Technical Physics Letters最新文献

The article presents the results of a study of changes in the operational properties of AERO 2T and M-5z/20 AERO engine oils under thermal oxidation conditions at temperatures of 150–200°C, simulating the operation of an aircraft rotary piston engine. The effect of topping up fresh oil (up to 20%), Avgas 100 LL aviation gasoline additives (up to 10%), and water (distilled and seawater, up to 1%) has been experimentally studied. Based on the data obtained, empirical dependences are proposed for calculating changes in the physicochemical and operational properties of oils over time. The discrepancy between the calculated and experimental values does not exceed ±5%.

A mathematical model of the problem of a cylindrical body flow by a supersonic gas flow in the boundary-layer area is considered. Classical difference schemes do not accurately describe the boundary differential problem due to the fact that its solutions allow for areas of large gradients. In this regard, a higher-order difference scheme was constructed and justified on a three-point pattern, which provides an adequate account of the approximation viscosity commensurable with the value of the grid step. A numerical experiment was performed, which allowed the effectiveness of the higher-order scheme to be evaluated.

In the paper, the results of a study of collisions between small-sized models and large single droplets have been presented. Methodological experiments have demonstrated the viability of a ballistic stand and developed methods for synchronizing the model’s flight through the measurement section and its photographic recording. Initial data on the characteristics of asymmetric and quasi-symmetric interactions between the model and a single large droplet have been obtained. Several objectives for further research have been formulated.

The development of digital technologies that improve diagnostics and increase the reliability of determining the functional characteristics of agricultural machinery in real time is important and relevant for the technical support of high-power machines. To develop an intelligent system for remote diagnostics of engines of high-power agricultural machinery, a neural network constructor with the ability to use up to ten input and output parameters has been used. An algorithm for a digital remote diagnostics system, a failure prediction model for online monitoring, and a digital platform for diagnosing high-power agricultural machinery have been developed. The developed platform has enabled the acquisition of diagnostic parameters of the internal combustion engine (fuel consumption, engine temperature, and engine speed). These parameters are remotely transmitted as encrypted data to a server via a GPS modem and digitized in a database, where the data is structured and analyzed using a developed artificial neural network model. The decrypted engine diagnostic parameters are sent to the operator, who views graphs of agricultural machinery technical condition parameters and reports on predicting possible internal combustion engine component failures. A method for collecting and storing diagnostic information obtained from monitoring the technical condition of agricultural machinery has been presented, and these data have been processed using a mathematical neural network model. The use of digital technologies in diagnosing equipment using artificial intelligence makes it possible to reduce significantly the labor intensity of operations, evaluate overall machine performance, predict failures, conduct timely maintenance and repairs, and reduce unplanned downtime of energy-intensive agricultural machinery.

A method for calculating the radiation characteristics of ozone under conditions of vibrational–rotational nonequilibrium is proposed for use in remote monitoring of the Earth’s atmosphere using aviation systems. The method is based on the use of the classical narrow-band k-distribution model, which includes corrections for disequilibrium. These corrections include vibrational and rotational distribution functions, as well as averaged Boltzmann functions over vibrational and rotational temperatures. To check the method, a series of nonequilibrium calculations were carried out, which were compared with the exact line-by-line method in the spectral range of 500 to 1150 cm^–1. The comparison, which was carried out over a wide range of pressures, translational, rotational, and vibrational temperatures, showed good agreement.

The relevance of the study is determined by the fact that in the presence of single and three phase loads, the network mode is almost always asymmetric, which causes additional losses of electricity. The aim of the study is to evaluate methods and develop algorithms for calculating electricity losses from consumers in 0.4 kV networks with single and three phase loads using measurement systems. The tasks of study are analyzing of the graph resulting from daily monitoring of loads by a device for measuring power quality indicators (RESURS UF); determining the coefficient of additional losses that arise when the loads are unbalanced; defining an algorithm of procedures and calculations to reduce electricity losses resulting from unbalanced loads and determining the losses for a 0.4 kV overhead line of standard length 600 m and 15 towers using method of loop currents. The results of the study are the need to monitor loads using smart meters to calculate electricity losses and determine the optimal load balance; an algorithm was developed to reduce electricity losses by balancing loads, which can be generalized to all power supply organizations and analysis of methods for calculating modes of four lines network with a load distributed along the line showed the rationality of using the method of loop currents.

To reveal the plasma acceleration mechanism of pulsed plasma thrusters (PPTs), a two-dimensional numerical model capable of reproducing the evolution of current sheet distortion is established in this paper, and simulation calculations are carried out taking the APPT prototype from University of Tokyo as the research object. The results show that after spark plug ignition, the main body of the current sheet moves toward the cathode with the discharge process, and the overall tilting trend continues to strengthen, which is consistent with the high-speed photography experimental observations. Model analysis indicates that the mismatch between voltage and current in the initial discharge stage is the core cause of current sheet distortion.

The results of a study of the effect of low-temperature plasma of a vapor–gas discharge on the surface of an aluminum part manufactured by direct metal laser sintering are presented. The features of electric discharge formation at the electrolyte–metal interface under atmospheric pressure are considered. The electrical characteristics of the discharge, the surface microrelief, and the phase composition of the material before and after processing were analyzed. It was found that electrolytic-plasma processing leads to smoothing of the surface microrelief and a reduction in surface roughness parameters. The obtained results demonstrate the potential of plasma-electrolytic technologies for the finishing treatment of parts manufactured by additive methods.

Electric-field control of terahertz wave scattering on a graphene nanoribbon metasurface has been numerically studied. It has been shown that, by varying the graphene Fermi level using an external field, one can control the effective scattering surface over a wide range at the plasmon resonance frequencies.

The work under consideration identifies and solves the problem of the operation of self-acting valves for low-speed long-stroke piston compressors (hereinafter referred to as LSLSPC), a feature of which is a significant length of the compression cycle compared to existing machines [1, 2]. Long working cycle times (more than 2 s) result in significant gas leaks. For this reason, ensuring a tight fit between the valve shut-off element and the seat is the main task of modernizing gas distribution systems. This problem was solved by installing an elastomeric element on the valve seat. This not only ensured a smaller gap, but also reduced the perimeter of the valve seat contact. A method is considered for determining the pressure coefficient of a gas flow on the shut-off element of a self-acting valve and the valve flow coefficient. The mathematical model of the working process of a low-speed long-stroke stage of a piston compressor has been improved by introducing a function for changing the pressure coefficient and flow coefficient due to changes in the stroke of the valve shut-off element. A mathematical model was verified, and integral characteristics of the working process of a low-speed long-stroke stage of a piston compressor with self-acting valves containing elastomeric elements were obtained.