Authors:Yifang Sun, Sen Zou, Guang Zhao, Bei Yang Pages: 4 - 13 Abstract: The Lattice Boltzmann Method (LBM) is a numerical method developed in recent decades. It has the characteristics of high parallel efficiency and simple boundary processing. The basic idea is to construct a simplified dynamic model so that the macroscopic behavior of the model is the same as the macroscopic equation. From the perspective of micro-dynamics, LBM treats macro-physical quantities as micro-quantities to obtain results by statistical averaging. The Finite-difference LBM (FDLBM) is a new numerical method developed based on LBM. The first finite-difference LBE (FDLBE) was perhaps due to Tamura and Akinori and was examined by Cao et al. in more detail. Finite-difference LBM was further extended to curvilinear coordinates with nonuniform grids by Mei and Shyy. By improving the FDLBE proposed by Mei and Shyy, a new finite difference LBM is obtained in the paper. In the model, the collision term is treated implicitly, just as done in the Mei-Shyy model. However, by introducing another distribution function based on the earlier distribution function， the implicitness of the discrete scheme is eliminated, and a simple explicit scheme is finally obtained, such as the standard LBE. Furthermore, this trick for the FDLBE can also be easily used to develop more efficient FVLBE and FELBE schemes. To verify the correctness and feasibility of this improved FDLBM model, which is used to calculate the square cavity model, and the calculated results are compared with the data of the classic square cavity model. The comparison result includes two items: the velocity on the centerline of the square cavity and the position of the vortex center in the square cavity. The simulation results of FDLBM are very consistent with the data in the literature. When Re=400, the velocity profiles of u and v on the centerline of the square cavity are consistent with the data results in Ghia's paper, and the vortex center position in the square cavity is also almost the same as the data results in Ghia's paper. Therefore, the verification of FDLBM is successful and FDLBM is feasible. This improved method can also serve as a reference for subsequent research. PubDate: 2021-02-26 DOI: 10.32620/aktt.2021.1.01

Authors:Борис Валерьевич Успенский, Константин Витальевич Аврамов, Игорь Игоревич Деревянко, Ирина Валентиновна Библик Pages: 14 - 19 Abstract: Honeycomb is described by orthotropic homogeneous media. The mechanical properties of the media are described by the simulation of the stress state honeycomb in commercial software ANSYS. The classical hexagonal honeycomb is analyzed numerically. The other types of the honeycomb are not considered in this paper. The media, which is obtained as a result of homogenization, has orthotropic mechanical properties. The honeycomb is produced from polycarbonate, which is orthotropic material. The suggested approach can be applied to other materials, which are used for 3D printing. The mechanical properties of this honeycomb material are determined experimentally for specimens, which are produced by FDM manufacturing. The matrix of the Hooke law is obtained in the result of six finite element calculations of the cell part of the honeycomb. To determine the different elements of this matrix, the cell part of the honeycomb undergoes different boundary conditions and different stressing. The fourth part of one cell is considered to calculate honeycomb mechanical properties. The software ANSYS is used to calculate the fourth part of the cell. The area near the cell part is filled up to cube using elastic air. The elastic air is isotropic material with a small Young modulus. The cube sides undergo constant displacements to perform numerical analysis. Such different displacements are equal to six. As a result of the numerical simulations, the elements of the stress tensor are determined by the stress averaging on the volume of the finite element. As a result of calculations, the set of nine engineering constants of orthotropic homogeneous media is obtained. Analysis of the convergence of the numerical simulation results is carried out for numerical simulations of the stress state by the concentration of the finite element mesh. As follows from the convergence analysis, 1745481 3D finite elements are enough for the discretization of the cube area. PubDate: 2021-02-26 DOI: 10.32620/aktt.2021.1.02

Authors:Anatoliy Kulik, Sergey Pasichnik, Dmytro Sokol Pages: 20 - 30 Abstract: The object of study in the article is the vortex effect of temperature separation in a rotating gas flow, which is realized in small-sized vortex energy separators. The subject matter is the models that describe the physical processes of energy conversion in small-sized vortex energy separators as objects of automatic control. The goal is to obtain models of a vortex energy separator reflecting its static and dynamic properties as an automatic control object. The tasks to be solved are: to develop a three-dimensional computer model of a small-sized vortex energy separator which will allow analyzing the parameters of the gas flow and physical processes of energy conversion directly inside the object and obtaining its static characteristics. A linearization method of static characteristics on the interval of input and output values is proposed which will expand the operating range without loss of linearization accuracy. A method of structural-parametric identification based on experimental logarithmic magnitude-frequency characteristics is proposed which will allow for the same set of experimental points to select the structure of the mathematical model of varying complexity depending on the specified accuracy. As a result of the work, the scheme for modeling the automatic control object was formed, consisting of the drive unit, sensor unit, and vortex energy separator, with the reflection of all the obtained operating modes. The methods used are the method of graphic linearization, Laplace transform, structural-parametric identification. The following results were obtained: a computer and linearized mathematical model of the small-sized vortex energy separator as an automatic control object reflecting its properties in the time and frequency domains was obtained. A comparative analysis of the reactions of the model and the real object to the same input action was carried out. Conclusions. The scientific novelty of the results obtained is as follows: 1) multiple graphic linearizations of one static characteristic to use the full range of the operation mode of vortex energy separator, which distinguishes it from the known;2) mathematical model structural-parametric identification for vortex energy separator with the help of known points of the Bode magnitude plots by using the interpolation polynomial and its derivatives graphs. PubDate: 2021-02-26 DOI: 10.32620/aktt.2021.1.03

