This study examines the effect of electrochemical grinding conditions and parameters on the surface roughness of steel specimens machined using small-diameter cubic boron nitride (CBN) grinding heads. The research focused on cylindrical specimens (10 mm in diameter) made of 12Kh18N10T corrosion-resistant steel. The experiments were conducted using AW 6×10×3×60 (LKV50 125/100 100% ME-3) CBN heads on an experimental test bench developed by the authors to implement small-size electrochemical  grinding technology. Surface roughness was selected as the key performance criterion to characterize the quality of the machined surface. The study was carried out in two stages: the first stage evaluated the impact of mechanical parameters (depth of cut, feed rate, and cutting speed), while the second stage focused on the combined process conditions (electrolyte temperature, etching current density, and NaCl concentration in aqueous electrolyte solution). Levels and ranges for these factors were selected drawing on the authors’ preliminary studies. A full factorial design was employed for experiment planning and data processing. The results indicate that the minimum surface roughness for 12Kh18N10T steel specimens is observed at a depth of cut of 0.04 mm, a feed rate of 230 mm/min, a cutting speed of 11 m/s, an electrolyte temperature of 50°C, an etching current density of 0.3 A/mm², and a 0.9 % NaCl concentration in the electrolyte. Consequently, empirical models were developed to evaluate surface roughness depending on the cutting parameters and combined process conditions. Within the specified constraints, the models provide a means to optimize the machining process to minimize surface roughness, evaluate the effect of factors on the selected performance criterion, and predict system behavior during the electrochemical grinding of 12Kh18N10T corrosion-resistant steel parts using small-diameter CBN heads. 

The study aims to determine the coefficient of convective heat transfer between a cemented carbide and a cutting fluid to assess its impact on thermal processes during deep grinding with profiled diamond wheels using the finite element method. This research analyzed heat transfer from a sleeve made of T15K6 and VK8 cemented carbides with the following dimensions: outer diameter of 24 mm, inner diameter of 17 mm, and length of 36 mm. A 3 % Na₂CO₃ solution was used as the cutting fluid; the experiments were conducted at a fluid temperature of up to 373 K and a heat source temperature of up to 603 K. Drawing on the obtained experimental data, the deep grinding process was simulated via the finite element method in SolidWorks Simulation 2015. The authors developed an experimental methodology to determine the convective heat transfer coefficient of cutting fluid within the machining zone during deep profiled diamond grinding of complex-shaped cemented carbide workpieces. This procedure provides a means to determine the coefficient with satisfactory agreement with theoretical calculations (10.49 %). Formulas are proposed for calculating the convective heat transfer coefficient from experimental data. The coefficient values obtained were 250.17 ± 4.42 W/(m²·K) for T15K6 and 250.61 ± 4.11 W/(m²·K) for VK8, respectively. A test bench was designed for the experimental determination of the convective heat transfer coefficient between structural or tool materials and a cutting fluid. The simulation of temperature fields during profiled grinding revealed that the use of a cutting fluid reduces the thermal stress of the grinding process by 30 %. The proposed method enables reasonably accurate determination of the convective heat transfer coefficient for cooling a cemented carbide in a given medium (cutting fluid) and allows the resulting data to be used for finite element modeling of thermal processes during grinding, taking convective heat transfer into account. 

