Статьи журнала - Siberian Aerospace Journal
Все статьи: 387
Differential evolution in the decision tree learning algorithm
Статья научная
Decision trees (DT) belong to the most effective classification methods. The main advantage of decision trees is a simple and user-friendly interpretation of the results obtained. But despite its well-known advantages the method has some disadvantages as well. One of them is that DT training on high-dimensional data is very time-consuming. The paper considers the way to reduce the DT learning process duration without losses of classification accuracy. There are different algorithms of DT training; the main of them being ID3 and CART algorithms. The paper proposes a modification of DT learning algorithms by means of the information criterion optimization for some selected attribute. The use of this modification allows avoiding optimization by means of enumeration search over the entire data set. The Separation Measure method is used to select the attribute. The method selects the attribute whose class-based averages are most distant from each other. Optimization of the selected attribute is carried out using the method of differential evolution, which is one of the evolutionary modeling methods designed to solve problems of multidimensional optimization. Self-configuring at the population level based on the probabilities of using mutation operator’s variants was applied for differential evolution. The classification problems were solved to compare standard DT learning algorithms with the modified ones. Algorithm efficiency refers to the percentage of correctly classified test sample objects. Statistical analysis based on Student's t-test was carried out to compare the efficiency of the algorithms. The analysis showed that the use of the proposed modification of the DT learning algorithm makes it possible to significantly speed up the training process without losses in the classification effectiveness.
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Статья научная
The power supply system (PSS) of a spacecraft (SC) is one of its most critical systems. The generation of electrical energy in modern SC PSS is typically carried out by solar panels (SP). In the absence of energy generation from the SP or during periods of low energy output, the necessary electrical energy is supplied to the load from battery packs (BP) through a charge-discharge device (CDD). Usually, the CDD is connected in parallel to the output buses of the PSS and, in battery discharge mode, provides stable voltage to the load. The replenishment of energy in the BP — its charging — occurs during time inter-vals when the energy generated by the SP exceeds the energy consumed by the load. Additionally, the CDD can provide voltage stabilization at the load. The article presents the power circuit of a pulse converter capable of reversing the flow of energy and operating in a buck-boost mode with high efficiency. It is shown that using the power circuit of this pulse converter in the CDD of SC power supply systems can improve several of their characteristics, namely, energy-mass and reliability metrics, enhance efficiency, and improve the quality of the output voltage of the PSS while reducing the level of generated electromagnetic interference. The article includes research results on the CDD, with the power section designed according to a prom-ising scheme obtained using a simulation model and a physical prototype. It is demonstrated that the synthesized control law allows for maintaining the astatism of the output voltage and a short duration of tran-sient processes. However, it was found that the simulation model of the CDD provides a shorter duration of transient processes compared to the physical prototype. This is explained by the fact that due to the short time interval during which the controlling microcontroller must perform calculations for switching mo-ments of the power transistors, the mathematical expressions used for calculations had to be simplified. The aim of the work is to find a technical solution for generating control signals that allows for the elimination of complex mathematical calculations of the switching moments of the power transistors in realtime. To achieve this, it is proposed to precalculate the switching moments of the power transistors for the entire range of power transmitted through the CDD and for the entire range of possible voltages on the BP. The obtained values of the switching moments of the power transistors in the form of tables should be recorded in the memory of the microcontroller controlling the power circuit of the CDD and used for control purposes. The article discusses the methodology for obtaining tables of switching moments for the power transis-tors of the CDD, which essentially serve as a digital twin of the CDD, and provides an example of such tables.
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Digital twin for combined casting and rolling line control
Статья научная
Aluminum alloys of all kinds are widely used in rocket and other space vehicles construction and operation - in structural elements, communication lines and power supply units. The parameters of alloys processing operations must be strictly maintained in order to exclude de-fects and obtain products of the required quality. Technologies of metal processing in space engineer-ing include such operations as casting, rolling and forming; continuous melt-crystallization-forming lines can also be used, which imposes additional requirements on the integrated control of such a line. The article is focused on the design of a digital twin to be used for controlling a combined casting and rolling complex. Basing on the previously worked-out mathematical models of the units and com-ponents of the complex (furnace, tray, mold, forming unit, rectifying and cooling assembly, spools), a special program has been designed in the TIA Portal software environment using the S7-1200 micro-processor controller, which simulates the parameter changes of both rolled metal and casting and rolling line units. The article also presents the structure and the user interface of the specified pro-gram. There are calculations of the technological cycle parameters for processing of three alloys - that gives an understanding of temperatures and speeds distribution in the rolled metal at each unit of the line. The program can be used for production lines and complexes both in preliminary processing calcu-lations for various alloys (to select the necessary control options) and during the process itself as part of the applied process control system (to confirm the cooling parameters and casting speed).
