Command governor‐based adaptive control for dynamical systems with matched and unmatched uncertainties

In this paper, we propose a command governor‐based adaptive control architecture for stabilizing uncertain dynamical systems with not only matched but also unmatched uncertainties and achieving the desired command following performance of a user‐defined subset of the accessible states. In our proposed solution, online least‐squares solutions for the matched and unmatched parameters are obtained through integration method and they are employed in the adaptive control framework. Specifically, the matched uncertainty is identified and its effect upon the system behavior is entirely attenuated. Moreover, using the unmatched uncertainty approximation obtained through radial basis function neural networks, the command governor signal is designed to achieve the desired command following performance of the user‐defined subset of the accessible states. With this command governor‐based model reference adaptive control architecture, the tracking error of the selected states can be made arbitrarily small by judiciously tuning the design parameters. In addition to the analysis of the closed‐loop system stability using methods from the Lyapunov theory, our findings are also illustrated through numerical examples.     

Effects of interlayer density and surfactant on coupled thermal stress and moisture absorption in modified montmorillonite/polypropylene nanocomposite

Modified montmorillonite/polypropylene nanocomposites (NCs) are increasingly used in industrial applications such as subsea pipelines because hexadecyltrimethyl ammonium montmorillonite (HDTMA⁺-Mt) enhances thermomechanical and barrier properties of the amorphous polymer. Two coupled physics of moisture adsorption and thermal loading are investigated. Molecular dynamics simulates HDTMA⁺-Mt polymer NC using three force fields including polymer consistent force field and condensed-phase optimized molecular potentials, and embedded-atom method. Mechanical properties and self-diffusion coefficient are investigated at temperature levels of 100 and 298 K, and water content of 0.021 and 0.133 g/g. These properties are evaluated at 1.0 atm pressure for four different volume fractions (vol%) of the HDTMA⁺-Mt. The modeling procedure is verified by obtaining the glass transition temperature (T_g) of the NC by scanning the temperature from 200 K (glassy state) up to 325 K (rubbery state). It is observed that the T_g is very close to the experimental value available in the literature. The result of the modeling shows that the increase of clay content of the NC decreases the self-diffusion coefficient of the material. It is seen that the clay nanoparticle can significantly hinder the degradation of mechanical properties of the NC even when both temperature and water content increase.     

Removal of 1,2,4-Trimethylbenzene from Water by Pervaporation Using Styrene–Butadiene–Styrene (SBS) Membrane Incorporated with Carbon Black Nanoparticles

Styrene–butadiene–styrene (SBS) membranes incorporated with carbon black (CB) were prepared and investigated for pervaporation (PV) removal of 1,2,4-trimethylbenzene (TMB) from its aqueous solution. The influence of CB concentration on membrane properties was assessed by applying field emission scanning electron microscopy, differential scanning calorimetry, thermogravimetric analysis, X-ray diffraction, Fourier transform infrared spectroscopy, and tensile test. Characterization of the prepared membranes implied increased water contact angles at higher CB concentrations. Moreover, membrane swelling was constant zero for all the membranes. Performance of the prepared membranes in PV separation of a volatile organic compound (1,2,4-TMB) from water was studied. The SBS/CB nanocomposite membranes revealed higher separation factor and PV separation index (PSI) compared to pure SBS membrane because of the CB hydrophobic nature. The separation factor and PSI of the nanocomposite membrane loaded with 1 wt. % CB were 3.6 and 1.8 times more than those of the neat SBS membrane, respectively. The membrane obtained at this appropriate CB concentration provided the total flux of 735 g/m²h, separation factor of 950, and PSI of 700,000 g/m²h. POLYM. ENG. SCI., 60: 257–266, 2019. © 2019 Society of Plastics Engineers     

Microstructural development during spark plasma sintering of ZrB2–SiC–Ti composite

The present study investigates the effect of Ti addition on the microstructure development and phase evolution during spark plasma sintering of ZrB₂–SiC ceramic composite. A ZrB₂–20?vol% SiC sample with 15?wt% Ti was prepared by high-energy milling and spark plasma sintering at 2000?°C for 7?min under 50?MPa. The X-ray diffraction test, microstructural studies and thermodynamic assessments indicated the in-situ formation of several compounds due to the chemical reactions of Ti with ZrB₂ and SiC. The Ti additive was completely consumed during the sintering process and converted to the ceramic compounds of TiC, TiB and TiSi₂. In addition, another refractory phase of ZrC was also formed as a result of sidelong reaction of ZrB₂ and SiC with the Ti additive.     

