| 1. |
- Forssén, Jens, 1968
(författare)
-
An analytical solution for a low barrier in a turbulent atmosphere
- 2004
-
Ingår i: Acta Acustica united with Acustica. - 1610-1928 .- 1861-9959. ; 90:6, s. 1142-1150
-
Tidskriftsartikel (refereegranskat)abstract
- The work presented here uses a previously developed substitute sources method (SSM) as the starting point for solving the problem with a low barrier in a turbulent atmosphere. The formulation of the SSM involves a double integral and the numerical solution is computationally demanding. The SSM results are here used as reference. As an intermediate step toward an analytical solution, an expression containing a single integral is found. Its implementation is computationally much less demanding and is here called the fast method. The analytical solution involves further approximations and has a smaller range of validity than the fast method, but could nonetheless be useful. Both the fast method and the analytical solution assume a flat geometry, whereby they can be useful as a complement to scattering cross-section based methods. Moreover, two-dimensional (2-D) modelling is done and no ground surface is considered. Agreement between the SSM and the fast method is reasonably good, and additional restraints are formulated for the applicability of the analytical solution.
|
|
| 2. |
- Forssén, Jens, 1968
(författare)
-
An extended substitute-sources method for a turbulent atmosphere: Calculations for upward refraction
- 2003
-
Ingår i: Acta Acustica united with Acustica. - 1610-1928 .- 1861-9959. ; 89:2, s. 225-233
-
Tidskriftsartikel (refereegranskat)abstract
- The substitute-sources method (SSM) was previously implemented for a single noise barrier in a turbulent atmosphere by applying a substitute surface between the barrier and the receiver [1, 2]. Here, the method is extended, aiming to more general applicability to traffic noise propagation in urban environments. In the method, multiple substitute surfaces are used along the propagation path. The atmospheric turbulence causes a transfer of the initially coherent field into a residual, random field along the propagation path. The mean sound level at the receiver position is found from uncorrelated addition of the substitute surfaces' contributions. The calculation of each contribution is based on a mutual coherence function (MCF) for a turbulent atmosphere. The strength of the substitute sources and the Green functions to the received pressure are calculated for a non-turbulent atmosphere, here by using a fast field program (FFP). A special MCF for the residual field is derived. Examples are calculated for a turbulent atmosphere with upward refraction or without refraction. The results are compared with those from a parabolic equation method (PE) for the refractive cases and with an analytical solution otherwise. The results show good agreement, which indicates that the SSM could be useful for predictions of outdoor sound propagation.
|
|
| 3. |
|
|
| 4. |
|
|
| 5. |
- Forssén, Jens, 1968
(författare)
-
Calculation of noise barrier performance in a turbulent atmosphere by using substitute sources above the barrier
- 2000
-
Ingår i: Acustica. - 0001-7884. ; 86:2, s. 269-275
-
Tidskriftsartikel (refereegranskat)abstract
- The paper presents a model that can be used for calculating the sound reduction by a noise barrier in a turbulent atmosphere. The field due to the acoustic source is substituted by a distribution of sources above the barrier (here called substitute sources). The mean power at the receiver is calculated as line-of-sight propagation through a turbulent atmosphere from all substitute sources using a mutual coherence function. In this study the strengths of the substitute sources are calculated using the Kirchhoff approximation. The calculated results show good averall agreement with those from using a parabolic equation method (PE).
|
|
| 6. |
|
|
| 7. |
|
|
| 8. |
|
|
| 9. |
- Forssén, Jens, 1968
(författare)
-
Calculation of noise barrier performance using the substitute-sources method for a three-dimensional turbulent atmosphere
- 2002
-
Ingår i: Acta Acustica united with Acustica. - 1610-1928 .- 1861-9959. ; 88:2, s. 181-189
-
Tidskriftsartikel (refereegranskat)abstract
- Substitute sources between a noise barrier and a receiver are used to calculate the effect of atmospheric turbulence on barrier sound reduction. The method is extended for application to three-dimensional situations with both high and low barriers. Calculations are made for a thin, hard screen, without the influence of a ground surface. The Kirchhoff approximation is applied for the low screens and a more accurate diffraction model is used for the higher screens. The calculated results are compared with corresponding ones for two-dimensional situations, by using the substitute-sources method (SSM) also. The two and three-dimensional calculations give very similar results, which indicates that, for a large variety of situations, only two-dimensional models are needed. The results are also compared with those obtained using a scattering cross-section method which, although it predicts a much weaker influence of turbulence than the SSM, shows mostly the same trend, namely that the turbulence influence is large only within a range of lower screen heights.
|
|
| 10. |
|
|