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Dynamic flow parameters in natural curvilinear coordinates for a current line in a rotating channel
Статья научная
A special interest in the topic of mathematical analysis of the flow of heat transfer processes is determined by the scientific significance and practical application in the development, design and production of rocket and space vehicles and installations. Substantiation of the developed techniques and modeling of the data obtained during the experiment using 3D process technologies gives an advantage. The accuracy and reliability of the calculation results play a key role in ensuring the safety and reliability of rocket and space systems. Regular verification and verification of the results are also necessary to ensure a high degree of reliability and safety. The comprehensive analysis of the fluid flow in the inter-vane channel of the impeller of a low-flow centrifugal pump presented in the article, with the construction of the energy characteristics of the impeller, can be used to clarify the number of vanes. The developed calculation method consists of four parts: firstly, an expression is obtained to determine the projection of the pressure gradient on the longitudinal axis φ, secondly, an expression is obtained to determine the projection of the pressure gradient on the transverse axis ψ, thirdly, the derivative of the longitudinal velocity in the transverse direction is determined, and fourthly, the results are presented numerical and experimental visualization: the power balance, the dependence of the pressure and the coefficient of influence of a finite number of vanes on the flow rate of a low-flow centrifugal pump. Based on the results of theoretical research, an algorithm and a calculation program were developed that allows calculating local values. The considered approach is confirmed by verification of the results of mathematical modeling by graphical visualization of the flow and measurement of the power balance of a low-flow centrifugal pump. The obtained expressions for pressure gradient projections, determination of the derivative of the longitudinal velocity and experimental visualization play an important role in the calculation and analysis of the operation of centrifugal pumps. However, there is a need for further elaboration of the method to bring it to a form that allows calculating the three-dimensional flow of the working fluid in an arbitrary channel.
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Dynamic hybrid recommendation model construction and user discovery research
Статья научная
This study tackles keyword dependency and latency in book recommendations via a hybrid model fusing collaborative filtering with matrix factorization. The results were used to build an intelligent book recommendation system (recommendation center) with a web interface. Traditional library book recommendation systems rely primarily on users actively searching for the titles they need. Their limitation lies in the large number of matching titles that appear when keywords are entered. In our study, to further improve recommendation accuracy, the recommendation system addresses the problem of professional cognitive limitations users face when making choices through similarity calculations. Furthermore, a user search module is added to the recommendation system to ensure accurate recommendations. When generating a recommendation item for a user, the recommendation system first searches related sentences, then calculates the similarity between the target user and the related user and uses the similarity value as a weight. Finally, based on the previously calculated similarity value, it performs a weighted average of the differences between all ratings. A time-decay clustering algorithm (λ = 0.85) using multi-source data achieves 41 % increase in user similarity and 35 % in new book discovery for a user. The tests demonstrate 27 % increase in accuracy with 3300 concurrent requests (5s/300ms response).
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Статья научная
The paper investigates areas of dynamically unstabilized flows characteristic of the elements of the flowing parts of turbopump units of liquid propellant rocket engines; studies of rectangular variable cross-section, cylindrical variable cross-section, rotational currents in cavities with fixed walls, fixed and rotat-ing walls. The specific elements include: delivery and discharge units, side cavities between the rotor and the stator, cavities of hydrodynamic seals and elements of the interblade channel of centrifugal pumps and gas turbines. Due to the specific features of the operating and design parameters, the initial components of dynami-cally unstabilized flows are predominant in the flow parts of the delivery units. These areas have a signifi-cant impact on the energy parameters of the assembly and affect the heat exchange processes and, as a result, the reliability of structural elements. In the specific elements of the feed systems, both laminar and turbulent modes of the flow of the working medium are realized. Using the methods of three-dimensional boundary layer theory, specific thicknesses of boundary layer such as thickness of dynamic boundary layer, displacement thickness and momentum loss thickness are determined. Dependences for determination of flow core velocities, necessary for evaluation of losses due to the length of specific sections, are obtained. Proper selection of friction laws and velocities profiles in the boundary layer and consideration of initial section is necessary for the purposes of reliable determina-tion of energy parameters. Obtained dependences consider velocity distribution profile in the boundary layer on specific sections of laminar and turbulent regimes cases.
