Nord 2000
General Information
The implementation of „Nord 2000 Industry“ in CadnaA makes use of two dynamic link libraries (32- or 64-bit DLLs) distributed by the Norwegian Public Roads Administration (http://www.vegvesen.no) and developed by the Scandinavian research organization SINTEF (http://www.sintef.no). Each DLL is part of the installation procedure, either with the 32- or the 64-bit version of CadnaA, respectively.
The main difference between both DLLs is:
- The 64-bit DLL has multi-threading capabilities (see Multithreading).
- The 32-bit DLL has no multi-threading capabilities. Consequently, just a single core will be used slowing down the calculation with complex sceneries.
Note
Since DataKustik is not the developer, we can neither comment, nor explain results obtained using these DLLs. In case of inquiries please contact NPRA or SINTEF.
Nord 2000 DLL-Version
On the list box „Version“ the most recent version 20 is selected by default.
Note
The version 16, although selectable, is no longer available in CadnaA.
After the first calculation using Nord 2000 (Industry) the DLL-version will be displayed.
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
Meteorology
The Nord 2000 model applies a specific input data set for the meteorological correction using the following input data:
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.
Height of Wind (m)
The height at which the wind speed was measured (default value: 10 m).
Roughness length (m)
The roughness length characterizes the turbulence conditions of the atmospheric boundary layer. This parameter is used in the vertical wind profile equations predicting the horizontal mean wind speed near the ground (default value: 0.025 m).
For information, some typical roughness lengths are listed in the table below referring to the CORINE cadastre:
| z0 in m | Classes according to the CORINE cadastre |
| 0.01 | Beaches, dunes, sands (331); Water bodies (512) |
| 0.02 | Dump sites (132); Pastures (231); Natural grasslands (321); Sparsely vegetated areas (333); Salt marshes (421); Intertidal flats (423); Water courses (511); Estuaries (522) |
| 0.05 | Mineral extraction sites (131); Sport and leisure facilities (142); Non-irrigated arable land (211); Glaciers and perpetual snow (335); Coastal lagoons (521) |
| 0.10 | Airports (124); Inland marshes (411); Peat bogs (412); Sea and ocean (523) |
| 0.20 | Road and rail networks and associated land (122); Green urban areas (141); Vineyards (221); Complex cultivation patterns (242); Land principally occupied by agriculture, with significant areas of natural vegetation (243); Moors and heathland (322); Bare rocks (332) |
| 0.50 | Port areas (123); Fruit trees and berry plantations (222); Transitional woodland-shrub (324) |
| 1.00 | Discontinuous urban fabric (112); Industrial or commercial units (121); Construction sites (133); Coniferous forest (312) |
| 1.50 | Broad-leaved forest (311); Mixed forest (313) |
| 2.00 | Continuous urban fabric (111) |
Stability Class D/E/N
This option is not available for the time being.
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 the specified height at which the wind speed was measured (see above).
Standard Deviation Wind Speed (m/s) D/E/N
This is the standard deviation of the wind speed in the direction of propagation.
In the documentation of Nord 2000 it says NORD-2006:
„The standard deviation ... accounts for the fluctuation in wind speed in excess of what is already included in the turbulence strength. Turbulent motion is fluctuations taking place within seconds or minutes. For calculation of instantaneous sound pressure levels (the standard deviation) shall be zero. For calculation of the equivalent sound pressure level with duration above a few minutes up to a few hours, the effect of slow variations in wind speed can be taken into account by this parameter. The parameter should not be used for calculating long-term effects where the weather is basically changing during the time. Instead a procedure where the weather is divided into a number of meteorological classes should be used.“
Temperature Gradient (°/km) D/E/N
The atmospheric temperature gradient in degrees centigrade per kilometer height.
Note
This gradient is negative under normal situations (temperature decrease with height, e.g. about -6°C/km or -0.006°C/m). In inversions, however, the gradient becomes positive, i.e. a temperature increase with height.
Turbulence Parameter for Wind Cv2 (m4/3s-2) D/E/N
In the documentation of Nord 2000 it says NORD-2006:
„The turbulence strength corresponding to the wind Cv2 accounts for the turbulent motion of the atmosphere. The parameter is not available in standard weather data. The maximum observed value of Cv2 is approx. 0.3 m4/3s-2, and it is recommended to use a value of 0.12 m4/3s-2 unless other information is available.“
Turbulence Parameter for Temperature CT2 (K/s2) D/E/N
In the documentation of Nord 2000 it says NORD-2006:
„The turbulence strength corresponding to the temperature CT2 accounts for the turbulent variation of the temperature in the atmosphere. The parameter is not available in standard weather data. The maximum observed value of CT2 is approx. 0.05 Ks-2, and it is recommended to use a value of 0.008 Ks-2 unless other information is available.“
Standard Deviation of Fluctuations of the Temperature Gradient σdt/dz (°C/m) D/E/N
In the documentation of Nord 2000 it says NORD-2006:
„The standard deviation of fluctuations in the temperature gradient σdt/dz accounts for fluctuation in temperature gradient in excess of what is already included in the turbulence strength. It is recommended to use a value of zero unless other information is available.
Together with the air temperature the relative humidity is used to predict the attenuation due to air absorption. The value is normally available in standard weather data.“
Additional Information
Ground Absorption
In CadnaA, the ground factor G and the absorption coefficient Alpha are transformed by linear interpolation to an airflow 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):
| absorption coefficient Alpha | airflow resistivity σ (kNsm-4) |
|---|---|
| 0 | 20000 |
| 0.25 | 1000 |
| 0.50 | 600 |
| 0.75 | 400 |
| 1.00 | 50 |