Статьи журнала - Siberian Aerospace Journal
Все статьи: 363
Beam support stiffness analytic solution for the first eigenfrequency and critical force
Статья научная
The problem of providing the required first natural frequency of bending vibrations of the beam under the action of a longitudinal force by introducing the necessary stiffness of the supports is discussed in the article. Considering and combining the equations of free vibrations of the beam and the equations describing the loss of its stability helped to obtain the operability condition based on providing a minimum given value of the first natural frequency of vibrations considering the action of the axial force. In this case, the achievement of the zero frequency of natural vibration corresponds to the loss of stability, which allows solving both problems. This task is mathematically complicated, and in the known scientific literature its solution is usually given only in graphical or tabular forms. The problem is in the nonlinear dependence of the coefficients of supports on the stiffness during vibrations and loss of stability. To solve this problem, the approximation of the nonlinear coefficients of the supports by the least squares method and the obtaining of quadratic approximating functions was used. As a result, the problem of determining the required stiffness of the supports brought to a fourth-degree resolving algebraic equation, for which an analytic solution exists. The obtained solution allows the stiffness of the beam supports, which provides the required value of the first natural frequency of vibrations of the beam and its first critical load in the form of external compressive force or temperature effects. Replacing the nonlinear dependencies of the support coefficients with the stiffness of the supports with simpler quadratic functions led to relatively simple analytic dependencies that allow the resolution equation to be transformed according to the particular problem being solved. At the same time, quadratic functions influenced the calculation error, to reduce which, the range of the support stiffness under consideration was limited and divided into three zones. The results of calculations using the proposed analytical solution were compared with numerical calculations using finite element method. The comparison of the calculation results showed an error of not more than 5 % for the considered range of stiffness of the supports, which is quite enough for engineering calculations of beam structures. To limit the error of the result, it is recommended that the stiffnesses of both supports be equal or of the same order.
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Статья научная
Technologies and production widely use composite materials now. “Mechanics of deformable solids” was formed as a science based on the study of materials used in the 19th and 20th centuries. Modern composite materials require new theoretical and experimental studies. Determining the stresses and deformations that occur at the points of contact of the matrix with the fibers is a special problem. Composites with a plastic matrix play an important role in modern technology. These materials successfully cope with cracking and significantly slow down the growth of cracks. In this article, the problem of the stress state of a composite beam with an elastic-plastic matrix and elastic fibers located along the axis of the beam is solved. It is assumed that in the zone of contact of the matrix with the fibers, according to the model of Yu. N. Rabotnov, a constant tangential stress is realized, less than the yield strength of the fiber. One end of the beam is fixed, and a constant force applied to the center of gravity coinciding with the origin of coordinates acts on the second. It is assumed that at the free boundary of the beam and at the points of contact of the beam with the fibers, the stresses reach the plasticity limit. The problem is solved with the help of conservation laws. This makes it possible to find the stress state at an arbitrary point of the section as a calculation of integrals along the outer boundary of the beam and the boundaries of the matrix and fibers.
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Buckling and stiffness analysis of a composite anisogrid conical shell with a fixed small base
Статья научная
Power elements of structures in the form of structural anisogrid shells of rotation are often used in the production of rocket and space technology. This is due, first of all, to high specific mechanical properties of composites, which allow to manufacture structures with a high degree of weight perfection. In addition, they are quite technological, as the method of continuous winding of composite fibers used in their production is widespread and well developed. In recent years, close attention has been paid to the design of composite mesh structures. An actual example of anisogrid cylindrical and conical shells is a spacecraft adapter for GLONASS sa-tellites orbit launching, different variants of which are still produced in the workshops of Reshetnev JSC. The shells are of the same type, but differ in dimensions (diameters and lengths of cylindrical and conical parts) and bearing capacity. For composite elements of rocket-space technology it is characterized by the presence of a large list of variable parameters, the determination of the optimal combination of which every time results in a complex problem of scientific search. An algorithm and a program for building a finite element model of anisogrid conical shells made by continuous winding of composite fiber have been developed. The small base is fixed and the large base is reinforced by a spandrel and loaded by concentrated forces and moments. Numerical investigation of sta-bility, stiffness and stress-strain state of the structure under varying parameters of its mesh structure for-mation is carried out with the help of FE model.
