Feedback methods for inverse simulation of dynamic models for engineering systems applications

Inverse simulation is a form of inverse modelling in which computer simulation methods are used to find the time histories of input variables that, for a given model, match a set of required output responses. Conventional inverse simulation methods for dynamic models are computationally intensive and can present difficulties for high-speed applications. This paper includes a review of established methods of inverse simulation,giving some emphasis to iterative techniques that were first developed for aeronautical applications. It goes on to discuss the application of a different approach which is based on feedback principles. This feedback method is suitable for a wide range of linear and nonlinear dynamic models and involves two distinct stages. The first stage involves design of a feedback loop around the given simulation model and, in the second stage, that closed-loop system is used for inversion of the model. Issues of robustness within closed-loop systems used in inverse simulation are not significant as there are no plant uncertainties or external disturbances. Thus the process is simpler than that required for the development of a control system of equivalent complexity. Engineering applications of this feedback approach to inverse simulation are described through case studies that put particular emphasis on nonlinear and multi-input multi-output models

Effect of Reynolds number and lithium cation insertion on titanium anodization

This work studies the influence of using hydrodynamic conditions (Reynolds number, Re = 0 to Re = 600) during Ti anodization and Li+ intercalation on anatase TiO2 nanotubes. The synthesized photocatalysts were characterized by using Field Emission Scanning Electron Microscope (FE-SEM), Raman Confocal Laser Microscopy, Electrochemical Impedance Spectroscopy (EIS), Mott-Schottky analysis (M-S), photoelectrochemical hydrogen production and resistance to photocorrosion tests. The obtained results showed that the conductivity of the NTs increases with Li+ intercalation and Re. The latter is due to the fact that the hydrodynamic conditions eliminate part of the initiation layer formed over the tube-tops, which is related to an increase of the photocurrent in the photoelectrochemical water splitting. Besides, the photogenerated electron-hole pairs are facilitated by Li+ intercalation. Finally, this work confirms that there is a synergistic effect between Re and Li+ intercalation

Passive and transpassive behaviour of Alloy 31 in a heavy brine LiBr solution

The passive and transpassive behaviour of Alloy 31, a highly alloyed austenitic stainless steel (UNS N08031), has been investigated in a LiBr heavy brine solution (400 g/l) at 25 °C using potentiostatic polarisation combined with electrochemical impedance spectroscopy and Mott-Schottky analysis. The passive film formed on Alloy 31 has been found to be p-type and/or n-type in electronic character, depending on the film formation potential. The thickness of the film formed at potentials within the passive region increases linearly with applied potential. The film formed at transpassive potentials is thinner and more conductive than the film formed within the passive region. These observations are consistent with the predictions of the Point Defect Model for passive and transpassive films on metals and alloys

Control of Nonlinear Systems With Friction

In this paper we introduce a new continuous dynamic controller for a class of nonlinear systems which includes mechanical system models with a bristle model for nonlinear friction effects. We obtain sufficient conditions for global stabilization using an estimate for bristle defection and present experimental results illustrating the benefits of our dynamic controller in the regulation of a high speed linear positioning table. Keywords: nonlinear systems, friction observers, Lyapunov stability. 1 Introduction Using model-based friction compensation in low velocity high precision tracking control can effectively reduce steady state error [3] without the need for excessive integral gains. Coulomb friction, viscous and static friction, and the Stribeck effect have been modelled successfully (c.f. [3, 4, 10]). In [1] friction in a lubricated journal bearing is both measured and estimated using a friction observer. System performance substantially improved when the friction estimate was u..

Global Approximate Output Tracking for Nonlinear Systems

This paper addresses the global output tracking problem for nonlinear systems with singular points. For nonlinear systems which satisfy a suitable observability condition, we identify a class of smooth output trajectories which the system can track using continuous open loop controls. This class includes all output trajectories generated by smooth state state feedback. We then study the problem of approximate output tracking using discontinuous time-varying feedback controllers. Given a smooth output trajectory for which exact tracking is possible, we construct a discontinuous feedback controller which achieves robust tracking of the desired output trajectory in the face of perturbations. Finally, it is shown that our results can be applied to the control of a chain system, and some numerical results are presented to illustrate the performance of our controller. Keywords: nonlinear systems, global output tracking, singular points, discontinuous state feedback. 1 Introduction The out..

Possible mechanism for the room-temperature stabilization of the Ge(111) T > 300 deg.C phase by Ga

At low coverages, Ga on Ge(111) induces a hexagonal, domain wall modulated (2×2) adatom phase, stable at room temperature, that is characterized in low energy electron diffraction (LEED) by split 1/2-order reflections. This pattern closely resembles the one observed for a phase of clean Ge(111) appearing at temperatures above 300 °C (T>300 °C phase). We report scanning tunneling microscopy, LEED, as well as surface x-ray diffraction measurements on the Ga-induced room-temperature (RT) phase and compare it with a model for the T>300 °C phase of clean Ge(111). RT deposition of Ga yields a metastable c(2×8) structure which upon annealing transforms to the hexagonal (2×2) one. The transition occurs at considerably lower temperatures compared to clean Ge(111) and is irreversible due to pinning of adatom domains at Ga-induced defects, preventing the reordering of the adatoms and the correct stacking of the c(2×8) structure when cooling to RT. For the lowest Ga coverages investigated, a stablized phase is obtained that resembles a striped (2×2) rather than a hexagonal (2×2) structure. We discuss the possible existence of a striped (2×2) phase as an intermediate state in the transition from the c(2×8) of clean Ge(111) to the T>300 °C phase. Driven by entropy—and in the presence of Ga by defects—this intermediate phase transforms to a quasihexagonal (2×2) structure above 300 °C