Статьи журнала - Siberian Aerospace Journal
Все статьи: 387
Features of modeling the electron beam distribution energy for the electron-beam welding process
Статья научная
The energy distribution of the electron beam by means of application of various scanning paths, affects for-mation of the weld, which relates to the quality of the welded joints. Experimental studies, conducted by the au-thors of the article showed that scanning the electron beam in the form of a raster shape gives the best quality of welded joints; therefore, the trajectories of a classical raster and a truncated raster are proposed for the elec-tron beam welding process. When conducting research in this direction, the authors discovered the following regularity: with an increase in the scanning amplitude along the junction, the vapour-gas penetration channel transforms into a stable cavity, along the front wall of which the metal melts, and along the side walls it is trans-ferred to the tail of the weld pool. The discovered effect of the formation of a penetration cavity is to be investigated in electron beam welding of various materials and thicknesses. For this the necessary equipment is to be created, allowing to make scan-ning in the form of various rasters. To improve the quality of the electron beam welding process, trajectories of a classical raster and a truncated raster across the joint are proposed. For these scanning trajectories, analytical expressions and families of calculated characteristics of the electron beam energy density distribution over the heating spot are obtained. Modulation of the electron beam oscillation in the form of a truncated raster across the junction makes it possible to obtain a two-humped distribution of the beam energy on the surface of the part along the heating spot. The obtained characteristics allow a more meaningful approach to optimizing the pro-cess of electron beam welding of various materials.
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Статья научная
Complex computational and experimental studies substantiate rational modes of milling of complex contour equiaxed surfaces with high accuracy of shape, dimensions and roughness parameters. Bars made of nanostructured carbide composite (produced by extrusion of WC-Co-Al2O3 bimodal powder mixtures) with increased strength, crack resistance and heat resistance were used as a workpiece material for the manufacture of new original tool designs. The combination of these properties is a necessary prerequisite for the effective operation of the developed designs of multi-blade cutters at high cutting speeds and under conditions of variable cyclic loads. A more complex kinematics of the joint rotational movement of the tool during milling dictates the need for new approaches when assigning rational cutting modes. To obtain reliable calculation formulae, numerical experiments were previously carried out, including simulation of the machining process using the VisualStudio integrated development environment, which supports Windows- Forms technology. The ability to display graphical 3D objects was implemented using an additional software product in the form of the Open CASCADE geometric core. Numerical experiments using MathCAD software products and based on the analytical provisions proposed in the work made it possible to evaluate the influence of cutting conditions, geometric parameters of the cutting part of the tool (profile and number of teeth), kinematics of relative movement in the “tool – part” system on the shape of surfaces and contour parameters (roughness) obtained during milling. A technique, algorithm and program for the automated calculation of cutting conditions have been developed, which have been verified during full-scale experiments and the manufacture of complex profile parts from aluminum alloys for drives of aerospace products (in the form of an equiaxial profile and parts of a pinion transmission of guidance mechanisms). At the same time, on the basis of a 3D model of products, control programs for CNC machines were created using MasterCAM. The practical significance and technical and economic efficiency of the proposed design and technological solutions is to increase productivity and reduce the complexity of processing (in comparison with the basic options) through the use of new multi-edge carbide tools for high-speed milling (including when processing composite materials).
