapsulations for trucks. The Transfer Matrix Method is applied to calculate the resulting absorption coefficient for an absorber with changed flow resistivity due to internal flow. The possibility to model the changed properties of the absorber with internal mean flow by means of Biot theory is also explored, together with a discussion on suitable experimental methods to verify and further investigate the effects.

Place, publisher, year, edition, pages
Acoustical Society of America (ASA), 2013
Series
Proceedings of Meetings on Acoustics, ISSN 1939-800X ; 19
Keywords
Absorbent materials, Absorbing materials, Absorption co-efficient, Absorption property, Attenuation properties, Experimental methods, Flow resistivity, In-vehicle applications
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-134241 (URN)10.1121/1.4799717 (DOI)2-s2.0-84878976617 (Scopus ID)
Conference
21st International Congress on Acoustics, ICA 2013 - 165th Meeting of the Acoustical Society of America; Montreal, QC; Canada; 2 June 2013 through 7 June 2013
Note

QC 20131121. QC 20160129. QC 20160207

Available from: 2013-11-21 Created: 2013-11-20 Last updated: 2016-03-11Bibliographically approved
Glav, R. (2012). Device for damping of sounds used for motor vehicle e.g. truck, has diffuser unit which is situated on wall opposite each aperture to deflect air towards wall, so that air flow proceeds in different directions in through-flow space. WIPO WO2012150896-A1.
Open this publication in new window or tab >>Device for damping of sounds used for motor vehicle e.g. truck, has diffuser unit which is situated on wall opposite each aperture to deflect air towards wall, so that air flow proceeds in different directions in through-flow space
2012 (English)Patent (Other (popular science, discussion, etc.))
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-180749 (URN)
Patent
WIPO WO2012150896-A1 (2012-11-08)
Note

QS 20170118

Available from: 2016-01-22 Created: 2016-01-22 Last updated: 2017-11-13Bibliographically approved
Färm, A., Boij, S. & Glav, R. (2012). On sound absorbing characteristics and suitable measurement methods. In: SAE Technical Paper 2012-01-1534, 2012: . Paper presented at th International Styrian Noise, Vibration and Harshness Congress: The European Automotive Noise Conference, SNVH 2012; Graz; Austria; 13 June 2012 through 15 June 2012. Society of Automotive Engineers
Open this publication in new window or tab >>On sound absorbing characteristics and suitable measurement methods
2012 (English)In: SAE Technical Paper 2012-01-1534, 2012, Society of Automotive Engineers, 2012Conference paper, Published paper (Refereed)
Abstract [en]

Noise encapsulations are widely used in automotive industry to enclose noise sources, such as e.g. the engine or the gearbox, to reduce externally radiated noise. The sound absorption factor of the material on the inside of the noise encapsulation is obviously vital for the sound attenuation. This parameter is in most cases determined experimentally for which there are several methods. The results received from the various methods may vary as different acoustic states are examined and thus influence the choice of method. The absorption factor is crucial since it is used in specifications to material manufacturers as well as being an input parameter in modeling the performance of the noise shield e.g. during a pass-by noise test.

In this paper, two standardized measurement methods along with a third, non-standardized method, are applied to determine the properties of an absorbing material used in a commercial noise encapsulation. The methods are based on normal-, random- and oblique incident sound waves. The first and the last methods are based on measuring the acoustic impedance from which the absorption can be calculated while the random incidence method measures the absorption directly. The results retrieved from the three methods are compared and discussed in the light of the differences between them. This paper clarifies the differences and gives a practical guidance for the choice of measurement method and the use of the different absorption factors in modeling.

Place, publisher, year, edition, pages
Society of Automotive Engineers, 2012
Keywords
Sound absorption coefficient, surface impedance, local reaction
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-128552 (URN)10.4271/2012-01-1534 (DOI)2-s2.0-84877167175 (Scopus ID)
Conference
th International Styrian Noise, Vibration and Harshness Congress: The European Automotive Noise Conference, SNVH 2012; Graz; Austria; 13 June 2012 through 15 June 2012
Note

QC 20130913

Available from: 2013-09-13 Created: 2013-09-13 Last updated: 2016-03-11Bibliographically approved
Färm, A., Glav, R. & Boij, S. (2012). On variation of absorption factor due to measurement method and correction factors for conversion between methods. In: 41st International Congress and Exposition on Noise Control Engineering 2012, INTER-NOISE 2012, Volume 11, 2012: . Paper presented at 41st International Congress and Exposition on Noise Control Engineering 2012, INTER-NOISE 2012, New York, NY; United States; 19 August 2012 through 22 August 2012 (pp. 9343-9350). Institute of noise control engineering
Open this publication in new window or tab >>On variation of absorption factor due to measurement method and correction factors for conversion between methods
2012 (English)In: 41st International Congress and Exposition on Noise Control Engineering 2012, INTER-NOISE 2012, Volume 11, 2012, Institute of noise control engineering , 2012, p. 9343-9350Conference paper, Published paper (Other academic)
Abstract [en]

Sound absorbing materials are used in many applications to reduce sound, and their soundabsorbing characteristics are most often determined experimentally since theoreticaldetermination is difficult. Sound absorption factors are used in material specifications aswell as input to numerical simulations.Several methods for experimental determination of the absorption factor exist, two of themstandardized and frequently used. It is commonly known that the absorption factorobtained by these two methods differs as different sound fields are prescribed by thestandards. However, the size of the differences has not been so well described. Due to thisdifference, the choice of method is critical in order to avoid errors in simulations andspecifications of material properties.Experimental determination of absorption factors for three commonly used absorbers wasperformed, resulting in significant differences between the two methods. Correction factorsto compensate the absorption factor determined at one acoustic state and used in anotherare given. Theory verifying the differences is also presented.

