Showing papers by "University of Maribor published in 1992"
03 Aug 1992
TL;DR: In this paper, an edge element representation of the rotational part of the magnetic field from a given source current distribution was obtained for finite element computation of static magnetic fields in three dimensions using reduced magnetic scalar potential.
Abstract: Some improvements to the finite element computation of static magnetic fields in three dimensions using a reduced magnetic scalar potential are presented. Methods are described for obtaining an edge element representation of the rotational part of the magnetic field from a given source current distribution. When the current distribution is not known in advance, a boundary value problem is set up in terms of a current vector potential. An edge element representation of the solution can be directly used in the subsequent magnetostatic calculation. The magnetic field in a DC arc furnace is calculated by first determining the current distribution in terms of a current vector potential. A 3-D problem involving a permanent magnet as well as a coil is solved, and the magnetic field in some points is compared with measurement results. >
83 citations
69 citations
01 Jan 1992
TL;DR: Numerical simulation is numerical modelling and simulation of flow circumstances, including numerical experiments by the computer, which may have several important advantages over physical measurements on a laboratory model.
Abstract: Very fast development of computing enabled also the development of numerical fluid dynamics. It is numerical modelling and simulation of flow circumstances, including numerical experiments by the computer. Such procedure may have several important advantages over physical measurements on a laboratory model. It is of great importance that fluid properties (density, viscosity, compressibility, etc.) may be simply and arbitrarily changed, numerical experiment does not disturb the flow, plane flows can simply be simulated what may not be the case with laboratory experiments. The numerical experiment also has its own drawbacks and disadvantages, known to all numerical procedures, since the numerical solution represents a result of a discrete equation systems, which are not completely identical to basic physical laws of mechanics of continua. Discretisation often changes quantitatively and qualitatively the behavior of equations and thus also the solutions. Numerical simulation has also similar limitations like a laboratory experiments, since the solutions are individual discrete values only, not the functions of the flow fields.
66 citations
59 citations
TL;DR: In this article, a phenomenological free energy is used to describe the stable ordering of nematic liquid crystals confined to supramicron spherical cavities, and the effects of the saddle splay elastic constant, K 24, on the equilibrium structures and phase diagram of droplets with homeotropic surface anchoring are discussed.
Abstract: A phenomenological free energy is used to describe the stable ordering of nematic liquid crystals confined to supramicron spherical cavities. In particular the effects of the saddle splay elastic constant, K 24, on the equilibrium structures and phase diagram of droplets with homeotropic surface anchoring are discussed. Some structures are illustrated by the corresponding simulated polarization microscope textures. Possibilities for an experimental determination of the saddle-splay elastic constant and surface anchoring strength by studying the radial-axial structural transition in such droplets are analysed. It is shown that the K 24 term in the elastic free energy stabilizes a deformed droplet structure even in the limit of the zero anchoring strength.
37 citations
TL;DR: In this paper, an asymmetrical multiprocessor architecture for hard real-time applications is presented, whose temporal behaviour is fully predictable, and several commonly used techniques which prevent temporal determinism of instruction execution are enumerated.
33 citations
TL;DR: The modelling, design, and initial experimental testing of a nerve cuff multielectrode system for selective stimulation of fibres in superficial peripheral nerve trunk regions which is capable of making a selective activation of multiple muscles are presented.
Abstract: In this paper we present the modelling, design, and initial experimental testing of a nerve cuff multielectrode system for selective stimulation of fibres in superficial peripheral nerve trunk regions which is capable of making a selective activation of multiple muscles. The developed multielectrode nerve cuff consists of 14 platinum stimulating electrodes embedded within a self-curling sheet of biocompatible insulation, exhibiting a spiral transverse cross-section. The spiral shape of the system is such that the number of stimulating electrodes which can be utilized depends on the diameter of the stimulated nerve. Nerves with a greater diameter automatically make use of more electrodes than thin ones. The development was based on results obtained by a histological examination of the peripheral nerves which were planned to be stimulated, and on models of excitation of myelinated nerve fibres. The modelling objectives were to determine the electric field that would be generated within a nerve trunk by a sp...
33 citations
TL;DR: In this article, a solution is proposed that is based on an automatic construction of a quantitative evaluation model from the qualitative one, which is used to rank options within classes and to reflect the sensitivity to small differences between options.
30 citations
TL;DR: The paper presents an extended approach to non-linear first-order approximation of non- linear programming problems and it explains how to transform an approximate problem into a strictly convex one.
Abstract: The paper presents an extended approach to non-linear first-order approximation of non-linear programming problems and it explains how to transform an approximate problem into a strictly convex one. The essence of the proposed approximation technique is to rewrite each given function hj as a composite gjo Ψj. The function Ψj has to be chosen—the paper explains how to do this—while gj is linear approximated with gj. The approximation of hj is then obtained as gjo Ψj.