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Features of reaching limiting speed values of track tests of ballistic type aircraft
Статья научная
The development of high-speed ballistic aircraft with speeds exceeding 1000 m/s is currently a priority abroad and in Russia. The effectiveness of new such products is confirmed by track tests at the speed of their use. Test sites with rail tracks exist in almost all countries, for example in the USA there are more than 15 of them. Double-rail, monorail and various combinations thereof, differing in length, width of the rail pair, rails and the design of the track itself, including a sealed shell over the rail track to fill it with a lighter one environment. The longest track in the USA is Holloman AFB, located in New Mexico with a length of 15536 m. They have track ranges with different lengths and their own special design in England, France, Germany, Canada, Italy, Japan, India, China, Korea, Turkey and other countries, including African continent. Highspeed range tests in Russia are carried out on the experimental installation “Rocket Rail Track 2500”, located on the territory of the FSE “Scientific test range of aviation systems named after L.K. Safronov”. The experimental installation consists of a rail track placed on a special base, providing the necessary vertical profile of the track with sections of ascent and straight horizontal movement, as well as a technological descent section for braking moving technological equipment. The product under test is placed on a rocket track sled moving along rails on sliding supports. To accelerate the track carriage, solid fuel rocket engines are used, the thrust of which is selected based on ballistic calculations to achieve the required test speed. The length of the track plays an important role in achieving the maximum acceleration speeds of moving track equipment. The enormous aerodynamic drag, proportional to the square of the speed of movement of the carriage, when tested at high speeds, leads to the need to reduce the midsection and mass of the mobile unit. An increase in engine thrust leads to an increase in the weight and cost of track equipment, as well as to the need to increase the safety margin of sliding supports. However, an increase in test speed can be achieved by replacing the air medium with gases that have a significantly lower density, for example, helium. Track testing of new aircraft or their elements, although cheaper than flight testing, is quite expensive. In this regard, work on the theoretical assessment of replacing the medium from ambient air with helium, as well as with a mixture of helium and air at different concentrations in an indoor gallery on a track rail track, is a new, relevant and practically useful task. The work performed a numerical simulation of the problem of supersonic flow around a helium-air mixture at different volumetric ratios. Numerical values of aerodynamic resistance were obtained at a sled speed of 830 m/s. The results of numerical calculations of the motion dynamics of a 3D model of monorail track equipment, which are planned for use in conducting full-scale fire experiments, are presented.
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Статья научная
This article addresses the Express-RV satellite system, which developers are currently creating. Its primary purpose is to provide subscribers in the Russian Federation and the Northern Sea Route with internet access. The subject of the study is the main features of the Express-RV system implementation, concerning communication in the forward and reverse satellite channel. Among the main features of the satellite system, in addition to the highly elliptical orbit (HEO), we can highlight multi-beam coverage of the service area, direct signal retransmission and the choice of DVB-S2X and DVB-RCS2 satellite communication standards. To implement multi-beam coverage of the service area and direct retransmission, the system employs a multi-beam Ku-band payload. Therefore, the work prioritizes the description of this payload. Objective of the work: to analyze the features and energy parameters of the Express-RV satellite system to confirm its operability, as well as to determine the operating modes in the forward and reverse channels according to the DVB-S2X and DVB-RCS2 standards. Methodology: analysis of the main solutions of the Express-RV system being developed, the DVB-S2X and DVB-RCS2 satellite standards and the recommendations of the International Radiocommunication Union ITU-R P.618-13, theoretical calculation of the energy budget of the radio link. The results confirm the system’s operability, as the study demonstrates the possibility of quasi-error-free reception of DVB-S2X and DVB-RCS2 signals under ideal synchronization conditions. In addition, based on the calculation, we identify the actually used types of modulation in the return channel from those presented in the DVB-RCS2 standard for 3 types of subscriber terminals. For the forward channel, the analysis reveals that the transmission mode adapts to the terminal with the smallest reflector diameter, eliminating benefits from larger-aperture terminals. Scope of application of the results: the researchers and engineers use the results to further develop the Express-RV satellite system.
