Robust fault-tolerant control for power systems against mixed actuator failures

Kaviarasan, B.,Sakthivel, R.,Kwon, O.M. Elsevier Ltd 2016 NONLINEAR ANALYSIS HYBRID SYSTEMS Vol.22 No.-

<P>This paper employs linear matrix inequality (LMI) based optimization algorithm to develop a method for designing fault-tolerant state feedback controller with mixed actuator failures for power systems subject to random changes. Meanwhile, the random abrupt changes are determined by a finite set Markov chain so the considered system is equivalently represented as a discrete-time Markov jump linear system (MJLS). Further, due to the variations of loading conditions in power system, an uncertainty term is incorporated to MJLS. For the proposed system, we construct a novel actuator fault model containing both linear and nonlinear terms which is more general than the conventional actuator fault models. The main purpose of this paper is to design the robust fault-tolerant controller such that for all possible actuator failures, time-varying delays and admissible parameter uncertainties, the closed-loop uncertain discrete-time MJLS is robustly stochastically stable. Based on free-weighting matrix approach and linear matrix inequality theory, anew set of sufficient conditions that guaranteeing the robust stochastic stability is presented by choosing an appropriate Lyapunov-Krasovskii functional candidate. In addition, a single-machine infinite-bus (SMIB) power system is considered as an application example and its simulation results demonstrate the effectiveness of the proposed design techniques. (C) 2016 Elsevier Ltd. All rights reserved.</P>

Application of Ca-doped mesoporous silica to well-grouting cement for enhancement of self-healing capacity

Lee, S.W.,Jo, M.,Kim, J.W.,Kim, T. Elsevier Ltd 2016 Materials & Design Vol.89 No.-

<P>Carbonation has been considered as an alternative to prevent CO2 leakage. In this study, calcium-doped mesoporous silica (CDMS) was introduced into Portland cement as a promoter of carbonation. An admixture of CDMS and American Petroleum Institute (API) Class G Portland cement exposed to CO2-saturated water was analyzed under geologic sequestration conditions (40 degrees C and 80 MPa) to assess the carbonation properties and self-healing effect of CDMS for CO2 storage. The capacity of CDMS to synthesize CaCO3 from CO2 via carbonation was identified in an in vitro crystallization test. Analysis of the cut surface of a cement core showed the rapid synthesis of CaCO3 including calcite and aragonite. Rietveld analysis was employed for quantitative phase analysis. The quantitative analysis of the cement carbonation showed that tricalcium silicate (C3S) and dicalcium silicate (C2S) play important roles in cement carbonation. Several crystal phases of CaCO3 were identified in this study including calcite, aragonite and amorphous CaCO3. X-ray diffractometry (XRD), a field emission-scanning electron microscope (FE-SEM) equipped with an energy dispersive X-ray spectrometer (EDS), Si-29 MAS-NMR (magic angle spinning-nuclear magnetic resonance) spectrometry, thermogravimetiy-differential thermal analysis (TG-DTA) and FT-IR (Fourier transform infrared spectroscopy) were applied to characterize the admixture. (C) 2015 Elsevier Ltd. All rights reserved.</P>

Design principle of super resolution near-field structure using thermally responsive optical phase change materials for nanolithography applications

Park, G.,Lee, J.,Kang, S.,Kim, M.,Kang, S.,Choi, W. Elsevier Ltd 2016 Materials & Design Vol.102 No.-

<P>The super resolution near-field structure (Super-RENS) which is composed of a thin layer of a thermally responsive optical phase change material (PCM) between two dielectric layers, can be a means of resolving the limited resolution of the laser beam for direct laser lithography. In Super-RENS, incident laser irradiation induces the direct, reversible opening and closing of a nanoaperture in the PCM layer, and a nanoscale pattern is realized in the lithography system. Here, we first introduce the complete modeling procedures and optimization methodology for Super-RENS in nanolithography based on a rigorous analysis of near-field structure, thermal analysis in the finite-element method, and analysis of the corresponding feature size on the photoresist (PR) layer. Multiple combinations of the PCM layer and the two dielectric layers with varying dimensions are considered as design parameters to achieve the required resolution in the nanolithography system. The feasible line profiles are investigated at the general operating conditions of the pulsed laser beam, based on varying dimensions of the PCM layer (5-30 nm) and the two dielectric layers (10-200 nm). This work will provide a detailed methodology for the design and optimization of the Super-RENS for applications in the nanolithography system. (C) 2016 Elsevier Ltd. All rights reserved.</P>

Formation mechanism of typical onion ring structures and void defects in friction stir lap welded dissimilar aluminum alloys

