Vol 23, No 2 (2022)

Internal network security is an important aspect of a successful enterprise. There are various means to prevent cyber threats and analyze visited Internet resources, but their speed and the possibility of application strongly depends on the volume of input data. This article discusses the existing methods for determining network threats by analyzing proxy server logs, and proposes a method for clustering Internet resources aimed at reducing the volume of input data by excluding groups of secure Internet resources or selecting only suspicious Internet resources. The proposed method consists of 3 stages: data preprocessing, data analysis and interpretation of the results obtained. The initial data for the method are the proxy server log entries. At the first stage, data useful for analysis is selected from the source data, after which the continuous data stream is divided into small sessions using the nuclear density estimation method. At the second stage, soft clustering of visited Internet resources is performed by applying the thematic modeling method. The result of the second stage are unmarked groups of Internet resources. At the third stage, with the help of an expert, the results are interpreted by analyzing the most popular Internet resources in each group. The method has many settings at each stage, which allows you to configure it for any format and specifics of the input data. The scope of the method is not limited in any way. The resulting method can be used as an additional preprocessing step in order to reduce the amount of input data.

Route building methods include the task of finding the shortest trajectory between two or more objects, which may vary depending on weather conditions, altitude coordinates, and other parameters. The methods discussed in the article allow building routes using GPS tracks for various fields of knowledge: designing routes within a city, region, country, or with remote sensing of the earth. The considered algorithms are used in the field of environmental monitoring in emergency situations, to search for optimal data transmission routes in satellite systems and their validation, as well as in organizational and economic systems. The most widely used approaches for building routes are graph theory and search in the state space, where any trajectory between objects is given its own weight. However, there is still no system that allows you to make a tourist route over rough terrain. The most widely used approaches are graph theory and search in the state space, where any trajectory between objects has its own weight. The article discusses such methods as the Dijkstra, Levitt, Floyd-Warshell algorithm, and also compares their effectiveness in terms of running time and complexity. The aim of the work is to develop an algorithm for finding the shortest path and building a tourist route from a given point A to point B. This development will open up new opportunities for citizens to independently visit new interesting areas, actively spend their free time and get to know the surroundings of the city. The system has been tested on the territory of the Torgashinsky ridge, includes more than 38 route points located at a distance of more than 25 kilometers, and allows you to build the desired routes within less than 15 milliseconds. At the same time, the system allows you to enter your own coordinates, which are considered when building routes.

It is a fact that during data transmission, inter-symbol interference can occur, caused by the presence of multipath propagation and frequency-selective fading in the radio channel, which can significantly reduce the energy efficiency of communication systems. One of the methods to combat such effects, relevant today, is the use of OFDM modulation (OFDM – Orthogonal Frequency Division Multiplexing), which allows to flexibly change the data rate, reduce the frequency resource by improving the spectral efficiency, and also deal with frequency – selective fading and selective interference.

However, there are channels that are particularly susceptible to inter-symbol interference, such as, for example, the tropospheric channel. Also, the problem of selective interference is particularly acute in near-field magnetic induction communication systems. For such channels, the use of OFDM modulation itself is not a panacea; the task of increasing the energy efficiency of an OFDM signal is an urgent one. This paper presents the key features of the OFDM mode of operation, which make it possible to increase the energy potential of the radio link in channels subject to intersymbol distortion. The results of modeling methods for PAPR reduction and digital predistortion for the linearization of the transmission path are presented.

The practical significance of the work lies in the fact that the use of transmission path linearization methods will increase the maximum bandwidth of communication systems, primarily those using tropospheric, radio relay and near-field magnetic induction communication channels. At present, this issue is particularly acute, since there are no high-speed tropospheric stations with a data transfer rate of 50 Mbps in Russia. Increasing the throughput in tropospheric communication will provide communication to hard-to-reach settlements with difficult terrain. Also, the use of high-speed tropospheric communication is a cost-effective alternative to satellite communication, since its use does not require the lease of a satellite channel.

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 the presentation of the material 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.

Sections of dynamically non-stabilized flows specific for elements of flow parts of turbo pump assemblies of liquid-propellant rocket engines are considered. Sections of cylindrical variable cross-section, rectangular variable cross-section, rotational flows in cavities with stationary walls, stationary and rotating walls are analyzed. Specific elements include: delivery and discharge assemblies, side cavities between rotor and stator, cavities of hydrodynamic seals and elements of interblade channel of centrifugal type pumps and gas turbines.