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CFD methods for cavitation modeling in centrifugal and axial pumps of LRE
Статья научная
Currently, design and manufacture of liquid-propellant rocket engines (LRE) are imposed with ever greater reliability requirements. Accordingly, the standards for the design and manufacture of rocket engine units are raising. One of these units is a turbopump unit (TNA), which provides continuous supply of liquid components from combustion reaction to the combustion chamber of a rocket engine to create traction or other engine units. TNA is also the main source of pressure increase for these liquid components in front of the LRE combustion chamber. Important requirements are imposed on a turbopump unit (TNA): ensuring work performance and basic parameters for a given resource with the necessary possible pauses of a specified duration; providing all engine operating modes, supplying the fuel components of the required flow rate and pressure, guarantying a high degree of reliability with acceptable entire unit efficiency; providing high anti-cavitation characteristics of the pump in all modes. In the article, the authors summarize the latest results of the study on cavitation in turbopump units of liquid propellant rocket engines alongside with the relevant research in the field of hydraulics. The problems of cavitation in cryogenic liquids, simulation of stall characteristics, and usability of various models to simulate cavitation flow are observed. A solution to the problems of flow modeling was considered with respect to applicability to the following structural elements of LRE units: interscapular space of the screw centrifugal main and booster pumps, axial pre-pump. Particular attention is paid to the implementation of various numerical methods based on the use of various cavitation models, computational fluid dynamics in various CFD packages, and also comparison of results with the model. In summary, the authors draw conclusions about the possibility of applying these methods to solve the problems of the cavitation phenomenon research in LRE.
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Статья
The article presents a computational and experimental study of the dynamic characteristics of a spacecraft telescope frame mock-up. The main attention is paid to the methodology of vibrodynamic tests using a three-component laser vibrometer and the creation of a finite element model of the mock-up under study. To analyze the dynamics of the structure, the main criteria such as modal parameters, model validation and harmonic analysis are defined. Particular attention is paid to the effect of experimental data transformation on the accuracy of calculating the modal assurance criterion. The research investigates telescope frame mock-up, which is a truss structure fixed on springs. The tests were carried out by applying a random impact of the “white noise” type. The dynamic characteristics of the structure were obtained, including the natural frequency of oscillations, which was 93.7 Hz. The experimental data were compared with the results of finite element modeling, which showed a significant discrepancy between them, especially in the area of natural frequencies. This indicates the need to adjust the finite element model. Various criteria for assessing the compliance of calculated and experimental models are considered, such as the coordinate modal assurance criterion (COMAC), the modal assurance criterion (MAC), the cross signature assurance criterion (CSAC) and the cross signature scale factor (CSF). These criteria help to assess the degree of coincidence of vibration modes and frequency characteristics. An analysis of the effect of transforming experimental data into different units of measurement on the results of calculating these criteria is carried out. It is concluded that the current calculation model requires revision and clarification of parameters to achieve better compliance with reality.
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Статья научная
The thermal control system (TCS) is one of the most important systems, which largely determines the design of the spacecraft. At the present stage of development of methods and tools for spacecraft design, a promising direction is the creation of thermal mathematical models of the TCS, calculation algorithms, which allow to create effective design solutions at various design stages. The purpose of this work is to bring the system of equations of heat balances of the liquid circuit (LC) of TCS to a form that allows programmatic numerical integration in the solution search algorithm along the length of the middle line of the heat and mass exchange fluid circuit taking into account certain complex thermal resistances. In fact, this means that the terms of the temperature of the contour and the linear coordinate, the integration variable, should remain as variables in the equation record, everything else should be numerically determined from the properties of the real object. For the boundary conditions of the LC TCS of the spacecraft, the coefficients of complex heat transfer were calculated taking into account the actual topology of the circuit and the thermal properties of the coolant. Using these values, the system of thermal balances of the spacecraft of the spacecraft on the characteristic surfaces of constant temperatures was reduced to a form that allows a numerical solution: the number of equations corresponds to the number of detected temperatures along the north and south panels and is closed through the temperature of the liquid circuit refrigerant. The resulting system of equations allows us to investigate the thermal state of nonhermetic formation spacecraft at the stage of preliminary design with varying operational and design parameters in order to determine the area of efficiency and the area of optimal operation under certain performance criteria.
