Harmonoise
Calculation in 1/3-Octave Bands
When this option is activated the propagation calculation is performed in third-octave band width (25 to 10000 Hz). In this case with a source spectrum supplied in octave band width (31.5 to 8000 Hz), for all three third-octaves within an octave the same input data (PWL) is used. The result is displayed just in octave band width.
Note
The main effect from this setting is that the impact of air absorption is more severe when calculating in third-octave band width resulting in a lower receiver level, especially at higher frequencies.
Obstacles within Area Source do not shield
When this option is active, any obstacle (e.g. buildings, foliage, barriers etc.) located within area sources (including parking lots and optimizable sources) provide no screening for any sub-source of that area source.
for an example see BS 5228
Sources in Building/Cylinder do not shield
By default, a screening effect results for sources inside buildings and cylinders as the outer walls act as barriers.
Note
In this case, prior to the calculation, a message will be displayed (dialog Consistency Check) which enables to proceed with the operation (button „Continue“).
This procedure is due to the fact that buildings and cylinders are treated as open boxes within the calculation of propagation (despite they are displayed as „closed“ objects, i.e. with roof, on the 3D-Special View).
With this option activated, sources located inside of the geometrical borders of buildings or cylinders are not screened as if the obstacle were not present. For sources outside, those obstacles are always screening and - if any - reflecting. This option enables to model e.g. sound radiating chimneys by using point or line sources located inside the cylinder. In this case, the directivity pattern of the chimney - whether entered or selected from the default directivities - will not distorted by the cylinder’s screening edge.
Example
see manual „Introduction to CadnaA“, chapter Directivity
Temperature / rel. Humidity
The air attenuation is calculated based on the temperature and relative humidity. Intermediate frequency values result from linear interpolation. The temperature specified serves also as the ambient temperature when calculating the exhaust stack’s directivity.
Harmonoise DLL-Version
After the first calculation using Harmonoise the version of the file PointToPoint.dll in the CadnaA-installation directory will be displayed.
Note
The Harmonoise DLL presently implemented in CadnaA is of version 2.020.
Meteorology
Harmonoise method applies a specific input data set for the meteorological correction, not considering any statistical distribution for long-term averaging. A proposal on how to handle the Harmonoise model to predict long-term average levels see IMA-2004, chapter 3.3.11.
Harmonoise offers five meteorological propagation classes depending on the following parameters:
- wind speed at 10 m above the ground, v (m/s) at z = 10 m,
- wind speed component in the direction of sound propagation at 10 m above the ground, u (z = 10 m),
- cloud cover in octas (i.e. as a multiple of 1/8), and
- time of the day (day/night).
Within the engineering model besides the five stability classes, eight distinct wind directions (i.e. in steps of 45°), and three wind speed classes are applied. In CadnaA, intermediate values are linearly interpolated.
Stability Class D/E/N
The stability class addressing the vertical stability of the atmosphere can be specified for the daily periods D/E/N separately. The five stability classes are characterized by day/night and cloud cover HAR-2004:
| stability class | day/night, cloud cover |
|---|---|
| S1 | day, 0/8 ... 2/8 |
| S2 | day, 3/8 ... 5/8 |
| S3 | day, 6/8 ... 8/8 |
| S4 | night, 5/8 ... 8/8 |
| S5 | night, 0/8 ... 4/8 |
From this a classification with respect to favorable or unfavorable propagation conditions depending on wind direction (see below) can be derived (simplified from HAR-2006):
| wind direction α (*1) | |||||
| stability class | -90° | -45° | 0° | 45° | 90° |
| S1: day, no clouds | very unfavorable | very unfavorable | favorable | favorable | favorable |
| S2: days, clouds 50% | favorable | favorable | favorable | neutral | neutral |
| S3: day, clouds 100% | favorable | favorable | neutral | neutral | favorable |
| S4: night, cloudy | favorable | neutral | neutral | favorable | very favorable |
| S5: night, clear sky | neutral | neutral | favorable | very favorable | very favorable |
(*1): α is the angle between the wind direction and the direction of sound propagation
Note
Note: From the wind speed class and the stability class the inverse of the Monin-Obukhov length 1/L results being used to predict the height difference Δh above the straight ray path.
