Abstract
Squeal noise is generated by a feedback mechanism. It occurs if two bodies are in contact and move relative to each other so that dry friction acts in the contact area. This can lead to an unstable oscillation driven by the feedback between the friction force and the relative velocity of the bodies. Sound is radiated from one or both oscillating bodies. Some well-known types of noise are generated by this phenomenon, for example squeal and the sound of a bowed string. Curve squeal (the noise produced by the wheels of a train that travels fast around a tight bend) is considered in this paper. The frequency spectrum of curve squeal is dominated by one or a few sharp peaks which correspond to certain bending resonances of the free wheel. Squeal noise can be controlled and even suppressed by a secondary feedback system, consisting of a sensor (to pick up the wheel oscillation or the squeal noise), filter, phase-shifter, amplifier, and transducer (to apply the control signal). This type of control amounts to the stabilization of an originally unstable wheel oscillation and is a special form of active control. A mathematical model for this secondary feedback method will be presented. Numerical results for its effectiveness will be shown.
Published Version
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