Origin of dielectric loss in Ba(Co1/3Nb2/3)O3 microwave ceramics

The microwave dielectric loss of stoichiometric and non‐stoichiometric Ba(Co_1/3Nb_2/3)O₃ ceramics have been measured from 2 to 300 K in magnetic fields ranging from 0 to 5 T using a dielectric resonator (DR) technique. The microwave absorption from spin excitations of unpaired d‐electrons in exchange coupled Co²⁺ ions dominate the loss of the Ba(Co_1/3Nb_2/3)O₃ ceramics at cryogenic temperatures. Two peaks in the loss tangent (tan δ) vs temperature relation from a distinctly different origin occur at 25‐30 K and 90 K, which increase in magnitude with increasing Co content in the bulk dielectric samples. Evidence that these peaks result from polaron conduction from hopping between Co²⁺ and Co³⁺ ions includes (i) the peak's observed temperature range; (ii) the decrease in peak intensity of approximately a factor of two in a large applied magnetic fields (5 T); and (iii) a strong correlation between the peak's magnitude and both the fraction of the minority Co³⁺ in the dominant Co²⁺ matrix and D.C. conductivity at elevated temperatures. A magnetic‐field independent high temperature peak with a maximum at 250 K dominates the room temperature microwave loss whose magnitude correlates with those of the low temperature peaks. This suggests that the defects responsible for carrier conduction play an important role in establishing the loss tangent at room temperature.     

Sensitivity analysis pertaining to effective parameters on electrohydrodynamic drying of porous shrinkable materials

Abstract

A phenomenological computational fluid dynamics model was developed to simulate drying process of a porous body using electric field corona discharge. The set of coupled nonlinear partial differential equations were solved simultaneously and compared with the experimental findings in the literature. The relative error of the corona wind velocity compared to the experiments was less than 1%. The main gradients of the EHD volume force and corona wind were close to the discharge electrode. Moreover, for no inlet air, the corona wind velocity and field distribution indicated the existence of vortices as the main factor for enhancing mass transfer during the drying process. At a constant air velocity, increase in the voltage caused increasing the corona velocity. In addition, by increasing the air velocity to some extent, the corona velocity first increased and then started to drop. As a result, for any voltage and electrode distance from the surface, an optimum air velocity could be determined. Due to the sweep impact of the primary air flow and moving the ionized molecules to the outside, the drying rates at air velocity of 1?m s^?1 were higher than those for air velocity of 1.5?m s^?1. Applying an intake air flow also altered the optimal electrode velocity from the surface due to the occurred change in the corona discharge. Therefore, is concluded that the severity of mass humidity changes is affected by the applied voltage, electrode distances from the surface, temperature, and the intake air velocity.     

Quasi-classical modeling of molecular quantum-dot cellular automata multidriver gates

ABSTRACT: Molecular quantum-dot cellular automata (mQCA) has received considerable attention in nanoscience. Unlike the current-based molecular switches where the digital data is represented by the on/off states of the switches, in mQCA devices, binary information is encoded in charge configuration within molecular redox centers. The mQCA paradigm allows high device density and ultra-low power consumption. Digital mQCA gates are the building blocks of circuits in this paradigm. Design and analysis of these gates require quantum chemical calculations, which are demanding in computer time and memory. Therefore, developing simple models to probe mQCA gates is of paramount importance. We derive a semi-classical model to study the steady-state output polarization of mQCA multidriver gates, directly from the two-state approximation in electron transfer theory. The accuracy and validity of this model are analyzed using full quantum chemistry calculations. A complete set of logic gates, including inverters and minority voters, are implemented to provide an appropriate test bench in the two-dot mQCA regime. We also briefly discuss how the QCADesigner tool could find its application in simulation of mQCA devices.     

PRSV equation of state parameter modeling through artificial neural network and adaptive network-based fuzzy inference system

Two different modeling methods have been proposed to relate the Peng-Robinson-Stryjek-Vera (PRSV) parameter, κ ₁, to some common thermodynamic constants, including critical temperature (T _c ), critical pressure (P _c ), acentric factor (ω) and molecular weight (Mw). The methods are artificial neural network (ANN) and adaptive networkbased fuzzy inference System (ANFIS). A set of 159 data points (116, 23 and 20) was used for construct training, validating and testing, respectively. The radius parameter of ANFIS was determined through genetic algorithm (GA) optimization technique. The ANN and especially ANFIS results are in a good agreement with most of the compound groups.     

Preparation and characterization of nanoporous polysulfone membranes with high hydrophilic property using variation in CBT and addition of tetronic‐1107 surfactant

Asymmetric polysulfone (PSF) membranes were prepared from PSF, Tetronic‐1107, and 1‐methyl‐2‐pyrrolidone (NMP) via immersion precipitation. Pure water was used as the gelation media. The effects of coagulation bath temperature (CBT) (0 and 25°C), and addition of Tetronic‐1107 on the morphology, wettability, and pure water permeation flux (PWF) of the prepared membranes were studied by scanning electron microscopy (SEM), atomic force microscopy (AFM), contact angle measurements, and experimental set up. The contact angle measurements demonstrated that the hydrophilicities of the nanoporous PSF membranes were significantly enhanced by addition of a small amount of Tetronic‐1107 surfactant in the casting solution, along with using the lower CBT. It was also found that addition of Tetronic‐1107 in the casting solution along with increasing the CBT from 0 to 25°C incites formation of bigger pores on the top surface and results in formation of membranes with higher thickness and more porous structure in the sublayer. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013