A fast‐built flux‐linkage model for switched‐reluctance motors

Abstract

This paper presents a simplified and fast‐built model for the analytical representation of the flux linkage of a switched‐reluctance motor (SRM). Presently, most conventional methods require numerous flux‐linkage‐current‐position data to build a model; however, this is time‐ineffective. In the proposed model, the flux linkage is represented by a limited number of Fourier series terms. The coefficients of the Fourier series are determined by the values of the flux linkage at the aligned position, unaligned position and a midway position. At either the aligned or the midway position, the non‐linear relationship between the flux linkage and the phase current is represented by a simplified function, which is derived from a linear relationship — the product of flux linkage and phase current versus phase current — in the saturated region. The proposed model can be built with only five data points of static characteristics, which are simply obtained through finite‐element analysis (FEA); this allows for easy implementation and high computational efficiency. The accuracy of the proposed model is verified via comparison to measurements of the steady‐state voltage and phase current waveforms of the machine as well as several characteristic curves. The proposed model is shown to have a good degree of accuracy.     

Application of variable‐structure system in dc‐motor velocity‐control

Abstract

The most important characteristic of variable‐structure system (VSS) is its insensitivity to parameter variations in the sliding mode. In this paper three methods of VSS are used to implement DC‐motor velocity‐control. The conventional VSS uses only a sliding line. The adaptive VSS uses multiple switching lines. The modern method uses a sliding curve. The modern method makes a system trajectory following the sliding curve which has been set up in the controller from the initial state to the origin in the phase plane. Hence it is insensitive to parameter variations from the initial state to the steady state. If parameter variations are the most critical factors, then the modern VSS is the right method to be considered to overcome the problem of parameter variations.     

Tabu search‐based approach to multi‐objective machine‐part cell formation

The machine‐part cell formation with respect to multiple objectives has been an attractive search topic since 1990 and many methodologies have been applied to consider simultaneously more than one objective. However, the majority of these works unify the various objectives into a single objective. The final result of such an approach is a compromise solution, whose non‐dominance is not guaranteed. A Pareto‐optimality‐based multi‐objective tabu search (MOTS) algorithm is presented for the machine‐part grouping problems with multiple objectives: it minimizes the total cost, which includes intra‐ and inter‐cell transportation cost and machine investment cost, minimizing the intra‐cell loading unbalance and minimizing the inter‐cell loading unbalance. A new approach is developed to maintain the archive storing non‐dominated solutions produced by the tabu search. The comparisons and analysis show that the proposed algorithm has considerable promise in multi‐objective cell design.     

High‐Temperature Radiative‐Convective Heat Exchange on the Surface of Glass‐Reinforced Plastics

The results of experimental investigations of heat exchange on the surface of a thermalprotective material — glassreinforced plastic — in the flows of hightemperature gases have been presented. It has been established that the influence of injection on the value of the heat flux does not exceed 10% in the range of variation of gas temperatures 300–2000 K and Reynolds numbers 350–9800.     

Picking strategies to the two‐carousel‐single‐server system in an automated warehouse

Abstract

An automatic storage system comprised of two storage carousel conveyors and a retrieval apparatus integrated by computers has been considered in this paper. The order picking problem for such a two‐carousel‐single‐server system is presented here. The retrieval time is analyzed by a two‐stage solution procedure for the scheduling sequence of retrieving items from the system in order to satisfy an order requirement. The analytical results can be directly applied for the scheduling of the carousel storage system.     

Quasi‐Self‐Similar Description of an Exhaust Jet

The method of construction of an analytical solution for the far field of an exhaust jet on the basis of the quasiselfsimilar solution of Prandtl equations and the turbulence model with one differential equation for the coefficient of kinematic viscosity is described. An exact numerical solution for distances to about 10¹ radii of the nozzle is constructed for the basic version. Then, a numerical solution and its analytical approximation by the quasiselfsimilar solution are constructed. Approximations of the similarity parameters of the selfsimilar problem as functions of the similarity parameters of the initial problem in the form of polynomials allow construction of analytical solutions for different situations, which are in satisfactory agreement with the exact numerical solution at distances of radii.     

Heat and Mass Transfer in a Two‐Component Developed Turbulent Gas‐Vapor‐Droplet Flow

A calculation model is developed and a numerical study is made of the heat and mass transfer characteristics in a turbulent gas–vapor–droplet flow moving in a round tube. The model takes into account the evaporation of droplets, the diffusion of vapor into air, and the acceleration of a carrier flow. Distributions of the parameters of the twophase flow are obtained with respect to the tube radius for different initial concentrations of the gas phase. Heat and masstransfer calculations are compared to the experimental and numerical works. On the whole, the evaporation of the droplets in the vaporgas flow leads to the intensification of heat transfer as compared to a onecomponent vapordroplet flow and singlephase flow of vapor.     

