Approximate controllability of infinite dimensional system with internal damping dependent on fractional powers of system operator

In this study, a class of models governed by a second-order (in time) evolution differential equation with damping and positive definite, self-adjoint system operator is studied. Damping term has a special, but practically important, form of a finite sum of fractional powers of the system operator. This type of damping operator can be used to model a variety of physical phenomena related to dissipation of energy empirically observed in physical systems. It may be used to model dissipation mechanisms resulting from air damping, internal structural damping, internal viscous damping, etc. Using spectral theory of linear unbounded operators and semi-group theory necessary and sufficient conditions of approximate controllability for second order infinite dimensional system with damping are formulated and proved. Some important, from the practical point of view, remarks and comments are also provided. In particular, necessary condition for approximate controllability is formulated and discussed. Finally, an illustrative example related to approximate controllability of distributed parameter system described by the partial differential equation with higher order spatial differential operators is presented. The example refers to a system describing dynamical behaviour of damped Kirchhoff-Love plate. The study extends earlier results on approximate controllability of damped second-order abstract evolution dynamical systems.