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Flexible composite structures with controlled physical and mechanical characteristics
Статья научная
The article presents the results of theoretical and experimental studies that are the basis for the devel-opment of a new class of aerospace engineering structures that allow implementing approaches to create structures with variable morphological and functional characteristics of products. Condensed soft sub-stances, such as elastomers, gels, gradually become functional elements on the basis of which the creation of soft machines and electronics develops [1–3]. Research in this direction has led to the creation of struc-tures with a special architecture that are mechanically compatible, deformable and capable, with a certain combination, of perceiving and transmitting a signal, changing their shapes and physical characteristics (thermal conductivity, electrical conductivity, etc.). The use of such structures in a certain sense models the multifunctionality observed in biological objects and structures (skin, muscles, nervous tissue) [4–7]. The creation of structures that change their shape, structure and change their functional and operational char-acteristics in the process of work, taking into account changing external and internal conditions, is an ur-gent task for many systems of aerospace technology. In this paper, morphologically changeable structures are considered, which include reconfigurable antennas, aircraft wings with variable shape and geometry, flexible robotic systems [8]. The use of such systems with flexible structural elements makes it possible to create structures capable of overcoming unpredictable obstacles due to their adaptive geometry, fit into limited spaces and withstand significant loads and vibrations. One of the most important tasks in the devel-opment of such systems is the organization of a distributed actuation system associated with the problem of creating an internal structure of actuators integrated into a flexible composite design of actuators made of elastic materials. In a number of works for the operation of thermoactive actuators, the use of rigid nano-particles as surface heating elements or as fillers for composites that are electrically sensitive, magnetical-ly sensitive and/or photoreactive has been investigated [9–13]. However, surface heating elements are lim-ited in use beyond a thickness of several hundred micrometers due to their low intrinsic thermal conductivi-ty [14]. In addition, rigid components significantly change the mechanical properties of the structure being created, which limits the morphological capabilities of the structures being created. For example, in [15], it is shown that reducing the electrical resistance for a thermal heater to acceptable values requires an increase in the filler to 15% of the mass of the structure, while the deformation of the actuation of the struc-ture is reduced by 35.0%. In this paper, overcoming the above limitations is carried out by creating a ma-terial architecture that dramatically expands the range of properties and dynamic functions of the heating element being developed for the actuator. Multifunctionality is achieved by embedding metal fibers of a certain configuration into an elastic medium based on polydimethylsiloxane elastomer, which provide mo-bility and conformality of the deformable structure of the actuator during its operation. It is shown that the inclusion of metal fibers of a certain configuration in the structure of the actuator does not interfere with its ability to change shape and perform mechanical work in response to external stimuli. Shape morphing in the absence of an external load can be programmed in the composite structure by including fibers with certain stiffness and thermal characteristics in it so that it can reversibly switch between programmed morphologies using electrical or thermal stimulation. Together, these properties allow the composite to demonstrate a rich variety of functionality, which allows it to simultaneously realize sensory and dynamic characteristics.
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Flight efficiency of solar thermal propulsion with double-stage thermal energy storage
Статья научная
The activity urgency is connected with requirement of heavy spacecraft ascent into high work-ing orbits. The solar thermal propulsion (STP) with double-stage latent heat thermal energy storage (TES) is intended for space vehicle delivery into geostationary orbit (GEO). Double-stage TES contains peripheral stage as “solar concentrator – sunlight absorber-thermal energy storage” system (CATS) with relatively low-temperature heat-accumulating phase-changing material (HAM) having high latent heat of fusion, for instance, lithium hydride, and high-temperature central stage with high power-intensive TES, for example, beryllium oxide, that allows to obtain high specific impulse 900 sec. Inter-orbital transfer time from low earth orbit (LEO)-to-GEO varies from 20 to 90 days. Expedient optical-energetic characteristic parameters of the STRE for each flight time shows that expedient accuracy of the solar mirror concentrator is much less in comparison with single-stage CATS with beryllium oxide as the HAM, therefore, the CATS Sun tracking conditions can be significantly simplified. Comparison between the STRE and alternative means of inter-orbital transportation shows that payload mass on GEO seriously exceeds that for liquid propulsion or combined upper stages with both chemical and electric propulsion. Use of the STRE with heated hydrogen after-burning allows payload mass to increase at relatively low transfer time, as well as reduce space vehicle dimensions and the CATS complication. The expedient oxidizer-to-fuel mass ratios depend on LEO-to-GEO trip time. The considered possible variants of payloads – geostationary communication satellites – can be injected into the target orbit with use of “Soyuz-2.1b” middle class launchers having the “solar” upper stage instead of “Proton-M” heavy rockets class with chemical liquid-propellant kick-stages.