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Calculation of heat transfer characteristics of a finned wall
Статья научная
The reliability and resource of the radio-electronic equipment of the spacecraft is increased by ensuring op-timal temperature conditions. Thermal control systems maintain the set temperature mode and heat removal from the onboard equipment to the surrounding space. Finned heat exchangers are an important element of the de-sign of thermal control systems, which allows intensifying the heat transfer process. The calculation of the char-acteristics of finned heat exchangers must be carried out taking into account their parameters and the physical properties of the heat transfer agent. The organic liquid LZ-TK-2, which has a very low freezing point and other useful performance characteristics, is considered as a heat transfer agent. The dependences of the local heat transfer coefficient of the LZ-TK-2 heat transfer agent on the wall temperature are calculated using criteria equations. Based on the numerical solution of the two-dimensional problem of thermal conductivity, the tempera-ture fields in finned walls of various configurations are determined. Calculations of the heat transfer coefficient of the finned wall of the heat exchanger were made in two model approximations, the error of using a simplified approximation that does not take into account the temperature dependence of the local heat transfer coefficient was determined.
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Calculation of the parameters and characteristics of a rotating lunar jet penetrator
Статья научная
The purpose of the work is to determine the parameters of the internal ballistics of a solid propellant jet engine mounted on a jet penetrator entering the ground at a high rotation speed around its own axis. Research methods: to determine the pressure in the chamber of a rotating engine, the known equations for the balance of gas inflow and consumption are usually used, as in the case of a non-rotating solid propellant jet engine. The difference between the internal ballistics of a rotating solid propellant jet engine is that the effect of rotation on the operating process is taken into account by the coefficient of gas flow from the chamber of the rotating engine; a change in the rate of erosive combustion of solid propellant during rotation of a solid propellant jet engine; heat loss coefficient. Results: it was found that the parameters of the internal ballistics of rotating jet engines of solid propellant are mainly influenced by the coefficient of gas flow from the chamber of the rotating engine; effect of erosive combustion of solid propellant and change in heat loss coefficient. The main calculated dependencies for determining the pressure in the combustion chamber of a rotating solid propellant engine are presented for periods when the pressure reaches a stationary mode of operation of the engine, operation of the engine in a stationary mode and during the period of free flow of gases from the chamber of a solid propellant jet engine. A method for selecting the linear and angular dimensions of a rotating engine nozzle is presented. An estimate of the thrust force for a single nozzle rotating solid propellant jet engine is given. It has been established that the magnitude of the thrust force of rotating engines (under other identical conditions in the combustion chamber) is 1.1–1.36 times less than that of non-rotating solid propellant jet engines. The experiments carried out showed a decrease in the degree of swirl of the gas flow of rotating solid propellant engines with an increase in the number of propellant pellets in the engine charge. Conclusion: the results presented in the article can be useful for scientists, graduate students and engineers involved in the creation and operation of aviation and rocket and space technology, and can also be useful for students of technical universities studying in relevant specialties.
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Статья научная
The paper proposes an analytical method to solve the problem of magnetometer calibration for a model that considers the vector of temperature dependence of zero offsets for each of the measuring axes of the magnetometer unit and the matrix of linear temperature dependence of each of the members of the sensitivity matrix, scaling the signal based on the actual sensitivity of each axis and including linear off-axis effects. When solving the problem of determining the calibration parameters of the magnetometer unit, it is taken into account that for measurements with any spatial orientation of the magnetometer unit, the magnitude of the measured magnetic field strength vector is preserved and is a known model value. A penalty function of 24 variables equal to the sum of the squares of the residuals is introduced into consid-eration. The algorithm for solving the problem of calibrating the measuring axes of the magnetometer unit is reduced to searching by the method of least squares for such values of the variables of this function that, with a given set of vectors of magnetometer measurements, provide it with a minimum. For this purpose, the specified function is examined for an extremum. Based on the necessary condition for the extremum of the penalty function, a system of 24 equations in the 24 variables is formed, which, for convenience, is di-vided into three systems (each of them is a system of 8 linear algebraic equations in the 8 variables). It is proved that the main matrix of each of these three systems is an invertible, from which it follows that each of them has a solution, and only one. The components of the solutions of these systems (the coordinates of the stationary point of the penalty function) are found using Cramer's rule. It is proved that the second differential of the penalty function at the found stationary point is positive, from which it follows that this point really provides the minimum of the specified function.
