• Atmospheric Observation and Radio Signal Measurements over the Black Sea Region for Assessment of Tropospheric Radio Propagation and Potential Radio Interferences

    pg(s) 121-124

    Due to various interferences arising from the tropospheric propagation of radio waves over big water basins, it is necessary to study in detail the mechanisms of propagation and to improve the existing models for determining propagation factor or path loss profiles at different frequencies, especially in UHF bands, caused by the growing interest of mobile communications and especially 5G technologies. To get enough information about radio wave propagation over the Black sea area, the state of atmosphere above points of interest is studied in detail and the results are compared with real measured radio signals distributed between those points. The results are compared with basic theoretical computed models. The results showed more than 10 dB and from 6 to10 dB difference respectively for VHF and UHF between measurement and computed with Three way path loss model EMF levels for the favorable cases which might be due to additional ray in the receiver. A clear relationship between received EMF levels and wind speed but in combination with different abnormal tropospheric environments and relationship between absolute value of modified refractivity and the levels of received signals for the surveyed regions

  • Mathematical modeling of automated production systems

    pg(s) 114-120

    The paper theoretically substantiates and practically implements mathematical methods of modeling production systems, proves the adequacy of mathematical models and optimization methods, as well as selected rational optimization methods and created software that implements the selected methods in practice. The analysis of methods of modeling and optimization of production technological systems is performed, the most effective methods of solving these problems for discrete production are selected. The main provisions of infinite-valued logic and ordinal determinants, on which the structural-logical approach to the study of complex systems, which include production systems in instrument making, are considered.

  • Simulation of the main components of a nuclear reactor under load, made of ultrafinegrained steel AISI-321 in the normal and irradiated state

    pg(s) 110-113

    The creation and calculation of computer models of various products under load with the properties of UFG materials in the normal and irradiated state was performed. To model the UFG properties of non-irradiated AISI-321 steel, hardening curves were constructed based on the Hall-Petch equation for the base state of the material at a grain size of 1500 nm and for two UFG states (with grain sizes of 700 and 200 nm). To simulate the properties of irradiated AISI-321 steel, plastometric tests were performed using uniaxial compression of cylindrical samples at constant values of the strain rate of 1 s-1 and the temperature of 20°C on the “Gleeble 3800” plastometric unit. Fast neutron fluence with the following values was selected as a variable parameter: 0.5∙1018 n/cm2, 1∙1018 n/cm2, 0.5∙1019 n/cm2, 1∙1019 n/cm2. The maximum operating pressure of 340 MPa was used as a static load. The simulation results showed that for both parts, the use of the material in the UFG state is the most appropriate solution.

  • Simulation of energy consumption for different types of hvac systems in a typical office building under tirana climate conditions

    pg(s) 93-95

    Thermal comfort and indoor air quality highly depend on proper design of Heating, Ventilation and Air Conditioned (HVAC) system. These system require large amounts of energy. Efficient use of energy leads to new concept design of HVAC systems. In this article, energy consumption in office building is analysed using Hourly Analysis Program (HAP) software. The aim of this research work is focused in estimation of office building energy consumption considering three different HVAC systems, respectively. Therefore, Variable Refrigerant Flow (VRF) system, HVAC 2-pipe and HVAC 4-pipe system were analysed with respect to energy consumption. A typical office building placed in Tirana, of 5000 m2 of total area is used for this study.

  • Linear synthesis of frame eddy current probes with a planar excitation system

    pg(s) 86-90

    A mathematical method of linear surrogate parametric synthesis of frame surface non-coaxial eddy current probes with a uniform eddy current density distribution in the testing object’s zone is proposed. The metamodel of a frame eddy current probe with a planar structure of the excitation system is constructed. Acceptable accuracy of the created metamodel is obtained by using the decomposition of the extremum search space and using associative neural networks. Examples of the synthesis of such excitation systems using modern metaheuristic stochastic algorithms for finding the global extremum are considered. The numerical results of the obtained solution and graphic illustrative material of the density distribution of the eddy currents on the surface in the testing object’s zone are given.

  • Comparison of three methods for the pump energy analysis

    pg(s) 82-85

    This paper presents a comparison of three methods for any pump energy analysis. Each method is used for the analysis of three different water pumps from the conventional steam thermal power plant – two feed water pumps (FWP1 and FWP2) and condensate pump (CP). For each pump three essential types of mechanical power which defines all energy analysis methods are: delivered power from power producer, real (polytropic) power and ideal (isentropic) power. Method 1 which compares delivered and real (polytropic) power show the best performances, while Method 3 which compare delivered and ideal (isentropic) power should be avoided because it results with too high energy power loss and too low energy efficiency of any pump. Method 2 which compares real (polytropic) and ideal (isentropic) pump power can be used as a good compromise for the pump energy analysis in the most of the cases – its results are similar to results of Method 1.

