Machines. Technologies. Materials.
Vol. 11 (2017), Issue 5

Table of Contents

  • MACHINES

    • STUDY OF THE INFLUENCE OF SUPPLY VOLTAGE ON THE DYNAMIC BEHAVIOR OF INDUCTION MOTOR LOW VOLTAGE DRIVE

      pg(s) 206-209

      Paper deals with the dynamic behavior of pump unit electric drive. The electric motor, subject of development, is a new standard efficiency induction motor with squirrel cage rotor, designed to operate in continuous operation. The determination of operating characteristics of induction motor in dynamic modes is necessary to establish the properties of the machine in specific conditions. In some industrial areas can occur very often sags with a depth of between 10% and 15% of the rated voltage as a result of switching electrical loads on systems of users. As a result of simulation studies the influences of the supply voltage and total torque of inertia of the electric drive have been assessed on arising impact torques and currents and electric energy losses of electric drive for pump unit. The results obtained are in addition to experimental studies of the same motor. Some of the study results have been presented graphically. An analysis and conclusions from the results obtained have been done

    • PASSAGE THROUGH RESONANCE OF STATICALLY UNBALANCED ROTOR WITH ECCENTRIC AUTOMATIC BALL BALANCER

      pg(s) 210-213

      Different modes of direct and reverse passage of the resonance region of the statically unbalanced rotor equipped with an imperfectly mounted eccentric ABB (Automatic Ball Balancer) are investigated with the help of the mathematical model. It is shown for the mode of a constant angular acceleration that the maximum amplitude during the reverse passage of the critical region is always lower than the maximum amplitude in the steady-state mode; at the same time the amplitude of whirling in the direct passage, on the contrary, may be greater than the maximum steady-state value. The case of rotor passing through the resonance under the action of a constant external torque was also investigated. The effect of viscous friction in the ABB’s cage was studied for both types of modes. The effect of the rapid oscillations of the amplitude caused by the slippage of the balancing balls was discovered in the case of insufficient damping in the ABB

    • FUZZY – ROBUST CONTROL OF A TWO-LINK ROBOT ARM

      pg(s) 214-217

      Parameters of the robots are always changed due to the load being carried. Robust control is a method that considers the changes of control system performance related to the modification of system parameters. Stability and performance of the system can be well protected in case the change of system parameters does not affect the system. Even if there is several modified parameters, robust control system still provides the ability of control in a desired manner.

      In this work, parameters are made changeable and the upper limit of the uncertainty parameter is kept constant unlike other robust control studies. Control parameter is updated over time depending on the trigonometric functions. The values of the constant control parameters in trigonometric functions affect the performance of the system and it is quite difficult to find appropriate control parameter values. Logical fuzzy compensator is designed to find this parameter and investigated the effects on the tracking error of two-link robot.

      Fuzzy Logic associated robust control methods developed using robust control has been compared through a computer simulation using the same trajectory and same model. Thanks to the designed fuzzy logic associated robust controller, robust control is improved and two-link robot’s trajectory tracking error has been reduced to a very small value.

  • TECHNOLOGIES

    • CONTACTLESS DIAGNOSTICS OF INDUCTION MOTORS

      pg(s) 218-220

      In the case of energy-efficient drives with induction motors, the tendency to implement optimally designed motors, combined with intelligent control, incorporating an integrated monitoring and diagnostics system, is becoming increasingly important. Induction motors in industrial systems operate with frequent starting, dynamic loads and sometimes unbalance of supply voltage. In order to maintain an optimal operating condition, reduce the number of failures and build up an optimal repair and maintenance system, it is important to have an advanced monitoring system coupled with fault identification techniques. The behavior of optimally designed three-phase induction motors designed to operate integrated into hydraulic units with continuous duty operating mode is considered

    • BENDING FORCE OF LLDPE MONOFILAMENTS IN RELATION WITH THE DISTANCE OF APPLIED FORCE

      pg(s) 221-224

      The present paper was focused on the importance of the distance of the applied force on the value of the measured bending force. The paper takes in to consideration six different monofilaments, differing from their linear density and their cross section profile. The filaments used as pile layer in artificial turf systems are produced from Linear Low Density Polyethylene (LLDPE). The filament samples were randomly chosen from different not used synthetic fields. The bending tests were performed in the Dynamic Mechanical Analyzer (DMA) TA instrument, where the bending force is monitored very precisely. The tests were focused on two different distances of the applied bending force respectively 2 mm and 3 mm. From the obtained results was found that by increasing this distance, the bending force decreases significantly. Also, was observed that this relation is the same for all the tested samples.

