Integrated analytical models for flexible manufacturing systems

Product form queueing networks (pfqn) and generalized stochastic Petri nets (gspn) have emerged as the principal performance modelling tools for flexible manufacturing systems (fms). In this paper, we present integratedpfqn-gspn models, which combine the computational efficiency ofpfqn and representational power ofgspn by employing the principle of flow-equivalence. We show thatfms that include nonproduct form characteristics such as dynamic routing and synchronization can be evaluated efficiently and accurately using the integrated models.     

Performance ofesprit in the presence of gain and phase mismatches in sensor doublets

esprit, an acronym for Estimation of Signal Parameters via Rotational Invariance Technique, is a novel method for estimating the Directions of Arrival (doa) of plane waves using an arbitrary array of sensor doublets. However,esprit requires an identical pair of sensors in each doublet, that is the gain and phase characteristics of the sensors in a doublet have to be matched, which may be difficult to ensure in practical situations. In this paper, assuming the sources to be uncorrelated, we analyse the performance ofesprit when the gain and phase characteristics of the sensors in a doublet are not identical. It is shown that the angle estimates are unbiased and expressions are derived for the variance in the estimates ofdoa, when gain and phase mismatches exist in doublets. Computer simulation results are also presented to assert the theoretical predictions.     

Repeated yield drop phenomena as a cooperative effect

We present a theoretical model of repeated yielding (ry) which reproduces many experimentally observed features, apart from showing how the temporal behaviour of the phenomenon emerges as a consequence of the cooperative behaviour of defects. We first consider the case of step-like creep curves. Our model leads to a coupled set of nonlinear differential equations which admit limit cycle solutions, and thence jumps on the creep curve. Approximate closed form solutions for the limit cycles and the steps on the creep curve are obtained. The model is then extended to the constant strain rate experiment by including the machine equation. The temporal ordering ofry is shown to follow, as well as several other features characteristic ofry. Chaotic flow is also exhibited: the model has a sequence of period-doubling bifurcations with an exponent equal to that of the quadratic map. Finally, we have analysed the fluctuations during the onset ofry using nonlinear Langevin equations. Fluctuations in the periodic (ry) phase are also investigated. We conclude thatry is another example of a dissipative structure.     

A novel method ofrf powder sputtering

A new method ofrf sputtering by which thin films of metals, semiconductors and insulators can be sputtered from their respective powders, has been successfully demonstrated. The films have been characterized for their surface and crystal structure using conventional methods ofsem andtem. All the films are amorphous with a relatively smooth surface topography. The relative merits and demerits of the technique have been briefly discussed.     

Über die Konvergenz des Verfahrens von Galerkin bei quasi-linearen Randwertproblemen

Zusammenfassung Für quasi-lineare Randwertprobleme wird die Konvergenz des Verfahrens vonGalerkin untersucht. Dazu wird dem eigentlichen Problem ein lineares Ersatzproblem zugeordnet. Führt man dasGalerkinsche Verfahren mit den Eigenfunktionen dieses Ersatzproblems durch, so läßt sich zeigen, daß das Verfahren konvergiert, wenn die Nichtlinearität stetig, beschränkt und in genügendem MaßeLipschitz-beschränkt ist.

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Summary Convergence of the method ofGalerkin is proved for quasi-linear boundary value problems. To this effect a linear problem with the same boundary-conditions is adjoint to the original nonlinear problem. If the eigen-functions of the adjoint problem are used as coordinate functions in the method ofGalerkin it can be shown that the method converges provided the nonlinearity is continuous, bounded and sufficientlyLipschitz-bounded.

     

Dispersion of photoelastic constants in doped KDP crystals

The photoelastic behaviour ofkdp crystals with additives like borax,adp, nickel phosphate, manganese phosphate and sodium dihydrogen orthophosphate has been studied as a variable birefringent compensator. The dispersion of the stress birefringence with wavelength was studied for a single orientation.     

Approximate transonic profile flow with shock

Summary The present work gives a procedure for computing approximately steady inviscid transonic profile flow with shock. Using an analysis similar to that adopted byHosokawa in [11] it extends the shock-free transonic solution ofNiyogi andMitra [9] to the case of flow with shock. Supercritical flow past parabolic are profiles and a NACA profile are computed and compared with theoretical results ofOswatitsch andZierep and finite difference solution ofMurman andCole [13] and with experimental results. The agreements are satisfactory.

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Eine Näherungslösung der schallnahen Strömung um Profile unter Berücksichtigung von Stoßwellen

Zusammenfassung In dieser Arbeit wird eine Methode zur näherungsweisen Berechnung der stationären, reibungsfreien, schallnahen Strömung um Profile unter Berücksichtigung von Stoßwellen angegeben. Unter Verwendung einer der vonHosokawa [11] angewendeten ähnlichen Vorgangsweise wird die vonNiyogi undMitra [9] ermittelte stoßwellenfrei schallnahe Lösung auf den Fall mit Stoßwellen erweitert. Die überkritischen Strömungen längs eines Parabelbogen- und eines NACA-Profiles werden berechnet und mit theoretischen Ergebnissen vonOswatitsch undZierep, mit solchen nach dem Differenzenverfahren vonMurman undCole [13] ermittelten und mit experimentellen Ergebnissen verglichen. Die Übereinstimmung ist zufriedenstellend.

