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  Subjects -> AERONAUTICS AND SPACE FLIGHT (Total: 124 journals)
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Aerospace technic and technology
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  This is an Open Access Journal Open Access journal
ISSN (Print) 1727-7337 - ISSN (Online) 2663-2217
Published by National Aerospace University Homepage  [1 journal]
  • Analysis of possibility of using commercial micro turbojet engines for
           high-speed small-sized operational-tactical UAVs

    • Authors: Olexander Khrulev
      Pages: 5 - 18
      Abstract: Despite the technological advances that made it possible to create serial commercial micro-turbojet engines with a thrust of up to 1.0 kN, engines of this type in the class of high-speed unmanned aerial vehicles (UAVs) weighing up to 200 kg have not yet received wide distribution. Nevertheless, the use of micro-turbojet engines continues to be considered as promising, and a large amount of work has been devoted to the study of these engines. However, existing studies often show a simplistic approach when a micro-turbojet is considered in isolation from its possible aviation application. The object of this study is micro turbojet engines for high-speed UAVs. The purpose of this study was to evaluate the effectiveness of the use of serial commercial micro turbine engines on high-speed UAVs. The task: to select a gas-dynamic calculation program, perform a mathematical modeling of the characteristics of a micro-turbojet engine, and analyze the conditions and effectiveness of the application of the considered type of engine on high-speed UAVs. Method of the study. The GasTurb14 standard program for gas-dynamic calculation of gas turbine engines was used, with the help of which gas-dynamic calculations were carried out, a structural diagram was obtained, and mathematical modeling of micro-turbojet characteristics was performed. The results. Possible manufacturers and models of engines produced by them and their equipment were identified. It was found that for the considering UAV class, the engine should have a pressure ratio in compressor in the range of 4.2-4.7, and it is advisable to choose the flight operating mode of the micro-turbojet engine at a speed of 92-95% of the maximum. It has also been determined that UAVs with micro-turbojet engines, in comparison with piston engines, easily provide the same flight range with the same fuel relative mass due to at least three times higher speed. Conclusions. The use of a micro-turbojet turns out to be more effective at a flight range of over 300 km, and at a flight speed of more than 150 m/s (540 km/h), a micro-turbojet engine provides a significant advantage over a piston engine for a number of operational and tactical tasks.
      PubDate: 2023-08-24
      DOI: 10.32620/aktt.2023.4sup2.01
  • Efficiency of marine power plants with heat exchangers made from tube
           bundles with dimple systems

    • Authors: Valerii Kuznetsov, Anatolii Shevtsov
      Pages: 19 - 27
      Abstract: The direction of increasing the efficiency of marine power plants by using heat exchange elements that implement intensive methods of heat transfer, which are characterized by a predominant increase in heat transfer over aerodynamic resistance, is considered. The research method is mathematical modeling of processes in power plants at the level of their individual elements – heat engine, power, and technological heat exchangers. The adequacy of the mathematical model for research the efficiency of power plants is justified by the results of verification and validation by comparing the results of calculations with the results of a physical experiment that have a discrepancy not exceeding 9.3 %. The goal of the research is to improve the economic, environmental, resource and weight-size parameters of power plants by using heat exchange elements with the intensification of the processes of convective transfer of heat and mass by using finned surfaces with dimples. Thanks to the performance of dimple systems on the edges of round pipes with spiral-ribbon finning and elliptical pipes with lamellar finning, it is possible to increase the heat transfer coefficient up to 36 %, while the resistance coefficient of the beam remains unchanged. The use of heat exchangers with the proposed heat transfer elements as part of ship power plants with low-speed engines and gas-and-steam turbine units allows to improve their economic and environmental characteristics. It was obtained that for tankers of the PANAMAX type, the increase in the efficiency of the ship's power plant is 1.3 % due to the use of elliptical surfaces with plate finning and hole systems on the ribs in the utilization boiler. The ship's EEDI index decreased by 1.7 %. For container ships with a deadweight of more than 100,000 tons, the change in these indexes was 2.5 and 2.7 %, respectively. For a marine gas-and-steam turbine plant, the efficiency increase was 2.4 %. The presented mathematical model of the power plant is characterized by positive results of approbation for constructive and verification calculations of power plants in marine energy, transport, and industry.
      PubDate: 2023-08-24
      DOI: 10.32620/aktt.2023.4sup2.02
  • Method of rational formation of braking surfaces of a flat supersonic

