Method to calculate L_(AFmax) noise map from L_(Aeq) noise maps, for roads and railways

摘要

This paper presents the simple theoretical relations between L_(AFmax) and L_(Aeq), for roads (simulation each vehicle as a moving point source) and railways (simulation of each vehicle/train as a moving line source with length l). From these relations -more valid for close proximity to the source - and knowing the typical values of L_(Aeq) for roads and railways, according with the standard methods available, the associated calculation of typical values of L_(AFmax) was performed. Knowing - by this way or another - the L_(AFmAx) close to the roads or railways, the typical noise source, on typical software, must be divided into small parts, with 1 m length each. After that, one of these small parts must be converted on a line source with a sound power that give, 1 m distance, an L_(Aeq) equal to the L_(AFMax) we want (the spectrum must be adjusted accordingly). All the other small parts, related, must be converted on a line source with the same sound power level. An independent noise map must be calculated for each small line source. For each noise receiver the L_(AFmax), from a pass-by, is the greater value of all line source independent noise maps. This procedure can consume too much time, depending on the number of small line sources we have. Fortunately, some available software - for example the Cadna A - permits the calculation of L_(AFmax) noise maps from different line sources. To do that, Cadna A needs the introduction of the difference value between L_(AFMax) and L_(Aeq) for each small line source, so that must be calculated. At major distances to the road or railway, this L_(AFMax) noise map gives smaller values than the regular L_(Aeq) noise map, so, by definition, the global Lafmox noise map must have the greater value, in each receiver point, from these two noise maps.