| 1. |
- Andersson, Patrik, 1974, et al.
(författare)
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The intensity potential approach for predicting sound power flow through partial enclosures
- 2011
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Ingår i: 18th International Congress on Sound and Vibration 2011, ICSV 2011, Rio de Janeiro, 10 - 14 July 2011. - 9781618392596 ; 2, s. 1261-1275
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Konferensbidrag (refereegranskat)abstract
- The intensity potential approach is developed for prediction of sound power flow through partial enclosures. A typical application is the prediction of radiated noise from an engine bay with respect to geometry, position and acoustical properties of screens and absorbers. The approach is based on the Helmholtz decomposition of the vector field of the time-averaged sound intensity into its irrotational and rotational components. The local power balance in a lossless medium and the Helmholtz decomposition gives a Poisson equation for the scalar intensity potential of the irrotational component only. The paper presents the approach and evaluates it by canonical examples and by comparison to measured data. It is demonstrated that the prediction of sound power through any closed surface is exact provided that the geometry and boundary conditions are correct. The comparison to experimental data shows that the method is useful in practical applications. The approach has its strength for cases with complex geometry and multiple broadband sources, but it has the potential to become more general by further development of boundary conditions. It is concluded that the intensity potential approach provides a robust prediction tool for the mid- and high-frequency range.
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| 2. |
- Bard, Delphine, et al.
(författare)
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Reflection and transmission properties of wooden wall/floor building elements
- 2011
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Ingår i: 18th International Congress on Sound and Vibration 2011, ICSV 2011. - 9781618392596 ; 2, s. 1065-1072
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Konferensbidrag (refereegranskat)abstract
- Various modal methods are frequently used to investigate the vibration pattern in construction elements of a building in the low frequency range. The experimental determination of time average transmission and reflection coefficient has been developed for the large scale building structures. In this study, we investigate a mock up of a wall/floor junction. The wave approach is combined with the continuity equation. In this fashion both the flexural wave propagation and the in-plane wave motion can be captured. The miss-match impedance was also an important factor, since there is a change of material in the junction. The goal of using scattering matrix formulation is to separate the transmitted wave and the reflected wave as the structural wave propagates towards a wall/floor junction, but also to calculate the rate of wave conversion. One type of junction has been studied with the help of accelerometer matrices: the T junction of the floor/wall structure with its reinforcement beams.
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| 3. |
- Hynninen, A., et al.
(författare)
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Acoustic source data for medium speed IC-engines
- 2011
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Ingår i: 18th International Congress on Sound and Vibration 2011 (ICSV 18). - 9781618392596 ; , s. 811-818
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Konferensbidrag (refereegranskat)abstract
- Knowledge of the acoustic source characteristics of internal combustion engines (IC-engines) is of great importance when designing the exhaust duct system and its components to withstand the resulting dynamic loads and to reduce the exhaust noise emission. Number of studies has been published earlier on the low frequency in-duct exhaust noise of high speed engines. The goal of the present study is to investigate the medium speed IC-engine acoustic source characteristics numerically and experimentally not only in the low frequency - plane wave range but also in the high frequency range. The low frequency acoustic source characteristics were predicted by simulating the acoustic multi-load measurements using a one-dimensional process simulation code. The engine model used in the one-dimensional process simulations was validated with measurements. In this study, it is shown that the low frequency in-duct exhaust noise of a medium speed IC-engine can be predicted quite accurately by using a onedimensional process simulation code. The high frequency source data is estimated by averaging the measured acoustic pressures with different methods. According to this study, using the simple cross spectra averaging method instead of two microphone method to estimate the induct downstream acoustic power of medium speed IC-engine exhaust noise seems promising. The simulation of the high frequency exhaust noise is beyond this study.
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| 4. |
- Lopez Arteaga, Ines, et al.
(författare)
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Viscoelastic contact model for the prediction of tire/road contact forces and rolling resistance
- 2011
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Ingår i: 18th International Congress on Sound and Vibration 2011, ICSV 2011. - 9781618392596
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A combined Hertz/Maxwell model is presented to approximately describe the interaction between a rigid indenter and a viscoelastic half-space, and therefore the force-indentation relationship including the deformation rate and energy losses. Thismodel is a numerically efficient alternative to the exact viscoelastic half-space formulation, to be implemented in a tyre/road interaction model for the prediction of tyre vibrations, rolling resistance and noise. Here the combined Hertz/Maxwell model is used to assess the influence of road texture on the contact stiffness and damping based on the analysis of 30 road surface types. The parameters of this model are obtained by fitting the load-penetration curves obtained from the exact viscoelastic half-space calculation. It is shown that both the stiffness and damping parameters decrease as the road texture depth increases, since, for a given penetration depth, the effective contact area decreases as the road texture depth increases. Assessing the relevance of these effects for the accurate prediction of tyre/road interaction is subject of ongoing work.
