Instability of vibrations of an oscillator moving along a beam on an elastic half-space

The stability of vertical vibrations of an oscillator moving uniformly alon g a beam on an elastic half-space has been investigated. Expressions for th e equivalent stiffness of the beam have been derived at the contact point w ith the oscillator. It has been shown that the imaginary part of the equiva lent stiffness can have a sign, which is interpreted as the so-called 'nega tive viscosity'. Frequency bands where the equivalent stiffness gives the ' negative viscosity' have been analyzed. Using the expressions for equivalen t stiffness the instability zones for the oscillator vibrations have been f ound. Instability can take place when the velocity of the oscillator exceed s the minimum phase velocity of waves in the beam. The effect of viscosity in the beam on the stability of the system has been considered. It has been shown that a small viscosity destabilizes the system. (C) Elsevier, Paris.