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Flow dynamics in the radial-annular cavity of turbomachines
Статья научная
This paper considers the problem of modeling a rotational flow in the radial-annular cavity of turbo machines with fixed walls. This case corresponds to the boundary conditions of the supply channel for a radial centripetal turbine. In the presented model, the flow is conventionally divided into radial and circumferential movement. The radial component of the velocity is determined by the mass flow rate from the continuity equation, the circumferential component is formed by the tangential channel supply. The main equation in the integration is the equation of the change in the momentum for the flow in the form of the Euler equation. In the case of the circumferential component of the velocity, the angular momentum law is used, assuming the potentiality of the flow and the constancy of the angular momentum within the integration step. As a result of the transformations of the motion equations, differential equations for the radial, circumferential component of velocity and static pressure are obtained, which represent a certain system of three equations in three unknowns. The system of equations allows integration under known boundary conditions at the inlet; as a result of integration, it is possible to obtain the field of distributions of velocities and pressures along the radius of the radial-annular cavity. The results of the study can be used in modeling the circumferential and radial forces on the rotor (impeller) of turbo machines.
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Flow model in the impeller of a centrifugal pump
Статья научная
In accordance with the results of the features analysis of foreign design technology and the creation of aerospace technology products, the certification orientation of all types of work can be traced, starting from the preliminary design stage, which imposes particularly high requirements on the quality of calcula-tion methods, algorithms and software used in the design development of the project. Without the advanced level of domestic developments in the field of modeling hydrodynamic processes in aircraft systems, in the next decade it will become impossible to compete with foreign developers of aviation and rocket-space sys-tems. In accordance with modern theoretical and experimental studies, the flow pattern in the flow path of a vane machine is a complex superposition of the main and secondary flows. The article discusses the method for calculating the fluid flow in the interscapular channel of a centrifugal impeller with a finite number of vanes, the construction of the energy characteristics of the impeller and its optimization by the number of vanes. The calculation consists of two parts: firstly, the determination of the theoretical head taking into account the influence of the finite number of vanes based on analysis of force interaction, and, secondly, determination of hydraulic losses in the impeller by integrating friction stresses along the limit-ing surfaces. The results from both parts are used to optimize the number of vanes in the pump impeller. Analytically, an equation for the pressure at a point and the coefficient of influence of a finite number of vanes are obtained. Taking into account the law of friction, an expression was obtained for the pressure loss. The described method for calculating the spatial boundary layer is quite simple and intuitive, and gives approximate results that make it possible to estimate the required quantities. However, there is a need for further elaboration of the method to bring it to a form that makes it possible to calculate the three-dimensional flow of the working fluid in a channel of arbitrary shape. Based on the results of theoretical studies, an algorithm and a calculation program were developed that allow calculating local values. The results of the calculation of the theoretical head in the impeller can be used for a more accurate calcula-tion of a centrifugal pump.
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![Formation features of the central layers of the alloy Fe – 3 % Si (110)[hkl] rolling textures](/file/thumb/148321699/formation-features-of-the-central-layers-of-the-alloy-fe-3-si-110-hkl.png "Formation features of the central layers of the alloy Fe – 3 % Si (110)[hkl] rolling textures")
Formation features of the central layers of the alloy Fe – 3 % Si (110)[hkl] rolling textures
Статья научная
The fields of solid-state physics, metallurgy, plastic deformation, mathematics and continuum mechanics are engaged in the studies of texturing of metals and alloys and their influence on the operational properties of products. As a rule, the most significant results are expected at the interface between these sciences. The technologies of obtaining textured materials by metal forming processes occupy a special place in the metalworking sphere. This is due to promising directions in technologies for producing semi-finished and final products with improved structure-sensitive properties, by regulating the texturing, taking into account initial crystallographic orientation of the workpiece. The first issue to note is the formation of an ideal, one-component crystallographic texture in anisotropic metallic materials. The second issue is to obtain semi-finished and final products with more specific service properties: crystallographic texture with specific predetermined components. For instance, due to the crystallographic texture, it is possible to increase the resistance of metals and alloys against corrosion and hostile environment. Considering textured materials as composite, we must note that directionally oriented crystallites with crystallographic directions relative to the laboratory direction perform as reinforced elements. The initial texture in the processing plane is especially important. The materials, which possess unique structure-sensitive properties acquired through pressure treatment, are very promising for a widespread use in the sphere of aerospace technology. Obviously, the properties and means of their achievement are diverse and require setting a specific task. Therefore, further research in this sphere is especially promising. The article presents the research findings, considering the effect of initial crystallographic orientation and deformation modes on the rolling texture in the central layer of Fe – 3% Si (110)[hkl] single crystals. Several groups of single crystal samples underwent rolling under laboratory conditions. The groups of samples were classified according to the final deformation rate, the ideal crystallographic orientation of the rolling plane and deflections of the ideal orientation plane direction from the rolling direction. The methodology of the experiment took into account the compression rate value during one rolling. We analyzed the results of rolling, using the radiographic method. The next step was to superimpose the radiographic data on a stereographic projection and to construct straight pole figures. The results of straight pole figures decoding revealed differences in the texture formation from the previously obtained data. The research shows the manifestation of the one-component deformation texture in the central layer.
