Izvestiya MGTU MAMI

Background: The paper addresses the problem of improving the energy efficiency and durability of heat exchange equipment. Particular attention is paid to improving the characteristics of heat exchange surfaces of heat exchangers, which play an essential role in many industries. The range of issues of pollution and corrosion of heat exchange surfaces and the causes that led to them are discussed.

Objective: Analysis of the effect of ion implantation on the contamination and corrosion resistance of heat exchange surfaces of the heat exchange equipment.

Methods: Within the framework of this study, comparative analysis methods to record changes in the composition of the surface layer of the samples under study were used. Microhardness studies were carried out in the direction from the surface to the depth of the test sample using the Neophot-2 device on transverse metallographic sections, which were cut perpendicular to the implantation.

Results: During the study, the data on changes in microhardness of aluminum samples after nitrogen implantation were obtained, as well as the data on changes in the structural composition of surface layers and increased resistance to corrosion, contamination, and prolonged exposure to surfactants.

Conclusions: As a result of the study, it can be said that a decrease in energy efficiency due to contamination of heat exchange surfaces is more pronounced in heat exchangers in which a high value of the heat transfer coefficient was initially designed. Ion implantation not only increases the microhardness and wear resistance of materials, but also prevents the appearance of an oxide film, which in turn reduces the contamination of the heat exchange surface, and also makes the heat exchange surface less susceptible to prolonged exposure to surfactants.

Background: Modern autonomous driving systems impose high demands on the quality of object detection and classification in the surrounding environment. Radar systems, due to their resilience to adverse weather conditions and ability to measure velocity, play a crucial role among the object and obstacle detection systems used in autonomous vehicles. However, various technical issues related to noise, incorrect classification, and errors in determining object characteristics can hinder the operation of these systems.

Objective: Identification and analysis of the main problems of object detection and classification based on radar data, and assessment of their impact on the safety and performance of autonomous driving systems.

Methods: In this study, experimental data collection was carried out in city traffic conditions using the ARS 408 automotive radar. Modern software tools including the Robot Operating System (ROS) were used to analyze and process the data. Detection quality evaluation metrics such as IoU, Precision, Recall and F1-score were applied in the study.

Results: Within the study, the methodology for radar system data analysis and identification of the main problems encountered during object detection, including the effects of noise, classification errors and object size biases, is developed. Approaches to assessment of quality of the detection algorithms are proposed and a comparative analysis of the convergence of object detection data under various conditions is carried out.

Conclusions: The results highlight the main problems of object detection by radar systems and help to assess the quality of current algorithms. The practical significance of the study lies in analyzing the weaknesses of object detection systems and providing data for algorithm improvement, which can enhance the safety of autonomous vehicles.

Background: In the peristaltic pumps, a significant gap can remain in the compressed working body, and therefore, unlike other positive-displacement hydraulic machines, volumetric losses may significantly affect the actual flow rate of the pump. The gap’s shape is determined by approximate dependencies or by numerical methods, but both of these approaches have their own drawbacks.

Objecive: Determination of the parameters of the gap in the compressed pump’s hose and calculation of fluid leaks in the pump using both theoretical dependencies and numerical methods.

Methods: The object of this study is a peristaltic pump that uses a hose compressed by two rollers. The theoretical flow rate was determined according to the existing theory of positive-displacement hydraulic machines, with the rotor velocity and the volume of the working chambers. It was assumed that the hose in the pump body has the shape of a torus, and the SolidWorks Simulation software product was used to determine the shape of the gap in the compression region and the amount by which the volume inside the hose decreases due to compression by the roller. The resulting geometry of the deformed hose was transferred to the STAR-CCM+ computational fluid dynamics software, where the velocity field in the gap and the dependence of the gap resistance coefficient on the Reynolds number were obtained. For the final determination of leaks in the gap, the Weisbach formula for local losses in the gap and the Darcy-Weisbach formula for friction losses along the length of the pump hose were used. The Darcy coefficient was calculated assuming that the flow in the pump hose is laminar.

Results: Comparison of the calculation results with the experimental dependencies showed that the proposed leaks calculation method in the pump can be used at laminar flow and rotation velocities of the pump rotor not less than 100 rpm.

Conclusions: The usage of theoretical dependencies and numerical methods to determine the gap’s parameters and to calculate leaks in the pump has shown its effectiveness, but for more accurate results, it is necessary to take into account additional factors, as the flow in the pump is non-stationary.