    • Authors: Artem Khorokhordin, Igor Kravchenko, Mykhailo Mitrakhovych, Katerina Balalaieva, Anton Balalaiev
      Pages: 28 - 34
      Abstract: This article deals with methodological support for the design of effective supersonic flat external compression input devices. A concise analysis of the contribution of well-known scientists in the study of braking processes of supersonic flows of the working body in the system of sealing jumps is presented in the input devices. The proposed method of rational formation of the braking surfaces of a flat supersonic inlet device is based on the main provisions of the gas-hydraulic theory of sealing jump proposed by Rankin and Hugoniot. The main goal of this study is the development of a method of rational formation of braking surfaces of a supersonic flat input device of external compression according to the criterion of its efficiency, namely the maximum value of the coefficient of preservation of full pressure in sealing jumps. The choice of the value of the angle of inclination of the braking surfaces of the supersonic input device and the corresponding angles of inclination of the oblique jumps of the seal for a given calculated value of the number M consists in finding such values of the angles of inclination of the braking surfaces, at which the intensity of the oblique jumps of the seal is the same, under this condition the coefficient of preservation of full pressure is maximum. The mathematical formulation of the problem of determining the rational position of the braking surfaces of the supersonic flat input device of external compression is possible in the form of finding the angle of inclination of the first braking surface, which corresponds to the maximum value of the coefficient of preservation of full pressure for the determined value of the number M before the first oblique jump of the seal and at a constant intensity of the oblique jumps of the seal. This article outlines the main elements of the proposed methodology. Using the given methodology, a rational value of the angle of inclination of the first oblique jump of the seal was searched for the calculated value of the number M=2.5. In the supersonic input device operating at the specified design number M, three oblique sealing jumps and one direct-closing sealing jump are selected. The dependence of the full pressure preservation coefficient of oblique sealing jumps, direct jump, and total pressure preservation coefficient in the sealing jumps of the supersonic inlet device is obtained. It is shown that with an increase in the angle of inclination of the first braking surface and the corresponding values of the angles of inclination of the second and third braking surfaces, the coefficient of preservation of the full pressure of oblique jumps of the seal decreases, and that of direct jumps increases, which determines the presence of an extremum and makes it possible to determine the rational value of the angle of inclination of the first braking surface. This technique allows for any number of M before the first oblique jump of the seal to determine the rational values of the angles of inclination of the braking surfaces of the flat supersonic external compression input device.
      PubDate: 2023-08-24
      DOI: 10.32620/aktt.2023.4sup2.03
  • Analysis of the influence of the place of water injection on the
           performance of turbofan engine with afterburner

    • Authors: Yurii Ulitenko, Maryna Minenok, Igor Kravchenko
      Pages: 35 - 42
      Abstract: An important direction for the development of high-speed aircraft is the expansion of the range of operation of aircraft engines as part of their power plants. Currently, the range of operation of aircraft engines in terms of altitude and flight speed is limited by the ability of construction materials to withstand the temperature of the working body. Therefore, to expand the range of operation, it is necessary to either change the construction materials or use technologies that involve cooling the working body. The water injection system in a turbofan engine with an afterburner allows cooling of the working body without significant interference with the structural profile of the engine, which significantly saves design time and development cost. In addition, water injection has long been used for a short-term increase in engine thrust, which is an additional advantage of using this system. The choice of the place of water injection into the engine tract has a great influence on its characteristics and on the ability of the high-speed aircraft to perform the assigned tasks. Therefore, the design of the engine must take place with an understanding of the intended purpose of the high-speed aircraft. This article analyzes the influence of the place of water injection on the characteristics of a turbofan engine with an afterburner. I will consider water injection at the inlet to the fan and at the inlet to the high-pressure compressor. The influence of injection site and flight conditions on water consumption is shown. Operating conditions were found in which it is impossible to use a turbofan engine with an afterburner due to restrictions not related to the temperature of the working fluid. The results of calculations regarding the influence of the water injection site on the main thermodynamic parameters and traction characteristics of the engine are given. The application of the obtained results will increase the thermodynamic efficiency and extend the operating range of two-circuit turbofan engines with afterburners using modern materials. The results of this work will also make it possible to shorten the period of development of competitive engines for high-speed aircraft through a targeted search for their rational thermodynamic and structural-geometric outline.
      PubDate: 2023-08-24
      DOI: 10.32620/aktt.2023.4sup2.04
  • Mathematical modeling of the wall oil film in the bearing chamber of the