Consequently, by class S1 a vertically very unstable atmospheric condition is addressed („sunny day“), while class S5 models a stable condition („clear night“). A neutral atmospheric condition would be represented by class S3 („heavily clouded/overcast“).
Wind Direction (°) D/E/N
The wind direction is the direction from which a wind originates (with 0° being North wind, i.e. wind blowing from North, with 180° being South wind etc.).
Wind Speed (m/s) D/E/N
The wind speed refers to a height of 10 m above ground. The following wind speed classification is used HAR-2004:
| wind speed class | wind speed at 10 m above ground v (z=10 m) |
|---|---|
| W1 | 0 ... 1 m/s |
| W2 | 1 ... 3 m/s |
| W3 | 3 ... 6 m/s |
| W4 | 6 ... 10 m/s |
| W5 | > 10 m/s |
Additional Information
Default Calculation Settings used by Harmonoise-DLL
The calculations when using Harmonoise method are performed by the dynamic link library PointToPoint.dll in the CadnaA installation directory. This DLL (Dynamic Link Library) represents the so-called „Engineering Model“ for industrial noise sources within the Harmonoise project IMA-2004. The calculation settings of the DLL used per default have been fixed in accordance with CSTB (Centre Scientifique et Technique du Bâtiment, Grénoble/France) which has implemented the engineering propagation model.
The following options are applied:
- EnableAveraging option: enabled
- EnableScattering option: not enabled
- For all three third-octaves within an octave the same input data is used (i.e. spectrum is a step function).
- The ground factor G and the absorption coefficient Alpha are transformed by linear interpolation to an air resistivity according to:
- for the ground factor G (as entered on the Configuration dialog, „Ground Absorption“ tab, see Ground Absorption Tab, and for the object „Ground Absorption“, see chapter 3.6):
| ground factor G | airflow resistivity σ (kNsm-4) |
|---|---|
| 0 | 20000 |
| 0.33 | 1000 |
| 0.50 | 600 |
| 0.67 | 400 |
| 1.00 | 50 |
- and for the absorption coefficient Alpha of buildings and barriers (see [Chapter 3 - Obstacles](Hindernisse.md)):
| absorption coefficient Alpha | airflow resistivity σ (kNsm-4) |
|---|---|
| 0 | 20000 |
| 0.25 | 1000 |
| 0.50 | 600 |
| 0.75 | 400 |
| 1.00 | 50 |
Batch Processing
Different meteorological configurations for a distinct situation can be processed automatically. The procedure to be followed consists of the following:
- the situation file with several receiver points (in the example below:
meteo.cna), - the macro-file specifying the configuration of calculation and the results to be exported (in the example below:
meteo.cnm). - The macro-file is loaded into CadnaA via menu File|Open. Select the option „All Files“ from the list box „File Type“ to select the cnm file.
- Upon opening of the file the batch processing start automatically and saves the results to a text file with file extension
*.log(in the example below:meteo.log).
Example
Path: Examples\Immissions\Harmonoise
An example file is provided. Follow the procedure as described above.
The macro-file meteo.cnm makes use of the keywords CalcConf and ObjAtt (see CadnaA-manual „Attributes, Variables, and Keywords, Datum/Date and ObjAtt).
File Structure of meteo.cnm
The file meteo.cna is loaded by the command: #(LoadFile, meteo.cna). The next line specifies the column headings. The keyword #(ObjAttAll, 02000000, ID) establishes a dynamic link to the name of each receiver (see CadnaA-manual „Attributes, Variables, and Keywords, ObjAttAll). The four subsequent lines define the configuration settings for meteorological classes S1 to S4 (of Harmonoise), start the calculation at receivers (using the keyword #(CalcImm)), and retrieve the results for level LP1 (using the keyword #(ObjAttAll)). The command #(QuitAtOnce) closes the file saving the result file meteo.log.