Railway wheels are designed to be sections through a cone, so that the effective wheel diameter may be varied by the position of the wheel relative to the track, and this provides a simple geometric differential. However, because the bogies have fixed axles, prolonged sliding of the wheel rims against the rails will occur when a train traverses a bend at speed. As the wheels slip sideways across the rails, the friction forces acting at the wheel rim excite transverse vibrations in the wheel. In an experimental context, the vibration of a structure known to be prone to squeal might be logged on a spectrum analyzer and the FFT (Fast Fourier Transform) of the data displayed in real time. Initially many of the vibrational modes of the structure would be excited, resulting in an FFT trace containing a number of spikes. As the vibration develops, typically one of the resonance spikes will dominate, and this increase in amplitude would indicate the incipience of squeal. A broadening of the resonance spike may also be observed, indicating a variability in the frequency. Squeal is a form of self-excited vibration; vibrations are induced in a structure such as a wheel or violin string by the action of a frictional driving force. The nature of this force is rather difficult to define: however, a phenomenological model is proposed which combines the concepts of static and dynamic friction, which seems intuitively reasonable and for which there is documented evidence. The vibrating structure is simplified to that of a block resting on a moving conveyor belt, restrained by a simple spring and dashpot to a rigid wall. It has been demonstrated that if another variable besides velocity (in this case acceleration) is considered in the friction model, it is possible to see more than one type of dynamical behavior for any given system, and that the type of long term behavior excited will depend critically on the initial conditions.


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    Title :

    A non-linear friction model for self-excited vibrations


    Additional title:

    Ein nichlineares Reibungsmodell der selbsterregten Vibration


    Contributors:

    Published in:

    Publication date :

    1997


    Size :

    13 Seiten, 11 Bilder, 1 Tabelle, 19 Quellen




    Type of media :

    Article (Journal)


    Type of material :

    Print


    Language :

    English






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