Nordic Prediction Method (1996)
Calc exactly one reflection order
With this option deactivate the maximum order of reflection is specified via the „Reflection“ tab (see Reflection Tab).
Railway Correction (dB)
Any entered railway correction will be considered upon calculation. Thus, to consider no railway correction a value of 0 dB has to be entered.
Parameters for calculation of maximum Pass-By-Level
Select evaluation parameters LmaxD/E/N to calculate the maximum Pass-By-Level (see Evaluation Parameters Tab).
The A-weighted maximum levels LAFmax and LmaxF are additional descriptors for railway noise in Nordic Prediction Method NPM524-1996. The different corrections are calculated in complete analogy with those of the A-weighted equivalent continuous sound pressure level LA,eq, but a different emission parameter is used (see Nordic Prediction Method 1996).
Note
Besides the emission level, the propagation models for Leq and Lmax calculations differ as well.
Option LmaxM/LmaxF
In CadnaA, the two A-weighted maximum sound pressure levels, LmaxM (energy average over train length) or LmaxF (highest level with weighting „Fast“) can be calculated (see Nordic Prediction Method 1996).
Note
The option „Diesel“ has to be set accordingly for each train class on the dialog Library: Train Class (see Train Class Libraries, Application Nordic Prediction Method).
In order to calculate maximum levels, CadnaA moves a line source for each train class in the train classes list of the railway object. This line source has the sound power level and length as specified in the list. This source is moved according to its speed and specified sampling interval (see below). The maximum level for this line source for each position with the specified sound power level and length is calculated.
Sampling Interval (s)
In order to determine the highest level, CadnaA shifts the source along the road in steps based on the sampling interval (in seconds). The default value for the sampling interval is 0.1 seconds.
Consequently, the resulting distance difference between two source positions is:
\(s=v*t_{\text{sampling}}*\frac{1000}{3600}\)
with
- s: distance steps (m)
- v: speed (km/h), as entered on dialog Railway
- t: sampling interval (s)
Note
Displaying rays (see Receiver) and the calculation protocol (see Calculation Protocol) do not make sense with maximum levels as the radiating points are defined by the sampling time. The rays coming from points outside result from the calculation procedure (in case the option „Extrapolate trains to 1/2 length on both sides of rail“ is activated, see below).
Option „Extrapolate trains to 1/2 length on both sides of rail“
By default, this option is activated. In this case, when calculating the maximum pass-by level, the length of each train class on the track is extrapolated by half of its length beyond the first and the last point of the drawn railway object to cope with segmented railways (e.g. due to different maximum speeds).
By deactivating this option, the train length will not be extrapolated beyond the first and the last point of the railway object. Deactivating this option may cause a substantial level decrease for receivers/grid points near the end of the rail source and at curves (see example below).
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Note
Instead, with the option deactivated, each railway object could be extended manually to overlap with the next railway object making up the railway track. However, this would require a separate railway object for each train class in order to extend the source line properly with respect to the train length of each class.
No extrapolation with maximum level calcs
In order to suppress the extrapolation in case of maximum level calculations define the following string variable/s in the memo window of the respective railway object:
LMAX_NO_EXTRAPOL_PFIRST=1
LMAX_NO_EXTRAPOL_PLAST=1
With the string variable set, the emission line will not get extrapolated extending either from the railway‘s first polygon point or from it‘s last point.
Other Properties: See Industry
This hint refers to the following settings on the „Industry“ tab:
- lateral diffraction
- if distance smaller
- temperature/relative humidity
Use Non-Standard Reference Time D/E/N
With this option activated the time intervals and penalties on „Reference Time“ tab are applied in the calculation.
As the specification of emission of NPM is based on the traffic data within 24 hours, the values have to be corrected when using daily periods D/E/N with END-calculations EU2002/49/EG-2002. The correction for each octave band is:
\(L'_{w0,D/E/N}=L'_{w0}-10 \lg \frac{t_{D/E/N}}{24}\:dB\)
with
- L’w0, D/E/N: octave band emission level in period D/E/N of length tD/E/N (in hours)
- L’w0: octave band emission level for 24 hours
Example
For a daily period D of 12 hours the following correction applies:
\(L'_{w0,D}=L'_{w0}-10 \lg \frac{12}{24}\:dB = L'_{w0} + 3 \: dB\)
Note
The values displayed on the „Reference Time“ tab (D/E/N=12/4/8 h) will be updated based on the defined time periods DEN.