Place, publisher, year, edition, pages
Institute of noise control engineering, 2012
Keywords
Sound absorption coefficient, measurements
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-128557 (URN)2-s2.0-84883591764 (Scopus ID)978-162748560-9 (ISBN)
Conference
41st International Congress and Exposition on Noise Control Engineering 2012, INTER-NOISE 2012, New York, NY; United States; 19 August 2012 through 22 August 2012
Note

References: Färm, A., Boij, S., Glav, R., On sound absorbing characteristics and suitable measurement methods (2012) Proceedings of the 7 International Styrian Noise, Vibration and Harshness Congress; (2003) Acoustics - Measurement of Sound Absorption in a Reverberation Room, , ISO 354; (1996) Acoustics - Determination of Sound Absorption Coefficient and Impedance in Impedance Tubes - Part 1: Method Using Standing Wave Ratio, , International standard ISO 10534-1; Delany, M.E., Bazley, E.N., Acoustic properties of fibrous absorbent materials (1970) Applied Acoustics, 3, pp. 105-116; Corcos, G.M., The structure of the turbulent pressure field in boundary layer flows J. of Fluid Mechanics, 18, p. 1964; Biot, M.A., Generalized theory of acoustic propagation in porous dissipative media (1962) Journal of the Acoustical Society of America, 34 (9), pp. 1254-1264; Attenborough, K., Acoustical characterization of porous materials (1982) Physics Reports, 82 (3), pp. 179-227; Sastry, J.S., Munjal, M.L., A transfer matrix approach for evaluation of the response of a multi-layer infinite plate to a two-dimensional pressure excitation (1995) Journal of Sound and Vibration, 182 (1), pp. 109-128

QC 20130913

Available from: 2013-09-13 Created: 2013-09-13 Last updated: 2016-02-15Bibliographically approved
Lindborg, M. N., Karlsson, M., Glav, R. & Karlsson, T. (2011). Acoustic characterization of shallow flow reversal chambers. In: : . Paper presented at 16 May 2011 through 19 May 2011, Rapids, MI. SAE International
Open this publication in new window or tab >>Acoustic characterization of shallow flow reversal chambers
2011 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Flow reversal chambers are common design elements in mufflers. Here an idealized flow reversal chamber with large cross-section but small depth has been studied. The inlet and outlet ducts as well as the cross-sectional area are fixed while the depth of the chamber can be varied. The resulting systems are then characterized experimentally using the two-microphone wave decomposition method and compared with results from both finite element modeling and various approaches using two-port elements. The finite element modeling results are in excellent agreement with the measurements over the whole frequency range studied, while two-port modeling can be used with engineering precision in the low frequency range. The influence of mean flow was studied experimentally and was shown to have relatively small influence, mainly adding some additional losses at low frequencies. This study yields an insight into the modeling approach necessary to capture the acoustical behavior of a flow reversal chamber. For initial studies of the performance the recommendation is to model the flow reversal as a straight duct two-port element connecting the inlet and outlet. For more in depth studies finite element modeling should be used to construct a two-port element for inclusion in a network model.

Place, publisher, year, edition, pages
SAE International, 2011
Series
SAE Technical Papers, ISSN 0148-7191
Keywords
Acoustic characterization, Cross sectional area, Design elements, Finite element modeling, Flow reversals, Frequency ranges, In-depth study, Low frequency, Low frequency range, Mean flow, Modeling approach, Network models, Outlet duct, Shallow flow, Straight duct, Wave decomposition, Exhibitions, Precision engineering, Acoustic noise
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-180779 (URN)10.4271/2011-01-1519 (DOI)2-s2.0-84877569744 (Scopus ID)
Conference
16 May 2011 through 19 May 2011, Rapids, MI
Note

QC 20160304

Available from: 2016-01-22 Created: 2016-01-22 Last updated: 2016-03-04Bibliographically approved
Karlsson, M., Åbom, M. & Glav, R. (2011). Aeroacoustics of duct branches: with application to silencers. Paper presented at 10th International Conference on Engines and Vehicles, ICE 2011; Naples; Italy; 11 September 2011 through 15 September 2011. SAE technical paper series
Open this publication in new window or tab >>Aeroacoustics of duct branches: with application to silencers
2011 (English)In: SAE technical paper series, ISSN 0148-7191Article in journal (Refereed) Published
Abstract [en]

The inclusion of flow-acoustic interaction effects in linear acoustic multiport models has been studied. It is shown, using a T-junction as illustration example, that as long the acoustic system is linear the required information is included in a scattering matrix obtained by experimental or numerical studies. Assuming small Mach numbers and low frequencies-as in most automotive silencer applications-the scattering matrix for the T-junction can be approximated using quasi-steady models. Models are derived that holds for all possible configurations of grazing and bias flow in the T-junctions. The derived models are then used to predict the performance of a novel silencer concept, where a resonator is formed by acoustically short-circuiting the inlet and outlet ducts of a flow reversal chamber. The agreement between experiments and simulations is excellent, justifying the use of the quasi-steady modeling approach.

Place, publisher, year, edition, pages
SAE International, 2011
Keywords
Acoustic systems, Flow reversals, Flow-acoustic interaction, Multi-port, Numerical studies, Outlet duct, Quasi-steady model, Quasi-steady modeling, Scattering matrices, T junctions, Acoustic fields, Mach number, Scattering parameters, Vehicles
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-148738 (URN)10.4271/2011-24-0218 (DOI)2-s2.0-84877191241 (Scopus ID)
Conference
10th International Conference on Engines and Vehicles, ICE 2011; Naples; Italy; 11 September 2011 through 15 September 2011
Note

QC 20140825. QC 20160129

Available from: 2014-08-25 Created: 2014-08-11 Last updated: 2017-12-05Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-3826-3055

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