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Статья научная
The article contains the results of research on the effect of abrasive flow machining on the roughness and microhardness of the surface of small channels (holes) in samples of workpieces made of 12X18H10T steel. Empirical dependencies of the change in roughness and microhardness of the surface of a small channel on the degree of filling of the working medium with a plasticizer and the shear pressure of the hydraulic system with the extreme of these functions in the studied area are obtained. Based on these dependencies, the composition of the working environment was selected: the degree of filling of the work-ing media base (with a constant content of white electro corundum – 30 %) with a plasticizer in the form of diamond paste (ACN 60/40 BOM Г) Ka 40 % and CKT rubber 30 %, respectively. As a result of abrasive flow machining, it was possible to reduce the roughness of the surface layer from Ra = 0.49…0.62 µm to Ra = 0.047…0.06 µm, and also to increase the microhardness of the surface from h = 188…192 HV to h = 213…220 HV. The thickness of the hardened layer is ≈ 7.24 µm. Analysis of surface profilograms shows that as a result of abrasive flow machining, both the height roughness parameters (average – Ra, Rz, Rp; maximum – Rmax) and the depth roughness parameters (Rk) were significantly reduced. Using electron microscopy (SEM MAG), a qualitative assessment of the structure of the surface layer of the small channel was carried out. The obtained results show good machinability by abrasive flow of austenitic steel blanks, in particular 12X18H10T steel.
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Effect of electron-phonon interaction on transport properties in TmxMn1-xS
Статья научная
In solid solutions TmxMn1-xS, based on measurements of IR spectra and thermal expansion coefficient in the temperature range 80–500 K, the temperatures of sample deformation and disappearance of the absorption intensity of IR spectra at some frequencies are established. Anomalies in the temperature behavior of the electrical resistance are found, the sign of the current carriers and the mobility are determined from the Hall coefficient. The correlation between the temperatures of coefficient of electrical resistance and lattice deformation has been determined. A model of lattice polarons is proposed. The spectrum of electronic excitations and the density of electronic states in the interaction of electrons with flexural and tensile modes of the octahedron are calculated in the random phase approximation.
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Статья научная
During the assessment of rocket components vibroacoustic loading using the finite element modeling, it is not feasible to analyze the entire rocket due to the design's complexity and its large spatial scales compared to high-frequency wavelengths. Therefore, in practice, individual structural groups (compartments, rocket fuel tanks, and the warhead) must be considered. This limited model for calculations under rigid constraint can produce distorted vibroacoustic parameter characteristics; these errors will be greater the shorter the considered compartment. To address this issue, it is proposed to use beam finite elements for modeling the missing components of the rocket. This should allow to consider the missing vibration modes propagating along its entire body and affecting the compartment under consideration, as well as the dynamics of its end frames. In this regard, in the proposed article, a finite element model of the stiffened shell of a launch vehicle's dry compartment was developed. The model is constructed from flat and solid finite elements, with brackets containing instruments positioned within it. These brackets represent concentrated masses with specified centering and inertial characteristics. Such structural elements, described by a system of oscillator equations, interact with acoustic (fluid) elements in the model, where the acoustic wave equations are solved. The missing parts of the launch vehicle were modeled using beam elements, considering the existing design of tunnel pipelines, fuel tanks, propulsion systems, etc. The rocket's beam structure is connected to the compartment frames by elastic contact elements. Solving the resulting systems of equations allowed us to determine the displacements of the structural finite elements and pressure pulsations in the acoustic domain. The calculations are presented under various boundary conditions, which take into account low-frequency vibrations that occur during engine operation and their influence on the internal acoustic pressure and the dynamics of the structure, with the beam part of the model and without it.