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Статья научная
The aim of the study is to form an approach to modeling the operations of the orbital assembly of a reconfigurable spacecraft (RS) in geostationary orbit. Reconfigurable spacecraft are a set of modular spacecraft (MS), where, in a particular case, one MS can be assigned the functions of the service systems module (MSS), and the second - the functions of the payload module (MPN). To ensure the assembly of the RC, or the replacement of some MC, for example, in case of its failure with a new one, it is necessary to provide a solution to the problem of bringing the MS with the RS. The article analyzes and studies the operation of the motion control system of the MS during the convergence of the MS with the RS. A list of necessary mathematical models for performing operations in solving the problem of convergence of the MS with the RS is formed, and a block diagram of the interaction of mathematical models is presented. The paper presents a brief description of the mathematical apparatus that allows modeling the operations of convergence of the MS with the RS. This mathematical apparatus includes: a model of the orbital motion of the MS and the RS, models of the angular motion of the MS and the RS, sensitive elements and executive bodies. In this paper, the mathematical modeling of the MS with the RS convergence operations is considered as the subject of research. The object of the study is the motion control system of the MS, which ensures the implementation of the approach of the RS in geostationary orbit.
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Статья научная
The purpose of this work is to detect the regularities of formation of the structure, mechanical and tribological properties of high-chromium steel subjected to complex treatment combining irradiation with a pulsed electron beam and subsequent nitriding in a low-pressure gas discharge plasma using a plasma generator with an incandescent cathode “PINK”. The object of the study was heat-resistant corrosionresistant austenitic steel grade AISI 310S. The relevance and practical significance of the research is due to the relatively low level of hardness and wear resistance of steels of this class, which have a wide range of applications in modern industry, including in the rocket and space industry. Irradiation of AISI 310S steel with a pulsed electron beam was carried out at the SOLO installation, subsequent nitriding (the QUINTA installation). It was found that irradiation of samples at an electron beam energy density of 30 J/cm2, 200 microseconds, 3 pulses and subsequent nitriding at a temperature of 793 K for 3 hours led to the following changes in mechanical properties. The maximum microhardness reached values of 19 GPa (exceeds the hardness of steel before modification by 11.2 times and the hardness of steel after electron beam irradiation by 8 times). The wear parameter has changed to values k = 0.7106 mm3/Nm (less than the wear parameter of steel before modification by more than 700 times and less than the wear parameter of steel after electron beam irradiation by more than 750 times). The thickness of the hardened layer is 40 microns. It was found that the samples that have the maximum (90.6 %) content of nitride phases (chromium and iron nitrides) in the surface layer. It was established that after nitriding at a temperature of 723 K in the surface layer of steel, iron and chromium nitrides are formed in the form of nanoscale particles of rounded shape. At nitriding temperatures of 793 and 873 K, a plate-type structure formed by alternating parallel plates of iron nitride and chromium nitride is formed in the surface layer of steel.