Authors:Рустем Юсуфович Турна Pages: 31 - 46 Abstract: For spacecraft (SC) with power unit capacity more than 4 ... 6 kW promising construction of thermal control system (TCS) based on two-phase mechanically pumped loops (2PMPL). The development of 2PMPL has been carried out quite intensively since the early '80s. However, so far there are no examples of practical implementation of such high-power systems. One of the main reasons mentioned is the novelty of the system, and insufficient study of its operation in space conditions, which adds risks. The most important component of such systems is a heat rejection subsystem (HRS), whose task is to reject heat from the coolant and radiate it into space. In its turn, HRS is also a system, the design of which requires using a system approach, considering various aspects of its operation. HRS includes a heat-hydraulic network and a radiation heat exchanger (RHE). The key elements of the HRS are condensers (CC), quite new devices for space technology. This paper presents an algorithm for the design and optimization of the heat rejection subsystem (HRS) of a satellite two-phase thermal control system. The methodology of engineering synthesis of complex technical systems and informal procedures for multi-criteria optimization of elements and subsystems at various stages of HRS design is repeatedly used. t is shown that optimization should be carried out both at the level of elements and subsystems, and at the level of the whole thermal control system. As a result of the study, the HRS design is proposed, which uses condensers in the form of smooth steel tubes of constant cross-section and their series-parallel connection scheme in the hydraulic network. Main advantages of the design: traditional for single-phase loops elements are used; operation of elements and subsystems in zero gravity conditions is predictable and allows complete testing on the ground without mandatory flight experiment; the system is operable at high saturation pressures (temperatures) (on ammonia - up to 85℃). PubDate: 2021-02-26 DOI: 10.32620/aktt.2021.1.04

Authors:Kun Tan, Sergii Markovych, Wenjie Hu, Oleksandr Shorinov, Yurong Wang Pages: 47 - 59 Abstract: Cold spray technology is an advanced spray technology, and its technical principle is the same as that of additive manufacturing technology. Cold spraying technology combines multiple advantages in the spraying field: not only can the deposition of thick coatings be achieved, but the coatings prepared by this technology have the characteristics of high density, low oxygen content, good mechanical properties of the coating surface, and high deposition efficiency. Cold spraying technology can prepare corrosion-resistant coatings, high-temperature resistant coatings, wear-resistant coatings, conductive coatings, anti-oxidation coatings, and other functional coatings. After decades of development and exploration, cold spraying technology is preparing metal coatings. The application is very wide and the process is mature; the same cold spray technology can also prepare non-metallic coatings. Mainly to immerse repair and protect the surface of metal alloy parts and a small part of non-metal parts, so that these parts have better mechanical properties and mechanical behavior. This article mainly reviews the application of cold spray technology in the field of spray materials and summarizes the existing conventional metal series, rare metal series and non-metal material, conventional non-ferrous metals: copper, titanium, aluminum and nickel. Metal materials are currently widely used in the field of cold spraying. Among them, titanium-based metals restrict their applications due to their own properties; rare metals: tungsten, tantalum, and niobium-based metal materials. The application of rare metals in cold spraying is still in its infancy stage; non-metallic materials: polymer materials and ceramic powder materials, non-metallic materials have the characteristics of surface modification and strengthening technology, but also have low oxygen content, low thermal stress, high density, good bonding strength, in the deposition process and the substrate will not change the advantages of physical organization structure. Finally, the existing problems of rare metal materials and non-metal materials are raised. PubDate: 2021-02-26 DOI: 10.32620/aktt.2021.1.05