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Efficiency improving of emergency monitoring and forecasting based on the information system
Статья научная
The article is devoted to the automated information system modification to solve monitoring and forecasting problems of natural and man-made emergencies in order to increase the efficiency of its functioning, namely, to increase the execution speed of the main operations, to reduce the error probability. Monitoring and forecasting of emergencies are among the priorities in the field of population from emergencies protection, as the prevention and elimination of their consequences are carried out on the basis of these tasks. At the same time, the data collection speed, processing and analysis largely determine the efficiency of the obtained results. The existing system of monitoring and forecasting of natural and man-made emergencies, its functional model in IDEF0 notation, characteristic features, advantages and disadvantages are considered. The existing system can be improved by automating a number of tasks related to the processing, transmission and storage of large data amounts, including real time data, as well as the generation of consolidated reports on the results of monitoring and forecasting of various objects. The information architecture of the solution reviewed and the corresponding database model form the basis of the proposed solution. The IDEF0 model of emergency monitoring and forecasting has been introduced taking into account the proposed modification of the automated information system. The main operation execution time comparative analysis based on the initial and modified automated information system (AIS) using the existing hardware confirms the effectiveness of the proposed solution. Data exchange and generation automation of consolidated reports on multiple monitoring objects will simplify analysis of the obtained results and solutions development based on them aimed at prevention of natural and man-made emergencies, as well as elimination of their consequences.
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Статья научная
High complexity and cost of developing flying models necessitate the use of such design and production techniques that would ensure the best flight technical and technological characteristics of the model also would raise of it operation effectiveness. These techniques include the experimental control method of flying model’s mass-inertia asymmetry parameters during final assembly of the model. Solution of the problem of optimization the process of bringing parameters of mass-inertia asymmetry of the conical flying model to specified standards is considered in the article. The only correction plane is designed to be positioned close to cone face, away from the center mass of the flying model. The flying model as a component of prefabricated rotor is being balanced in dynamic mode on a low-frequency dynamic vertical stand, which based on gas bearings. Before balancing experiment the weigh, longitudinal center of mass and inertia moments of the flying model have to be controlled with use of another measurement equipment. As a criterion of optimization is sorted the reaching of minimum of the angle of deviation of principal longitudinal centroidal axis of inertia from geometrical axis of the flying model. But simultaneously the pre-set standard of center-mass shift from the geometrical axis must be ensured. Balancing algorithm, easy-to-realized by modern computers, is presented. Numerical illustration of balancing is given. The algorithm enables omitting intermediate steps of balancing, reducing them to one step (as a rule), and shortening the balancing time, as well. In one step of balancing the engineering model permits either bringing parameters of mass-inertia asymmetry of the flying model to specified standards, or diagnosing impossibility of attaining the specified standards with available design of flying model. The algorithm and balancing method are experimentally tested at newly-designed vertical dynamic stand on conical gas bearings. It’s high precision and efficiency are corroborated.
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Elastic-plastic problem in the case of inhomogeneous plasticity under complex shear conditions
Статья научная
In this research, the authors solved a two-dimensional elastic-plastic problem of the stress state under com-plex shear conditions in the body weakened by a hole that is bounded by a piecewise smooth contour. The stress state of a complex shear occurs in a cylindrical body of infinite length under the action of loads directed along the cylinder generators and constant along the generators. At the same time, with a sufficiently large load, both elastic and plastic zones appear in the body. As in any problem of this kind, it is necessary to find a previously unknown boundary separating the elastic and plastic zones. Finding such a boundary is not an easy task, but the specificity of elastic-plastic problems of complex shear is that solving such problems is easier than solving simi-lar elastic problems. Apparently, for the first time this fact was noted by G. P. Cherepanov. A lot of research is devoted to elastic-plastic problems of complex shear in the case of homogeneous and iso-tropic plasticity. All articles that solve complex shear problems essentially use the representation of stresses and displacements in the elastic zone in a complex form. In this research, the problems of complex shear are solved using conservation laws. It is assumed that the yield strength is a function of the coordinates of the point where the stress state is being studied. It is known that the elastic properties of structural materials can be homogene-ous and isotropic, while their yield point and strength are inhomogeneous. This situation is observed, for exam-ple, in the case of neutron bombardment of structural materials. This research will examine exactly this situa-tion. The article presents conservation laws for equations describing a complex shear. It was assumed that the components of the conserved current depend on the components of the stress tensor and coordinates. The com-ponents of the stress tensor are included in them linearly. The problem of finding the components of the con-served current was reduced to the Cauchy-Riemann system. The solution of this system allowed us to reduce the calculations of the stress tensor components to a curvilinear integral along the contour of the hole and thus find the boundary between the elastic and plastic areas.