Yoon, T.J.,Yun, J.G.,Kang, C.Y. Elsevier Ltd 2016 Materials & Design Vol.90 No.-

<P>The formation mechanism for typical onion ring structure and void defect with heat input during FSLW was continuously visualized by an exit-hole continuous observation technique. Based on this result, the compatibility between microstructure, microtexture, element maps and strain maps using electron backscattered diffraction (EBSD) with the chemical indexing assisted by EDS analysis was simultaneously investigated. The results revealed that the threaded probe was significantly correlated to typical onion ring structure and the onion structure formed as soon as it touched the probe. This result is different from the results so far. On the other hand, the remnant of original interface between top and bottom plates after FSLW and asymmetrical flow around rotating tool were significantly correlated to the formation of void defect in low heat input condition. (C) 2015 Elsevier Ltd. All rights reserved.</P>

Molecular simulation for thermoelectric properties of c-axis oriented hexagonal GeSbTe model clusters

Vora-ud, A.,Rittiruam, M.,Kumar, M.,Han, J.G.,Seetawan, T. Elsevier Ltd 2016 Materials & Design Vol.89 No.-

<P>Using a combination of molecular orbital and molecular dynamics simulations, electronic and thermoelectric properties of GeSbTe model clusters are presented. The unit cells of Ge13Sb20Te52, Ge7Sb12Te40 and Ge14Sb6Te26 model clusters are designed corresponding to GeSb2Te4, GeSb4Te7 and Ge2Sb2Te5 compositions in hexagonal phase, oriented in the c-axis direction. The electronic structures of clusters have been simulated by discrete-variational molecular orbital calculation using Hartree-Fock-Slater approximation to determine the electrical conductivity and Seebeck coefficients in Mott expression. For thermal properties, molecular dynamics simulations have been employed on clusters in amorphous, cubic and hexagonal phases using Verlet's algorithm and subsequently using Green-Kubo relation for lattice thermal conductivity. We assumed inter-atomic interaction, defined by the Morse-type potential function added to Busing-Ida potential function, which considers partial electronic charges on the ions, bond length of the cation-anion pair, and depth and shape of the potential. Based on our simulations, detailed variation of electrical conductivity, carrier thermal conductivity, lattice thermal conductivity, Seebeck coefficients, power factor and figure of merit, are presented as a function of temperature in 300-700 K range. Thermoelectric parameters obtained in present study were compared and explained with those of experimentally results of Ge2Sb2Te5 composition in hexagonal phase. (C) 2015 Elsevier Ltd. All rights reserved.</P>

Understanding the relationship between microstructure and mechanical properties of Al-Cu-Si ultrafine eutectic composites

Kim, J.T.,Lee, S.W.,Hong, S.H.,Park, H.J.,Park, J.Y.,Lee, N.,Seo, Y.,Wang, W.M.,Park, J.M.,Kim, K.B. Elsevier Ltd 2016 Materials & Design Vol.92 No.-

<P>Systematic investigations for the influence of the microstructural change derived from compositional tuning in Al-rich corner of Al-Cu-Si system on mechanical properties demonstrate that mechanical characteristic of ultra fine eutectic composites strongly depend on the crystallinity, length scale and volume fraction of constituent phases. Ultrafine eutectic composites can be divided into two categories: 1) whether primary phases exist or not and 2) the types of matrix phases, i.e., single eutectic or bimodal eutectic. The features of primary phases play a principal role on the macroscopic property. Ductile alpha-Al phase is very effective to improve the plasticity while brittle Al2Cu intermetallic phase deteriorates obviously mechanical performance. In addition, bimodal eutectic matrix alloys composed of eutectics with different length scale and morphology show superior mechanical properties than single eutectic matrix alloys. Based on the microstructural studies, it is believed that high strength is originated from ultrafine scale microstructure and enhanced plasticity is supported by strain gradient plasticity. These results reveal that mechanical properties of the ultrafine eutectic composites can be properly optimized via control of chemical and topological governing factors. (C) 2015 Elsevier Ltd. All rights reserved.</P>

New results on passivity-based H_~ control for networked cascade control systems with application to power plant boiler-turbine system

Mathiyalagan, K.,Park, J.H.,Sakthivel, R. Elsevier Ltd 2015 NONLINEAR ANALYSIS HYBRID SYSTEMS Vol.17 No.-

<P>This paper is concerned with the problem of passivity-based H-infinity controller design for a class of networked cascade control systems (NCCSs) with random packet dropouts. The NCCS under consideration is modeled by using state feedback controllers and the network-induced imperfections like packet dropouts and time-varying delays. The model is defined with a stochastic packet-dropout case by using the Bernoulli distributed white sequence with time-varying probability measures. The probability-dependent conditions for stabilization of NCCSs are established to guarantee the resulting closed-loop system to be stochastically stable and achieve a prescribed mixed H-infinity and passivity performance. The Lyapunov stability theory and linear matrix inequality (LMI) approach are used to derive criteria for the existence of the state feedback controllers. The proposed probability-dependent gain scheduled controller can be designed by solving the convex optimization problem by means of a set of LMIs, which can be easily solved by using some standard numerical packages. Finally, a practical application is presented to illustrate the effectiveness and potential of the proposed results. (C) 2015 Elsevier Ltd. All rights reserved.</P>

Joining of metal-ceramic using reactive air brazing for oxygen transport membrane applications

