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Recent 19

Vol. 8 (2007), Nr. 1 (19)

The 19th issue of RECENT journal was edited and multiplied with support of:

  • Transilvania University of Brasov, Romania

  • Romanian Association for Nonconventional Technologies

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


CONTENTS


  • Ioan CIOBANU, Mihai MAŞNIŢĂ, Vlad MONESCU

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Determination of the Castings Solidification Constant by Analytical Calculation and by Computer Solidification Simulation

» Abstract. Starting from the analytical expression of the temperature field from the mould-casting assembly it is established an analytical relation for the castings solidification constant calculation. It is verified the validity of this relation comparing the results obtained with it, with the solidification constant values determined by computer solidification simulation. The verification was made for a plate with thickness a = 20 mm poured from an eutectic grey cast iron in quartz sand moulds with sodium silicate.

» Keywords: casting, simulation, solidification


  • Sorin COCORADĂ

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Experimental Evaluation of the Throughput of Unacknowledged UDP Traffic in an IEEE 802.11e/g WLAN

» Abstract. While the 802.11 protocol has been extensively studied in the literature through analytical modeling and simulations, this work is exclusively concerned with 802.11e/g networks and their throughput measurement under unacknowledged UDP traffic, generated from a single source, being different from other performance studies. The wireless network used for our experiments was configured in infrastructure mode and was confined to a single room. It consists only of a desktop PC acting as an access point (AP), another desktop PC acting as a client. Also, a formula for the expected throughput is deduced and provided which permits to compare the measured values with the theoretical limits. In good channel conditions and when only a very few number of stations are present, the NoAckPolicy can be used to raise the actual throughput of IEEE 802.11e/g.

» Keywords: 802.11e/g, performance evaluation, NoAckPolicy, UDP, measurement


  • Aurel FRATU, Mariana FRATU

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AVOIDANCE OBSTACLES TECHNIQUE USING REDUNDANT ROBOTS

» Abstract. A control structure for a redundant robot must assure the obstacles avoidance in a workspace, during motion of the end-effector, along a pre-selected trajectory. The stopping motion must be done in the path critical point closest to the obstacle, situated on the imaginary sphere surface, namely sphere of influence surrounding the obstacle. The robot control algorithms of robot motion, must allow the identifying the critical points of the motion path and critical distance until obstacle. In this paper, for testing the control algorithms, the authors propose the using of the modeling and behavioral simulation method. On the virtual robot model one test is behavior inside virtual operating environment.

» Keywords: Obstacles avoidance algorithms, virtual operating environment, real operating environment


  • Cătălin GHEORGHE

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NEW CRITERIONS OF BASIC MACHINE TOOLS COMPONENTS DESIGNING

» Abstract. The sustainable development requires the necessity to take in consideration new criterions beside those economical and technical for machine tools. Newly criterions will consider all life time periods machine tools and their relation with the environment. All of these are determined by the increase of the production volume on the world level and the reducing until their exhaustion of the environment resources. The frame constitutes the mechanical component that contains mostly content of metal and energy from the machine tool structure. In consequences is the part that generates the main impact above the en environment and costs. Through the identification of the new criterions of designing is watching the evidence all production costs.

» Keywords: machine-tool, design, component, environment


  • Stancho KAVALDJIEV, Alexander YANKOV

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ON THE EFFICIENCY COEFFICIENT OF A WORM GEARING

» Abstract. The efficiency coefficient of a mechanism is an important parameter, which quantifies the rate of energy loss. Compared with other gearing mechanisms, the worm gearings are characterized with lower values of the efficiency coefficient, which makes the ways of studying and measures for its increase particularly relevant. This work offers an analytical expression for the efficiency coefficient as a function of characteristic geometrical and kinematical parameters of the gearing (module, gear teeth numbers and angular velocity of the gearing, speed ratio). A numerical study was carried out to determine the direction and the degree of influence of these factors.

» Keywords: worm gearing, efficiency coefficient, loss coefficient, friction forces


  • Lachezar NENKOV LAZOV

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DYNAMICAL MODELING OF IMPACT CRUSHER'S ROTOR SYSTEM

» Abstract. In this paper is performing a dynamical analysis of 3D forced vibration on a heavy rotor of impact crusher. Dynamical model with three mass and eight degree of freedom has been created. The applied loads are transient impulse load. Differential equations of motion are obtained with account of mass, elastic, damping and geometrical properties. The numerical solution of differential equations of motion is obtained with MATLAB program. Numerical experiments show influences of dynamical characteristics of crusher are performed.

» Keywords: nonlinear vibrations, vibration of rotary shaft, impulse load, impact crusher


  • Aurel LUNGULEASA

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UN-REGULARITY OF DENSITY INSIDE OF WAFERBOARD

» Abstract. The paper presents some aspects about the variation of chipboard density inside of board, on thickness and on surface, too. It is also studied the influence of this density variation upon the main chipboard strength, namely the bending strength, using original methods for working.

» Keywords: waferboard, un-regularity of density, bending strength


  • George NICOLAE, Dan LOZNEANU

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MEASURING THE SIGNAL-NOISE-RATIO PROCEDURE FOR DETERMINED QUALITY OF THE TV RECEIVERS (1st PART)

» Abstract. In this article are presented the experimental results and the conclusions found following the measures for determining the signal-noise-ratio depending on the quality of the received image. The experimental measurements were concentrated for the determination and the establishing of the practical methodology to determine the signal-noise-ratio in different measure points of the TV receiver. 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.

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


  • Radu SĂULESCU, Nicolae BERCAN, Livia HUIDAN

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DYNAMIC MODELING OF CARDAN TRANSMISSIONS IN MODULAR VARIANT. PART III: MODELING OF CARDAN TRANSMISSIONS WITH ELASTIC SECONDARY SHAFTS

» Abstract. Based on modular correlations presented in the first part and the algorithm shown in the second part, in this paper it is proposed an algorithm for modeling of forces and torques of n-cardan transmissions, considering that the secondary shafts are elastic; this algorithm relies on the assemblage of analytical models (of modular type), established previously, and is exemplified on a representative 2-cardan transmission. To point out distinctively the influence of the secondary shaft elasticity, inertial effects are neglected. The influence of secondary shafts elasticity in presence of mechanic moments of inertia will be presented in a following paper.

» Keywords: elastic secondary shafts, general algorithm, computational dynamic modeling


  • Atanas STOEV, Petar GORANOV

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MODELLING OF MECHANICAL ASSEMBLY STRUCTURE IN CAD ENVIRONMENT USING THEORY OF BASING

» Abstract. In this work the authors’ concepts about modeling of structure of mechanical assembly, aimed to creation of an integrated CAD model, as well as reached results are presented. The model of structure is formed in virtue of the approach, developed by authors for integration the conceptual representation of geometry on level "structure" with the final geometrical model in CAD environment. An extended structural scheme, that includes the all components of the assembly and relationships between them, is used as an integrating element. This structural scheme is loaded up with additional engineering information that includes basing scheme of each component according to Theory of basing. This engineering information is used in the next stages of design process as embodiment design and creation of CAD assembly model. The general principles of developed approach are: the structural scheme contains information about basing schemes of components and this extra information guarantees to stand by some of main suggestion of design theory in a formal manner; there are defined rules that allow part skeletons to be generated from the mentioned structural scheme in a formal manner; the part skeleton is used as base, on which part geometry is shaped up; there are originated formal rules that permit the definition of basing schemes to be transferred to CAD assembly model as geometrical constraints.

» Keywords: modeling, CAD, structure, assembly unit, basing


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