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With 5 Figures     

Fuzzy medial axis transformation (fmat): Image representation,skeleton extraction and uncertainty management in computer vision

The problem of extraction of medial axis transformation of a gray image with reference to skeletonization, image representation and uncertainty management in a vision system has been addressed. The Fuzzy Medial Axis Transformation (fmat) of a fuzzy setf is a set of fuzzy disks whose sup isf. Unfortunately, specifying thefmat sometimes requires more storage space than specifyingf itself. The present paper describes some techniques to improve the compact representation offmat; thereby making it practically useful to an image for its skeleton extraction and compact representation, for shape analysis and template matching, for representation and retrieval, for uncertainty management in recognition and for creating new images of various poses. The algorithms involve reduction of redundancy infmat, its approximation, and reduction of the searching spaces for its computation. Computational aspects for the convenience of writing an efficient program have been described. Some applications of thefmat have also been mentioned. This work was done while SKP held annrc-nasa Senior Research Associateship at the Lyndon B Johnson Space Center, Houston, Texas.     

On the elastic stability of thick columns

Summary Stability of a rectangular strip of isotropic highly elastic incompressible material is analyzed using the theory ofGreen, Rivlin andShield. The strip is subject to a uniaxial compression in planes of plane strain. Both the asymmetric and symmetric forms of buckling are studied and the results found in full agreement with the corresponding results obtained from the theory ofBiot.

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Zur elastischen Stabilität dicker Säulen

Zusammenfassung Die Stabilität eines rechteckigen Streifens aus isotropem, elastischem inkompressiblem Material wird mittels der Methode vonGreen, Rivlin undShield untersucht. Der Streifen steht unter einachsigem Druck in Ebenen des angenommenen ebenen Verzerrungszustandes. Sowohl die asymmetrischen als auch die symmetrischen Beulformen werden studiert. Die Ergebnisse befinden sich in voller Übereinstimmung mit den entsprechenden Resultaten der Theorie vonBiot.

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With 3 Figures

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Research supported by a grant of the National Science Foundation.     

X-ray spectroscopy and local structures in glasses

X-ray spectroscopy which is a combination of two techniques, namely x-ray absorption near edge structure (xanes) and extended x-ray absorption fine structure (EXAFS) analyses, is a unique technique for the study of local structures in glasses. Availability of synchrotron radiation sources has made the technique quite attractive and useful because the photon flux from synchrotrons is very intense and polarized. In this article, a brief summary ofxanes andEXAFS techniques is given along with a few applications to the study of local structures in glasses. Communication No. 323 from Solid State and Structural Chemistry Unit.     

Personal computer-basedcamac system for data acquisition

A single board auxiliarycamac crate controller for a Z80-A based personal computer ZX-spectrum to drive thecamac crate housing multipleadc, tdc, dac and 16 I/O ports has been developed. Thecamac crate controller used in this system is of A2 type which supports multiple auxiliary crate controllers. Acamac exerciser/training software for the use ofcamac commands in process control as well as data acquisition has been developed.     

Legal counselling system

Legal reasoning involves case analysis in statutory as well as real world perspectives. The impact of real world perspective on case analysis poses a serious challenge to knowledge engineers for building legal expert systems. A legal expert system intends to provide intelligent support to legal professionals. The proposed legal predictive system is an attempt to predict the most probable outcome of a case according to statutory as well as real world knowledge of the legal domain. The system accepts the current fact situation of a case and analyses it interactively with legal personnel. This work introduces a frame-like knowledge structure,lattice, with two-dimensional attributes. This paper contains a detailed discussion on artificial intelligence-based case analysis of theft cases in a real world perspective.     

Understanding design: Artificial intelligence as an explanatory paradigm

A substantial part of the intellectual content of what H A Simon called the ‘sciences of the artificial’ is contained in the activity we calldesign. A central aim ofdesign theory is to construct testable, explanatory models of the design process that will serve to enhance our understanding of how artifacts are, or can be, designed. In this paper, we discuss how some of the basic concepts underlying the discipline ofartificial intelligence (ai) can serve to provide anexplanatory paradigm for understanding design. We present an AI-based model of the design process and describe some of the implications of this model for our understanding of design — including that aspect of it we call ‘invention’.     

R & D work in composites at the fibre-reinforced plastics research centre

This paper briefly presents some of the R & D activities taken up by the Fibre-Reinforced Plastics (Frp) Research Centre, Indian Institute of Technology, Madras, in the last seven years. The studies covered in this paper include the analysis of heat shield, development of vibration mounting for rocket motor casings, design and development of metal-lined pressure bottles, study of the effect of nuclear radiation on filament wound shells, design and development of high voltage disc insulators, study of underwater-acoustic characteristics ofFrp and development of some of the processing techniques. The paper also lists a number of products developed by the Centre for meeting the immediate needs of society. Finally, the ongoing academic and sponsored research programmes are briefly outlined.     