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Статья научная
Modern and promising dynamic systems of aviation weapon systems of the Aerospace Forces (hereinaf-ter for brevity in the text – the system) are characterized by a more complex structure and increased re-quirements for reliability and efficiency of functioning. Moreover, systems of generation 4 ++ and 5 are quite unique and (or) small-scale, and their constituent elements are basically miniature and expensive, therefore, a prerequisite for fulfilling the requirements for traceability to systems and constituent elements is the maximum possible preservation of the quality of the initial basis with the inevitable new interpreta-tion of additional information. Further introduction of artificial intelligence technologies into the practice of solving problems of technical diagnostics makes it possible to obtain adequate results with almost any accuracy. The reliability of the results will be determined solely by the punctuality of the data assignment and the completeness of the mathematical description of systems, processes and events in the subject area under consideration. Therefore, it should be expected that the further development of the theory and prac-tice of technical diagnostics will follow the path of a deeper study of the physical processes occurring in systems, and a more accurate mathematical specification of procedures for finding the place of failure of systems. The aim of the work is to establish the development of an interconnected set of mathematical and logical block diagrams for obtaining and applying diagnostic knowledge in the software and mathematical support of modern and advanced onboard means of monitoring the technical state of systems. The priority direction in such studies is the differentiated selection of approved methods of technical diagnostics with the choice of the appropriate mathematical and algorithmic apparatus for direct probabilistic modeling of systems. A block diagram is presented and a variant of the practical application of the developed algorithm for sequential recognition of system failures (hereinafter referred to as an algorithm, if it is clear from the context of the presentation of the material that it is the developed algorithm) is considered. By using the algorithm, there is no need for decomposition of systems, and the potential for multiple repetitions of the results of a random process of changing the technical states of systems predetermines the possibility of ob-taining large samples with high accuracy of software compilation.
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Change in magnetoresistance in manganese chalcogenides MnSe1-XTeX from bulk to thin-film samples
Статья научная
The electrical and optical properties of anion-substituted antiferromagnetic semiconductors MnSe1-ХTeХ (0.1 ≤ X ≤ 0.4) in the temperature range 77-300 K and magnetic fields up to 13 kOe in bulk samples and in poly-crystalline thin films are investigated. Negative magnetoresistance was found in the MnSe1-XTeX solution in the neighbourhood with a Néel temperature for X = 0.1 and for a composition with X = 0.2 in the paramagnetic re-gion up to 270 K. A correlation was established between the spin-glass state and magnetoresistance for X = 0, 1 and 0.2. The opti-cal absorption spectra were measured in the frequency range 2000 cm-1 < ω < 12000 cm-1. A decrease in the gap in the spectrum of electronic excitations and a several of absorption peaks near the bottom of the conduc-tion band were found. Coexistence of two crystalline phases was found in polycrystalline films of the MnSe1-XTeX system by X-ray diffraction analysis. Resistance maxima were established in the region of polymorphic and magnetic transitions. A model of localized spin-polarized electrons with a localization radius varying in a magnetic field as a result of competition between ferromagnetic and antiferromagnetic interactions is proposed. In the paramagnetic region, negative magnetoresistance is caused by tunneling of spin-polarized electrons during orbital ordering.
