Active control of squeal

Summary form only given. Squeal noise is generated by a feedback mechanism. It occurs if two bodies are in contact and move relative to each other so that a dry friction force 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. Curve squeal (the noise produced by the wheels of a train that travels fast round 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, filter, phase-shifter, amplifier and transducer. This type of control amounts to the stabilisation of an originally unstable wheel oscillation and is a special form of active control. A mathematical model for this secondary feedback method is presented. Numerical results for its effectiveness are shown