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Recent 20

Vol. 8 (2007), Nr. 2 (20) July 2007

The 20th issue of RECENT journal was edited and multiplied with support of:

  • Romanian Association of Unconventional Technologies,

  • Transilvania University of Brasov,

  • Brasov County Council (by Scientific Activities, Education, Culture, Cults Committee)


CONTENTS


  • Constantin BUZATU

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MODELLING OF SURFACE ROUGHNESS OBTAINED BY SUPERFINISHING BASED ON CUTTING MATERIAL VOLUME IN UNIT TIME

» Abstract. In the paper is presented a possibility of mathematical modeling of surface roughness obtained by superfinishing, based on cutting material volume in unit time, through the influence of process parameters, of tool and of dimensional and geometrical accuracy from previous machining process. Also is shown based on mathematical modeling of roughness the influence of these factors in some machining processes.

» Keywords: superfinishing, roughness, modeling, technological optimization


  • Mariana DELIU, Gheorghe DELIU

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A SIMPLE METHOD TO ESTIMATE THE WIND POTENTIAL OF A REGION

» Abstract. Starting from the conviction that the problem of wind power conversion should deserve a greater attention in Romania, the authors present a simple method to estimate the wind potential of a region. An evaluation and comparison modality for the wind power potential on different geographical zones is proposed, as well as a method to estimate the useful part of this potential. The illustration is made by processing measured data, supplied by INMH, for 23 meteorological stations, during a month (March, 2007).

» Keywords: wind energy, potential, estimation


  • Aurel FRATU, Laurent VERMEIREN

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ADAPTIVE CONTROL ARCHITECTURE FOR REDUNDANT ROBOTS

» Abstract. In this paper, a control architecture with variable structure for redundant robot is proposed. The cooperation of the robot’s actuators, to realise a robot task is made by the sub-tasks dynamically allocation for each sub-controller of the architecture. The control algorithm of a sub-controller with self-governing is based on robot Jacobian matrix. The algorithm for the estimation of Jacobian matrix’s elements uses the covariance matrix. In this paper, the factorization technique of the covariance matrix for the identification of the redundant directions inside the actuator motion space is used.

» Keywords: sub-controllers, sub-tasks dynamical allocation, redundancy


  • Daniela GOTSEVA, Ognian NAKOV, Luka BEKIAROV

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QUALITY CODE ANALYSIS IN STUDENTS' PROJECTS

» Abstract. In this study we focused on three ASA tools for C/C++ programs. After short ASA tools description, we examine the faults identified by ASA tools, manual inspections and system failure testing. Additionally we categorize raw output from ASA tools that help us to make conclusions about the efficiency of static analysis for software fault detection in students’ projects. We analyze 500 student projects during the last 12 years.

» Keywords: static analysis, bug reviews, C/C++ and Java programming


  • Dalila KHALFA, Abdelouahab BENRETEM, Rachid CHAIB

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ASSESSMENT OF THE TWO PHASE HEAT TRANSFER COEFFICIENTS IN THE VAPORIZER TUBES BY SEVERAL MODELS

» Abstract. Flowing fluids undergo boiling in many of case in which we transfer heat to fluids moving tubes. When we use the terms boiler, steam generator, or evaporator we usually refer to equipment that involves heat transfer within tubes .the prediction of heat transfer coefficients in these systems is often essential. The object of this research is aimed to the assessment of the heat transfer coefficient in the vaporizer tubes in saturated regime by several models. Two mechanisms appear in this regime: the nucleate boiling and the convection boiling; these two mechanisms can coexist or one can be dominant. Every model gives the interaction between the two mechanisms and precise their variations according to the different thermohydraulics parameters. The finalized trial program concerns the prevision of the heat transfer coefficients; and the evaluation of the nature of two phase flow in the vaporizer tubes. The application on the vaporizer tubes of the dynamic boiler of the thermal power station Sonelgaz - Annaba, Algeria and the comparison between the models gave us a very important databank.