    • Authors: Illia Petukhov, Artem Kovalov
      Pages: 43 - 49
      Abstract: The most preferable result of modeling the flow in the BC is the determination of the heat transfer coefficient to the inner wall. The complexity of solving this problem is due to both the complex geometry of the BC and the presence of a two-phase flow, the structure of which changes from air-droplet in the core to a nearly liquid in the wall oil film. Available research results show that even three-dimensional CFD modeling of such a flow does not completely solve the problem. At the same time, the calculation time is long, and the results require, at a minimum, selective experimental validation. At the same time, it can be considered proven that the main mechanism of heat transfer from the core to the wall region of the BC is related to the radial flow of droplets, and the thermal resistance of the wall oil film has a decisive effect on the value of the internal heat transfer coefficient. It is advisable to model these media on the basis of a two-dimensional problem with the averaging of phase parameters along the axis. Considering the small volume fraction of droplets, the Lagrangian approach can be used to model the two-phase flow in the core of the BC. This allows consideration of not only the polydispersity of the droplets, but also the creation and movement of secondary droplets during the formation of the wall oil film. One of the main problems in the modeling of the wall film is the definition of its flow regime and the corresponding criterion equations for calculating the coefficients of friction and heat transfer. Most of the equations use the longitudinal coordinate of the plate as a geometric parameter and cannot be applied to the bearing chamber. In this study, the possibility of converting the film flow into a flow similar to that occurring in a flat pipe is substantiated. This allows not only to consider the geometric features of the BC, but also to use the corresponding Reynolds numbers and similarity equations for the equivalent flow. Along with the use of a two-layer model for the boundary region and the concept of the analogy of transfer processes, this made it possible to form a mathematical model of the film, which considers all the components that determine the formation, movement, and heat transfer of the wall oil film. In addition, the model does not contain restrictions on the appearance of the parameters transverse profile, which are, for example, for the EWF model of the oil film in ANSYS FLUENT. The obtained results along with the previously developed air-droplet flow model in the core provide a complete two-dimensional model of the gas-liquid flow in the GTE bearing chamber, which allows the main geometric and all mode parameters to be used to determine the heat transfer coefficient to the inner wall of the chamber. Given the short calculation time, the proposed model allows for a detailed investigation of each factor’s contribution and element-by-element identification of the model based on the results of more detailed modeling and by comparing calculated and experimental data.
      PubDate: 2023-08-24
      DOI: 10.32620/aktt.2023.4sup2.05
  • A method for evaluation of the dependence of gas turbine blade vibrations
           on monocrystalline anisotropy

    • Authors: Yevhen Nemanezhyn, Gennadiy Lvov, Yuriy Torba
      Pages: 50 - 58
      Abstract: The subject of study of this article is one of the key tasks that arises during the development and operation of aviation gas turbine engines, namely ensuring the strength of their parts. The turbine blade is one of the most heavily loaded parts of an aircraft engine. Therefore, at the stage of designing these blades, it is necessary to be able to identify and avoid possible resonance modes that appear during the flight cycle of an aircraft gas turbine engine. Such resonant oscillations of gas turbine blades can occur due to time-varying gas-dynamic forces from the action of the gas flow and are periodic in nature, as they are determined by the frequency of rotation of the rotor. In order to regulate the frequency characteristics of the blades to prevent dangerous resonant forms of oscillations that arise under the action of various harmonics of the exciting force during variable modes of operation of the aircraft engine, it is necessary to carry out a complex of various technological or structural changes. At the current stage, turbine blades of aircraft engines are manufactured by the method of single-crystal casting. As is known, single crystals have anisotropic properties, namely they manifest themselves as materials with the characteristics of cubic symmetry. A very urgent task is to investigate the effect of the anisotropy of the elastic characteristics of monocrystalline blades on their natural frequencies and forms of oscillations. In this research, the authors developed a method for determining the elastic characteristics of a single crystal, namely Young's modulus of elasticity, Poisson's ratio and pure shear modulus, which is based on available experimental data for typical heat-resistant alloys. With the help of finite element analysis on the example of a typical model of a cooled blade of a gas turbine, its modal analysis was carried out and its resonance diagram was constructed. The trend of changing the natural frequencies and forms of blade oscillations when the elastic constants of the single crystal change due to the rotation of the crystallographic system of directions was also investigated. The three-dimensional model of the blade was built using the capabilities of the NX graphics complex, all calculations were performed in the Maple computing complex, and the capabilities of the ANSYS software complex were used for finite element analysis.
      PubDate: 2023-08-24
      DOI: 10.32620/aktt.2023.4sup2.06
  • Comparison of the strength of trend presence criteria in time series