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Characteristics of low thrust liquid-propellant rocket engines testing process
Статья научная
Low thrust liquid-propellant rocket engines (LTLPRE) are the main type of rocket engines for control systems of space aircrafts. The thrusters are able to work either in continuous or impulse regime, which is one of their main characteristics. The suggestion about engines` reliability should come from the results of tests which create real or greatly approximated to the real conditions. The development process of thrusters takes into a great account the problems of bench testing methodic, technical equipment of test benches for creating the closest possible to space conditions and the use of diagnostic methods and instruments for various types of physical research and dimensions. The ground test effectiveness depends on the level of real conditions imitation and the level of attention to all operational factors that influence the credibility of reliability parameter estimation during the development. One of the most important questions in terms of testing effectiveness is the question of testing result accuracy and credibility. The testing process of thrusters mainly goes under the requested conditions of vacuum, created in pressure chambers. To increase the effectiveness of space conditions imitation the paper suggests using the pressure chamber, equipped with the tube shield with the circulating liquid nitrogen under required mass flow rate. The impulse working regime creates instability of propellant moving in pipelines. The paper considers the methods of providing dynamically similar characteristics of supply systems in propulsion systems as well as conformity of hydraulic, inert and wave characteristics of supply pipelines.
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Characteristics research of a low thrust rocket engine manufactured using additive SLM technology
Статья научная
The development and improvement of rocket and space technology are largely determined by the application of manufacturing technologies that enable the production of high-reliability products with energy efficiency, while simultaneously reducing material intensity and shortening the production cycle. Among these progressive technologies, additive technologies should be mentioned. The essence of these technologies lies in obtaining parts through layer-by-layer melting of material based on a computer 3D model of the product in a chamber of a specialized 3D printer equipped with a laser device. The application of additive technologies in rocket engine construction requires extensive scientific research and experimental work to confirm compliance with industry standards, rules, and mandatory certification at the state level. In accordance with the program of priority research at SibSU, in collaboration with the industrial partner “Polychrome” LLC a complex of experimental work is being carried out to test and refine the 3D printing modes of a demonstrator model of a low thrust rocket engine (LTRE). The design of the LTRE, operating on environmentally friendly gaseous fuel components, has been developed and adapted for 3D printing on the ASTRA 420 printer. The parameters and characteristics of the printer are considered, and the sequence of experimental work on selecting printing modes for the engine chamber housing and mixing head is outlined. The fundamental possibility of adjusting the modes of laser material melting and forming of the part has been established. The main technological stages of post-printing processing of LTRE chamber parts are presented. A description of the equipment for heat treatment and electrochemical polishing of parts is provided. The sequence of material structure research is outlined, and the results of metallographic and X-ray analysis of the internal state of the metal are presented. The importance of stand tests of rocket engines in the development of innovative design solutions and the implementation of innovative production technologies is demonstrated. A description and composition of the testing stand system at SibSU are presented. The results of stand firing tests indicate the fundamental possibility of manufacturing LTRE using selective laser melting of heat-resistant alloy.
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Статья научная
A turbopump unit (TPU) is one of the main units of a liquid propellant rocket engine. Ensuring the op-erability and the possibility of continuous supply of fuel and oxidizer components with a given flow rate and pressure throughout the entire operation cycle of a liquid-propellant rocket engine is one of the main tasks in the design of a heat pump. A negative effect that manifests itself in the case of a local decrease in pressure to the pressure of saturated steam is cavitation. Currently, in connection with the growth of the computing power of modern computer systems, the methods of computational fluid dynamics (Сomputational Fluid Dynamics, CFD) are increasingly being used to test the anti-cavitation parameters of the pump in various areas of general mechanical engineering. For the rocket and space industry, which has special requirements for reliability, more statistical data is needed. At the moment, there is no cavitation model capable of fully simulating the entire process of nucle-ation, growth and collapse of a cavitation bubble. However, there are a number of simplified models of this process, among which we can single out the numerical model Zwart – Gerber – Belamri, designed to simu-late the cavitation flow in pumps. The mentioned model is the most suitable and is applied in all the works discussed below. This paper analyzes the experimental data and the results of numerical simulation of pumps with vari-ous parameters of flow, pressure and geometry. In the course of work with the model, calculations were performed in the ANSYS environment. In the final part, a conclusion was made about the relationship be-tween the characteristics and applicability of the Zwart – Gerber – Belamri model to the design of the cavi-tation flow in the TPU of an LRE taking into account the peculiarities of the pump operation.