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Generalized equivalent strength conditions in the calculations of composite bodies
Статья научная
Structures with an inhomogeneous regular structure (plates, beams, shells) are widely used in engineering, especially in aviation and rocket and space. It is important to know the solution error in the strength elastic calculations for composite structures using the finite element method (FEM),. To analyze the error of the solution, it is necessary to use a sequence of approximate solutions constructed according to the FEM using the grinding procedure for basic discrete models that take into account the non-homogeneous, micro-homogeneous structure of structures (bodies) within the micro-approach. The implementation of the grinding procedure for basic models requires large computer resources. This paper deals with the method of equivalent strength conditions (MESC) for testing the static strength of elastic bodies with an inhomogeneous regular structure, for which sets of different loads are given. According to the MESC, the calculation of the strength of a composite body for which the loading is set is reduced to the calculation of the strength of an isotropic homogeneous body (having the same loading as a composite body) using equivalent strength conditions. In the numerical implementation of the MESC, adjusted equivalent strength conditions are used, which take into account the error of approximate solutions. Here, the MESC is implemented on the basis of the FEM. If a set of different loads is specified for a composite body, then generalized equivalent strength conditions are applied in this case. The procedure for constructing generalized equivalent strength conditions is shown. The calculation of the strength of composite bodies according to the MESC using multigrid finite elements requires 3 6 10 ÷ 10 times less computer memory than a similar calculation using crushed basic models of composite bodies. The given example of calculating the strength of a composite beam, for which a number of loads is set with MESC using generalized equivalent strength conditions shows its high efficiency.
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Статья научная
The purpose of the study is to develop a technological process mathematical model of creating permanent joints of dissimilar materials based on electron-beam welding using machine learning algorithms. Each of the connected elements is a responsible unit of the complex device, due to this fact, strict criteria are set for the quality of the welded joint. In essence, the set task is a regression task. There are many algorithms suitable for solving the regression problem. However, often the use of one algorithm does not provide sufficient accuracy of the result. One way to solve this problem is to develop a composition of algorithms to compensate for the prob-lems of each of them. One of the most effective and potent compositional algorithms is the gradient boosting al-gorithm. This algorithm use will improve the quality of the regression model. The proposed model will allow the technologist to set the process parameters and to get an assessment of the final product quality, as well as by setting input and output values. The use of assessment methods and forecasting will reduce the time and labor costs of searching, developing and adjusting the process. A description of the gradient boosting algorithm is given, as well as an analysis of the applicability of this algorithm to the model and a conclusion regarding the areas of its applicability and the reliability of the forecasts obtained by its direct use. In addition, we consider the process of direct model training based on the data obtained as part of search experiments to improve the quality of final product. The results of the applicability analysis allow us to judge the admissibility of using the proposed method for processes that have similar statistical dependencies. The application of the proposed ap-proach will make it possible to support the adoption of technological decisions by specialists in electron-beam welding during the development of the technological process and when new types of products are put into pro-duction.
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Ground control system for distant space vehicle
Статья научная
The demand for research of a promising ground-based long-range spacecraft control complex, which has great capabilities not only in the control of deep space vehicles, but also in carrying out fundamental and applied radio astronomical research. Much attention is paid to the analysis of the requirements to the radio complex, which must be fulfilled to realize the possibility of several directions of scientific research and, first of all: planetary radiolocation; interferometry with ultra-long baselines; radio-reflecting; radi-oastronomy. Based on the analysis of the state of the ground control system of deep spacecraft, the direc-tions of its development on the basis of modernization of existing facilities are revealed, and the prospects for the use of new technologies for the development of deep space on flight paths to the Moon, Mars, other celestial bodies of the solar system, the objects of alien and interplanetary infrastructure are shown.
