The SILDIS®[0][1] software (in Excel format) allows noise impact assessment for industrial stacks-chimneys, taking directivity into account, as illustrated by a calculation example (numbered 8.4.1 in the User's manual).
Problem statement for the noise impact study of industrial stacks-chimneys, accounting for directivity, using SILDIS® software (example)
The aim is to calculate the noise directivity of a stack-chimney with a height of 100 m (above ground) [1] and a diameter of 4 m [2], for a reception point (for sound waves) at a height of 5 m (above ground) [3] and a horizontal distance of 300 m [4], considering:
- for the transported fluid: air with a specific gas constant of 287.1 J/kg/K [5], a temperature of 110 °C [6], a pressure of 100,000 Pa [7], and an exit velocity of 20 m/s [8]
- for the ambient air: a temperature of 20 °C [9], a pressure of 100,000 Pa [10], and a wind speed of 3 m/s [11]
Regarding the choice of model for the direct sound ray angle θo, the PHR model is selected [12], and the correction for curvature Δθ (°) is included [13].
For the calculation of the directivity index per one-third octave band, the general INT model [14], the sub-model for the database used for ISO interpolations [15], and the sub-model for NAT conversion [16] are selected. For the calculation of the directivity index per octave band, the CEN model [17] is selected. The language used is English [18].
Input data to be entered for the noise impact study of industrial stacks-chimneys, based on directivity, using SILDIS® software (example)
The input data required for the calculation are listed below, referencing the information provided earlier (cf. the figures in brackets in the preceding section, which serve as references for explaining the selection below). The input cells are identified by their Excel coordinates (column/row) in the following excerpt from the User' manual.
Input data to be entered into the "in-out 10logS & teta" Excel sheet of Module 8A for the industrial stack-chimney noise impact study, based on directivity, using SILDIS® software
| Item | Cell for input | Foreseen action | Input | Landmark / comment |
| Inner radius r0 (m) | B4 | Enter a positive real number | 2 | [2] radius is half diameter |
| Source (in stack outlet plan) height zS (m) | S10 | Enter a positive real number | 100 | [1] |
| Receiver point height zR (m) | S11 | Enter a positive real number | 5 | [3] |
| Distance SR projected to the horizontal plane dp (m) | S14 | Enter a positive real number | 300 | [4] |
| Model for straight sound ray angle θo | S18 | Select a model (in a drop-down menu) | PHR | [12] |
| Correction due to curvature Δθ (°): consideration (0/1) | Y21 | For "yes", entrer 1; for "no", entrer 0 | 1 | [13] |
Input data to be entered into the "in-out CODIR" Excel sheet of Module 8A for the industrial stack-chimney noise impact study, based on directivity, using SILDIS® software
| Item | Cell for input | Foreseen action | Input | Landmark / comment |
| Individual gas constant (J/kg/K) | C1 | Enter a positive real number | 287.1 | [5] |
| Temperature - service conditions t (°C) | C4 | Enter a real number | 110 | [6] |
| Pressure - service conditions P (Pa) | C5 | Enter a positive real number | 100000 | [7] |
| Fluid speed u (m/s) | C9 | Enter a positive real number | 20 | [8] |
| Temperature - ambient air ta (°C) | K11 | Enter a real number | 20 | [9] |
| Pressure - ambient air Pa (Pa) | K12 | Enter a positive real number | 100000 | [10] |
| Wind speed (m/s)) | K16 | Enter a positive real number | 3 | [11] |
| Conversion model 1/1 oct for DI | B16 | Select a model (in a drop-down menu) | CEN | [17] |
| General model for DI | K20 | Select a model (in a drop-down menu) | INT | [14] |
| Database model for DI for general model INT | T20 | Select a model (in a drop-down menu) | ISO | [15] |
| Conversion model 1/3 oct for DI | AD20 | Select a model (in a drop-down menu) | NAT | [16] |
| Langage | AD15 | For English, select E; for French, select F | E | [18] |
Output data: directivity calculation results for the industrial stack-chimney noise impact study using SILDIS® software (example)
For the example under consideration, the results of the directivity calculation for the industrial stack-chimney noise impact study can be viewed:
- in the "in-out CODIR" Excel sheet, when all the input data listed above are taken into account, including what concerns the interpolation database, the ISO model being used [15] (see Figure 1)
- curves and tables: per 1/3-octave and 1/1-octave frequency band
|
Figure 1 Result of the predictive calculation of the directivity of an industrial stack-chimney for the study of noise propagation using SILDIS® software - with ISO database |
- in the "in-out CODIR" Excel sheet, when all the input data listed above are taken into account, with the exception of what concerns the interpolation database, the ENC model being used instead of the ISO model [15] (see Figure 2)
- curves and tables: per 1/3-octave and 1/1-octave frequency band
|
Figure 2 Result of the predictive calculation of the directivity of an industrial stack-chimney for the study of noise propagation using SILDIS® software - with ENC database |
Remark:
The results of calculations based on the ISO database (recent - dating from 2024 and derived from the work of an organization that typically provides consensus-based information) and the ENC database (used much earlier, without subsequent issues) differ quite significantly at certain frequencies, for reasons that have not yet been clarified as of September 2026.
[0] Sound Impact Limitation - Design for Industrialized Solutions