Due to specific features of operating and design parameters, initial sections of dynamically non-stabilized flows are dominant in flow parts of delivery assemblies. These sections have significant influence on energy parameters of the assembly and affect heat exchanging processes and, as a consequence, reliability of constructional elements. Both laminar and turbulent flow regimes of the working fluid are realized in specific elements of delivery systems.

With the use of 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 determination of energy parameters. Obtained dependences consider velocity distribution profile in the boundary layer on specific sections of laminar and turbulent regimes cases.

A mathematical model of the working process of the vortex ejector has been compiled, on the basis of which a method for calculating the optimal geometry has been developed. The calculation method takes into account the exchange of work and heat between a high-pressure (ejecting) gas and a low-pressure (ejected) gas.

The effect of viscosity and the resulting tangential stresses on the exchange of work and heat in the vortex ejector is shown. The coincidence of calculated and experimental data is satisfactory.

The article contains the results obtained by the authors in the study of the possibility of using electron beam welding (EBW) for thin-walled structures made of AD31 aluminum alloy. Today, EBW of similar designs are not used due to the lack of technology. Currently, other technologies for connecting similar structures are used in production, but they have a high cost, the reason for which is due to the high percentage of defects. The method of using EBW proposed by the authors will significantly improve the quality of the joint in thin-walled structures and the reproducibility of the technological mode of welding products. The authors have developed a technological solution to the presented problem, based on many years of experience in the use of models of thermal processes, accompanied by electron beam welding. As a subject of research, modeling of the parameters of electron-beam welding of thin-walled pipes for waveguide paths made of aluminum alloy AD31 is proposed. The article presents the results of mathematical modeling of technological parameters during heating of an aluminum alloy by energy sources equivalent to an electron beam during EBW. The analysis and evaluation of the simulation results was carried out using the optimality criterion developed by the authors. The calculations performed by the authors are based on functional using mathematical models of metal heating by a complex heat source consisting of moving instantaneous point and linear energy sources. The article presents the results of calculations for a plate with a thickness of 0.12 cm, which corresponds to prototypes used in the manufacture of waveguide paths. As a result, by changing such values as: beam current and welding speed, the temperature distribution on the surface of the product during the EBW process was obtained, which showed the applicability of modeling for developing a new technological process.

The reliability of electronic equipment, including in the aerospace industry, both under normal and extreme conditions, is associated with the degradation of materials due to the formation and development of a defective network. Cadmium telluride is one of the semiconductors that is actively used in the creation of solar cells and modern microelectronic devices. In this paper, the model of the point defects distribution in cadmium telluride before exposure to any ionizing radiation is proposed, that made it possible to calculate the effective thermal activation energy of a Frenkel pair equal to 1.37 eV. Studies of the features of the defects formation and evolution using modeling methods in cadmium telluride, in the future, will improve the quality of its technological use, saving financial resources and increasing the reliability of products.

In the production of rocket and space technology, difficult-to-machine steels and alloys are used by traditional methods. Therefore, electrical methods for processing parts are used that use a variety of thermal effects of an electric current directly in the process of removing a layer of material. In the technology of dimensional electrical processing, the role of electroerosive methods is increasing, which are increasingly used in all branches of mechanical engineering as the most effective, and often, and as the only possible ways of processing parts made of modern high-strength and viscous structural materials. One of the most promising methods of electrical processing of metal blanks is electrocontact. Performance is applied to evaluate the effectiveness of this method. The carried out literary analysis showed that the product of the current strength and the coefficient taking into account the processing mode and the material of the electrodes is used to assess the productivity. Later, this coefficient was called the coefficient of electrical erosion. For metals used in switching equipment, the value of the coefficient is given. However, it cannot be used to calculate the performance of electrical contact processing due to the significant difference in erosion processes occurring in the interelectrode gap. According to the literature data, the erosion coefficient was calculated during electrical contact processing, the results are presented in the table. In several works it is indicated that the erosion coefficient depends on the polarity of the inclusion of the rotating disk electrodes and the workpiece being processed. The data presented are contradictory; therefore, studies were carried out on the influence of the inclusion polarity on the erosion coefficient. With the same grade of the processed material and the rotating disc, the polarity of the inclusion does not matter. It was revealed that for steel grade St.3 the erosion coefficient depends on the voltage on the electrodes and, when approaching the arcing voltage, increases sharply, regardless of the polarity of the inclusion. For stainless steel, a sharp increase in the erosion coefficient is observed only at the straight polarity of the inclusion