Experimental assessment of structure borne noise generated by a braking resistor

This paper presents an application of modal analysis to the assessment of the structure borne noise level for a braking resistor to be mounted on the floor of a train carbody. This topic is becoming more and more important since the dynamic behavior of auxiliary components attached under the carbody strongly affects the passengers' comfort. In particular, a braking resistor contains one or more fans used to cool the electrical resistances that dissipate the braking energy by Joule effect. The rotation of these fans can represent a relevant source of vibrations even in presence of low eccentricity. In order to assess the transmitted vibrations before the real carbody has been built and to optimize the supporting elements of the braking resistor, an auxiliary fixture has been designed to reproduce the carbody mechanical impedance at the mounting point of the braking resistor. Thus, the first step is to design the fixture to have the same mechanical impedance of the carbody under construction (through finite element analysis); then, to measure its mechanical impedance along all three directions through impulsive tests and finally to assess the braking resistor's behavior when mounted on the fixture and operated as during real life conditions