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Acta polytechnica HungaricaVolume 4, Issue No. 2 (2007.)


  • István Harmati ,
    Péter Várlaki :

    Abstract: Car body deformation modelling plays a very important role in crash accident analyses, as well as in safe car body design. The determination of the energy absorbed by the deformation and the corresponding Energy Equivalent Speed can be of key importance; however their precise determination is a very difficult task. Although, using the results of crash tests, intelligent and soft methods offer an automatic way to model the crash process itself, as well as to determine the absorbed energy, the before-crash speed of the car, etc. In this paper a model is introduced which is able to describe the changing of the energy distribution during the whole deformational process and to analyze the strength of the different parts without any human intervention thus significantly can contribute to the improvement of the modelling, (automatic) design, and safety of car bodies.

    Keywords: car-crash, deformational energy

  • Jaroslav Dudrik ,
    Juraj Oetter :

    Abstract: The paper presents soft switching PWM DC-DC converters using power MOSFETs and IGBTs. The attention is focused mainly on the full-bridge converters suitable for high power applications. The properties of the PWM converters are described in comparison to other categories of soft switching converters. An overview of the switching techniques using in the DC-DC converters is included. Considerations are also given to the control methods. The principles of the switching and conduction losses reduction in the PWM converters are illustrated. Various types of snubber circuits are mentioned and their operation and limitations are discussed.

    Keywords: DC-DC converter, PWM converter, soft switching, snubber

  • Abdellatif Hamouda ,
    Khaled Zehar :

    Abstract: The aim of this paper is the presentation of a new analytical formulation of the reactive energy compensation on distribution lines, which are characterised by their radial configuration. It will be devoted to the determination of the sizes and locations of a given number of fixed capacitor banks placed on a non-homogeneous radial line with a nonconstant voltage. For the network solution, it is required to know the voltage at each node and at the capacitors location. On the basis of what has been just said and due to the radial type of the line, an iterative method called voltage drop method will be applied. The voltage rms values and phase-angles at all the nodes and on the capacitor banks will be calculated. The mathematical models of the current distributions are made considering the line active and reactive power losses. In the reactive energy optimisation process and for the power and energy loss reductions, we have used new models. The latter take into account the effect of all the capacitors in the calculation of the loss reductions due to a particular one. The results obtained then, are compared to those of authors having previously worked on the subject.

    Keywords: shunt capacitors, voltage drop, radial line, optimal capacitor sizes, optimal capacitor locations

  • Ágnes Szeghegyi ,
    Ulrich H. Langanke :

    Abstract: Each problem always originates from constraints. The decision is a response to the challenges by the environment. In order to chose appropriate decision support techniques the structural complexity of the problem has to be determined. The aim of the application of knowledge based systems is to obtain decision support. In this paper the application of the system ‘Doctus’ is illustrated and exemplified in connection with processing the problem of the potential co-operation between the industrial companies and institutes of higher education. The analysis was carried out by the application of inductive and deductive inference procedures taking into account the requirements of the companies and the abilities and skills of the higher educational institutions. The assessment of the results obtained may generate further dilemmas for the solution of which appropriate knowledge bases can be brought about or the already existing ones have to be refined.

    Keywords: Knowledge-based Systems, Knowledge-based Technologies, Deductive Graph, Deductive Reasoning, Model Graph, Inductive Reasoning, Interdisciplinary Co-operation

  • Ladislav Samuelis :
    Notes on the Components for Intelligent Tutoring Systems77-85en [95.51 kB - PDF]EPA-02461-00010-0060

    Abstract: The aim of this contribution is to present briefly several views on the components for the intelligent tutoring systems (ITSs) and to analyze the concepts behind them. We will briefly analyze the concepts provided by the classical machine learning (ML) approaches and then we discuss the role of the components in distributed environment. Finally we synthesize the converging trends of the ITSs technologies and try to outline further possible research directions in building ITS from components.

    Keywords: intelligent tutoring systems, components, e-learning, inductive and deductive inference

  • Gábor Fekete ,
    Sándor Horváth ,
    Árpád Czifra :

    Abstract: The article deals with a special problem area of the filtering and evaluation techniques of surface roughness measurement and calls attention to the contradictions of parameters to characterize surface microgeometry. Differences in the value of parameters are presented through tests of the operating surfaces of three disparate component types. Each chapter discusses the evaluation of measurement results according to various methods, on the basis of which it can be established that value differences are caused by the use of different filters, on the one hand, and by discrepancies between the profiles detected. From the practical point of view, it is most expedient to characterize surfaces with unfiltered parameters.

