Study of inertial forces in roller test rigs using differential geometry and classical mechanics

Abstract

This study clarifies a doubt on the validity of using roller tests rigs for evaluating the dynamics of rail vehicles running on straight tracks. The tested vehicle has no forward speed and stands on a wheel equipped with rails of which the tangential constant velocity, V, simulates the real vehicle velocity. Using this test method assumes that bogie dynamics depend only on contact forces. Recently, ref. [1] argue that, due to the lack of forward speed, roller test rigs are lacking inertial ‘centrifugal’ forces. As these forces cannot be calculated on test rigs where the vehicle forward speed is zero, hence comes the validity question. We answer by developing an imaginary scenario where a mass, representing a railway wheelset, is associated to a spring forming a pendulum oscillating along the normal to the vehicle speed. The paper demonstrates that the calculated inertial forces are split into two forces, normal and tangential to the trajectory, and that, although each one of these two forces depends on V, only their resultant, which does not depend on V, has a mechanical meaning and does not contradict classical mechanics which support the validity of test rigs. A numerical example supports this conclusion.