    • Authors: Volodymyr Myrhorod, Iryna Hvozdeva
      Pages: 59 - 64
      Abstract: The subject of research is methods, mathematical models, and methods of continuous analysis of a multidimensional set of output variables and state variables of power and energy installations built on the basis of gas turbine engines, which in general constitute time series. The purpose of this work is to establish the power of trend and randomness criteria by statistical modeling of time series with a linear trend and the use of known trend and randomness statistics to establish their empirical distributions and operational characteristics for comparing trend criteria by their power. The tasks faced by the developers were to determine the empirical distributions of known parametric and non-parametric trend statistics when applying the linear trend model in superposition with a random component, and set the level of errors of the first kind (false solution), with a given level of errors of the second kind (false anxiety). The methods that were used to achieve the established goal of the research: general methods of trend analysis, methods of applied statistics, and methods of conducting computer experiments. The results of the research provide a rationale for the approach to establishing the power of known criteria of trend and randomness. The limitation of the known methods of applied statistics is that it is theoretically only possible to refute the hypothesis regarding the randomness of the initial data at a certain level of significance, which determines the level of errors of the second kind (false alarms). Establishing the level of errors of the first kind (wrong decision) poses significant difficulties, because in the presence of a trend, the time series can no longer be stationary. But it is the statistical level of such errors that actually determines the strength of the criteria for the presence of a trend in the time series. The resolution of this contradiction is proposed by means of statistical modeling of time series with a linear trend and the use of well-known trend and randomness statistics to establish their empirical distributions and operational characteristics and to compare trend criteria according to their power. Statistical modeling was performed for a number of trend and randomness statistics, namely: the most common parametric statistics: correlation criterion and its modifications, Fisher's criterion, and Student's criterion; and non-parametric Wald-Wolfowitz criteria; Bartles; as well as the inversion criterion. According to the results of statistical modeling, it was established that the Student's criterion is the most powerful of the parametric criteria, and the inversion criterion is the most powerful of the non-parametric criteria. It is understood that such conclusions are valid when the assumptions regarding the initial statistical model of data generation in the form of a superposition of a linear trend and a random component as a sample from the general population of independent and normally distributed random variables and the corresponding algorithm for processing time series counts for the formation of decisive statistics are fulfilled. The scientific novelty of the obtained results lies in the fact that for the first time, the issue of comparing the power of parametric and non-parametric criteria of trend and randomness with respect to the applied model of data generation in the form of a linear trend in superposition with a random component was considered. The practical significance of the obtained results lies in the fact that the research results make it possible to choose an appropriate criterion based on its power for solving applied tasks of monitoring the technical condition of power and energy installations built on the basis of gas turbine engines.
      PubDate: 2023-08-24
      DOI: 10.32620/aktt.2023.4sup2.07
  • Comparative analysis of STM32 series microcontroller integrated
           development environment in aviation products

