Analytical performance prediction for robust constrained model predictive control

This paper presents a new analysis tool for predicting the closed-loop performance of a robust constrained model predictive control (MPC) scheme. Currently, performance is typically evaluated by numerical simulation, leading to an extensive computation when investigating the effect of controller parameters, such as the horizon length, the cost weightings and the constraint settings. The analytic method, in this paper, avoids this computational burden, thus enabling a rapid study of the trades between the design parameters and the performance. Previous work developed an MPC formulation employing constraint tightening to achieve robust feasibility and constraint satisfaction despite the action of an unknown but bounded disturbance. This paper shows that the expected performance of that controller can be predicted using a combination of the gains of two linear systems, the optimal control for the unconstrained system, and a candidate policy used in performing the constraint tightening. The method also accounts for the possible mismatch between the predicted level of disturbance and the actual level encountered. The analytic results are compared with simulation results for several examples and are shown to provide accurate predictions of performance and its variation with the system parameters.     

Role of Chain Entanglements in the Electrospinning of Wheat Protein-Poly(Vinyl Alcohol) Blends

The aim of this investigation was to determine if the rapid solvent removal evaporation that occurs during electrospinning enabled the gluten protein and poly(vinyl alcohol) (PVOH) chains to remain at least partially entangled in the final product. Natural and synthetic biopolymer blends are known to phase separate in the melt. Differential scanning calorimetry (DSC) was used to test our hypothesis, which we achieved by systematically comparing the thermal profiles of the nonwoven fibrous sheets comprising: 1) 100% commercial wheat gluten, 2) 100% PVOH, and 3) the (75/25) wheat gluten/PVOH blend. The DSC scans of the two PVOH-containing, nonwoven fibrous sheets exhibited differences in the characteristics and positions of the melting peaks (T_m) of the PVOH crystalline phase, while the DSC scans of the nonwoven fibrous sheets comprising either 100% commercial wheat gluten or the wheat gluten/PVOH blend yielded neither a measurable glass transition temperature (T_g) nor a T_m. Energy dispersive spectroscopy (EDS) was used to compare the elemental compositions of the individual fibers with the compositions of the spherical domains found in the nonwoven fibrous mats. These scans revealed that the mineral matter found in commercial wheat gluten (roughly 1% by weight) had phase-separated from the bulk gluten protein as a result of electrospinning.