  We study a class of elastic systems described by a (hyperbolic) partial
differential equation. Our working example is the equation of a vibrating
string subject to linear disturbance. The main goal is to establish conditions
for stabilization and asymptotic stabilization by applying a fast oscillating
control to the string. In the first situation studied we assume that system is
subject to a damping force; next we consider the system without damping. We
extend the tools of high-order averaging and of chronological calculus for
studying stability of this distributed parameter system.