    • Authors: Serhii Vialov, Andrii Dunai
      Pages: 65 - 69
      Abstract: The subject of the research is the software development environment for STM32 series microcontrollers, which play an important role in the electronic support of modern aviation and are an integral part of the development process of aircraft systems. Goal. The selection of the most current STM32 series microcontroller programming system for aviation products. Tasks. Overview of major popular software development environments for STM32 microcontrollers such as STM32CubeIDE, VisualGDB, IAR Embedded Workbench for ARM, Keil MDK, Arm Development Studio, and Simulink. Various aspects of programming systems are considered, including software development, feature availability, and integration with development tools and environments. Research methods. Carrying out a comparative analysis; separation of the characteristic features of the use of programming environments in avionic devices using the example of JSC "Element". In view of the use of environments in the field of avionics, special attention was paid to certification and reliability using examples of safety standards, verification, and testing tools. The results. It was found that code debugging, memory analysis, code optimization, and other basic functions are inherent to all considered development environments. Distinguishing features inherent in individual programming environments are identified, including microcontroller robot simulation, high performance and compilation speed, open source code, optimization, support from the manufacturer, and a wealth of documentation, including user manuals, code examples, support forums, training courses, webinars, and articles from development companies. Conclusions (scientific and practical novelty). The results of the analysis provide important conclusions regarding the better choice of STM32 microcontroller programming systems in aviation products. The comparisons and analyses made will help software developers choose the most suitable programming system for their specific needs. A conclusion was made about the feasibility of using development environments such as IAR Embedded Workbench for ARM and STM32CubelIDE for developing aviation software based on STM32.
      PubDate: 2023-08-24
      DOI: 10.32620/aktt.2023.4sup2.08
  • Influence of temperature drop on the pressure rise in the fan circuit of
           the gas turbine engine turbo-fan attachment

    • Authors: Roman Maiboroda
      Pages: 70 - 75
      Abstract: The subject of this study is the working process in a turbofan attachment of a gas turbine engine. The object of study is the fan part of the impeller of a turbofan attachment. The aim of this study was to evaluate the effect of temperature difference in a two-tier impeller on the degree of pressure increase in the fan part of a two-tier impeller of a turbofan attachment of a three-circuit engine. To achieve this goal, the following tasks were solved: to simulate the flow in a turbofan attachment; to calculate the dependence of the degree of pressure increase in the fan part of the impeller of the turbofan attachment on the Mach number for the operating mode at altitudes of 0 km, 9 km and 11 km; to evaluate the temperature difference in the two-tier impeller of the turbofan attachment. The study was carried out by the method of numerical experiment. Results: The dependence of the degree of pressure increase of the fan circuit of the turbofan attachment on the Mach number at the inlet is obtained, taking into account the effect of hot gases of the turbine circuit of the turbofan attachment. It is shown that the flow of hot gases affects the degree of pressure increase in the fan circuit. The presence of the turbine part of the two-tier impeller leads to a slight deterioration in the characteristics of the fan part. The degree of pressure increase is reduced by 0.2 ... 4.8 %. The greatest influence is manifested in the operating mode H = 11 km. Visualization of the flow velocity field in the fan part of the turbofan unit showed that during the operation of the turbine circuit, the nature of the leakage in the fan part changes by approximately 50% of the blade height. An increase in temperature contributes to the intensification of the energy of the boundary layer around the lower part of the blade of the fan circuit, which has a positive effect on the reduction of zero velocity zones during the flow. Scientific novelty and practical significance: new data were obtained on the effect of temperature difference in a two-tier impeller on the degree of pressure increase in the fan part of a two-tier impeller of a turbofan attachment of a three-circuit engine. The results obtained can be used to optimize the turbofan attachment of a gas turbine engine.
      PubDate: 2023-08-24
      DOI: 10.32620/aktt.2023.4sup2.09
  • Prospects for the application of electrochemical polishing of scaffold
           samples manufactured by additive technology