In this study, we evaluate the quality and microstructure of the surface layer of railway wheels subjected to laser hardening using a device for shaping the spatial intensity profile of a laser beam. Experiments were  carried out using a robotic processing system comprising a FANUC M710iC-50 manipulator, an IPG LS-10 fiber laser with an active fiber diameter of 200 μm, an IPG FLW D50 optical system providing precise beam positioning and stabilization of processing parameters, and a device for shaping the spatial intensity profile of the laser beam based on an optical configuration incorporating a cylindrical lens and a perpendicularly arranged Fresnel lens. Test specimens were cut from wheelset fragments of railway rolling stock bogies. The microstructure of the specimens was examined using a LEICA DM ILM metallographic microscope. Microhardness measurements were performed with a DuraScan 20 tester along the hardening direction at intervals of 0.05 and 0.1 mm through the depth of the hardened layer. The study established the influence of hardening parameters on the quality and structural condition of the railway wheel surface layer. The depth of the hardened layer ranged from 1.42 to 1.65 mm, meeting the requirements specified for wheelset heat treatment. The formation of a distinctive metallographic structure within the hardened area was identified. The presence of this specific structure, resulting from laser irradiation with a linear beam profile, ensures the required service characteristics in terms of wear resistance and contact fatigue strength compared to treatment using a conventional circular laser spot. The developed laser hardening technology enables the production of a hardened layer in wheel steel whose characteristics fully satisfy the requirements imposed on heat-treated railway wheelsets. 

This study aimed to analyze the effect of nonuniform heating on the free vibrations of cyclically symmetric structures and to identify vibration modes exhibiting the strongest localization. The analysis was performed using displacement-based finite-element modeling. Thermal mistuning was introduced by local heating of one blade. A numerical modal analysis was carried out in APM WinMachine for a simplified turbine-wheel model containing eight blades, with and without mistuning. The results show that additional heating of a relatively small region with a diameter of 10 mm near the periphery of a single blade leads to substantial variation in the vibration modes of the cyclically symmetric structure. Vibration localization becomes noticeable even when the temperature difference between the heated peripheral region and the temperature prescribed on the inner bore surface is relatively low (10–15°C). The strongest localization was observed for modes with nodal circles and no nodal diameters. In par ticular, the highest localization ratio, defined as the amplitude of the mistuned blade relative to the amplitudes of adjacent blades, was observed for the eighth vibration mode of the mistuned model. Analysis of the dependence of the localization ratio on the temperature difference showed that, for temperature differences exceeding 60°C, the localization ratio for the eighth mode exceeds 60. Under these conditions, only the mistuned blade undergoes bending vibrations, while the remainder of the structure remains effectively stationary. These findings indicate that thermal mistuning produces the strongest localization in specific vibration modes of cyclically symmetric structures. This effect must be taken into account when assessing the durability of such components. Future work will examine the influence of thermal mistuning on the vibrations of a cooled turbine wheel model. 

The study aimed to evaluate the performance of a newly developed chatter-resistant face mill and to assess its effectiveness in the suppression of chatter during milling. Asymmetric up‑milling tests (workpiece width – 134 mm, axial depth of cut – 1.5 mm, feed per tooth – 0.15 mm/tooth, spindle speed – 380 rpm, dry machining) were performed on a DMG DMU 80P DuoBlock machining center. A steel 35 workpiece was mounted on a Kistler 9253B23 dynamometer. The test tool was a prototype face mill with a diameter of 160 mm and an adjustable pitch of 12 carbide teeth, developed at Irkutsk National Research Technical University, Irkutsk, Russia. For comparison, a standard 160‑mm face mill compliant with TU 2‑035‑618‑78 and equipped with 10 tangentially mounted carbide inserts was used. The tools were mounted on the spindle using a standard NT50‑FMB50‑070 arbor and a Showa SK50‑CTH 50‑120 power collet chuck combined with an adapter with a diameter of 50 mm  and a length of 155 mm. Four experiments were carried out in which the milling cutters, their mounting on the toolholders, and the configuration of the tooth pitch were varied. It was established that replacing the toolholder, which increased the overhang of the constant-pitch cutter by a factor of 1.54, led to a dramatic increase in the amplitude of the first harmonic of chatter vibrations from 13.2 to 31.1 times, depending on the coordinate direction, while the second harmonic rose more moderately, from 1.8 to 5.4 times. It was shown that tuning the difference between alternating tooth pitches to half the chatter wavelength reduced the amplitude of the fundamental chatter harmonic by a factor of 13.1–28.3, depending on the coordinate direction, whereas the second harmonic decreased by a factor of 2.5–6.2. Thus, the experiments confirmed the effectiveness of the chatter-resistant face mill with adjustable tooth positioning and demonstrated its ability to suppress chatter under conditions of low system stiffness. 

