| 1. |
- Ducret, Fabrice, 1975-
(författare)
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Studies of sound generation and propagation in flow ducts
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis contains three papers investigating problems of interest for noise control in ducts. The first part of this thesis treats the sound propagation in rectangular ducts with flexible walls. Various experimental techniques are performed to measure the internal sound propagation and radiation to the surrounding. An analytical model is derived to calculate the coupled propagation wavenumber and radiated sound power. The two-port formalism is used. The second part starts with the sound propagation in open ended circular straight pipe with airflow (a tailpipe). Various aspects such as: acoustic damping, reflection and transmission at the open termination are investigated. Sound absorption due to vorticity shed at the opening is also treated. The geometry of the opening is then modified (oblique cuts, diffusers) and comparisons with the reference straight pipe is made for the sound transmission and flow induced noise generation. The effect of an upstream bend close to the opening is also investigated. In the third part the acoustic impedance of perforated plates are investigated. In particular the application to small perforation ratios ( ≈ 1% ) and holes or slits with apertures of sub-millimetre size, so called micro-perforated plates, are of interest. Linear and non-linear regimes are investigated. A model is derived to calculate the linear acoustic impedance of perforated elements.
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| 2. |
- Henriksson, Mats, 1976-
(författare)
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On Noise Generation and Dynamic Transmission Error of Gears
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Noise from heavy trucks is an important environmental issue. Several sources contribute to the total noise level of a vehicle, such as the engine, gearbox, tires, etc. The tonal noise from the gearbox can be very disturbing for the driver, even if the noise level from the gearbox is lower than the total noise level. The human ear has a remarkable way of detecting pure tones of which the noise from loaded gears consists of. To be allowed to sell a heavy truck within the European Union, the so called pass-by noise test must be completed successfully. The maximum noise level permitted is 80dB(A) and undercertain conditions, the gearbox can be an important contributor to the total noise level. Gear noise is therefore an important issue for the automotive industry. In this thesis gear noise and dynamic transmission error is investigated. Traditionally, transmission error (TE) is considered to be the main excitation mechanism of gear noise. The definition of TE is ”the difference between the actual position of the output gearand the position it would occupy if the gear drive were perfect”. Measurements of dynamic transmission error (DTE) and noise have been performed on a gearbox. The measurement object was a commercial truck gearbox powered by an electrical motor. The torque used was in the normal operating range of the gearbox and the correlation between gear noise and DTE, when the torque is changed, is investigated. The result differs for different gear pairs and for the first gear stage, located close to the housing, the correlation is high for most speeds. The measured DTE and noise show a poor correlation with calculated transmission error. A minimisation of TE therefore does not necessarily mean a minimisation of gear noise. A transfer function can be employed to calculate the relationship between DTE and noise. The general trend of the gear noise is an increase of 6dB per doubling of the rotational speed together with fluctuations around the mean due to resonances of the system. The magnitude of the transfer function can be estimated using the amplitudesof the gear mesh orders and harmonics. Two gear pairs with similar macro geometry but different profile modifications are investigated. Although the gear pairs have similar transmission error, the noise level display a significantly different trend, further strengt hening the position that transmission error is not the single most important gear noise excitation mechanism. Further analysis concludes that shuttling forces and friction forces can be more important than what is often suggested. A dynamic model including transmission error and shuttling forces is used to investigate the two gear pairs. The bearing forces show that for some frequency regions shuttling forces can be of the same order of magnitude as the forces caused by transmission error. This work highlights the importance of considering other excitations of gear noise besides transmission error when designing quiet gears. The influence of transmission error can not be determined by investigating the gears only. A deeper knowledge of the gear system is needed in order to minimise gear noise for a specific gear design.
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| 3. |
- Persson Waye, Kerstin, 1959, et al.
(författare)
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Rail freight vibration impacts sleep and community response: An overview of CargoVibes
- 2014
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Ingår i: ICBEN 2014, the 11th International Congress on Noise as a Public Health Problem. Nara, Japan, 2014 June 1 to June 5.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The European Union funded CargoVibes project involving 10 partners from 8 nations has aimed to examine ground-borne vibration affecting residents close to freight railway lines. This poster presents an overview of the work package investigating human response to vibration, with particular focus on physiological and psychological impact on sleep, community annoyance and the development of guidance in evaluating response. The effects of vibration on sleep were measured in a series of laboratory trials at the University of Gothenburg. Existing field studies of community response were supplemented with further field work in the Netherlands and Poland, and a meta-analysis conducted to determine dose-response relationships for railway vibration. Numerous outcomes of vibration exposure were found, with physiological markers such as greater heart rate response and cortical reactions during sleep, and annoyance and sleep disturbance increasing with higher vibration amplitudes. A guidance document considering current state of the art regarding vibration measurement and assessment was produced pertaining to human perception, evaluation methods, annoyance, sleep impacts, and non-exposure factors. The outcomes of this work represent a significant advance in the understanding of the human response to railway vibration and a step towards a much needed harmonisation of assessment methods. The findings presented in this poster highlight the importance of considering environmental vibration in the planning, construction, and maintenance of railways in residential environments.
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| 4. |
- Waddington, David, et al.
(författare)
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Cargovibes: Human response to vibration due to freight rail trafiic
- 2015
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Ingår i: Proceedings of 22nd International Congress on Sound and Vibration, 12 - 16 July, Florence, Italy 2015. - : Informa UK Limited. ; 3:4, s. 233-48
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this paper is to present an overview of the research concerning human response to vibration conducted in the EU FP7 CargoVibes project. The European Union funded pro-ject CargoVibes involved ten partners from eight nations and ran from April 2011 to April 2014. The project was concerned with railway-induced ground-borne vibration affecting res-idents close to freight lines, with one work package that investigated human response to vi-bration, including sleep disturbance, community annoyance, and the production of a best practice guide for evaluating response. Laboratory trials at the University of Gothenburg were used to measure the effects of vibration on sleep. Physiological and psychological im-pacts of vibration exposure were found. TNO led a meta-analysis (N = 4129) to determine exposure-response relationships for railway vibration, with existing data for community re-sponse supplemented with field studies in the Netherlands and Poland. The University of Salford led production of a guidance document that presents the state of the art regarding vi-bration measurement and assessment. Specific topics in the guide include human perception, evaluation methods, annoyance, sleep impacts, and non-exposure factors. The outcomes pre-sented in this paper represent a significant advance in the understanding of the human re-sponse to railway vibration and a step towards much needed harmonization of assessment methods.
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