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| 5. |
- Orrenius, U., et al.
(författare)
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Sound transmission through a high-speed train roof
- 2011
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Ingår i: 18th International Congress on Sound and Vibration 2011, ICSV 2011. - 9781618392596 ; , s. 2392-2399
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Konferensbidrag (refereegranskat)abstract
- Low internal noise in train carriages is of great importance to the comfort of the passengers, and accordingly also for train manufacturers and operators who want to keep a comfort advantage in relation to other means of transportation. With increased speed the aerodynamic noise becomes an important contributor. Here a train roof section is studied containing a recess where a pantograph is mounted. Significant excitation is present both from aerodynamic forces directly acting on the roof as well as forces transmitted via the pantograph structure and the power input to the compartment is studied for speeds up to 350 km/h. The train roof was modeled using a hybrid FE-SEA approach with input excitation data from transient and compressible CFD calculations as well as from measured structural forces from a full scale wind tunnel test. For reference, turbulent boundary layer (TBL) excitation was studied using a Corcos model. For the transmission model the outer roof structure is described by FE whereas the interior parts are represented by statistical subsystems. Experimental validation of the approach was made on an existing train. The result indicates that for the configuration and sources analysed the contributions to the interior noise from all three sources analysed are significant. Ranking of transmission paths into the train interior and perspectives for application of such models for parametric studies of design parameters are discussed.
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| 6. |
- Pedrosa, A. M., et al.
(författare)
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Experimental measurement of acoustic properties by a two source method with simultaneous excitation
- 2011
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Ingår i: 18th International Congress on Sound and Vibration 2011, ICSV 2011. - 9781618392596 ; , s. 879-886
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Konferensbidrag (refereegranskat)abstract
- In this work, an experimental technique is presented for the acoustic characterization of materials and devices. The developed technique is based on the two source method with simultaneous excitation, thus reducing the time requirements in comparison with the standard two source technique. A decomposition technique is applied to the pressure measurements associated with each microphone, that include noise of two sources acting simultaneously, and the input signals used to excite the two sources. The procedure allows the calculation of the transfer functions between each microphone and each input separately. Once the individual transfer functions have been obtained, it is possible to characterize an acoustic device by means of its four-pole matrix as well as its transmission loss. The technique has been validated by comparison with theoretical results and experimental methods of earlier studies, for several test cases including a straight duct and a reactive muffler.
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| 7. |
- Winroth, Julia, 1981, et al.
(författare)
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Evaluation of approximations used for the tread layer response and road surface roughness in numerical models of the tyre/road contact
- 2011
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Ingår i: 18th International Congress on Sound and Vibration 2011, ICSV 2011, Rio de Janeiro, 10 - 14 July 2011. - 9781618392596 ; 2, s. 1666-1673
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Konferensbidrag (refereegranskat)abstract
- The detailed behaviour at the interface between automotive tyres and roads is important in numerical contact models aiming at prediction of rolling resistance, traction, wear, excitation of vibrations, and noise generation. The detailed behaviour depends on the local dynamic response of the tread and the small-scale roughness of the road surface. For complete tyre-road interaction simulations predicting global vibrations, the tread layer has commonly been modelled using approximations such as a set of uncoupled linear springs or an elastic half-space. These computational efficient approximations have been introduced in an ad hoc manner and they have seldom been evaluated in detail. This paper evaluates these two simplified approaches by comparison to results from a detailed numerical model for a tread layer on a rigid backing that is pressed into a road surface. The detailed contact model is formulated in the time-domain and includes the effect of small-scale roughness by non-linear force-indentation functions between each pair of contact elements. The results show that the effect of the inertia in the tread layer is insignificant for typical contact conditions. The stiffness of the linear springs and the elastic half-space must be tuned to account for the actual coupling within the tread layer and the small-scale roughness of the road. The set of uncoupled linear springs can be tuned to closely follow the force-indentation relation of the detailed model. The elastic half-space can only be tuned for a specific indentation, force or contact stiffness, since its relation has a slightly different character. It is concluded that purely elastic models of the tread are relevant and that the set of uncoupled linear springs performs better than the elastic half-space. However, the tuning of the stiffness is not trivial without results from more elaborate models including the influence of local tread properties and small-scale surface roughness.
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