This approach enables one to obtain approximate functions with variable conservativeness, which implies an adjustable approximate problem. A solution procedure, which replaces the original problem with a sequence of approximate problems, can therefore adjust each succeeding approximate problem to improve the convergence properties.
The theory is illustrated with a three parameters controlled approximation. This technique represents, together with an optimality criteria based solution procedure, a powerful and economic tool for solving nonlinear programming problems. The three parameters, which influence to a great extent the conservativeness of the approximate functions, are under full control of the optimizer. They are varied automatically during the process of optimization to speed-up the convergence or to prevent oscillations.
The benefits gained from the proposed approach are demonstrated on several numerical examples involving structures and a dynamic multibody system.
21 citations
21 citations
TL;DR: In this article, a theoretical approach to determine nearly spherical shapes of phospholipid vesicles is developed, in which equilibrium shapes are assumed to correspond to the minimum of the membrane bending elastic energy at constant values of membrane area, the vesicle volume and the difference of areas of the two leaflets of the polygonal bilayer.
Abstract: A theoretical approach to determine nearly spherical shapes of phospholipid vesicles is developed. The method is general in the sense that it does not depend on any symmetry restrictions. Equilibrium shapes are assumed to correspond to the minimum of the membrane bending elastic energy at constant values of the membrane area, the vesicle volume and the difference of areas of the two leaflets of the phospholipid bilayer. The bending energy and the constraints are expanded up to fourth order terms in the deviation from a sphere, and in the subsequent calculations all terms up to the third order are included. The deviation is expressed as a series of spherical harmonics. It sis shown that the stability of the solutions can be tested by inspecting the eigenvalues of the matrix of second derivatives of the bending energy with respect to independent amplitudes of spherical harmonics expansion. The method is applied to the calculation of axisymmetric and nonaxisymmetric shapes, and the influences of different approximations are discussed. It is shown that at variations of the leaflet area difference stable oblate and stable prolate shapes are transformed into each other in a continuous manner.
TL;DR: Oleic acid esterification has been performed in a stirred batch reactor by lipase from Mucor miehei in solvent free system and in supercritical carbon dioxide as mentioned in this paper.
Abstract: Oleic acid esterification has been performed in a stirred batch reactor by lipase from Mucor miehei in solvent free system and in supercritical carbon dioxide. The reaction rate was influenced by temperature and reaction media. Future research will be concentrated on the influence of the process parameters on final conversion, initial velocity, enzyme stability and on fractionation of the product from the substrates and scaling up of the production process.
22 Sep 1992
TL;DR: The novelity of the present work is the proposed fault-tolerant scheme, where multiple paths are achieved by adding extra links between stages, but not by intrastage links.
Abstract: The authors present the performance results of the generalized shuffle network (GSN), the multipath multistage interconnection network (MMIN), and an interconnection network proposed by the authors in a packet communication environment with the focus on cost analysis and reliability. The proposed interconnection pattern has the property of strong reroutability. There are eight paths between each input and each output; four of them are disjoint. The network is built up of four stages, with the same interconnection pattern at the first and third level. The novelity of the present work is the proposed fault-tolerant scheme, where multiple paths are achieved by adding extra links between stages, but not by intrastage links.
TL;DR: A glass-ceramic bond which can be applied in alumina/CBN abrasive systems was developed by the method of liquid-phase sintering of a homogenized mixture of alumina abrasives and bonding medium containing various amounts of B2O3.
Abstract: A glass-ceramic bond which can be applied in alumina/CBN abrasive systems was developed by the method of liquid-phase sintering of a homogenized mixture of alumina abrasives and bonding medium containing various amounts of B2O3. Microstructural and mechanical examinations have shown that the amount of B2O3 present in the starting glass frit determines the ultimate properties of the glass-ceramic bond which can be successfully used in the Al2O2/CBN abrasive systems.
TL;DR: A probabilistic analysis of the safety of a railway traffic system down to the level of human errors and hardware failures using the fault tree technique has been presented.
TL;DR: In this article, isothermal analysis for the mixture of Sb 2 O 3 and SnCl 2 in atmospheres of argon and air has been performed, and the X-ray powder diffraction method was used to characterise residues after thermal analyses, and volatile components were identified by mass spectrometry (MS) using the Knudsen cell technique.
09 Jun 1992
TL;DR: The paper demonstrates how geometrical constraints can be applied to add a new level of abstraction to description ofGeometrical objects to support incremental design and override the ambiguities at constraint solving.
Abstract: The paper demonstrates how geometrical constraints can be applied to add a new level of abstraction to description of geometrical objects. Special attention is given to the interactive insertion of constraints. To support incremental design each inserted constraint has to be solved as soon as possible. Because of this requirement a local propagation of known states is used for constraint solving. It is supported by a biconnected constraint description graph structure. The benefits of this structure are insensibility to the order of inserted constraints and ability of replacing constraints with their inverse couples. To override the ambiguities at constraint solving the approximal values of geometrical elements which are inserted through a sketch are used. From the biconnected constraint description graph an acyclic constraint description graph is generated easily. It is suitable for the generation of instances of generic objects.
