Validation of a FEM structure-borne sound radiation model for railway rolling noise

Railway rolling noise is a structure borne sound radiation mechanism that accounts for one of the major sources of noise arising from railways traffic. This mechanism has been extensively studied and dedicated software can perform reliable predictions, taking into account rail and wheel vibrations. This paper presents the derivation of a full three dimensional finite element model to calculate the acoustic radiation of a railway superstructure (rail, rail pads, and sleeper), including the underlying ballast. It focuses on the procedure to characterise and implement the ballast as a frequency dependent acoustic body. This can be done using an equivalent fluid for perforated material with complex effective density and sound velocity properties. The input information are lateral and vertical harmonic excitations performed on a test track and measured by means of a scanning laser Doppler vibrometer. The resulting track vibrational velocities are used as source excitation inputs for the three dimensional finite element model. The acoustic FEM model is validated by comparing the numerical predictions of the radiated sound field with experimental measurement of sound pressure levels.