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Heat transfer in the centrifugal force field for gas turbines elements
Статья научная
The study of heat transfer from combustion products (CP) to the impeller and the casing of gas turbines of liquid rocket engines (LRE) is an urgent task. The solution of the flow problem, taking into account heat transfer, in rotational flows, in the flowing parts of the turbopump units (TPU) of the rocket engine, is carried out by the following methods: numerical methods; analytical approach, when solving the equations of dynamic and temperature boundary layers; as well as using empirical dependencies. The temperature parameter of the gaseous combustion products and, as a consequence, the heat exchange between the combustion products and the structural elements of the flow part, significantly affects the working and energy characteristics of the TPU LRE. When designing gas turbines of LRE, it is necessary to take into account the presence of heat exchange processes, the working fluid temperature distribution and the structural element temperatures in the cavities of the TPU LRE (since energy losses and viscosity depend on the temperatures of the working fluid, and also determine the flow parameters). The temperature distribution in the structural elements determines the performance and reliability of the unit. In the case of the use of cryogenic fuel components in the TPU LRE units the heating of the component leads to the implementation of cavitation modes and a drop in operating and energy characteristics. On the other hand, a lowered temperature of the working fluid leads to an increased viscosity of the components and, as a consequence, a decrease in the efficiency of the unit (especially when using gel-like components). When studying heat transfer in the field of centrifugal forces for elements of rocket engine gas turbines it is necessary to obtain a joint solution of the equations of dynamic and temperature boundary layers in the boundary conditions of the flow parts. This article offers a model of the distribution of dynamic and temperature boundary layers taking into account the convective component (for the case of a gaseous working fluid, i. e. Pr < 1), which is necessary for the analytical solution and determination of the heat transfer coefficient in the boundary conditions of the flow cavities of the LRE turbine. The energy equation has been analytically obtained for the boundary conditions of the temperature boundary layer, which allows integration over the surface of any shape, which is necessary in determining the thickness of the energy loss. Taking into account the integral relation, the heat transfer law of the turbulent boundary layer for the rotation cavities is written. The equations for determining the heat transfer coefficient in the form of the Stanton criterion for rectilinear uniform and rotational flows for cases of turbulent flow regimes were obtained analytically. The obtained equations for heat transfer coefficients are in good agreement with experimental data and dependences of other authors.
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Honeycomb fillers manufacturing technology from polymeric composite materals
Статья научная
The honeycomb filler is an integral part of the spacecraft's sandwich panel. Currently, a honeycomb filler made of aluminum alloys is used. The proposed technology makes it possible to replace the honeycomb filler material from aluminum alloys with polymer composite materials (PCM). The main difference between the developed technology for the production of honeycomb filler by the RTM method is that corrugated tape is glued during the formation of the composite material. This is a separate process in the existing methods for the production of honeycomb cores from PCM. This paper presents the results of creating a prototype of a honeycomb filler by the RTM-method, a technological process has been developed.
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Статья научная
An artillery shot is a complex gas and thermodynamic process of rapidly converting the chemical energy of gunpowder into heat, and then into mechanical work of moving the projectile and the recoil parts of the artillery gun. A distinctive feature of the use of aviation artillery weapons is the short time during which firing from an aircraft at a target is possible, which requires the production of not one artillery shot, but the firing of the maximum number of shells with minimal interruptions between bursts of shots. An analysis of the existing physical concepts of the processes occurring in a small-caliber artillery barrel (hereinafter referred to as the barrel) makes it possible to single out the main quantitative characteristic of the temperature state that affects the quality of the functioning of aviation artillery weapons – the temperature field of the barrel. The temperature field, high in level and gradients, formed in the barrel wall during firing, bursts and series of shots, has a significant impact on the reduction in the tactical, technical and operational characteristics of aviation artillery weapons. Therefore, the problem of synthesizing a mathematical model of thermophysical loading of a wellbore (hereinafter referred to as the model if it is clear from the context of material presentation that we are talking about the developed model) and the definition of the temperature field is of great importance for solving a number of practical applications. These include: assessment of bore wear depending on heating; analysis of the thermal strength of the barrel material; analysis of the conditions of projectile guidance along the bore and cartridge case extraction during firing; evaluation of various ways and methods of artificial cooling of shafts; determination of the safety of aviation artillery weapons by eliminating the event of self-activation of a thermally loaded cartridge located in a barrel heated by firing; ensuring the conditions for maintaining the operability of fuses, etc. At the same time, an adequate calculation of non-stationary heat transfer in the bore is difficult, due to the incomplete reliability of the initial data and the dynamics of fast processes in the use of aviation artillery weapons. The aim of the work is to improve mathematical tools that describe the thermodynamic states of the barrel based on the basic functional dependencies of internal ballistics and a dispersed combination of heat transfer methods and finite differences. Numerous and comprehensive testing of the synthesized model, comparison of the calculation results with the data of the classical theory, self-similar solutions and experimental data confirmed the reliability and predetermined the sufficient suitability of the model for its intended use as the objects of research become more complex.