» Keywords: two phase flow, saturation, heat transfer coefficient, convective boiling, nucleate boiling


  • Aurel LUNGULEASA

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INSTALLATIONS FOR INDUSTRIAL COMBUSTION OF WOODEN BIOMASS

» Abstract. This work-paper presents some consideration about combustion of wooden biomass and its industrial installation. It is presented the main technologies that utilise wood waste to produce renewable energy and the main key elements which make up a typical wood combustion systems.

» Keywords: wooden biomass, industrial installation, renewable energy


  • Dana-Adriana LUPŞA-TĂTARU

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INDUSTRIAL REGIONAL DEVELOPMENT OF ROMANIA IN EU CONTEXT

» Abstract. Considering the importance of regional development in the context of Romania's accession to EU, the present paper highlights, using the newest theories in the field, an original model for determining the industrial regional development degree. The paper aims to answer the problem of evaluating the industrial regional development of Romania, presenting the results of a comparative analyze, from the point of view of industrial production for which the most recent statistical data, meaning the 1995 and 2004 years were used. Analyze is then completed with the calculation of an aggregate indicator called the degree of industrial development, using the theory of subtle sets. There are changes concerning the grouping of the regions, the structure of the principal components and the value of aggregate indicator from a period to another.

» Keywords: industrial regional development, subtle sets, principal components analyze, cluster analyze


  • Alexandru MANIU, Irina APOSTOL

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SEMICONDUCTORS BASED ON CONTROLLED DOPED BARIUM TITANATE (1st PART)

» Abstract. This paper presents the experimental results of doping barium titanate in order to obtain a semiconductor. The semi conducting materials based on controlled doped barium titanate are termosensible materials with a strong dependence of electric resistivity with temperature (PTCR effect) and may be used for obtaining electronic components. These materials can be elaborated by method of solid state reaction. The controlled doping of barium titanate, which is an insulating material in its pure state, can lead to semiconductorial or dielectrical properties in terms of the type of doping elements and the level of doping. There were used as doping elements Pb, Ca, Co, Se, Zr. The calcined powders and sintered compacts were micro structurally characterized by X-Ray diffractometry and electric measured. The application of these materials is large: in electronic and electro technical industry, telecommunication, automatization, automobile industry.

» Keywords: semiconductors, barium titanate, controlled doping


  • Alexandru MUNTEANU

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THE HEAT TREATMENT OF THE NICKEL BASED SUPERALLOYS

» Abstract. The present paper shows several theoretical and practical aspects regarding the heat treatment of some nickel-based superalloys, the influence of the semi-finished products obtaining processes over the heat treatment and over the structure and final properties. There are explained in a particular way the effects of the modification of the heat treatment operations technological parameters and of the obtaining method of these alloys, over the mechanical resistance and high temperature creep.

» Keywords: isotherm forging, powder metallurgy, isostatic squeezing, quenching, aging


  • Ognian NAKOV, Dessislava PETROVA

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OPTIMIZATION TECHNIQUES FOR VEHICLE DYNAMICS MODELING

» Abstract. This paper covers the dynamic modeling of the vehicle. The basic mathematical modeling of the vehicle’s non-linear lateral and roll dynamics are covered. Assumptions are made in order to linearize the model. This non-linear vehicle model uses the non-linear Pacejka tire model. The vehicle model is used for development of autonomous control method, which is optimized for parallel execution.

» Keywords: vehicle modeling, linearization, parallel optimization, speed up


  • Ion NEAGOE

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ANGLE MEASUREMENT DEVICES FOR THE SPRING-BACK AFTER BENDING

» Abstract. The paper presents the principle designs of some measurement devices for the β spring-back angle of the V shaped metal sheet parts obtained by bending and establishes the calculus formulas for their measurement precision.