    • HAMILTONIAN – BASED TECHNIQUES FOR SOLVING PENDULUM – LIKE NONLINEAR OSCILLATORS

      pg(s) 225-228

      In the paper, HE’s energy balance method and HE’s Hamiltonian approach are used to derive simple approximate formulas for the dependence of the frequency of a pendulum-like nonlinear oscillator on its amplitude. Such kind of oscillators are frequently encountered in many fields of engineering and three examples from mechanical domain are given and utilized in the numerical simulations. By comparison with the exact solution, it is shown that obtained formulas lead to high accuracy for initial amplitudes lower than 900 (when the relative errors do not exceed 0.2%) and acceptable closeness for amplitudes well beyond the small-angle regime (here the relative errors are about 5-6% for amplitudes as high as 1500). Results furnished by energy balance method and Hamiltonian approach are contrasted with those provided by other techniques which generally need much more sophisticated procedures

    • CREEP ANALYSIS OF ELASTIC BEAMS UNDER CONSTANT TORQUE

      pg(s) 229-232

      This paper presents a two-dimensional numerical algorithm for creep analysis of the elastic beams under uniform torsion. Torque is assumed to be constant during the whole creep process. Tangential stresses are calculated following the warping function distribution. Material creep behaviour is simulated using the effective stress function. Analysis takes in consideration the torque acting on cross-sectional surface independently on the beam length. The proposed numerical algorithm enables the stress analysis to be carried out regardless of the cross-sectional shapes. Viscoelastic effects of the material are modelled by the creep power law formula. Numerical algorithm was developed in Python code and its effectiveness is validated through the benchmark example.

    • HYDRO-MAGNETIC FLOW OF A VISCOUS FLUID WITH HEAT TRANSFER PHENOMENA BETWEEN TWO VERTICAL PLATES

      pg(s) 233-235

      The paper aims to study the combined effects of uniform magnetic field and inertia on a three-dimensional flow of a viscous fluid in a vertical channel. It is assumed that the fluid is injected into the channel through one side of the channel. The flow and heat transfer phenomena have been characterized by non-dimensional parameters R (cross-flow Reynolds number), M (magnetic parameter), Pe (Peclet number), and 𝛼𝛼 (heat generation parameter). The basic equations governing the flow and heat transfer are reduced to set of ordinary differential equations using the appropriate transformations for velocity components and temperature. These equations have been solved approximately subject to be relevant boundary conditions by employing a numerical technique. The effects of the above-mentioned parameters on the velocity and temperature distributions have been examined carefully.

  • MATERIALS

    • DIGITAL VERSUS ANALOG GRADED-GAP QUANTUM WELLS IN THE PRESENCE OF APPLIED CONSTANT ELECTRIC FIELD

      pg(s) 236-239

      In this paper we study in detail the influence of the longitudinal constant electric field on the energy values of a digital quantum well AlxGa1-xAs/GaAs structure and its equivalent graded-composition analog quantum well. We calculate the energies of the electron and hole bound states, the energies of the main optical transitions and their Stark shifts. The spatial distributions of the main electronic and hole states at various given values of the applied electric field are also calculated. The semi-empirical tight-binding approximation in the spin dependent sp3s* basis is used and is carried out by surface Green function matching employing an algorithm previously developed and used to study inhomogeneous systems. The aim of these calculations is to find out in detail to what extent these two structures have similar or different properties in the presence of an applied electric field. We compare our results with the results for the conventional rectangular quantum well and with the available experimental data for quantum wells with similar parameters.

