Instability of vibrations of a mass moving uniformly over periodically and randomly-inhomogeneous elastic systems

Vibrations of a mass are studied moving uniformly along an infinite string on an weakly inhomogeneous visco-elastic foundation. Periodical and quasi-periodical types of the inhomogenity are considered. It is shown that the mass vibrations can be unstable. The conditions of instability are analytically derived. The instability zone occurs at lower mass velocities as the period (characteristic period ) of the inhomogenity decreases. The larger the mass, the wider the instability zones. The stabilisation influence of the foundation viscosity increases when the mass velocity grows.