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Elastic-plastic torsion of a two-layer rod
Статья научная
We study the elastic-plastic torsion of a two-layer rod under the action of torque in this article. It is as-sumed that the rod consists of two layers. Each layer has its own elastic properties, but the plastic proper-ties of both layers are the same. The contact boundary of the layers is located along the ох axis. The lateral boundary of the rod is stress-free, displacements and stresses are continuous at the interface. The compo-nents of the stress tensor at a point are calculated using contour integrals derived from conservation laws calculated along the lateral boundary. Next, the second invariant of the stress tensor is compared with the yield strength. At those points where the yield point is reached, the plastic state is realized, in the rest – elastic. This allows you to build a boundary between the plastic and elastic regions. This technique pro-vides a way to calculate elastic-plastic boundaries for the main rolling profiles of rods. This is supposed to be done in subsequent works. We remind you that earlier, with the help of conservation laws, the main boundary value problems for a plastic two-dimensional medium, elastic-plastic torsion of isotropic rods and elastic media for bodies of finite dimensions were solved.
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Статья научная
Cation-substituted solid solutions YbXMn1-XS were prepared by the melt method from polycrystalline sulfide powders. The synthesized samples are antiferromagnetic semiconductors and, according to the results of X-ray structural analysis, have an FCC structure of the NaCl type. Structural, electrical, optical, and acoustic properties of the chalcogenide system YbXMn1-XS were studied in the temperature range 80–500 K. The effect of variable valence elements on the electronic structure of cationic substitution of manganese sulfide has been studied. The change in the electronic structure in the YbXMn1-XS system occurs due to the electron-phonon interaction. Samples with variable valence have anomalous compressibility, which is confirmed by the data on the thermal expansion coefficient and the change in the attenuation coefficient. As a result of inelastic interaction with d- electrons, the density of states at the Fermi level changes, this is reflected in the temperature dependence of the conductivity. The positions of the f-level and two electronic transitions were determined from the IR spectra. A zone of temperatures and concentrations was found, where a correlation of structural, electrical, optical and acoustic properties is observed. To explain the experimental results, the electronic structure of the semiconductor is considered and a model is proposed that qualitatively describes the experiment.
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Electrooptical response of the films of polymer dispersed nematic with conical boundary conditions
Статья научная
The electrooptic response of films of polymer dispersed nematic under conical boundary conditions has been investigated. An axial-bipolar director configuration is formed in nematic droplets. It has been shown that initially, the orientation of droplet’s bipolar axes is chaotic both in the sample plane and relative to the normal to the substrates. The applied voltage U orients the droplet’s bipolar axes parallel to the electric field and the reorientation process is threshold only when the bipolar axis is initially orthogonal to the substrate normal. Accordingly, the samples strongly scatter light in the initial state, and the optical response to an electric field is thresholdless. The samples with a film thickness of 5, 10, 20 and 30 μm have been studied. All the samples under study are characterized by a high transmittance and contrast ratio, which for a 30 μm sample are equal to 84 % and 5536, respectively, and achieved at U = 12 V. The results obtained are relevant for use in low-power optoelectronic devices required for the development of energy-saving technologies in aerospace engineering.