    • Authors: Sergey Adjamskiy, Ganna Kononenko, Rostyslav Podolskyi, Sergey Baduk
      Pages: 76 - 81
      Abstract: In recent years, the actual production of metal products directly from electronic data according to a three-dimensional model based on layer-by-layer manufacturing has evolved from rapid prototyping to additive manufacturing. As the quality of additively manufactured metal products continues to increase and their manufacturing processes improve and develop, the demand for additive manufacturing is increasing. Additive manufacturing technology, also known as 3D printing, has become increasingly popular recently. Using additive manufacturing, almost any complex geometry can be manufactured with high degree of precision. After the production of parts using the SLM technology from metal powder, post-processing is applied, in particular electrochemical polishing, the main purpose of which is to reduce surface roughness, increase the gloss of surface elements, and remove metal powder that has partially melted onto the outer surface of the product at the point of contact between the molten metal and the border of the part and the powder, which is located next to the melt. This is especially important for inclined surfaces, internal channels and cellular structures with developed outer surface. For research, samples were made using SLM technology from AISI 316L austenitic steel powder. The samples have a cube shape with a base of 10 mm, a height of 10 mm, and a thickness of 10 mm, with cell widths of 4 mm and 2 mm. The main body of both samples was printed using the same modes at a laser power of 220 W, a scanning speed of 1000 mm/s and a distance between laser passes of 0.14 mm. Samples were printed on Alfa-280 3D printer manufactured by ALT Ukraine LLC. Electropolishing was carried out in a solution of orthophosphoric acid (H3PO4) with glycerol (C3H8O3) by immersing the test samples in the electrolytic solution at a voltage of 17 V and a current density of 3 A/cm2. The control of weight and geometric parameters was carried out with the help of ADV-2000 analytical balances and MKC-25 micrometer. The electropolishing of the experimental samples took place in four stages: 1) visual - optical inspection with fixation, weight control before the start of the process; 2) electropolishing for 3 minutes, visual - optical inspection with photo fixation; weight control after 3 min. polishing process; 3) electropolishing of the same samples for another 3 minutes, visual – optical inspection with photo fixation, weight control after 6 minutes. polishing; 4) electropolishing of the same samples for another 3 minutes, visual - optical inspection with photo fixation; weight control after 9 min. electropolishing process. At each stage, a real current-voltage curve was recorded using an oscilloscope. As a result of weight control before and after the test, it was established that the samples lost approximately the same weight in the range of 6.9...7.1 % relative to the initial one. Based on the analysis of the obtained results, it was established that at a current density of 3 A/cm2 and at a voltage of 17 V, effective active uniform polishing of the surface of samples with a cellular structure of scaffold type with a variable cell size from 4 to 2 mm is realized.
      PubDate: 2023-08-24
      DOI: 10.32620/aktt.2023.4sup2.10
  • Study of the effect of the gas temperature of the cold gas dynamic
           spraying process on the adhesion strength of nickel-containing coatings

    • Authors: Oleksandr Shorinov, Anatolii Dolmatov, Sergii Polyviany, Kostyantyn Balushok
      Pages: 82 - 88
      Abstract: The subject of the research is the influence of low-pressure cold spraying process parameters on the adhesive strength of the coatings. The goal is to ensure the maximum values of the adhesive strength of nickel-based coatings deposited by cold spraying by controlling the gas temperature at the nozzle inlet. The task is to investigate the effect of the temperature mode of the DYMET-405 machine on the adhesive strength of the coatings obtained from the Ni+Zn+Al2O3 powder mixture at constant other spraying parameters. Research methods. The experimental study of the adhesive strength was conducted on the tear using adhesive method in accordance with DSTU 2639-94. The metal-matrix composite powder mixture Ni+Zn+Al2O3 was used as powder material. VT3-1 titanium alloy was chosen as substrate material. Coatings were deposited using DYMET-405 low-pressure cold spraying machine. Temperature regulation at the nozzle inlet was performed by turning on the required temperature mode on the equipment control panel. Other spraying parameters remained constant during coating deposition process. The results. It was established that with an increase in the temperature of the gas in the nozzle, an increase in the adhesive strength of coatings is observed, on average from 9.5 MPa to 28.7 MPa. This can be explained by the fact that an increase in gas temperature leads to an increase in the velocity of the gas flow and, accordingly, of the powder particles in this flow. Higher particle impact velocity has a positive effect on the process of their deforming, filling of pores, densifying of coating layers, and finally increasing the adhesive and cohesive strength. The scientific novelty of the obtained results is that the dependence of the gas temperature at the nozzle inlet during low-pressure cold spraying on the adhesive strength of Ni+Zn+Al2O3 powder mixture coatings deposited on VT3-1 titanium alloy substrates was obtained. Conclusions. The practical value of the obtained results is that the obtained dependences of adhesive strength on gas temperature can be used for the development of cold spraying recommendations for the deposition of restorative coatings on parts made of titanium alloys, in particular in aircraft engines to eliminate operational defects.
      PubDate: 2023-08-24
      DOI: 10.32620/aktt.2023.4sup2.11
  • Influence of carbon nanoparticle inoculation on the structure of ML5
           casting magnesium alloy