  • Harmonic regression based on the output signals of vibration processes

    pg(s) 72-74

    Тhe article deals with probabilistic and statistical models of vibration processes. The covariance moment is considered. A dimensionless normalized covariance is introduced. To evaluate these theoretical characteristics, we used a statistical set of observational data. Observations that are cleared of measurement errors are combined into a sample of a specific volume. Random processes in vibration analysis are considered in detail. The characteristics of random processes are given: attenuation with a random beginning, a linear process with a random slope, and a harmonic process with a random amplitude. A statistical model of a linear system based on observations of input and output vibration processes is considered in detail.

  • Development of a simulation model of an information-measuring system of electrical characteristics of the functional coatings of electronic devices

    pg(s) 68-71

    The article develops a simulation model (based on the MatLab Simulink mathematical processor) of an information-measuring system of electrical characteristics (residual surface electric charge, surface layer capacity, etc.) of functional coatings of electronic devices. The main purpose of the simulation model was to determine the rational parameters of measurement and control of the informationmeasuring system developed by the authors, which would simplify the process of setting up such a system, as well as explore the dynamic modes of its operation. The main advantage of the developed simulation model is the ability to conduct an interactive study of the operation of the information-measuring system under various, including limiting, modes. Tests of the simulation model of the information-measuring system made it possible to study its operation under various conditions and modes of the measurement experiment, as well as to virtually determine the rational operating parameters of such a measurement and control system. A satisfactory discrepancy of 8-11,5% was established for the experimental results compared with the data obtained analytically, which proves the correctness and adequacy of the compiled model.

  • Model of hydraulic turbine taking into account the impact of efficiency

    pg(s) 64-67

    Research, optimization and practical implementation of a Small Hydropower Plants as a source of clean electricity are one of the actual tasks in the current energetics, which is virtually impossible to solve without powerful computer support due to the strongly nonlinear nature of such systems. The article presents an overview of the most common simulation model schemes of Small Hydropower Plants, whereas explores the sub-models of its individual subsystems. The hydraulic turbine is considered as a core of the hydropower plant, whose efficiency calculation is analytically demanding and dependent on parameters that are often obtained only by theoretical estimation. In the article a fuzzy system was used to create its model based on measured operating data on the turbine flow rate and the height of its water column without the need to know the turbine parameters. Such a model is applicable in practice for the design of an energy-optimized hydroturbine control as well as to the effective determination of the deterioration rate. The correctness of the results was verified by simulation measurements in the MATLAB program.

  • Development of information model of power transmissions in the light of Industry 4.0

    pg(s) 54-63

    The main features of creating an information model (Digital Twin) for a technically complicated item are formulated. These include: a multitude of systemic representations of the item, individualization of its behavior and state under specific operating conditions, fatal uncertainty in the description of component properties, reconstruction of data based on sensors readings, individual lifetime expense in operation. Above features are illustrated by authors’ developments in application to power transmissions. The key issues of synthesis, calculation, design and diagnostics of transmissions based on the created complex of lifetime-and-functional models are solved. Transmission is considered as a multicomponent system with a variable structure and states. Creating a single universal model to reproduce basic properties of the technically complicated item is impossible. Principles of constructing models and methods for calculating, monitoring and predicting functional and lifetime properties are described. The basic representations of the transmission (structure, regular mechanical system, kinematic and dynamic diagrams, diagnostic model, schemes of limiting states, lifetime expense model) and the mathematical models serving them are developed. The approaches considered are methodologically typical for complex mechanical and combined objects based on mechanical systems.

  • Determination of empirical coefficients of heat dissipation characteristics by optimization methods for a spark-ignited car engine

    pg(s) 35-38

    For the development of new engines, as well as to obtain the correct results from mathematical modeling, numerical methods should be used, with the help of which verification of mathematical models takes place. This approach can significantly reduce the material and time costs at the development stage. The influence of the optimization method used in processing the experimental data of engine indexing to obtain semi-empirical coefficients of the form Wiebe is explored. A comparison is made of the rate of calculation of the coefficients of the Wiebe formula using brute force and gradient methods. In both methods, the integral using the modulus of the difference between squares of the experimental and calculated dependences is chosen as the target function. Analysis of the rate of calculation of the coefficients of the Wiebe formula showed the need to use the combined use of both methods: the global minimum of the objective function by the method of brute force with a large step and near the optimal point – the gradient method