Experimental analysis of the influence of the passengers on flexural vibrations of railway vehicle carbodies

It has been recently pointed out that railway vehicle passengers do not behave as inert masses but as dissipative elements: they increase modal damping without significantly affecting the natural frequencies of the carbodies. The phenomenon is more prominent in current lightweight high-speed railway vehicles, because weight reduction is usually attained at the expense of reduced stiffness. The few works that deal with the influence of passengers in actual structures are confronted with a large number of coupled structural vibration modes with cumbersome mode shapes, and this hinders the understanding of the physical mechanisms that make passengers attenuate vibrations. This work sheds some light on this topic from three points of view: new experimental tests on an actual carbody to corroborate and broaden existing results; simplified experimental tests, with small living beings (toddlers and pets) on a simplified pinned-pinned beam without modal coupling, to better determine the physical phenomena involved in the interaction between the passenger and the flexible structure; and improved analytical beam-cushion-passenger models to clarify the experimental results. All results suggest that passengers do indeed behave as classical dynamic vibration absorbers the positions of which with respect to the anti-nodes of mode shapes is key in vibration attenuation.