    • Authors: Spartak Makovskyi, Kostyantyn Balushok, Kyryl Obnosov, Viktor Greshta, Vadym Shalomeyev, Daria Tkach
      Pages: 89 - 96
      Abstract: The object of this study is to investigate the structure of cast magnesium alloy (Mg-Al-Zn) inoculated with nano particles of different allotropic forms of carbon. The aim of this study is to improve the processability and quality of critical load bearing magnesium alloy part castings. The tasks of the study are: attainment of efficient control of the alloy structural features by introduction of incremental additions of carbon nano particles; determination of the relationship between the quantity of the added inoculating carbon agent and α - solid solution grain size; determination of the influence of allotropic forms of carbon on the morphologic characteristics of the intergranular borders and the eutectoid (a+Mg17Al12); and comparative analysis of the phase composition of the standard ML5 alloy and the experimental alloy ML5 inoculated with carbon black, nanographite, and single-wall carbon nanotubes. The phase composition was determined by X-ray diffraction analysis using copper radiation. Micro X-ray spectral analysis was performed. The following findings were obtained. Using an optical microscope α – solid solution grain size was measured in the standard and inoculated alloy. In the samples of the alloy variants inoculated with 0.1 % wt. of carbon black, nanographite, and single-wall carbon nanotubes, the grain size was reduced by appox. 50 % compared with the standard alloy. In the samples of the alloy inoculated with 0.1 % wt. of nanographite and single wall carbon nanotubes, eutectoid (a+Mg17Al12) precipitates along the grain boundaries were thinner than those in the standard alloy samples and those inoculated with carbon black. X-ray diffraction analysis revealed no new phase formation. The X-ray diffraction patterns of the alloy samples with nanographite and nanotubes display weak peaks of free carbon, which may indicate the presence of free carbon in small quantities in the structure. The scientific and practical originality of the obtained results consists of the following: a technology of inoculation with incremental additions of allotropic forms of nano carbon, namely carbon black, nanographite, and single-wall carbon nanotubes, has been tested on a standard cast magnesium alloy (Mg-Al-Zn system) in an environment similar to the industrial production of critical magnesium cast components. It has been shown that the introduction of nanocarbon in a quantity of 0.1 % wt. can have a beneficial effect on the structural characteristics of ML5 cast magnesium alloy with no change in its phase composition. Nanographite and single wall carbon nanotubes with a regular structure contribute to the formation of thinner intergranular boundaries than amorphous carbon black.
      PubDate: 2023-08-24
      DOI: 10.32620/aktt.2023.4sup2.12
  • The technology of restoration hydrogenerator rotor shape

    • Authors: Pavlo Makarov
      Pages: 97 - 104
      Abstract: The object of research in this article is the change in the rotor shape during the operation of hydraulic units. The subject of study in this article is the design and geometric state of the shape of a rotor with irregular geometry of hydraulic generators-engines. This study produced a three-dimensional mechanical calculation of the rotor segment for further use during strain gauge tests. Tasks: investigate the peculiarities of the rotor shape restoration technology; to describe the basic assumptions for the three-dimensional mechanical calculation of rotor deformations at the overspeed; and perform a three-dimensional calculation of rotor movements considering the main forces falling on the pole connection, which are obtained using classical methods. The methods used are: finite element method of mathematical modeling of the thermal stress state of nodes. The following results were obtained: a detailed description of the technological process of restoring the shape of the rotor using the hot wedging method is given. Three-dimensional models of the rotor segment were developed, and a three-dimensional mechanical calculation of this model was performed, as a result of which satisfactory values of the displacement of the rotor of the hydraulic generator at the overspeed were obtained, considering the recovery technology. To reconstruct the rotor rim, it is necessary to heat the rotor rim to a temperature difference between the rim and the frame of at least 60 °C. Next, the hot wedging of the rotor rim is performed with the driving of each of the driving wedges by the same amount, which ensures the creation of the necessary diametrical tension between the rim and the frame of the rotor and avoids the displacement of the rotor rim relative to the frame. The control of this process is performed using strain gauges. If necessary, it is necessary to cool the rotor rim until the temperatures of the rim and the frame of the rotor are equal. Conclusions. The scientific novelty consists of a combined approach to the evaluation of the deformation of the rotor rim after restoring its shape, which includes elements of analytical mechanical calculation and calculation in a three-dimensional setting. The presented technology for the rotor restoration process meets European requirements.
      PubDate: 2023-08-24
      DOI: 10.32620/aktt.2023.4sup2.13
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