Reduced‐order modelling of linear discrete‐time systems using cauer third continued‐fraction method

Abstract

In this paper a generalization of the Cauer third continued‐fraction expansion (CFE) is introduced for the reduced‐order modelling of linear time‐invariant discrete‐time systems. First, a new algorithm is presented for obtaining the Cauer third continued‐fraction expansion about z=1 and z=8 of the z‐transfer function of a discrete‐time system from its time‐moments and Markov parameters. Next, a realization of the Cauer third continued‐fraction expansion about z=1 and z=8, and the corresponding CFE canonical state‐space model are derived. Finally, an approximate aggregation matrix is constructed for relating the state‐vector of the reduced‐order CFE canonical state‐space model to that of the original system. An example is included to illustrate the use of the method.     

Sinusoidal frequency estimation at low signal‐to‐noise ratio

Abstract

In this paper, an algorithm is developed to estimate the frequencies of the sinusoids corrupted by white noise. First, the input data is analyzed by a large order autoregressive (AR) spectral estimator, and then we root the prediction error filter (PEF) to get a set of zeros. Using a zero‐clustering algorithm, we partition the zeros into clusters. From these zero clusters, we construct filters to enhance the sinusoids. Then, using frequency estimators, we estimate the frequencies of the sinusoids from the filtered data. The results presented in this paper demonstrate that the proposed algorithm provides a better resolution ability and estimate accuracy than that of the conventional AR spectral estimator, especially for close sinusoids at low SNR.     

Strength development of blended blast‐furnace slag‐cement mortars

Abstract

Blast‐furnace slags cooled at different rates were used to study the effect of fineness, mixing method and content of slag on the strength development of blended‐slag mortar. Activator and curing temperature were used to activate the early strength. The microstructure of blended‐slag paste was also investigated in this study to explain the strengthen effect.     

Modeling of the dynamic characteristics of two‐bolt‐joints

Abstract

In this paper, a method to identify the damping and stiffness properties of bolted joints from a substructure synthesis scheme is presented. The easily measured frequency response functions of substructures and the assembled structure are the only data needed in this method. A synthesis formula used to predict the frequency response functions of two‐bolt‐joint structures is proposed. The formula makes use of the extracted properties of a single‐bolt‐joint. Some experiments with two free‐free steel beams jointed with one or two bolts are made to check this method. The close correlation between predicted and measured results demonstrates that this method is acceptable.     

An AlGaAs/GaAs oxide‐stripe double‐heterostructure laser

Abstract

An AlGaAs/GaAs oxide‐stripe double‐heterostructure (DH) laser is fabricated by liquid‐phase epitaxy (LPE) successfully. This laser consists of four epilayers, i.e., (N) Al_0.35Ga_0.65As cladding layer, (p) Al_0.05Ga_0.95As active layer, (P) Al_0.35Ga_0.65As cladding layer and (p) Al_0.05Ga_0.95As contact layer, and a top SiO₂ insulating layer. The stripe window opened through the SiO₂ layer is either 5 or 10 μm wide. The emission properties of the laser diodes were all measured under pulse mode. The lowest threshold current measured is 95 mA for a 10, μm‐wide stripe laser which corresponds to a threshold current density of 3,200 A/cm². The best power output is more than 30 mW per facet with a differential quantum efficiency of 10% per facet. In addition, the single filament operation is also observed in a 5 μm‐wide stripe laser. The lasing wavelength is centered around 8,500 Å.     

Maximum‐likelihood localization of closely‐spaced sources by MLSUM algorithm

Abstract

In this paper, we present a new scheme called the maximum log‐likelihood sum (MLSUM) algorithm to simultaneously determine the number of closely‐spaced sources and their locations by uniform linear sensor arrays. Based on the principle of the maximum likelihood (ML) estimator and a newly proposed orthogonal‐projection decomposition technique, the multivariate log‐likelihood maximization problem is transformed into a multistage one‐dimensional log‐likelihood‐sum maximization problem. The global‐optimum solution of the approximated ML localization is obtained by simply maximizing the single one‐dimensional log‐likelihood function. This algorithm is applicable to coherent sources as well as incoherent sources. The computer simulations show that the MLSUM algorithm is much superior to the MUSIC when the element SNR is low and/or the number of snapshots is small.     

