Experimental determination of pass-by noise contributions from the bogies and superstructure of a freight wagon

Pass-by noise from freight trains on straight tracks is dominated by rolling noise. The main contributions are generally accepted to originate from vibrations of the track and the wheels. However, there is uncertainty about the contributions from the bogie and the wagon superstructure. This article describes experimental methods to determine these. The methods combine vibration measurements on a rolling wagon and measurements of structural and of vibro-acoustical transfer functions under static conditions. Firstly, an inverse method is used to determine the equivalent structural excitation of a wagon. Secondly, two reciprocity methods are described for detailed vibro-acoustic transmission path analysis, with the wagon parts excited by the equivalent forces. As an example, some data will be shown from experiments on a widely used freight wagon. It appears that the contributions from two bogies and from the wagon superstructure are respectively 20 and 30dB(A) lower than the measured pass-by noise levels. Detailed information is obtained about the ranking of sub-areas which contribute to the sound radiation. The results illustrate the practical value of the methods even in the case of weak partial sources. (C) 2000 Academic Press.