Time-Optimal Control of Thin-Film Growth under a Time-Fractional fourth-order parabolic Equation with Caputo Derivative
摘要
In this paper, we study a time-optimal boundary control problem for the evolution of thin film thickness governed by a time-fractional biharmonic (fourth-order) parabolic equation with a Caputo time derivative. The model accounts for the interplay between surface-tension effects and memory-driven anomalous diffusion, both of which play a key role in the dynamics of thin film growth. By employing a spectral decomposition method, we represent the solution in terms of eigenfunctions and Mittag-Leffler functions, and reformulate the control problem as a Volterra integral equation of the second kind. We construct admissible control functions that drive the system to a prescribed average thickness in minimal time, and derive explicit estimates for this time in terms of the model parameters. The results highlight the novelty of the fractional-order extension and extend the classical time-optimal control framework for the biharmonic equation to the subdiffusive regime, emphasizing how fractional memory affects controllability of thin film systems.