Null-controllability for the beam equation with structural damping. Part 2: Integration by parts for fractional Laplacians and boundary control

Abstract

Let $Δ$ be the Neumann Laplacian on the interval $(0,π)$, and let $T>0$. An integration by parts formula is proven for the spectral fractional Laplacian, $(-Δ)^α$, for $α\in (0,1)$. As an application, we prove well-posedness results for the structurally damped beam equation $$u_{tt}+Δ^2 u+ρ(-Δ)^αu_t=0, x\in (0,π),t>0$$ with various boundary conditions including $$ u_x(0,t)=u_{xxx}(0,t)=0;\ u_x(π,t)=f(t),\ u_{xxx}(π,t)=0, $$ and $f\in L^2(0,T)$ and appropriate initial conditions. Viewing $f$ as a control, we prove null-controllability. Analagous results are proven for higher order controls, and for the Dirichlet Laplacian.