This study develops computational models and methods capable of accurately accounting for the single-phase time-varying traction load and the design features of current-carrying components during ice-melting operation in a 6 kV DC overhead contact system. The approach is based on a multiphase representation of powersystem elements using transmission-line and transformer models formulated in phase coordinates. The method was  implemented in the industrial software Fazonord AC–DC. Simulation results showed that removal of glaze-ice and rime deposits from the contact suspension conductors is completed within 13–14 min, while melting on the contact wire proceeds approximately 1 min faster than on the messenger wire. Since the currents remain within permissible limits, the conductor temperature continues to increase following ice removal. Under these conditions, the allowable temperature of the contact wire (80°C) is reached after 21 min, whereas that of the messenger wire (100°C) is reached after 25 min. Therefore, the ice-melting process should be terminated once ice removal is completed, approximately 14 min after the start of operation. During the first 15 min of operation, the temperature of the hottest point in the step‑down transformers increases by 20–40°C, indicating elevated winding losses. Subsequently, the rate of temperature rise decreases, and the temperatures approach their maximum values. The study proposes a modeling approach that enables accurate determination of operating parameters in DC traction‑power systems during ice‑melting on 6 kV overhead contact conductors. The results can be used to simulate ice‑removal processes and determine the required melting time. They may also be applied to configuring relay‑protection devices for looped connection schemes between contact suspensions to the 6 kV terminals of traction substations. 

This study reviews spectral decompositions of the controllability and observability Gramians, expressed in terms of the eigenvalues of the system dynamics matrix, and evaluates their application in monitoring  and control of electric power systems. The approach is based on a new concept of Lyapunov modal analysis, which combines traditional selective modal analysis with the spectral decomposition of specially constructed Lyapunov functions over the spectrum of the dynamics matrix. Unlike conventional participation factors, the method employs Lyapunov participation factors, which quantify the contribution of individual system modes to Lyapunov functions characterizing the integral energy of state variables or signals through the squared L2-norm over finite or infinite time intervals. In contrast to existing nonlinear modal-analysis methods, the proposed indicators account for time-varying nonlinearities and resonant interactions between modes with closely spaced frequencies. Three applications of Lyapunov modal analysis to power‑system problems are considered. First, a method is proposed for characterizing the structure of low‑frequency oscillations and their interactions both in the state‑space representation and with respect to their location on the network graph. The proposed indicators enable analysis of individual inter‑area modes, as well as of the geometry of their pairwise interactions at network nodes. Second, a selective tuning procedure for a global linear quadratic regulator (LQR) is developed to suppress a selected group of inter-area oscillations. The proposed method provides improved damping of the targeted modal group compared with the baseline LQR design. Third, a method is presented for locating the source of a forced oscillation whose frequency is close to a natural system mode. Test cases demonstrate the high effectiveness of the proposed approach. The examples confirm that modal analysis based on spectral decompositions of solutions to matrix equations arising in control theory can serve as an effective tool for developing new algorithms and intelligent control methods for both macrogrids and microgrids. 