    • THE COMPARISON OF THE KNOWN MODELS OF SELF-TAPPING SCREW JOINTS

      pg(s) 240-245

      During the latest decades the polymer pieces have been appearing in the different areas of the industry. Nowadays polymer and composite materials are used not only as covering but as the material of concrete mechanical elements as they have a wide workable and usability spectrum. The pieces made of polymer materials in the telecommunication industry take an honoured place. It is because they are good insulators, they are light, and cheaper than the metal materials. In the European Union it is a regulation that the most of the pieces must be recyclable. It means not only the reuse of the raw material but the recycle of the pieces. So the new and economical types of connection in the polymer pieces have appeared, and their examination have become important, too. Detailed technical literature is available for self-tapping screwed joints applied on thermoplastic polymers and duromers. The screwed joints’ aspects (screw geometry, binding strength, parameters of assembly, possibilty of automatization) have been examined by way of experiments and by theoretical models. On the basics of these experimental investigations they have created application-oriented connections which give an important fact to the calibration of the self-tapping screwed joints and to the choice of the material. The aim of this essay is to make a basis for the further research by the comparison of known experience and theory so as to create a more developed, and extended model with more parameters.

    • THE PHYSICO-MECHANICAL PROPERTIES OF ASPHALT MIXTURES CONTAINING BITUMINOUS SAND

      pg(s) 246-249

      The continuous evolution and development of the society caused a significant increase in the number of construction works. Regarding road works, in the recent years, these have escalated as the need for bitumen increased. Given Romania’s conditions, for fulfilling the need of bitumen economy and thus reducing the costs correlated with road pavement, due to the fact that this material is currently brought only from abroad, it is desired to design an asphalt mixture with a smaller quantity of contained bitumen or even replacing it with bituminous sand, a solution which is advantageous in areas where one can find these natural resources. In Romania, bituminous sand or oil sand can be found in two geographic areas, namely: in Bihor County, Derna-Tatarus-Budoi in Prahova County, at Matita, and Pacureti. Further, these bituminous sands have a naturally occurring bitumen percentage of approximately 20% in their composition. In this context, this paper aims to emphasize, through static and dynamic methods, the physical and mechanical characteristics of two bituminous asphalt mixtures containing bituminous sand from Derna – Tatarus – Budoi. Both of asphalt mixtures have been designed based on departmental normative CD 42-85, containing various sorts of crushed gravel, natural sand and bituminous sand and are intended to be used for the base course of the road pavement. Furthermore, one of bituminous mixtures is performed with bituminous sand and hard paving grade bitumen compared with the second one, which only contains bituminous sand, in this case the bituminous binder consisting in the bitumen contained into the oil sand.

    • INNOVATIVE SOLUTIONS USING NITROGEN-CONTAINING STEELS

      pg(s) 250-253

      The report provides examples of two innovative solutions using nitrogen-containing steels. The use of nitrogen-containing steels allows to increase the durability and reliability of products; to reduce the thickness of work sections; to reduce the cost of maintenance and repair downtime. The proposed solutions: 1. Austenitic corrosion resistant cast steel with 0,5%N. After homogenizing heat treatment the steel surpasses traditional cast austenitic steels at yield strength at ~1.5-2 times, impact toughness ~ 4.5 times, hardness – by about 25%. It is recommended for the manufacture of cast valves. 2. The martensitic steel grade with 0,11-0,17% N. This steel is well proved as a material for the manufacture by cold heading of very high strength corrosion resistant fasteners.

    • DEVELOPMENT OF ROLLING MODES FOR SAMPLES MADE FROM NICHROME POWDER ALLOY AND THEIR TESTING AT OPERATING TEMPERATURES

      pg(s) 254-257

      The rolling modes for samples of various thicknesses made of dispersed-hardened powder nichrome alloy have been developed. An alloy sample has been tested at operating temperatures on a stand of the Institute of Strength Problems of the National Academy of Sciences of Ukraine. It has been demonstrated that the existing set of properties makes it possible to use the created alloy for aerospace aircraft, which repeatedly operate at extremely high temperatures under aerodynamic heating conditions.

    • INTERNAL OPTICAL BISTABILITY OF QUASI-TWO-DIMENSIONAL SEMICONDUCTOR NANOHETEROSTRUCTURES

      pg(s) 258-260

      We represent the results of numerical computations of the frequency and temperature domains of possible realization of internal optical bistability in flat quasi-two-dimensional semiconductor nanoheterostructures with a single quantum well (i.e., nanofilms). Particular computations have been made for a nanofilm of layered semiconductor PbI2 embedded in dielectric medium, i.e. ethylene-methacrylic acid (E-MAA) copolymer. It has been shown that increasing thickness of a nanofilm results in the long-wavelength shift of the frequency interval of realization of bistability, increasing size of the hysteresis loop, and broadening temperature interval of realization of this phenomenon.