Damping and Stability Evaluation under an Accurate Description for the Hunting Motion of the Bullet Train Wheel Axle

Abstract

In order to further augment the bullet train's travelling velocity, a profounder comprehension of the wheel axle hunting motion is indispensable. An analytical expression for the natural frequency was early derived for the so-called geometrical hunting, but such model was unable to describe the inherent damping effects. Recently, analytical expressions for the damped natural frequency and damping ratio were proposed for the so-called dynamical hunting, by imposing restrictions on the ratio between the lateral and vertical creep coefficients, and also, on the ratio of the track span to the yawing diameter. However, instead of finding a pair of complex conjugate roots, and two real roots for the characteristic equation, two pairs of complex conjugate roots were obtained. Thus, due to the faulty model, the damping effect induced by the contact of the wheels with the rails was somewhat inaccurately predicted. Purpose of this work is to achieve accurate expressions for the hunting natural frequencies and damping ratios, without imposing geometrical and/or tribological limitations into the model, and furthermore, to evaluate the stability of the wheel axle.