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Impact of the reinforcement technique on characteristics of composite tubular structures
Статья научная
Different composite elements including tubular structures are used as support structures in spacecraft optical systems. The compliance with the specified dimensional stability over a wide temperature range, in particular from –269 up to 100 °C, is important for the design of tubular structures. The promising method of manufacturing tubular structures of CM – radial braiding combined with RTM molding method is discussed in this paper. In addition, the paper describes the method of determining the optimal reinforcement technique for a braided perform which allows to reduce geometrical deflections occurring during a molding process. The impact of the reinforcement technique on the dimensional stability of tubular structures is illustrated in this paper by the example of several reinforcement techniques and manufacturing methods. The paper also contains the analysis of these techniques and the determination of the optimal one to comply with the specified characteristics.
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Impedance and dielectric properties of Bi2Sn2-xFexO7 stannates
Статья научная
Bismuth stannates Bi2Sn2–хFeхO7, х = 0,1; 0,2, which reveal the properties of multiferroics, are investigated. The mechanism of interaction between dielectric and electronic subsystems is studied, based on measurements of electrical resistance at alternating current, impedance, capacitance and dielectric loss tangent in the temperature range 100–600 K at frequencies 102–106 Hz. From the comparison of dielectric permittivity and the reactive component of impedance, the paramagnetic contribution of electrons to the dynamic magnetic susceptibility was established. Impedance jumps on temperature were detected as a result of changes in structural characteristics. The temperature dependences of the permittivity are described in the Debye model. The activation character of relaxation time and two relaxation channels are found. The activation energy of electrons in the migratory polarization is calculated.
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Статья научная
Creating the spacecraft propulsion systems with high energy efficiency and minimal weight and size parameters is an urgent scientific and technical task of the domestic rocket engine industry. At the same time, requirements are put forward to optimize the cost and time of design, development and manufacturing of engines, as well as environmental safety at all stages of the product life cycle. In this regard, it is proposed to use advanced laser 3D printing technologies (additive technologies) from metal powder using CAD models of engine parts in the production of space low thrust rocket engines (LTRE). Laser melting technology on modern 3D printers makes it possible to produce complex monolithic engine structures without the use of labor-intensive and resource-intensive operations of machining, welding, and soldering, as well as a significant reduction in the volume of fitting and assembly operations, control and measuring work, and a decrease in the influence of some non-production factors. The article discusses issues of practical application of promising technologies in the creation of LTRE. The results of fire tests are presented, which will be used to refine the previously developed calculation models of oxygen-hydrogen LTRE when creating advanced rocket engines for spacecraft. The object of the study was an experimental sample of LTRE with a nominal thrust of 150 N using gaseous propellant components oxygen and hydrogen, developed and manufactured using additive technology. The experimental LTRE is considered as a prototype of the engine for orientation, stabilization and launching of the oxygen-hydrogen upper stage. The purpose of the work is to study the effectiveness of previously unexplored design solutions for organizing mixture formation and cooling of an oxygen-hydrogen LTRE, to determine their influence on the perfection of the working process and the thermal state of the engine chamber. Fire tests were carried out in single switching mode with a duration sufficient for the LTRE chamber to reach a stationary thermal regime, with the determination of the energy characteristics and thermal state of the structure.
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