Background: Any motorsport events consider some restrictions for engines, such as power restrictions or volumes restrictions, for the sake of safety. An air restrictor, which is a gauged orifice in an intake manifold, is one kind of used restrictors. The most efficient and permitted by competition regulations method of engine power increasing is turbocharging.

Objective: Study of power increasing of a 1-cylinder four-stroke engine with an air restrictor at the intake by means of turbocharging.

Methods: The study was conducted as simulation of operation of the 1-cylinder four-stroke engine with an air restrictor at the intake and a turbocharger. To simplify the simulation, the air restrictor was considered as a direct diffuser. The simulation was performed in the Ricardo WAVE software package, capable of performing complicated simulations of various intake and exhaust systems with or without restrictors or turbochargers.

Results: The procedure of using the Ricardo WAVE software package for simulation of the 1-cylinder four-stroke gasoline engine is considered. Using the built mathematical model, simulation of main operation modes of the engine with a turbocharger, with and without a restrictor was performed in order to obtain its optimal characteristic curves. The scientific novelty lies in choosing and optimization the inlet nozzle length and using the restrictor for improvement the engine characteristic curves.

Conclusions: The turbocharged air-restricted four-stroke engine of the Formula SAE racecar showed considerable advantages in comparison with the naturally aspirated one. Thus, the naturally aspirated engine has a maximal power of 31 kW and a maximal torque of 34 Nm, whereas the turbocharged engine has a maximal power of 40 kW and a maximal torque of 54 Nm that gives a significant improvement of racecar performance. Therefore, turbocharging is capable of not only solving problems caused by a restrictor but also improving key engine indicators significantly.

Background: When the vehicle slows down, especially on slippery surfaces, it is possible to lose the motion stability of the electromechanical drive system, accompanied by the excitation of self-oscillations with high amplitudes. The origin of self-oscillations occurs when the sliding speed increases and the friction force decreases. At the same time, the dynamic load of the drive system increases sharply, which can lead to its failure. As a result, the development of methods for suppressing self-oscillatory phenomena is a relevant task.

Objective: Using the methods of field experiments, to test the operability and effectiveness of the method of suppressing self-oscillations in the electromechanical wheel drive system during braking.

Methods: The study of the efficiency and effectiveness of the algorithm was carried out using the methods of field experiments.

Results: Using the method of field experiments, the operability and effectiveness of the algorithm for suppressing self-oscillations during deceleration has been found, as it is capable of reducing the values of maximum amplitudes by 6 times, averaged amplitudes by 3–3.5 times, while excluding changes in the sign of the torque during intense vehicle decelerations.

Conclusions: The algorithm for suppressing self-oscillations can be recommended for the practical development of vehicle deceleration control systems.

Background: The analysis of the frequency response of pulse-width converters is necessary at the stage of their design in order to ensure their stability. The most accurate results can be achieved using nonlinear dynamic mathematical models of these systems. At present, obtaining of frequency response data of pulse-width converters is carried out using the models created in the existing software that uses numerical methods for solving systems of differential equations to calculate electromagnetic processes, which leads to the accumulation of errors in the calculation of time dependencies, and also requires significant computation time to obtain the result. Therefore, the development of a mathematical model that eliminates these downsides is a relevant task.

Objective: Development of a nonlinear dynamic mathematical model of a DC/DC converter with a closed automatic control system with feedback on the output voltage when exposed to measuring signals from a frequency response analyzer.

Methods: The methods of mathematical modeling of electronic circuits and the theory of differential equations were used. The frequency response data were calculated using a program written using the C++ language. The results obtained using the proposed mathematical model were also compared with the results obtained using the model in the MATLAB/Simulink and using analytical expressions.

Results: A mathematical description of electromagnetic processes in a push-pull bridge DC/DC converter on the interval of invariance of the structure of the power section in analytical form is given. Nonlinear transcendental equations are also given, allowing to calculate the moments of switching the circuit valves. The frequency response data were calculated using the proposed mathematical model and a comparative analysis was carried out with the frequency response data obtained using other methods and the correctness of the developed model was confirmed. Thus, it is shown that the calculation speed increased more than five times compared to the calculation carried out using the MATLAB/Simulink model.

Conclusions: The results obtained in this work make it possible to conduct large-scale studies of the frequency response of push-pull DC-DC converters at an acceptable calculation speed. The calculation program based on the developed model can be implemented in any high-level language, as well as in the built-in MATLAB language.