Rolf Tore Randeberg, Research scientist, SINTEF. Tel. 735 92668 / 416 70 206
The Norwegian Public Roads
Administration (NPRA) has since 2004 commissioned the development of a new tool
for calculation of (road) noise. Version 3.0 was released at the end of 2009,
and supports the requirements of the new ”Støybygg 3”
software for calculation of indoor noise.
Norstøy’s central calculation kernel,
which calculates the point-to-point ground attenuation, is the Nord 2000
method. Compared to earlier methods, Nord 2000 has a very
high computer power consumption. Hence, new procedures had to be developed to
achieve a reasonable balance between calculation time and precision, when the
method is used for large scale mapping.
The Norstøy software consists of a user
interface and a calculation module, the latter developed by SINTEF. The
calculation module consists of a central core, a number of calculation cells
distributed on computers in the network, and a service which administers the
tasks and the calculation cells.
The distribution of noise calculation on
networked computers reduces the total computation time. To additionally reduce
the total (CPU) computation time, further steps were required, as listed below.
• Advanced
interpolation of receiver points. Noise contours are generated from an
irregular grid of receiver points. This grid consists of a regular grid
interspersed with points along constricting lines such as buildings and
screens. The latter, non-regular points are calculated using the fast, but
lesser accurate, Nordic method for industrial noise. The regular points are
calculated using both Nord 2000 and the industrial noise method. The noise
level difference between the two methods is then added to the non-regular
points in the vicinity of the regular points.
• Significance
testing of sources. The road sources are split into a large number of straight
segments. These source segments are then tested for proximity and contribution
to the total noise level at each receiver point, using the fast, but lesser
accurate, industrial noise method. Only significant source segments are subsequently
calculated using the Nord 2000 method.
• Reuse
of reflected sound. For each source point along the road, subsources are
created for each of the lanes of the road and for three source heights. For
direct sound, the contribution from each of these subsources
are calculated separately. However, for groups of subsources where the
direct sound contribution is approximately equal, the reflection contribution
is calculated only once, and the resulting reflection factor is applied to the
reflection contribution from all subsources in the group.
The presentation will explain the technology and its influence on the resulting quality and calculation time of Norstøy.