Change search
ReferencesLink to record
Permanent link

Direct link
Pass-by noise simulation: - inuence of trim representation
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.ORCID iD: 0000-0003-1604-8263
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. Scania CV AB.ORCID iD: 0000-0002-3826-3055
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.ORCID iD: 0000-0003-4103-0129
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The necessity of accurate pass-by noise simulations of vehicles has increased as the requirements on noise levels is becoming stricter. Also, the design of noise reducing measures is needed early in the design process when measurements are not possible to perform. The impact of the sound absorbing materials representation on simulated pass-by noise levels from a truck is analysed in this paper. The material may be fully resolved in FEM, including bulk reaction, or represented by a surface impedance, either at normal or a specic angle of incidence. The first representation requires FEM simulations and more material data. This puts higher demands on input data, and more importantly, prevents the use of BEM simulations which signicantly would improve computational efficiency. The two latter representations may be implemented in BEM. The necessary assumption of local reaction may hold for some materials, but it is not always valid. The simulations presented in this paper show that the local reaction assumption underestimates the effect of sound absorption, giving up to 5 dB higher radiated sound power levels and pass-by noise levels up to 2 dB higher than obtained using the bulk-reacting representation. The difference is shown to depend on the material properties and the position of the source in relation to the noise shields and absorbing parts. The directivity of the radiated noise is not affected, although the regions of largest sound pressure levels are more pronounced. The choice of representation of the material is shown to be important for the simulated pass-by noise levels. To choose the level of complexity in the model, it is important to be aware of the effect this may have on the accuracy of the results in order to draw correct conclusions from the results.

National Category
Fluid Mechanics and Acoustics
Research subject
Vehicle and Maritime Engineering
Identifiers
URN: urn:nbn:se:kth:diva-183412OAI: oai:DiVA.org:kth-183412DiVA: diva2:910851
Projects
Surface impedance, Bulk-reaction, Pass-by noise, Enclosure ratio
Note

QS 2016

Available from: 2016-03-10 Created: 2016-03-10 Last updated: 2016-03-11Bibliographically approved
In thesis
1. Absorption of Sound: On the effects of field interaction on absorber performance
Open this publication in new window or tab >>Absorption of Sound: On the effects of field interaction on absorber performance
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Environmental noise has for decades been a well known problem, especially in urban areas. As noise requirements for vehicles are sharpened, noise reducing concepts are needed in early design stages requiring accurate simulations to support the design. Specifically for optimization of noise treatments, the absorber performance must be simulated correctly.

So called noise encapsulations are placed below the powertrain on heavy vehicles to enclose the engine and reduce noise radiation. The attenuation of the absorbers on these shields must be represented correctly in simulations, even in environments with complex sound field, cooling flow and high temperature variations which may affect the absorber performance. This thesis studies the performance variation due to different absorber representations and due to these factors and how to include this in simulations.

It is shown that the material representation significantly affects the attenuation performance in the simulations. Assuming locally reacting absorbers neglects the full interaction between the sound field and the material, which was shown to affect the noise reduction considerably. A measurement method to determine the angular dependent surface impedance was evaluated. It was shown sensitive to small samples and a method to improve accuracy was suggested. Including the angular dependence, either by full resolution or an angular dependent impedance, the field-absorber interaction is included in the simulations and more accurate results are obtained. The influence of flow and temperature fields on the absorber performance was also investigated. A method to include these effects was developed and the attenuation performance shown significant, especially for materials with bulk reaction.

In conclusion, thorough knowledge of the material behavior and the field in the applications is required to choose appropriate material representation to enable reliable simulation results.​

 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. 45 p.
Series
TRITA-AVE, ISSN 1651-7660 ; 2016:09
Keyword
Sound absorption, Porous absorbers, Bulk reaction, Local reaction, Boundary layer, Grazing flow, Temperature gradients, Surface impedance, Sound field, Pass-by noise
National Category
Fluid Mechanics and Acoustics
Research subject
Vehicle and Maritime Engineering
Identifiers
urn:nbn:se:kth:diva-183413 (URN)978-91-7595-883-5 (ISBN)
Public defence
2016-04-08, F3, Lindstedtsvägen 26, KTH, Stockholm, 09:00 (English)
Opponent
Supervisors
Note

QC 20160311

Available from: 2016-03-11 Created: 2016-03-10 Last updated: 2016-03-11Bibliographically approved

Open Access in DiVA

No full text

Search in DiVA

By author/editor
Färm, AnnaGlav, RagnarBoij, Susann
By organisation
Marcus Wallenberg Laboratory MWL
Fluid Mechanics and Acoustics

Search outside of DiVA

GoogleGoogle Scholar
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Total: 28 hits
ReferencesLink to record
Permanent link

Direct link