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Spécial “ 5es Assises sonore ”
61
Acoustique
&
Techniques n° 51
Noise mapping for railway noise: assessment of NMPB method as implemented in different software, comparison with RMR method
Theoretical comparison of NMPB-RMR methods
The difference in noise mapping when applying the French
method NMPB or the Dutch method RMR has been also
assessed. First of all, it is necessary to compare the
noise emission of similar trains.
Then, the database of the
SNCF emission values has been
compared with the categories
proposed in the RMR method.
Assignation of the SNCF
trains emission to a train
category of the RMR
database
The SNCF trains emission
database contains measured
noise levels at the reference
position (distance of 25m from the
track centre and height of 3,5m
above the rail). These values are
compared with the results of the
calculations carried out by means
of acoustic softwares at the same
position. The assignation is done
to the most similar train in noise
spectrum and overall value.
The figure 2 shows the measured noise spectrum of the
TGV-Duplex train (double-decker high speed train) and the
noise spectrum calculated with CadnaA using the “category
9” source and the noise spectrum calculated with Immi
using “category 9B” source.
Sound pressure levels and
spectra are very simi lar at
25m from the track. Even if the
source models are not the same,
mainly in terms of directivity,
the isophones of the high speed
train presented figure 3 turn
out to be quite similar in both
methods.
The same analysis has been
carried out for freight train. It
seems to be difficult to find a
category in the RMR database
which fit the measured data
from the SNCF. As presented
f igure 4, the noise of the
f re ight t ra i n measured by
SNCF is 2 dB(A) noisier than
the noise calculated with Immi
or CadnaA using the “category
4” noise source.
Fig. 1 : Noise levels difference in absolute values between Mithra and CadnaA
Différence des valeurs des niveaux de bruit entre Mithra et CadnaA
Fig. 2: Noise levels at the reference point (25 m from track centre and 3,5
meters above ground) measured for TGV-D train (+), and category 9
calculated with CadnaA (
Δ
) and category 9B calculated with Immi (o)
Niveaux de bruit au point de référence (25m du centre des voies, et
3.5m au dessus du terrain), mesurés pour un TGV-D (+), de catégorie 9,
calculé avec CadnaA (
Δ
), et de catégorie 9B calculé avec Immi (o)
Fig. 3 : Noise levels for a high speed train at 300Km/h with absorptive ground and meteorological conditions 100% favourable.
Above NMPB TGV-D, below RMR category 9 both calculated by means of CadnaA
Niveaux de bruit d’un Train à Grande vitesse à 300km/h, avec un sol absorbant et des conditions
météorologiques 100% favorables. TGV-D avec la NMPB et RMR catégorie 9 calculés avec CadnaA