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Energy saving simulation test complex for spacecraft power supplies full-scale electrical tests
Статья научная
The aim of this paper is to describe an energy saving automatized simulation test complex used for spacecraft power supplies full-scale electrical ground-based tests. The complex allows you to simulate the operation of solar array, lithium- ion-battery and spacecraft payload. The distinctive features of the test complex are a continuous and impulse control methods combination with an improved dynamic accuracy, and recuperation of consumed energy into its internal DC network for the better energy efficiency. Test complex operational time from uninterruptible power supply accumulator batteries is significantly increased due to the recuperation of excess power into the test complex internal DC network. The results are experimentally proved. The authors of the paper analyzed dynamic accuracy improvement and energy saving during ground-based spacecraft power system electrical tests. The process of ground-based spacecraft electrical testing includs the following tasks: – the accurate simulation of static and dynamic characteristics of spacecraft power system energy sources and loads; – the utilization of energy produced by power system under load and during spacecraft battery charge simulation. The paper deals with the description of energy saving automatized simulation test complex (ESAST) including complex subsystems structure and experimental study of the test complex characteristics. Commercially available simulation test complexes usually use continuous or impulse control methods. The continuous control methods decrease energy efficiency, as the most part of energy is dissipated on the regulator, which requires massive heat sink, increasing weight and size. It makes difficult to produce high-power test complexes. The impulse control methods provide better energy efficiency, but limit dynamics and real devices fast response reproduction accuracy. The paper describes the combination of continuous and impulse control methods with the aim of taking the advantages of both. The energy consumed by the test complex can be utilized either by the heat dissipation in the environment or by the recuperation into industrial AC grid. The heat dissipation reduces the energy efficiency, increases the testing room temperature (in case of high-power spacecraft power system) and an air conditioning system. The recuperation into AC grid is free of specified disadvantages, but it requires the recuperated excess energy parameters matching with AC grid requirements through the network of grid-tied inverters, which leads to the increase of weight and size of the test complex. Moreover, the recuperation into AC grid is difficult during grid emergency shutdown, which can result in long test failure. The paper describes the method of excess energy recuperation into the complex internal DC network. The method significantly reduced test complex energy consumption, which in case of powering test complex from uninterruptible power supply (UPS) notably increase operating time from UPS accumulator batteries during AC grid emergency shutdown. In conclusion the main advantages of ESAST are given: – more than twice wattage reduction of test complex main power supply; – the ability to work during AC grid emergency shutdown with increased operating time from UPS; – the significant reducing of ESAST main parts weight and size.
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Статья научная
Currently, in the field of engine building, development of three-component propulsion systems (PS) is a very promising task. Liquid-propellant rocket engines (LPRE) operating at the initial stage of launching a launch vehicle (LV) on liquid oxygen + kerosene fuel and at high-altitude launch sites using cryogenic fuel (liquid oxygen + liquid hydrogen) are in particular interest. LPRE that use three-component fuel have a high pressure level in a combustion chamber (CC) (up to 30 MPa) and temperatures (up to 4000 K). In this regard, arise questions related to reliable cooling of such engines, as well as ensuring minimal hydraulic fluid losses in a cooling passage in order to further use re-frigerant as a working fluid for driving the turbine of a booster turbo pump unit (BTP). The object of research is a two-mode single-chamber three-component liquid-propellant rocket engine, made in a closed circuit with generator gas afterburning. Oxidizing agent is liquid oxygen, fuel is RG-1 kerosene and liquid hydrogen. Cooling of the chamber is combined: it consists of regenerative and internal. Regenerative cooling passage is formed by longitudinal integral-machined fins. Hipercritical hydrogen is used as an engine coolant. Internal cooling includes a tantalum coating applied to a fire wall of the chamber in a critical section. The article examines the problems of organizing cooling system (CS) and implementation of effective heat removal from a firing wall of a three-component rocket engine. Basing on existing liquid-propellant engine cooling systems, optimal circuit solutions and measures to remove thermal load in the most stressed places are proposed. A mathematical model has been developed for calculating a CS of a three-component LPRE. The results of the design calculation of cooling using several calculation methods are presented.