    Keywords: surface roughness, filtering, motif, height difference correlation

  • András Farkas :

    Abstract: This paper develops the spectral properties of pairwise comparison matrices (PCM) used in the multicriteria decision making method called analytic hierarchy process (AHP). Perturbed PCMs are introduced which may result in a reversal of the rank order of the decision alternatives. The analysis utilizes matrix theory to derive the principal eigenvector components of perturbed PCMs in explicit form. Proofs are presented for the existence of rank reversals. Intervals over which such rank reversals occur are also established as function of a continuous perturbation parameter. It is proven that this phenomenon is inherent in AHP even in the case of the slightest departure from consistency. The results are demonstrated through a sample illustration.

    Keywords: multiple criteria decision making, algebraic eigenvalue-eigenvector problem, rank reversal issue

  • Ákos Nemcsics :
    Behaviour of RHEED Oscillation during LT-GaAs Growth117-123en [196.97 kB - PDF]EPA-02461-00010-0090

    Abstract: The behaviour of decay constant of RHEED oscillation during MBE growth on GaAs (001) surface at low temperature growth conditions is studied in this work. The dependence of decay constant on As-to-Ga ratio, substrate temperature and the excess of As content in the layer are examined here.

    Keywords: MBE, RHEED, LT-GaAs

  • M. M. Awad ,
    H. M. Mostafa ,
    G. I. Sultan ,
    A. Elbooz ,
    A. M. K. El-ghonemy :
    Performance Enhancement of Air-cooled Condenser125-142en [540.60 kB - PDF]EPA-02461-00010-0100

    Abstract: Heat transfer by convection in air cooled condensers is studied and improved in this work. In order to enhance the performance of air cooled condensers, it is important to take into consideration both of condensation inside condenser tubes and convection outside, where the enhancement in convection side is the dominant one. Aluminum extruded micro-channel flat tubes improve the performance of condensation more than conventional circular tubes but still has potential for air side improving. So the enhancement of convective heat transfer in air side is achieved in this study by inclination of the flat tubes by a certain angle with respect to horizontal in two cases. The first proposed case is to make convergent and divergent channels for air flow (case 1), while the second case is tilting all tubes in parallel to each other (case 2). A parametric study is performed to investigate the optimum inclination angle (β) and aspect ratio (Ar). Mathematical modeling for air cooled condensers was applied to aluminum flat tubes to study and evaluate these proposed two cases. A computational fluid dynamic software (CFD) is used to solve the problem. Theoretical results show that the optimum angle for the proposed two cases is about 4 deg. With corresponding aspect ratio of 0.58. This leads to enhancement of heat transfer coefficient by factor (Kh) of 1.469 and 1.46 against increase in pressure drop factor (KP) of 2.12 and 1.95 for case 1 and case 2 respectively.

  • Sándor Csiszár :
    Two-Phase Heuristic for the Vehicle Routing Problem with Time Windows 143-156en [295.84 kB - PDF]EPA-02461-00010-0110

    Abstract: The subject of the paper is a complete solution for the vehicle routing problem with time windows, an industrial realization of an NP hard combinatorial optimization problem. The primary objective –the minimization of the number of routes- is aimed in the first phase, the secondary objective –the travel distance minimization- is going to be realized in the second phase by tabu search. The initial route construction applies a probability density function for seed selection. Guided Route Elimination procedure was also developed. The solution was tested on the Solomon Problem Set and seems to be very compeitive with the best heuristics published in the latest years (2003-2005).

    Keywords: Metaheuristics; Vehicle routing problem; Time windows; Tabu search; Combinatorial optimization

  • Valerie Novitzká ,
    Dániel Mihályi :
    Resource-oriented Programming Based on Linear Logic157-166en [195.21 kB - PDF]EPA-02461-00010-0120

    Abstract: In our research we consider programming as logical reasoning over types. Linear logic with its resource-oriented features yields a proper means for our approach because it enables to consider about resources as in real life: after their use they are exhausted. Computation then can be regarded as proof search. In our paper we present how space and time can be introduced into this logic and we discuss several programming languages based on linear logic.

    Keywords: linear logic, programming languages, resource-oriented programming