The study aims to improve the accuracy of modeling hourly solar radiation data in the Kyrgyz Republic, a region characterized by complex terrain, climate variability, and a lack of reliable climate data—factors critical for solar energy development amid a persistent energy shortage. The research involved comparing the long-term mean hourly global and diffuse solar radiation from the Meteonorm database with actinometric data from the Handbook on Climate of the USSR (Part 1) for four actinometric weather stations: Bishkek, Cholpon-Ata, Suusamyr, and Tian Shan. Regression analysis was employed to process the data. Based on its results, a procedure was developed to determine correction factors for adjusting monthly mean hourly solar radiation data depending on geographical latitude and elevation. The data points were divided into two groups: elevations below and above 2000 m above sea  level. Linear regression equations with a high coefficient of determination (0.93–0.99) were obtained, significantly reducing discrepancies between modeled and observed solar radiation data. The developed procedure was implemented as a web application using the Laravel PHP framework, which enables the automatic calculation, storage, and visualization of solar radiation data. Testing at the 80-kW solar power plant of the Kyrgyz State Technical University (Bishkek) showed a 20 % reduction in the normalized root mean square error (to 10–15 %) and a decrease in prediction error to below 5 %. The proposed Meteonorm data correction system improves the reliability of solar resource assessments, making it a valuable tool for the design and verification of photovoltaic power plants, as well as for refining the calculations of solar energy potential in the mountainous regions of Central Asia. 

This study aimed to ensure the dynamic stability of operating modes in power plants equipped with synchronous generators having an inertia constant of 1–2 s and operating either in islanded mode for local loads or  in parallel with an external power grid. A method for rapid detection of emergency disturbances and determination of balancing control actions using an electromechanical filter was examined under step increases and decreases in generator load. The analysis was performed using both physical and digital models of transient electromechanical processes in a simple power system. The results show that the dynamic stability of low-inertia generation under severe disturbances, such as generator or major-load disconnections, transmission-line outages on interconnections with the external grid, and connection of large loads, can be maintained only if emergency balancing control actions (disconnection of a part of the generation or load) are applied within no more than 0.1 s, with their magnitude determined over an interval of 1–2 cycles of the power-system frequency. It was found that the required response speed and robustness to disturbance type are achieved when an electromechanical filter is incorporated into the generator-voltage measurement circuit. The filter consists of two mechanically coupled synchronous machines (micromachines). The study demonstrates that reliable disturbance detection and accurate control actions can be achieved by evaluating the derivative of the output voltage frequency of the electromechanical filter over 1–2 cycles of the power-system frequency. Experiments on both physical and digital models confirmed that existing methods for detecting emergency disturbances and determining control actions are insufficient to maintain dynamic stability in low-inertia synchronous generation, particularly in gas-engine units. The incorporation of electromechanical filters into the anti-emergency control loop can provide the required response speed and ensure adequate control actions regardless of the operating mode or configuration of generating units at the power plant. 

The study provides an analytical review of domestic and international research on voltage control systems for distributed induction-generator units, which can operate within power supply systems of various scales (centralized, isolated, and off-grid). Over 60 sources were reviewed, covering key approaches and methods for voltage regulation in distributed generation units with wound-rotor and squirrel-cage induction generators. The findings highlight that creating new and upgrading existing automatic control solutions for such units remains a critical task. This is particularly vital for the development of generation sources within Russian isolated and  centralized power systems to enhance the efficiency and reliability of electricity supply. It was found that woundrotor induction generators are widely used abroad, while squirrel-cage induction generators are more common in domestic practice due to their simpler and more robust design. The analysis shows that implementing voltage control strategies using both advanced and current components is fundamental to the evolution of electric power sources in Russian isolated and centralized power supply systems. The study concludes that the challenges of developing automatic voltage control systems for distributed induction-generator units based on reactive power sources have been partially addressed in recent years by both Russian and international researchers. However, comprehensive systematic studies have yet to be conducted on such power sources and their control systems within complex centralized and isolated power supply systems. The discussed voltage control systems can serve as a basis for upgrading existing and developing new automatic voltage control systems based on modern digital technologies. 