Conducting polymer‐coated, palladium‐functionalized multi‐walled carbon nanotubes for the electrochemical sensing of hydroxylamine

Electrochemical sensors of hydroxylamine were fabricated on glassy carbon electrodes (GCEs) by the electropolymerization of 3,4‐ethylenedioxypyrrole (EDOP) and 3,4‐ethylenedioxythiophene (EDOT) on palladium (Pd) nanoparticles attached to thiolated multi‐walled carbon nanotubes (MWCNTs), denoted as PEDOP/MWCNT‐Pd/GCE and PEDOT/MWCNT‐Pd/GCE. The sensors were characterized by field emission scanning electron microscopy and electrochemical impedance spectroscopy. They showed strong catalytic activity toward the oxidation of hydroxylamine. Cyclic voltammetry and amperometry were used to characterize the sensors' performances. The detection limits of hydroxylamine by PEDOP/MWCNT‐Pd/GCE and PEDOT/MWCNT‐Pd/GCE were 0.22 and 0.24 μM (S/N = 3), respectively. The sensors' sensitivity, selectivity, and stability were also investigated.     

Self‐Organization and Dynamic Chaos in Chemical‐Technology and Heat‐Exchange Devices: Problems and Tasks

Nonlinear phenomena in thermophysical and chemicaltechnology processes are considered in the context of nonlinearity, instability, nonuniqueness, nonstationarity, and irreversibility. The perturbation frequency (phase)toamplitude ratio is the governing parameter of the nonlinear interaction of perturbations that are described by the proposed general nonlinear parabolic equation. The nonlinearity of this ratio characterizes turbulence, while its linearity characterizes selforganization. It is shown that chaotic conditions can be selforganized under the action of white noise, which favors the system getting into the domain of attraction of a stable node. The mechanism of the occurrence of turbulence is substantiated.     

Generalized Equations of One‐Dimensional Filtration with Fractional‐Power Differentiations

Based on the formalism of fractionalpower integrodifferentiation, the theory of filtration in porous media with fractal structure is generalized. Consideration is given to the cases of steady and unsteady filtration. For the steady filtration, nonlinear solutions are shown to exist. In the unsteady case, a new class of periodic solutions may exist.     

Process of Cooling of a High‐Temperature Two‐Phase Flow

A technique and a design of a transducer for measuring the enthalpy of twophase flows using the thinwall method have been developed. Working formulas for calculating the heat capacity and the enthalpy of a gas flow are substantiated. Results of a test of the transducer in hightemperature flows of powder gases, including those after the packing of a coolant, are presented. The results obtained show that cooling of powder gases due to an endothermic reaction makes it possible to decrease the enthalpy flux by a factor of 5 and the temperature by a factor of 2.     

The engineering properties of rice‐hull‐ash as a soil stabilizer

Abstract

The notation of functional programming (FP) provides a clear and general syntax for writing programs which have extremely simple semantics and exhibit a clear hierarchical structure. Unfortunately, functional languages have a reputation of being hard to learn. This paper suggests an FP style of programming in which programmers deal with graphs as primary representations in programming, editing and executing programs. Programming becomes constructing system by which programs are built up as structured assemblies of functions. The programming technique developed in this paper follows four steps: (1) to define object types; (2) to define type clauses; (3) to construct program graphs; and (4) to automatically convert program graphs into FP programs. These programming processes help programmers easily form clear and correct mental images of a program's structure and function.     

Transformation of continuous‐time state equations to discrete‐time state equations

Abstract

A method is proposed for transforming a continuous‐time state equation, x(t)=Ax(t)+Bu(t), to a discrete‐time state equation, x[(k+1)τ]=ø(τ)x(kτ)+B(τ)u(kτ). It is based on expanding the matrix exponential exp (Aτ) into a shifted matrix Chebyshev series. An example is given to demonstrate the superiority of the method over other methods.     

Comparisons on discrete‐time modeling techniques of DC‐DC switching converters

Abstract

The performance and effectiveness of several discrete‐time modeling techniques of dc‐dc switching converters, including new ones devised in this paper, are compared and evaluated. It is shown in this paper that the latest bilinear discrete‐time modeling method by Rajasekaran et al., 2003 suffers in both steady state and transient analysis due to the bilinear approximation of the original mathematical model. The proposed alternative discrete‐time models are obtained by using the well‐known Cayley‐Hamilton theorem, and they are shown, via examples, to be superior to the previous results.