Wave Equations With Kelvin-Voigt Damping and Boundary Disturbance: A Study of the Asymptotic Gain Properties

This paper provides estimates for the asymptotic gains of the displacement of a vibrating string with endpoint forcing, modeled by the wave equation with Kelvin-Voigt and viscous damping and a boundary disturbance. Two asymptotic gains are studied: the gain in the L
²
spatial norm and the gain in the spatial sup norm. It is shown that the asymptotic gain property holds in the L
²
norm of the displacement without any assumption for the damping coefficients. The derivation of the upper bounds for the asymptotic gains is performed by either employing an eigenfunction expansion methodology or by means of a small-gain argument, whereas a novel frequency analysis methodology is employed for the derivation of the lower bounds for the asymptotic gains. The graphical illustration of the upper and lower bounds for the gains shows that the asymptotic gain in the L
²
norm is estimated much more accurately than the asymptotic gain in the sup norm.