Vol 22, No 4 (2021)

The shock gas-dynamic processes, which have found wide application in rocket and space technology in the design and optimization of devices and power plants, were considered. An analysis of the known exact and asymptotic relations/conditions on the shock wave were carried out, in particular, generalized differential relations (GDR) on a curvilinear oblique shock wave for a model of a viscous heat-conducting gas at large Reynolds numbers. The advantages of using the discrete-analytical approach were shown, for example: 1) the ability to make the most of smoothness of the shock gas-dynamic formation (jump) in the tangential direction; 2) build efficient computational algorithms devoid of the negative action of approximation/ artificial viscosity on a schematized discontinuity. At the same time, a very widespread graphical method for displaying the results of gas-dynamic calculations on the plane of shock polars, proposed by Busemann, and a volumetric (3D) polaroid, proposed by V. N. Uskov, was reviewed. The mathematical method of shock polars was built on exact relations of the Rankine – Hugoniot type and was proven itself quite well even in the simulation of viscous heat-conducting gas flows. However, in numerous literary sources there are assisting results (shock solutions) of both physical and computational experiments, which are not strictly reflecting in shock polars. In this abstract, it was shown that in rare cases this and a very widespread way of such a mapping may be incorrect. It was proved that the main reasons for such a defect are the combined action of three main factors: non-uniformity of the flow before the shock formation, the edge effect behind it, the action of the external viscosity factor and the mechanism of heat conductivity.

In this paper, we consider the solution of the filtering problem using the Kalman filter with the optimal tuning of the radio-reflecting net. A large-sized transformable space-based reflector is considered. In the process of placing in orbit this structure, it is possible that the real form of the radio-reflecting net can deviate the desired one. To ensure point-to-point adjustment of the active part of the mesh, a cable-cable system is used. The nodal points of the radio-reflecting surface are connected to the back side of the net through cables. They have built-in actuators that allow you to change the length of the cables. A piezo actuator was selected as a control device. By point-by-point adjustment of the piezo actuators, the net is stretched to the required shape. This allows you to provide a high-quality radiation pattern and a high signal level when receiving and transmitting data. Specific values of the disturbing influences are given. To measure the supply voltage on the piezo actuator and the cable length, a voltage converter and a laser scanner are used. Possible deviations from the calculated initial position are determined. In accordance with the principle of separation, the estimation problem is solved first, then the control problem. The estimation problem is solved using the Kalman filter. The control problem is solved using the optimal control algorithm according to the hierarchy of target criteria. The results of numerical simulation are presented. The successful solution of the problem is shown with variable values of measurement noise and disturbing influences. Comparison with trajectories obtained using various optimal control algorithms is given.

In this paper, we consider nonparametric identification and control methods for multidimensional discrete-continuous processes with delay, which are typical for many real industries. Of course, such systems are typical for practice, including in the rocket and space industry, as well as in technological processes for the production of space technology. In multidimensional processes, we must take into account the relationships between input and output variables, as well as their relationship with each other. Moreover, these connections are not always known to the researcher. Taking into account the unknown connections of the input variables, the researcher will deal with tubular processes or H-models, and if the unknown connections of the output variables are taken into account, the model along one or another channel of the object will be analogs of implicit functions. In general, the model of a multidimensional object will be represented as a system of nonlinear implicit equations. In this case, the solution to the identification problem will be reduced to finding the forecast of the vector of output variables from the known values of the vector of input variables and can be obtained only as a result of solving the corresponding system of equations, which were called T-models, which will be discussed in this article. The solution of a system of nonlinear implicit equations by parametric identification methods will not lead to the desired result, due to the lack of sufficient a priori information, this is where the need to use nonparametric identification methods arises, as well as the necessary use of system analysis methods. A priori information in problems of nonparametric statistics is insufficient, which cannot be dealt with by generally accepted identification methods.

When managing multidimensional processes, the dependencies of the output variables should be taken into account. Here another important feature arises, which consists in the fact that random values from the range of definition of output variables cannot be used as reference influences, they must be selected from their common intersection.

To analyze the stress-strain state of homogeneous and composite bodies (CB), the method of multigrid finite elements (MMFE) is effectively used, which uses multigrid finite elements (MgFE). MMFE generates multigrid discrete models of small dimension, in which the inhomogeneous structure of bodies is taken into account within the framework of a micro-approach using MgFE. Basic discrete models (BM), taking into account the heterogeneous structure of bodies, have a high dimension. To reduce the dimensionality of discrete models of bodies, MMFE is used. However, there are BM CB (for example, BM bodies with a microhomogeneous structure), which have such a high dimension that the implementation of MMFE for such BM, due to limited computer resources, is difficult. In addition, for multigrid discrete models of high dimension, the MMFE generates numerically unstable solutions, which is associated with the error of computer calculations. To solve these problems, it is proposed here to use fictitious discrete models in calculations, the peculiarity of which is that their dimensions are smaller than the dimensions of BM CB.

In this paper, we propose a method of fictitious discrete models (MFDM) for calculating the static strength of elastic composite bodies with an inhomogeneous, micro-homogeneous molecular structure. MFDM is implemented using MMFE using adjusted strength conditions that take into account the error of approximate solutions. The MFDM is based on the position that the solutions that meet the BM CB differ little from the exact ones, i. e. we consider these solutions to be accurate.