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Статья научная
In this article, a comparative analysis of two methods of increasing the pressure in the zone of subsidence of the energy characteristics of a low-speed axial pump is carried out: the installation of inlet guide vanes (IGV) and an upper-rotor device with axial grooves (J-Grooves). Axial pumps are widely used in power systems for liquid rocket engines, as well as in aircraft hydraulic power systems. Modern aircraft engines are capable of deep throttling, which puts forward important requirements for high-speed pumps. One of these requirements is multi-mode – the ability to work in a wide range of costs and operating speeds. The relevance of the work is due to the fact that the pressure characteristics of axial pumps in the vast majority of cases have non-monotonic curves, which complicates the process of their design and regulation. Increasing the head in the area of falling productivity and striving for a monotonically falling pressure characteristic of the axial pump is one of the most important goals in the design of the unit. In this work, the energy characteristics of an axial pump with an inlet vane device installed in the form of guide vanes (IGV), which create a preliminary twist of the flow at the peripheral sections in the inlet line and an optimal upper-rotor device (J-Grooves) in the form of axial ducts, were obtained by numerical computer modeling. Their influence on the energy characteristics of the object of the study and the magni-tude of reverse currents is shown, and a comparison is made with the research results of foreign and do-mestic authors.
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Статья научная
One of the main systems of a spacecraft (SC) is a power supply system (PSS). The basis of a PSS are secondary power sources (SPSs), which use various methods of controlling and converting electricity, which leads to significant differences in their dynamic properties. On the onboard consumer side, the dynamics of the PSS is determined by the total internal resistance (impedance) of the SPSs. When conducting ground electrical tests of spacecraft EES (electrical engineering systems), due to the complexity of using power supply systems, test complexes are used, the basis of which is simulators of electrical characteristics of the PSS (PSSS). Modern PSSSs use a modular configuration principle, which makes it possible to produce PSSSs of different powers, but energy modules have fixed or adjustable impedance frequency response over a narrow frequency range, which leads to the limitation of the types of PSS being simulated. Equipping the PSSS with the property of regulating frequency response in a wide frequency range expands the functionality of the PSSS, as it allows simulating the dynamic properties of the PSS containing different types of SPSs. The purpose of the work is to study and carry out the comparative analysis of three methods for regulating the impedance frequency response (IFR) of the PSSS module. The methods for regulating the frequency response of a PSSS are being considered on the basis of its generalized functional diagram containing mathematical models: adder amplifier (AA), feedforward compensator (FC), power amplifier (PA), voltage divider (VD) and load (L). The article analyzes options for regulating the impedance frequency response of PSSS, and considers three methods for regulating the IFR: two with a passive FC and one with an active FC. The paper presents a simulation model in the MicroCap package of the electrical circuit of the PSSS module, and computational experiments have been carried out on each method of regulating the IFR of the PSSS. Based on the results of the study, a method for correcting and regulating the IFR of the PSSS is recommended, which makes it possible to separately regulate the low-frequency and mid-frequency regions of the IFR, which allows us to significantly simplify the configuration and provision of the IFR of the PSSS in accordance with the specified requirements.
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Статья научная
The paper proposes the use of clustering methods to determine the most appropriate number of fuzzy terms when building a genetic fuzzy system. At the same time, a fuzzy logic system is used to solve data classification problems and is automatically generated by a genetic algorithm. We used a genetic algorithm with the encoding of terms and classes in a binary string, while each individual encoded a rule base. To build a rule base, it is necessary to set such a parameter as the number of fuzzy terms, since it significantly affects the quality of the generated classifiers. A comparison of the most well-known algorithms such as DBSCAN, k-means and the mean shift algorithm was carried out to identify the best data clustering meth-od. Computational experiments were carried out on several data sets to evaluate the effectiveness of the selected number of fuzzy terms. According to the results, it was determined that the mean shift algorithm selects such a number of terms that allows building more accurate classifiers in comparison with two other methods involved in testing. A comparison was also made with alternative classification methods such as k nearest neighbors, support vector machines and neural networks, as a result of which the proposed method showed comparable classification quality. The developed approach to automating the determination of the number of terms makes it possible to exclude manual selection of granulation for various data, reducing the cost of creating an effective fuzzy system for the classification problem.