Authors:Дмитро Вікторович Коновалов, Роман Миколайович Радченко, Сергій Георгійович Фордуй, Віктор Павлович Халдобін, Олексій Олегович Зєліков, Олександр Анатолійович Різун Pages: 60 - 66 Abstract: The paper shows and analyzes circuit solutions for improving the existing schemes of ejector heat-using refrigeration machines, which are used as part of cogeneration plants. One of the promising areas is the use of an aerothermopressor, which implements the effect of thermogasdynamic compression, which is to increase the pressure while reducing the temperature in the evaporation of liquid, which injected into the flow of vapor moving at speed near the sound. To analyze the efficiency of ejector refrigeration machines, the developed calculation model was used, which takes into account the use of an aerothermopressor in the cycles of refrigeration machines with the features of the calculations of cycles and circuits. To select and determine possible circuit solutions, the efficiency of an aerothermopressor for different refrigerants was evaluated and a comparative analysis of the characteristic parameters of the efficiency of an aerothermopressor in the range of cooling temperature differences is 20–100 oC was made. It is possible to increase the efficiency of ejector heat-using refrigeration machines when using an aerothermopressor by providing a temperature difference of 60–100 oC. The analysis showed that the most important are: R717, R134a, R227ea, R1234ze (E), R1234yf (2–4%). It is possible to provide a higher thermal coefficient for ejector heat-using refrigeration machines by using an aerothermopressor in the circuit using the circulation of liquid refrigerant. The corresponding increase in the thermal coefficient is 1.5–2.0%. The use of an aerothermopressor in the scheme with heat recovery allows removing additional overheating of vapor before suctioning into the ejector with a corresponding increase in the thermal coefficient by 4-8%. The analysis shows that the total increase in the thermal coefficient due to the combined use of an aerothermopressor, heat recovery, and recirculation is 10–15% at a base value of 0.30–0.40. PubDate: 2021-02-26 DOI: 10.32620/aktt.2021.1.06

Authors:Олег Ігорович Савенков, Олексій Павлович Попов, Микола Іванович Радченко, Юрій Георгійович Щербак Pages: 67 - 74 Abstract: The influence of skew axes of the connecting shafts of marine aggregates on the efficiency and reliability of ship power plants is investigated. The reasons for the occurrence of centerings of axes of connecting shafts of marine aggregates are considered and their classification is offered. Failures of ship power plants are classified according to their impact on the efficiency of the installation (according to the consequences), according to the methods of their elimination, and by their nature and are divided into the groups according to the classes. It is shown that during operation, in the conditions of axial skew, traditional designs of the toothed clutch are characterized by non-uniform distribution of forces between pair of gears, which leads to their overload and, as a consequence, reduced load capacity, increased contact stresses, deterioration of lubrication surfaces of gears, increase in power consumption for friction, reduction of efficiency and deterioration of vibroacoustic characteristics due to shock load of gear. Ways to increase the efficiency of ship power plants by providing parameters of reliability of the main power plants by eliminating the negative impact of the centering axes of the connecting shafts of marine aggregates through the use of compensating devices are considered. It is proposed to use as compensating devices, the design of high-efficiency clutch, which in the conditions of axial skew, are characterized by a more uniform distribution of forces between pair of gears than existing ones, ie work almost as a perfect hinge. Regarding the proposed toothed couplings, a previously unknown objectively existing property of the toothed clutch operating at the skew of the axes of the connecting shafts is established, which is that under a certain nonlinear law changes in the generating side surfaces of the outer teeth evenly between all conjugate pairs of teeth. The use of a high-efficiency clutch in the ship power plants is considered and the basic and functional (structural) scheme of the main marine aggregate with a series connection of elements is made to assess the impact on reliability parameters. PubDate: 2021-02-26 DOI: 10.32620/aktt.2021.1.07

Authors:Андрій Олексійович Прохоренко, Сергій Сергійович Кравченко, Олександр Васильович Грицюк, Анатолій Петрович Кузьменко Pages: 75 - 83 Abstract: The article provides the substantiation of the rational scheme of the boost system of the aircraft diesel engine KhADI-100A to ensure its altitude from the point of view of the lowest losses of the effective engine power. A method is proposed for assessing the power loss of an aircraft diesel engine depending on the flight altitude. Three variants of the supercharging system are considered: with one free turbocharger; parallel drive compressor and free turbocharger; sequential drive compressor and free turbocharger. As a result of the computational study, it was shown that in the case of using one free turbocharger at an altitude of h > 1500 m, the normal operating process of a diesel engine cannot be realized, since in this case, the excess air ratio falls below the critical value for a diesel engine α <1.4. Even if a constant excess air ratio is maintained, the effective engine power, with one free turbocharger, decreases by about 6 ... 11 kW per 1000 m with an increase in flight altitude. In schemes with a driving compressor, the quality of the fuel-air mixture will not change with altitude, and the power losses for their drive are insignificant in comparison - within 1 ... 2 kW per 1000 m of lifting height and can be compensated by increasing the cycle fuel supply without losing the quality of the working process. As a result of the computational study, it was concluded that the most rational from the point of view of the least power consumption is the scheme with a sequential drive compressor and a free turbocharger, the power consumption for the compressor drive at an altitude of 5000 m is 1.4 kW less than in the scheme with a parallel drive compressor and is the maximum value of 8.5 kW. The use of an electrically driven compressor is proposed since in this case the unit gains control flexibility to select the optimal operating mode and the possibility of using alternative energy sources for the drive electric generator (solar batteries, accumulators, thermoelectric generators, etc.). PubDate: 2021-02-26 DOI: 10.32620/aktt.2021.1.08