» Keywords: bending, spring-back angle, comparator, orthotest, measurement precision


  • George NICOLAE, Dan LOZNEANU

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MEASURING THE SNR FOR DETERMINED QUALITY OF THE TV RECEIVERS (2nd PART)

» Abstract. In this article are presented the experimental results and the conclusions found following the measures for determining the signal-noise-ratio use the pinnacle value of the noise, measured to the floor of the blanking impulse or of the TV lines synchronization impulse, depending on the quality of the received image. The experimental measurements have aloud the establishing of new methodologies of measuring making in the TV receivers for establishing the performance parameters of these, in the processing and remaking of the image information. The processing of the measurement’s results, acquisition and stocked on the computer had aloud the establishing of conclusions regarding the correlation between the TV image quality and the signal-noise-ratio, measured at the output of the video demodulator and at the output of the video-frequency amplifier use de test signals.

» Keywords: noise in television, signal-noise-ratio measuring, measurement in television


  • Radu SĂULESCU, Livia HUIDAN, Nicolae BERCAN

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DYNAMIC INFLUENCES IN CARDAN TRANSMISSIONS

» Abstract. The main objective of the paper is the analysis of some representative parameters on the kinematic and dynamic behaviour of n–cardan transmissions; with this purpose a program, using the soft Excel, was elaborated. The obtained results are useful in the design of these transmissions.

» Keywords: cardan transmission, elastic effects, inertial effects, homokinetical deviation


  • Ivan SHOPOV, Ivan IANCHEV

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A STAND ABOUT COMPLEX RESEARCH OF THE PROCESS OF AUTOMATIC SCREW DRIVING

» Abstract. The assembly process using threading fastening parts includes three stages: “adapting” of the threading parts and subsequent catching, driving the basic part of the thread and subsequent tightening by a definite moment. Various factors influence the gathering of the parts during the automatic screw driving. A part of them is dynamically changed during the screw driving, by the reason of which the process of their research is troubled. In this work is described a device about complex research of the process of automatic screw driving including measuring of the basic parameters influencing the process.

» Keywords: automation, screw, stand, research


  • Luchesar TOMOV, Emil GARIPOV

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CHOICE OF SAMPLE TIME IN DIGITAL PID CONTROLLERS

» Abstract. A generalized type of analogue PID controller is presented in the paper. A digital versions of it based on various methods of discretization are examined and corresponding tuning rules are tested in the optimization manner. The research works are focused on the best choice of sample time as a compromise between the desired control system behavior and the constrained control signal. The main results are connected with the optimal sample times in the hybrid two-rate control systems. New performance criteria for its choice are suggested and the satisfied control is shown on the number of numerical simulations.

» Keywords: digital PID, optimization tuning, optimal sampling time, two-rate digital control systems


  • Mihaela URDEA

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THE METAL STRUCTURE MODELLING TECHNIQUE IN SOLIDWORKS

» Abstract. The purpose of this paper is to design, to model and to assembly a metal platform, using SolidWorks detailing all models alternatives. This work presents a designing and a modelling solution for a platform using the Weldments parts. The components of the platform assembly are normalized profiles, simple parts and sheet metal parts, and SolidWorks is the best fitted for design and model this parts. This design method by modelling in SolidWorks is a quick checking method of the assembly, by viewing it. The platforms can be visualized before their physic building.

» Keywords: SolidWorks, metal platforms, Weldments module, Sheet Metal module


  • Ion VERZEA, Rachid CHAIB

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THE CONCEPTION AND THE UTILISATION OF MAINTENANCE MANAGEMENT'S SCOREBOARD BY DEPENDABILITY BREAKEVEN POINTS

» Abstract. A competent manager wishes to have available in every moment the necessary information on the state of the system he or she is managing. The manager’s efficiency emerges from the rightness of his/her decisions taken in an optimum time range, and from the efficient allocation of the available resources. Tracking the efficiency indices' evolution leads to the best solutions to everyday problems. A useful instrument at the foundation of modern management is the scoreboard. The paper presents the conception method and the utilization algorithm of the maintenance management’s scoreboard by dependability breakeven points.

» Keywords: scoreboard, dependability, reliability, maintainability, security, availability, breakeven points


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