High voltage electron microscope irradiation and observations in metallic glasses

High voltage electron microscope (hvem) has been extensively used to produce radiation damage and to study the characteristics of defects so produced in crystalline solids. To understand the defect production in metallic glasses and to evaluate the influence of such defects on physical properties like crystallisation temperature etc., high voltage microscopy and subsequentin situ heating and observation has been extremely useful technique. This paper gives a qualitative overview of such work performed in metallic glasses. In particular results obtained on a nickel based metallic glass using ahvem and an electron accelerator are presented. The advantages and limitations ofhvem irradiation are highlighted.     

On approximate constitutive equations in nonlinear viscoelasticity

Summary In this paper a simplified constitutive equation for nonlinear slightly viscoelastic materials is derived by a method similar to that ofColeman andNoll. This equation is also valid for short times, slow motions, or small deformations superposed on a large steady deformation for all viscoelastic materials. An experimental method for determining the material parameters contained in this constitutive equation for dynamic conditions is also presented.

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Über genäherte Materialgleichungen in der nichtlinearen Viskoelastizität

Zusammenfassung Mittels einer Methode ähnlich der vonColeman undNoll wird eine vereinfachte Materialgleichung für nichtlineare, schwach viskoelastische Stoffe hergeleitet. Diese Gleichung gilt auch für das Kurzzeitverhalten, für langsame Bewegungen, oder für die Überlagerung kleiner Deformationen auf große stationäre Verformungen bei allen viskoelastischen Materialien. Eine experimentelle Methode zur Bestimmung der in der Materialgleichung auftretenden Stoffkonstanten für dynamische Bedingungen wird gleichfalls angegeben.

     

Optoelectronic devices towards monolithic integration

Starting from the present state-of-the-art of discrete devices up to the realization of monolithic semiconductor integrated prototypes, an overview of optoelectronic devices for telecommunications is given. Among discrete devices single frequency lasers, tunable and multi-sectionDFB lasers andPIN andAPD photodiode detectors are analysed, including the use of new technologies in progress for a second generation of devices. On the future perspective ofIBCN distribution networks, some economics of the hybrid and monolithic form of integration are attempted. Finally a short outline of the most recent achievements in monolithic integration is presented, taking into particular consideration the activities in this field byEEC ESPRIT andRACE programmes.     

Vibration of beams with exponentially varying properties

Summary The equation governing the transverse vibration of beams with exponentially varying properties is solved. The solution is expressed in terms ofBessel functions for a sequence of special cases of property variations.

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Zusammenfassung Die Gleichung für die Biegeschwingung von Stäben mit exponentiel veränderlichen Querschnittseigenschaften wird gelöst. Für verschiedene Spezialfälle der Eigenschaftsvariation wird die Lösung durchBesselsche Funktionen ausgedrückt.

     

Reissner's variational principle and elastodynamics

Summary There are two variational principles in elastostatics:Green's principle andCastigliano's principle. These are special cases ofReissner's variational principle.Green's principle andCastigliano's principle have been generalized in a symmetric manner to include elastodynamic problems. In the present paper,Reissner's principle is generalised to include these problems.

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Zusammenfassung In der Elastostatik gibt es zwei Variationsprinzipe: das Prinzip vonGreen und das Prinzip vonCastigliano. Diese sind Spezialfälle desReissnerschen Variationsprinzips. DasGreensche Prinzip und dasCastiglianosche Prinzip wurden in einer symmetrischen Weise verallgemeinert, um elastodynamische Probleme umfassen zu können. In der vorliegenden Arbeit wird dasReissnersche Prinzip so verallgemeinert, daß es die genannten Probleme beinhaltet.

     

CFD codes and applications at boeing

The use of computational methods for three-dimensional flow design and analysis at the Boeing Company is presented. A range of computational “tools” consisting of “production” tools for everyday use by project engineers, “expert user” tools for special applications by computational researchers, and a new “emerging” tool which may see considerable use in the near future is described. These methods include full potential and Euler solvers, some coupled to three-dimensional boundary layer analysis methods, for transonic flow analysis about nacelle, wing/body, wing/body/strut/nacelle, and complete airplane configurations. As the examples presented show, such a tool box of codes is necessary for the variety of applications typical of an industrial environment. Such a tool box of codes makes possible aerodynamic advances not previously achievable in a timely manner, if at all. With a few exceptions, this paper is a version of the paper entitled “TransonicCFD applications at Boeing”, by E N Tinoco, presented at the Transonic Symposium,nasa Langley, April 1988. The paper was presented at the Specialists’ meeting onCFD, held at National Aeronautical Laboratory, Bangalore, December 1988. This paper is based in part on work conducted for the Boeing Independent Research and Development Program.