Motion planning for parabolic equations using flatness and finite-difference approximations
Soham Chatterjee, Vivek Natarajan
TL;DR
This work extends flatness-based motion planning to 1D linear parabolic PDEs with spatially varying, potentially discontinuous coefficients by combining finite-difference spatial discretization with a flatness parametrization of the resulting ODE in time. The authors prove convergence of the semi-discrete input to a limiting input that achieves the desired state transfer as the discretization refines, and they establish null controllability for such PDEs along with a constructive numerical scheme. They provide rigorous convergence results linking semi-discrete and continuous solutions, and they demonstrate the approach with a detailed numerical example, including a scheme to obtain null controls for piecewise continuous initial data. Collectively, the results yield both theoretical guarantees and practical algorithms for transferring parabolic PDEs between steady states and for achieving null controllability in the presence of coefficient discontinuities. The methods have implications for applications requiring precise startup/shutdown and setpoint changes in systems modeled by 1D parabolic dynamics with heterogeneous media.
Abstract
We consider the problem of finding an input signal which transfers a linear boundary controlled 1D parabolic partial differential equation with spatially-varying coefficients from a given initial state to a desired final state. The initial and final states have certain smoothness and the transfer must occur over a given time interval. We address this motion planning problem by first discretizing the spatial derivatives in the parabolic equation using the finite-difference approximation to obtain a linear ODE in time. Then using the flatness approach we construct an input signal that transfers this ODE between states determined by the initial and final states of the parabolic equation. We prove that, as the discretization step size converges to zero, this input signal converges to a limiting input signal which can perform the desired transfer for the parabolic equation. While earlier works have applied this motion planning approach to constant coefficient parabolic equations, this is the first work to investigate and establish the efficacy of this approach for parabolic equations with discontinuous spatially-varying coefficients. Using this approach we can construct input signals which transfer the parabolic equation from one steady-state to another. We show that this approach yields a new proof for the null controllability of 1D linear parabolic equations containing discontinuous coefficients and also present a numerical scheme for constructing a null control input signal when the initial state is piecewise continuous.