The calculation of CB by MFDM is reduced to the construction and calculation of the strength of fictitious discrete models (FM), which have the following properties. FM reflect: the shape, characteristic dimensions, fastening, loading and type of inhomogeneous structure of the CB, and the distribution of elastic modulus corresponding to BM CB. The dimensions of FM are smaller than the dimensions of BM CB. The sequence consisting of FM converges to BM, i. e. the limiting FM coincides with BM. Calculations show that the convergence of such a sequence ensures uniform convergence of the maximum equivalent stresses of the FM to the maximum equivalent stress of the BM CB, which allows the use of such FM in the calculations of elastic bodies for strength.

Two types of FM are considered. The first type is scaled FM, the second type is FM with variable characteristic sizes. In this paper, the FM of the second type is considered in detail. Calculations show that the implementation of MMFE for FM with one, two or three variable characteristic sizes leads to a large saving of computer resources, which allows the use of MFDM for bodies with a micro-homogeneous regular structure. Calculations for the strength of CB according to MFDM require several times less computer memory than a similar calculation using BM CB, and does not contain a procedure for grinding BM. The given example of calculating the strength of a three-dimensional composite beam according to MFDM using FM with three variable characteristic dimensions shows its high efficiency.

Today, we can single out a number of promising reusable launch vehicles “SV Wing” – a reusable cruise stage of a light-class launch vehicle; “Baikal-Angara” reusable booster of the first stage of the Angara launch vehicle; “Soyuz-7” is a reusable two-stage medium-class launch vehicle; flight design tests of “Soyuz-7” are planned for 2025. To maintain the operational characteristics of aircraft, it is necessary to develop a maintenance system that ensures the specified reliability of aircraft assemblies. The purpose of this work is to develop a model for detecting malfunctions in the process of maintenance of units and systems of aircraft. Within the framework of this work, an algorithm has been developed, which is based on the method of statistical testing, which allows, at low computer time, to analyze the maintenance process in more detail, taking into account the duration of individual operations and their effectiveness. Data on the duration and efficiency of individual operations can be obtained in the process of special tests of equipment by timing and analysis of service results. For modeling it is necessary to have the following initial data: the law of distribution of the duration of individual operations; the effectiveness of troubleshooting during individual operations. The algorithm implements two types of maintenance: full and reduced. Reduced maintenance provides for operations that are most effective in terms of the number of faults to be eliminated: adjustments, adjustments, search for faulty elements. The developed model makes it possible to investigate the possibility of reducing the downtime for maintenance without a significant decrease in the quality of maintenance, namely: to assess the effectiveness of maintenance when it is carried out according to the full and reduced scheme; evaluate the effectiveness of maintenance when performing maintenance in a limited time; justify the most appropriate ways to improve the quality of service, provided that the downtime for maintenance is limited and predict the likelihood of detecting malfunctions during the maintenance process. The practical significance of the results of this work can be achieved in the aerospace industry, in particular, at the design stage (testing and operation) of a maintenance system for reusable elements of launch vehicles.

The turbopump unit is one of the main units of a liquid propellant rocket engine. Ensuring the operability 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 nucleation, 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 simulate 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 various 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 between the characteristics and applicability of the Zwart – Gerber – Belamri model to the design of the cavitation flow in the HPA LPRE taking into account the peculiarities of the pump operation.

The purpose of this work is to detect the regularities of the 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 310. 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 310 steel with a pulsed electron beam was carried out at the SOLO installation, subsequent nitriding (the QUINT 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 = 0.7´10^-6 mm³/N´m (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. Shown 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 K 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.

Due to the absorption of solar energy in chloroplasts – green plastids, solar energy is converted into the energy of chemical bonds. Studying the processes of photosynthesis and increasing its efficiency is relevant for the development of closed life support systems, including during long flights in space. Chloroplasts are filled with stacks of highly ordered tilakoid membranes (granas). Pigment-protein photosynthetic complexes are located on the border of these membranes. For a long time, the structural characteristics of chloroplasts were not given due attention and they were studied as isotropic substances, but in recent years it has been shown that they have anisotropic properties and a high conversion coefficient during charge separation. In this work, an approach was proposed for a more accurate spatial determination of grains in plant chloroplasts and determination the single unit. Thylakoid membranes and the boundaries of the facet consisting of them are clearly visible in an electron microscope if the electron beam is directed strictly perpendicularly. It was noticed that when the stage is rotated, different regions of the membranes become either blurred or more distinct, which suggests that the granules in chloroplasts are not located in the same plane. Also, a comparison was made of the influence of different external conditions on the chloroplast structure of a plant, not only through a comparison of morphological characteristics, but also through numerical modeling and comparison of the objects spectral properties. For numerical simulation, periodic lattices were determined for the main structural units of chloroplasts of different samples. On the basis of these gratings, the transmission spectra were calculated using the transfer matrix method. Also, the obtained values of the electromagnetic wave along the lattice made it possible to calculate the graphs of the density of photon states. The results of the calculation method of plots of the density of photon states based on the structure of chloroplasts made it possible not only to assess the possible efficiency of photosynthesis, but also to directly relate these models to the external conditions affecting the plant.