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Comparison of methods for initializing starting points on the optimization genetic algorithm
Статья научная
The way to initialize the starting points for optimization algorithms is one of the main parameters. Currently used methods of initializing starting points are based on stochastic algorithms of spreading points. In a genetic algorithm, points are Boolean sets. These lines are formed in different ways. They are formed directly, using random sequences (with uniform distribution law) or formed using random sequences (with uniform distribution law) in the space of real numbers, and then converted to boolean numbers. Six algorithms for constructing multidimensional points for global optimization algorithms of boolean sets based on both stochastic and non-random point spreading algorithms are designed. The first four methods of initialization of Boolean lines used a random distribution law, and the fifth and sixth methods of initialization used a non-random method of forming starting points-LP sequence. A large number of optimization algorithms were restarted. Calculations of high accuracy were used. The research was carried out on the genetic algorithm of global optimization. The work is based on Acly function, Rastrigin function, Shekel function, Griewank function and Rosenbrock function. The research was based on three algorithms of srarting points spreading: LP sequence, UDC sequence, regular random spreading. The best parameters of the genetic algorithm of global optimization were used in the work. As a result, we obtained arrays of mathematical expectations and standard deviations of the solution quality for different functions and optimization algorithms. The purpose of the analysis of ways to initialize the starting points for the genetic optimization algorithm was to find the extremum quickly, accurately, cheaply and reliably simultaneously. Methods of initialization were compared with each other by expectation and standard deviation. The quality of the solution is understood as the average error of finding the extremum. The best way of initialization of starting points for genetic optimization algorithm on these test functions is revealed.
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Compound bending of an orthotropic plate
Статья научная
The problem of longitudinal-transverse deformation and strength of an orthotropic plate on the action of a local transverse force and stretching along the contour of the membrane forces is studied. The direction of laying the fiber of a unidirectional composite that provides the lowest level of stress and deflection is determined. In the zone of application of concentrated force in thin-walled structures, significant bending moments and shear forces occur, which are a source of stress concentration. To reduce stresses, the method of plate tension by membrane forces applied along the contour is chosen. The maximum possible order of membrane tension forces is selected, which provides conditions for the strength and rigidity of the solar panel plate structure, which has a hinge-fixed support along the contour. Pre-tensioning the plate web allows to reduce the stress by 50 times. The problem of compound bending of isotropic and anisotropic plates when applying transverse and selection of longitudinal loads, with restrictions on strength and stiffness, can be called a problem of rational design of the structure. The resulting equations and calculation program can be used in the design of plate structures, as well as in the educational process.
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Concentration of carbon dioxide in products of combustion of GTE NK-16ST and NK-16-18ST
Статья научная
This paper considers the design of two combustion chambers of a gas turbine engine running on natural gas. One combustion chamber has 32 burners, and the other has 136 nozzles located in two rows in the flame tube head. A major contributor to global warming is considered to be the significant emissions of greenhouse gases, primarily CO2, including those emitted by gas turbine engines and power plants. The reduction of carbon dioxide levels by developing a set of structural measures in the combustion chamber is one of the urgent tasks of engine construction which requires a solution in order to meet modern environmental requirements for gas turbine engines serving as blower drives for gas compressor units. The presented research is dedicated to the analysis of influence of changes in combustion chamber design on reduction of CO2 level in exhaust gases of gas turbine engine NK-16ST. Two modifications of the combustion chamber are considered. The first one was a serial combustion chamber with diffusion combustion; the second one was a modernized combustion chamber with a modified front device. Each of the chambers considered was tested as part of the engine. During the study, combustion products were sampled directly in the exhaust tower and their concentrations, including the CO2 content, were determined. As a result of this work, it was confirmed that there is a possibility to reduce the concentration of CO2 in the engine combustion products up to 20 % without affecting the engine parameters. This reduction in carbon dioxide content was made possible by reducing the completeness of fuel combustion in the combustion chamber. The obtained data on changes in CO2 concentration can be useful in selecting the most suitable mode of engine operation, and the presented approaches to combustion processes organization can be used by developers in designing combustion chambers of natural gas-fired gas turbine engines.
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