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Статья научная
The reliability of ring current-collecting devices during a given service life plays a decisive role in the operation of power supply systems of various equipment and largely depends on the strength and reliability of all its components, in particular, contact rings. One of the most important characteristics of ring current collectors is the contact resistance, which is reduced by using non-ferrous and precious materials with low resistance, while increasing the downforce between the rings of the current collector. With an increase in the compression force F of the contact ring, the resistance of the contacts decreases to a certain minimum value and practically does not decrease with further growth of the force. The dependence of the contact resistance on the compression force has the form of a power function, the coefficients of which are determined experimentally. However, the operability of the contact rings in such severe conditions can be ensured in the case of low speeds and a small number of loading cycles by using the low-cycle fatigue area on the Weller curve. Having determined the coefficients of the equation of the inclined section on the Weller curve in the area of low-cycle fatigue, it is possible to determine the number of permissible loading cycles at a given stress level or solve the inverse problem of determining the permissible stress level if the number of loading cycles is known. To substantiate the correctness of the selected compressive force and the corresponding stresses, methods for calculating the fatigue margin coefficient, as well as a method for calculating the reliability of the ring material, are proposed. Reliability is estimated by the Gauss curve and is numerically expressed in the form of the probability of failure-free operation and the probability of failure, for which the corresponding theoretical dependencies are obtained. According to the proposed methods, calculations of the rings of the current-collection device used in EXPRESS-type spacecraft were performed, which showed the operability of the methods and allowed to ensure the required service life of the contact rings and their reliability. A very simple analytical formulation of the methods allows us to solve both verification and design calculations of rings, depending on the task at hand.
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Статья научная
Heterogeneous energy sources and homogeneous energy sources with different characteristics are frequently used in autonomous power supply systems. Solar batteries are widely used as primary energy sources for on-board power supply systems of spacecrafts, unmanned and manned aircrafts. Renewable energy sources such as solar, wind, geothermal and hydro energy, serve as primary energy sources of terrestrial autonomous power supply systems. Matching primary energy sources with different characteristics and operating conditions within a unified power supply system leads to problems connected with the power control of energy sources, which determines the relevance of the considered problems. The main aim of the study is to develop a combination of primary energy sources and control techniques which allow using primary energy sources with different characteristics and operating conditions in unified autonomous power supply system. The objectives of the study are to create the simulation model of a power supply system using MATLAB/Simulink software; to develop and test control algorithms for primary energy source controllers that would allow to maintain the needed battery charging current; to develop and test control algorithms for primary energy source controllers that would allow the primary energy sources to operate in the maximum power point tracking mode and to minimize the maximum power point search time. Methods used in the study: the simulation of a power supply system using MATLAB 7.9 Simulink software. Results: the simulation model of a power supply system including two primary energy sources with different characteristics is designed. In the case of excess power generating by the primary energy source, its controller operates in the battery charging mode. When the primary source power shortage occurs, its controller operates in the maximum power point tracking mode. The proposed power supply system structure allows controlling two energy sources independently, thus the primary energy source controllers can operate in different modes. This provides flexibility of the power supply system. The use of fuzzy logic control algorithm increases the accuracy and search speed of the maximum power point tracking algorithm. Simulation results confirmed the efficiency of the proposed solar controller operation algorithms in all modes stated above. The efficiency of controller operation modes selection algorithm was confirmed in different operating conditions. The proposed algorithms allow implementing the effective control of primary power sources depending on power supply system operating conditions.
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Ensuring the thermal regime of spacecraft structures
Статья научная
The main requirement for the smooth operation of the spacecraft is its stable thermal regime. A particularly difficult task is to ensure a stable temperature control system of the device, taking into account strict restrictions on energy and mass costs for temperature control devices. These tasks need to be solved at every stage of the creation of satellites. At each stage, thermal calculations are carried out with the choice of optimal thermophysical parameters. This amount of work is about a tenth of all work with the satellite. The need for theoretical and experimental refinement of calculation methods is an urgent task that will significantly reduce the material and time costs of designing, testing and fine-tuning the device. Therefore, the calculation and analysis of the thermal regimes of spacecraft is an important stage in the design of satellites. Ground thermal vacuum tests are very costly, both in time and financially. The essence of the concept is to conduct only stationary thermal modes under conditions of maximum and minimum thermal loads on the satellite as a whole and its individual external elements, followed by ensuring convergence of test results with calculated results. And the confirmation of intermediate requirements to ensure the specified thermal conditions is carried out by calculation. The article considers the tasks of ensuring the thermal regime of spacecraft structures. Classification of devices used to ensure the thermal regime. Ground-based testing of the thermal regime of communication satellites during thermal vacuum tests. Ensuring the thermal regime of the communication spacecraft during ground-based electrical tests. Thermal regime of spacecraft structures during transportation from the manufacturer to the technical position.
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