Raju, K.,Muksin,Kim, S.,Song, K.s.,Yu, J.H.,Yoon, D.H. Elsevier Ltd 2016 Materials & Design Vol.109 No.-

<P>This study examined the joining of dense Ce0.9Gd0.1O2 (-) (delta)-La0.6Sr0.4Co0.2Fe0.8O3 (-) (delta) (GDC-LSCF) ceramics to high temperature metal alloys for the fabrication of multilayered oxygen transport membrane (OTM) stacks. Reactive air brazing using a silver-based paste was performed at 1050 degrees C for 30 min in air to join GDC-LSCF/high temperature alloys, such as AISI 310S, Inconel 600 and Crofer 22 APU. The effects of the various filler materials, including CuO, GDC, LSCF, and GDC-LSCF mixture, in the Ag paste were also examined. The Ag-10 wt% CuO braze filler ensured in a reliable and compact joining without the formation of cracks and voids at the joining interface, while the addition of other ceramic fillers resulted in incomplete joining. Although none of the GDC-LSCF/metal alloy joints showed gas leakage at room temperature, the GDC-LSCF/Crofer joint only maintained the gas-tightness up to 800 degrees C under pressurized air up to 7 bars, which was explained by the microstructural rigidness of the oxide layer formed on the filler/alloy interface at high temperatures. This was supported by the minimal decrease in shear strength of the GDC-LSCF/Crofer joint, which was 91.1 and 88.3 MPa for the as-brazed and isothermally aged joint at 800 degrees C for 24 h in air, respectively. (C) 2016 Published by Elsevier Ltd.</P>

Mechanical and high temperature wear properties of extruded Al composite reinforced with Al₁₃Fe₄ CMA nanoparticles

Nemati, N.,Emamy, M.,Penkov, O.V.,Kim, J.,Kim, D.E. Elsevier Ltd 2016 Materials & Design Vol.90 No.-

<P>The mechanical and tribological properties of extruded aluminum matrix composites reinforced with various weight percentages (1, 3, 5, 7, 10 wt.%) of Al13Fe4 complex metallic alloys (CMAs) were investigated. The nano-composites were produced using conventional powder metallurgy and a hot extrusion process. The tribological behavior of the composites was investigated under normal loads in the range of 20-80 N using a reciprocating high-temperature tribo-tester over a temperature range of 25-350 degrees C. At an optimized reinforcing agent concentration of 5 wt.%, the composite showed a significant enhancement in Young's modulus (similar to 108 MPa) and hardness (similar to 1.85 GPa). The lowest coefficient of friction of 0.1 was attained at a temperature of 250 degrees C with a reinforcing agent concentration of 5 wt.%. Also, the wear rate was reduced by a factor of similar to 25 compared to the unreinforced aluminum specimen. The significant improvement in the tribological properties of the nanocomposite was attributed to the enhanced mechanical properties due to severe plastic deformation incurred during the extrusion process and incorporation of well distributed CMA nanoparticles in the matrix which provided oobstacles for dislocation motion. Detailed microstructural analyses revealed that incorporation of the second phase to the Al matrix led to microstructure refinement and increased the hardness up to similar to 2 GPa. Furthermore, the nanoparticles aided in the formation of hard and temperature-resistant tribo-layers which reduced the wear rate of the composite (Al-5 wt.% Al13Fe4) down to 1.5 x 10(-4) at 250 degrees C. (C) 2015 Elsevier Ltd. All rights reserved.</P>

Study of pulsed-DC sputtering induced Ge₂Sb₂Te₅ thin films using facile thermoelectric measurement

Kumar, M.,Vora-ud, A.,Seetawan, T.,Han, J.G. Elsevier Ltd 2016 Materials & Design Vol.98 No.-

<P>Thermoelectric measurement is an exhaustive exercise for the case of thin films, requiring meticulous attention to the thermal contact interfaces and the instrumentation. Usually, different set-ups are combined for the temperature dependent measurement of different thermoelectric key quantities. Here, a facile 6-probe measurement set-up is presented, which can measure Seebeck coefficients and electrical properties of thin films in the temperature range of 300 K-600 K. Using this set-up, the thermoelectric properties of Ge2Sb5Te5 thin films, prepared with pulsed DC magnetron sputtering method are studied. The effects of working pressure, post-deposition thermal treatment and variation of film thickness on the microstructure, surface, electrical and thermoelectric properties are investigated systematically. Plasma diagnostics, performed using optical emission spectroscopy provided the information about various radicals' excitations and the electron temperature. Microstnictural studies show the phase transformation from amorphous to metastable cubic phase. FESEM study exhibits highly dense films with uniform grains compactness. It has been found that lowering average crystallite size by optimum electron temperature and pressure conditions governs the enhancement in Seebeck coefficient. The throughput of process >400 nm/min, and obtained Seebeck coefficients values 271.50 mu V/K are highly promising for industrial utilization. (C) 2016 Elsevier Ltd. All lights reserved.</P>