| 1. |
- Forssén, Jens, 1968, et al.
(författare)
-
Thick barrier noise-reduction in the presence of atmospheric turbulence: Measurements and numerical modelling
- 2002
-
Ingår i: Applied Acoustics. - 0003-682X .- 1872-910X. ; 63:2, s. 173-187
-
Tidskriftsartikel (refereegranskat)abstract
- Atmospheric turbulence causes scattering of sound, which can reduce the performance of sound barriers. This is an important inclusion in prediction models to obtain a correct picture of the sound reduction at higher frequencies. Here a prediction method is applied that uses the strengths of the wind and temperature turbulence to estimate the scattered power into the shadow zone of a barrier. The predictions are compared to full-scale measurements on a thick barrier, where both acoustic and meteorological data were recorded simultaneously under both calm and windy conditions. Comparison between the measurements and the predictions indicate that the method gives reasonably accurate results for mid to high frequencies and a slight overestimation at very high frequencies.
|
|
| 2. |
- Kropp, Wolfgang, 1959, et al.
(författare)
-
The failure of traditional traffic noise control for quiet areas
- 2004
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- One can consider the acoustic soundscape as consisting of two parts the direct acoustic soundscape and the diffuse acoustic soundscape. This fact has important consequences when attempting to change the acoustic soundscapes. The traditional approach to control traffic noise by means of noise barriers or change of traffic distribution is only valid for the areas directly exposed from sources (direct acoustic soundscape). These areas will experience a certain decrease of sound pressure levels when applying these noise control measures. However there will be a lower limit for reduction due to the presence of a diffuse acoustic soundscape. To control/modify such a diffuse acoustic soundscape has been shown very difficult by traditional means of noise control. Main characteristic of diffuse acoustic soundscapes is the presence of a multitude of sources, distributed over a wide area contributing evenly to the acoustic soundscape in a certain areas. Screening will only lead to a redistribution of sound, however consequences of such a redistribution will not be recognised in a diffuse sound field. Absorption has been identified as a main parameter to control diffuse acoustic soundscapes. Reducing sound pressure levels in shielded areas such as inner-yards can only be achieved by adding acoustically absorbing areas along the transfer path between source and receiver, but especially inside the inner-yard. Redistribution of traffic flow has been shown to have a tremendous effect on the directly exposed side, but only a small effect in shielded areas.
|
|
| 3. |
|
|
| 4. |
- Ögren, Mikael, 1972, et al.
(författare)
-
Modelling of a city canyon problem in a turbulent atmosphere using an equivalent sources approach
- 2004
-
Ingår i: Applied Acoustics. - : Elsevier BV. - 0003-682X .- 1872-910X. ; 65:6, s. 629-642
-
Tidskriftsartikel (refereegranskat)abstract
- The sound propagation into a courtyard shielded from direct exposure is predicted using an equivalent sources approach. The problem is simplified into that of a two-dimensional city canyon. A set of equivalent sources are used to couple the free half-space above the canyon to the cavity inside the canyon. Atmospheric turbulence causes an increase in the expected value of the sound pressure level compared to a homogeneous case. The level increase is estimated using a von Kármán turbulence model and the mutual coherences of all equivalent sources' contributions. For low frequencies the increase is negligible, but at 1.6 kHz it reaches 25 dB for the geometries and turbulence parameters used here. A comparison with a ray-based model shows reasonably good agreement.
|
|
| 5. |
|
|
| 6. |
- Ögren, Mikael, 1972
(författare)
-
Prediction of Traffic Noise Shielding by City Street Canyons
- 2004
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Reducing the sound level on the exposed building facades due to traffic noise in cities is difficult and expensive. Creating access for the inhabitants to a quiet side can be an alternative method for reducing the annoyance. Therefore it is of interest to predict the level on shielded positions such as courtyards. This is however difficult using traditional methods. Distant sources contribute to the level, and multiple reflections can be very important. The equivalent sources method is used here to make predictions for canyon-like geometries. This method is extended to include effects of diffusion, absorption and atmospheric turbulence in order to improve the predictions. Substantial decreases on quiet side sound levels have been shown when introducing absorption and diffusion, and small increases have been shown due to turbulence. Measurements indicate that the level is relatively constant for courtyards throughout a city area, and a very simple model called the flat city model is proposed to explain this effect. This model assumes that all sources and receivers are located on a flat rigid plane. The effect of shielding by buildings is introduced as a correction term determined from measurements, and this term is within a relatively small range (6-10 dB) for all the areas studied.
|
|
| 7. |
|
|
