  We study the problem of the minimum-time damping of a closed string under a
bounded load, applied at a single fixed point. A constructive feedback control
law is designed, which allows bringing the system to a bounded neighbourhood of
the terminal manifold. The law has the form of the dry friction at the point,
where the load is applied. The motion under the control is governed by a
nonlinear wave equation. The existence and uniqueness of solution of the Cauchy
problem for this equation are proved. The main result is the asymptotic
optimality of the suggested control law.