This study examines the dissolution kinetics of stibnite in nitric acid in the presence of tartaric acid, which acts as a selective complexing agent. The feed material was natural stibnite with a particle size below 74 µm. The composition of the reaction products was determined by optical emission spectroscopy for the leach solutions and by X‑ray diffraction for the solid residues. Statistical analysis and graphical processing of the data were performed in MS Excel. The effects of temperature (50–80°C), nitric acid concentration (4–7 mol/L), tartaric acid concentration (20–80 g/L), and leaching time on the dissolution process were investigated. The shrinking core model was used to interpret the kinetic data. The experiments showed that the concentration of the complexing agent is the major factor controlling process intensification. An increase in the tartaric acid concentration to 80 g/L promotes  the breakdown of the sulfide matrix, enabling an antimony extraction level of approximately 90 %. Temperature and acidity have a positive but secondary effect on the overall leaching performance. Linearization of the kinetic data showed that nitric‑acid dissolution of stibnite in the presence of tartaric acid proceeds with an activation energy of 62.5 kJ/mol. The reaction orders were 2.7 with respect to nitric acid and 2.3 with respect to tartaric acid. The kinetic analysis indicates that antimony leaching under the studied conditions is controlled by the chemical reaction step. The results may be used in the development of processing technologies for antimony‑bearing concentrates. 

In search of alternatives to cyanidation in gold-uranium ore processing, the study aims to develop a two-stage method for the selective elution of gold and uranium from strongly basic anion exchangers loaded in sulfuric acid-thiocyanate solutions. The research utilized a D201 macroporous strongly basic anion exchange resin (PRC). After each elution stage, the resin was analyzed for gold, uranium, and iron levels. Gold concentrations were determined using the atomic absorption method, while the presence of iron and uranium in the solution was confirmed via inductively coupled plasma atomic emission spectrometry and inductively coupled plasma mass spectrometry, respectively. This study presents the first experimental evaluation of the effectiveness of alkaline and acidic eluents in a two-stage selective elution scheme for gold and uranium. In the first stage, a sulfuric acid eluent provided nearly complete removal of uranium, iron, and thiocyanate from the resin (> 99 %) without co-elution of gold. In the second stage, two approaches to gold elution were investigated: use of alkaline thiocyanate and acidic thiourea. The alkaline thiocyanate eluent was found to be extremely ineffective, with gold recovery not exceeding 1.7 %. This can be attributed to the high stability of Au–SCN complexes on the functional groups of the anion exchanger. It was shown that a sulfuric acid solution of thiourea ensures nearly complete elution of gold (>99 %), with the formation of a highly concentrated gold-bearing eluate free from uranium. The proposed approach enables the production of separate concentrated gold and uranium eluates without the use of cyanides. This fact opens up prospects for its implementation in hydrometallurgical schemes for processing complex gold-uranium ores and various industrial solutions. 

The article aims to analyze and characterize the main existing methods for processing spent acidic copper electrolytes containing non-ferrous and impurity metals in order to identify the optimal technology  for producing marketable products. By reviewing known literature and information sources, the study examines current technologies for processing multicomponent acidic sulfate solutions, including hydrochemical, electrochemical, and combined recovery methods. The multicomponent sulfuric acid solution removed from the electrorefining circuit contains copper, nickel, and impurity metals, which must be recovered. Processing starts with decopperization; the choice of recovery method depends on whether the copper is to be recovered as metal or copper sulfate. For example, electrochemical decopperization combined with salt evaporation and crystallization is used for concentrated solutions, allowing ~ 99.5% copper recovery. In order to increase the concentration of sulfate salts and create optimal conditions for the crystallization of copper sulfate, the acid concentration is reduced by adding metallic copper to hydrolytically precipitate the electrolyte components, followed by liquid phase evaporation. Ion-exchange purification reduces impurity levels by 10–20 times, restores up to 90% of the electrolyte’s original concentration, and extends its service life by 3–5 times. Solvent extraction of electrolyte components, where sulfuric acid is bound by tertiary amine solutions diluted to 20–40%, enables a reduction in their high viscosity. The review concludes that the most optimal method for purifying conventional copper electrolytes is a combination of electrochemical decopperization, salt evaporation/crystallization, and neutralization of residual sulfuric acid with metallic copper, followed by solution evaporation and copper sulfate crystallization.