Tethered space orientation via adaptive sliding mode

Here, we study the problem of a rotating tethered satellite system (TSS) orientation. The rotation TSS is used for propellantless delivery of the payload from low earth orbits to geostationary orbits or other transfer orbits. Driving the angular positions to correct desired orientation in rendezvous and tossing moments, in fact, is important operation in many real sceneries. We suggest the mathematical model describing the dynamics of TSS and catch mechanism/payload rendezvous with external disturbance terms. Here is shown that using sliding mode control (SMC), we are able to control successfully the position of TSS. The conventional and adaptive versions of SMC are considered. We show that SMC with the gain matrix adaptation based on the equivalent control method can significantly reduce the undesirable chattering effect provoking possible damages of TSS. Copyright © 2015 John Wiley & Sons, Ltd.     

Structural changes in molten high-speed steels before atomizing

Molten high-speed steel R6M5F3 has been studied by the x-ray method under different temperature and time conditions. It has been found that transformations of the microheterogeneous structure of the melt with an increase in temperature to 1750°C are associated with a change in atom packing both within microgroups of Fe ( ) and in microregions enriched in carbon (Me₆C, Me_2C MeC). The structural state of high-speed steel powders as a result of temperature-time treatment of the melt varies considerably: There is a high degree of homogeneity due to an increase in the fineness and similarity of carbide-like regions.Institute of Problems of Materials Science, National Academy of Sciences of the Ukraine, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 7–8, pp. 8–12, July–August, 1994.     

Invariant ellipsoid method for minimization of unmatched disturbances effects in sliding mode control

A new sliding mode control design algorithm for a linear and a class of nonlinear quasi-Lipschitz disturbed system is presented. It is based on the appropriate selection of the sliding surface via invariant ellipsoid method. The designed control guarantees minimization of unmatched disturbances effects to system motions in a sliding mode. The obtained theoretical results are approved by numerical simulations.     

New Sliding-Mode Learning Law for Dynamic Neural Network Observer

This brief deals with a state observation problem when the dynamic model of a plant contains an uncertainty or it is completely unknown (only smoothness properties are assumed to be in force). The dynamic neural network approach is applied in this informative situation. A new learning law, containing relay (signum) terms, is suggested to be in use. The nominal parameters of this procedure are adjusted during the preliminary "training process" where the sliding-mode technique as well as the least-squares method are applied to obtain the "best" nominal parameter values using training experimental data. The upper bounds for the weights as well as for the averaged estimation error are derived. Two numeric examples illustrate this approach: first, the nonlinear third-order electrical system (Chua's circuit) with noises in the dynamics as well as in the output, and, second, the water ozone-purification process supplied by a bilinear model with unknown parameters     

Observer matrix gain optimization for stochastic continuous time nonlinear systems

It is shown that for a class of stationary stochastic nonlinear systems (satisfying a global Lipschitz condition) the high-gain observer with a constant gain matrix may guarantee an upper bound for the averaged quadratic error of state estimation. The nonlinearity is assumed to be a priory known. The main contribution of this paper consists in designing of a numerical procedure for the optimal gain matrix minimizing this upper bound. The convergence analysis of this procedure is presented as well as an example illustrating its finite steps workability: it is shown that within a neighborhood of the optimal matrix gain the others provide lower estimation performance.     

Bush‐Mosteller learning for a zero-sum repeated game with random pay-offs

This paper deals with the design and analysis of a modified version of the Bush-Mosteller reinforcement scheme applied by partners in a zero-sum repeated game with random pay-offs. The suggested study is based on the learning automata paradigm and a limiting average reward criterion is tackled to analyse the arising Nash equilibrium. No information concerning the distribution of the pay-off is a priori available. The novelty of the suggested adaptive strategy is related to the incorporation of a 'normalization procedure' into the standard Bush-Mosteller scheme to provide a possibility to operate not only with binary but also with any bounded rewards of a stochastic nature. The analysis of the convergence (adaptation) as well as the convergence rate (rate of adaptation) are presented and the optimal design parameters of this adaptive procedure are derived. The obtained adaptation rate turns out to be of o(n 1/3 ).     

Output integral sliding mode control based on algebraic hierarchical observer

The problem of the realization of integral sliding mode controllers based only on output information is discussed. The implementation of an output integral sliding mode controller ensures insensitivity of the state trajectory with respect to the matched uncertainties from the initial time moment. In the case when the number of inputs is more than or equal to the number of outputs, the closed loop system, describing the output integral sliding mode dynamics, is shown to lose observability. For the case when the number of inputs is less than the number of outputs, a hierarchical sliding mode observer is proposed. The realization of the proposed observer requires a filtration to obtain the equivalent output injections. Assigning the first order low-pass filter parameter small enough (during this filter realization), the convergence time and the observation error can be made arbitrarily small. The results obtained are illustrated by simulations.     

Characteristics of a melt of the corium–high alumina cement system

The characteristics (composition of the quenched samples, ingot, and evaporation products) are studied of the melt of the corium–high alumina cement system in a weight ratio of 1: 1. In the quenched samples of the melt and ingot, signs of phase separation in the molten state are found. Below a temperature of 2100°C above the melt, aerosol particles with trimodal size distribution are formed; however, above this temperature, the nature of the granulometry of aerosols is bimodal. Moreover, the formation rate of aerosols increases dramatically. The form of aerosol particles under all the experimental conditions was spherical.     

Active protection coatings with layered double hydroxide nanocontainers of corrosion inhibitor

Novel LDH-based nanocontainers of corrosion inhibitor are developed in the present work. The reservoirs are composed by nanostructured layered double Mg/Al and Zn/Al hydroxides with divanadate anions located in the interlayer regions. The nanocrystalline LDHs (layered double hydroxides) are able to release vanadate ions in a controllable way.XRD, EDS and SEM methods were used in this work to study morphological and structural properties of the synthesized LDH powders. Corrosion protection effect of the LDH powders directly added to corrosive electrolyte or to commercial coatings used for aeronautical application has been studied by electrochemical impedance spectroscopy and standard accelerated corrosion tests. Aluminium alloy 2024 was used here as substrate.The results demonstrate that both of the LDH pigments being added to corrosive media confer corrosion inhibition effect, especially Zn/Al based nanocontainers obtained by the anion-exchange approach. The coatings doped with Zn/Al LDH-nanocontainers provide well-defined self-healing effect and confer corrosion protection properties superior than currently used environmentally unfriendly chromate-based systems.