TL;DR: A method is presented for defining ranges of normal stress values, based on the construction of the membership function from the fuzzy set theory, which is applied to a stress analysis for a sample of station foremen in the railway traffic system of Slovenia.
TL;DR: In this article, a mathematical description of a multi-component titration system of metal ions based on the hydrolytic reaction of the anion of the weak acid involved is given.
TL;DR: An integrated programming environment for static partitioning of time critical tasks into concurrent modules, called grains, and scheduling those modules for the shortest execution time possible on a macro dataflow computer are presented.
01 Jun 1992
TL;DR: Proposed network and model which allows integration of different today known types of decision support systems is derived could be used as a framework for researching office information systems from a decision support system view.
Abstract: Office information system is presented as a network of decision support systems where the basis of linking decision support systems between them are decision making situations. After introducing concept of the network, basic components of it are briefly described. According to this context a model of decision support system which allows integration of different today known types of decision support systems is derived. Proposed network and model could be used as a framework for researching office information systems from a decision support systems view.
TL;DR: In this paper, a computer aided design of a specialty chemical product plant is presented, where decisions about batch/continuous operation, time fraction of operation, plant capacity, amount and energy balances including energy integration are the first decisions to be met.
01 Jan 1992
TL;DR: In this paper, a transformation of a fractional piecewise linear programming problem into a linear mixed integer programming problem is described, which can be used while maximizing the quotient of the revenue and the cost.
Abstract: In business optimization, the piecewise linear programming problem arises [1]. When taking into account the investments, the cost is a discontinuous piecewise linear function of decision variables. In this paper, a transformation of a fractional piecewise linear programming problem into a linear mixed integer programming problem is described. This transformation can be used while maximizing the quotient of the revenue and the cost. A similar transformation can be applied when a constraint contains this quotient.
01 Oct 1992
TL;DR: Benefits of the presented constraint-based geometric modeling system named FLEXI are unnecessity of giving constraints in correct order and the ability of replacing incorrect constraints with their inverse constraints by the system itself.
Abstract: We present our constraint-based geometric modeling system named FLEXI. Creation of an object begins with a sketch carrying a topological information and approximal values of object’s geometry. Geometrical constraints are then interactively inserted. Benefits of the presented geometric modeling system are unnecessity of giving constraints in correct order and the ability of replacing incorrect constraints with their inverse constraints by the system itself. Special attention is given to the iterative constraint solving. A new structure - a biconnected constraint description graph enables these benefits. A triggering mechanism for controlling of the constraint propagation is developed for this structure. An algorithm for converting the biconnected constraint description graph into an acyclic constraint description graph is briefly explained. Managing of the over-dimensioning is solved by introduction of a priority mechanism.
01 Jan 1992
TL;DR: In this article, the authors deal with the numerical simulation of the turbulent flow using the vorticity-velocity formulation by Boundary Element Method (BEM) and a time averaged form of the Navier-Stokes equations is employed through the Reynolds decomposition of the instantaneous value of each variable.
Abstract: This paper deals with the numerical simulation of the turbulent flow using the vorticity-velocity formulation by Boundary Element Method (BEM). A time averaged form of the Navier-Stokes equations is employed through the Reynolds decomposition of the instantaneous value of each variable. Turbulent stress terms are interpreted in the Boussinesq manner and Prandtl’s mixing length hypothesis is used. Only algebraic turbulent model is considered in this paper.
TL;DR: An integrated programming environment for static partitioning of time critical tasks into concurrent modules and for scheduling those modules for the shortest possible execution time on a model of a macro dataflow computer (MMDFC).
TL;DR: An approach to modelling and verification for networks of processes that communicate solely via shared variables is presented and a linear-time temporal logic formalism is introduced for the specification and verification of safety and liveness properties.
TL;DR: In this paper, the authors present an approach that leads to a relatively simple model of a brushless dc motor in the rotor d-q reference frame which enables the use of some known methods in the design process of the control.
01 Jan 1992
TL;DR: In this article, a method for off-line parameter identification and estimation of the SCARA robot with two degrees of freedom is described, where the recursive least square method is used to identify the parameters of inertia and viscous friction for each degree of freedom.
Abstract: In this paper a method for off-line parameter identification and estimation of the SCARA robot with two degrees of freedom is estimation of the SCARA robot with two degrees of freedom is described. The recursive least square method was used to identify the parameters of inertia and viscous friction for each degree of freedom. The Coulumb friction parameter was estimated from input and output system data. The PADSIM simulation package was used to verifiy the identification-estimation method.