Vol 29, No 4 (2025)

This study aimed to optimize turning parameters for Ti–Nb–Zr alloys in order to minimize surface roughness. Billets of two ultrafine-grained (UFG) titanium alloys, melt batches 92 and 94 of the Ti–Nb–Zr system, were investigated. To enhance mechanical properties, we produced a UFG structure by abc-pressing of billets followed by groove rolling. Experimental design employed the Taguchi method of orthogonal arrays, which enabled ranking of the technological parameters of the turning process according to their influence on the output characteristics. The experiment determined the optimal turning parameters for achieving minimal surface roughness in UFG titanium alloys. The lowest surface roughness was achieved at a feed rate of 0.07 mm/rev. The cutting speed was 60 m/min for alloy 94, which contained tin and tantalum as alloying elements, and 30 m/min for alloy 92, which contained neither tin nor tantalum. Cutting speed was found to exert the greatest influence on surface roughness. For the samples with the lowest surface roughness, the microhardness of the surface layer was measured. The average microhardness HV0.05 was 321 HV for alloy 92 and 252 HV for alloy 94. The microhardness of alloy 92 increased by 14.6% compared to its initial value of 280 HV. Thus, the turning parameters established in this study can be considered optimal for achieving minimal surface roughness in alloys 92 and 94 of the Ti–Nb–Zr system. The optimized turning parameters were applied in the fabrication of implants for osseointegration prosthetics. Future work will focus on determining the optimal combination of technological parameters for the thread-cutting process in the manufacture of biomedical implants from Ti–Nb–Zr alloys.

This study aims to verify the mathematical models, numerical methods, and software suite developed for assessing the service life of actual turbomachine rotors and confirm their adequacy for industrial applications. The strength analysis of highly loaded turbomachine rotor components, accounting for parameter mistuning, represents a critical challenge in power generation and aerospace engine design. The primary investigative method employed is the finite element method (FEM) in a three-dimensional formulation. The research utilizes theories of elasticity and vibration, mechanics of deformable solids, damage summation methods, and fatigue accumulation hypotheses. The computational framework involves matrix computations, numerical integration, and methods for solving systems of algebraic equations. A durability analysis of a steam turbine wheel model was carried out using TET10 three-dimensional finite elements within the commercial ANSYS WORKBENCH software, enhanced with custom-developed codes. The numerical results from these finite element models for all mistuning types were compared with the experimental data, analytical solutions, and computational results from the ABAQUS software, which incorporated geometric mistuning. This integrated validation confirms the accuracy of the models and facilitates their application not only to simplified steam turbine models but also to real industrial components. The computational experiments verified the proprietary software and the interface that connects it with conventional commercial software for analyzing the service life of a steam turbine with geometric mistuning. The practical significance of this work lies in the applicability of the developed approach for durability assessment in the design and fine-tuning of real axial and radial turbomachinery. This methodology substantially reduces the time and financial costs associated with the development of new compressors and turbines.

This study investigates the mechanisms of defect formation in polyurethane foam (PUF) insulation used in pipelines for energy and central heating applications. The research focuses on PUF insulation placed between a steel pipe and a polyethylene casing. A numerical thermomechanical analysis was performed using ANSYS software on a U-shaped section of an insulated pipe to simulate the operational conditions with a heat-transfer fluid temperature of 130°C and ambient temperatures varying from –20°C to +20°C in 5°C increments. Various causes of insulation defects were examined, including manufacturing factors (e.g., uneven application, incorrect foaming temperature, and moisture contamination), mechanical loads (impact and vibration), and thermal stress. The PUF failure process, which involves condensation, corrosion, and chemical degradation, is described. The investigation established that significant stress concentrations occur at the bends of pipes covered with PUF insulation. The maximum von Mises stress was determined to be 0.45678 MPa at an ambient temperature of –20°C with a temperature differential of 150°C between the fluid and environment. This value approaches the ultimate strength of the polyurethane foam, indicating that cyclic compression and expansion processes can initiate defects and lead to subsequent degradation of the insulating layer. Thus, the study demonstrates that thermal loads, along with manufacturing defects and mechanical impacts, are the primary factors in the formation of defects in PUF, such as cracks, delamination, and fatigue, which compromise the structural integrity and thermal performance of insulated pipes.

The study aimed to assess the feasibility of using higher phase voltage harmonics as a means of detecting single-phase faults at an early stage of their development. An analysis of oscillograms obtained during emergency events was carried out for the medium-voltage distribution grids of Kaliningrad Oblast. The oscillograms were obtained using reclosers for the period from 2018 to 2023. Out of over 2,000 recorded oscillograms, the phase voltage oscillograms corresponding to the gradual development of a single line-toground fault were selected. These oscillograms were harmonically analyzed using the fast Fourier transform algorithm. The results of this analysis showed that the third voltage harmonic distortion begins to increase steadily several industrial frequency cycles before the occurrence of a single line-to-ground fault. The study revealed that in over half of the cases, the third phase voltage harmonic distortion exceeds the value permitted by the power quality standard as early as 200 ms before the fault occurs. Starting from 110 ms, the number of such exceedances reaches 75%. The identified regularity can be used to improve automatic grid restoration systems and protection against single line-to-ground faults. An increase in the third phase voltage harmonic can serve as one of the early signs of a single-phase insulation fault in power grid equipment and can be used to preventively run algorithms for localizing faulty grid sections as part of developing adaptive protection against single line-to-ground faults.

This study developed a single‑criterion mathematical model for selecting optimal sites for wind and solar power plants within an electric power system, taking into account renewable generation variability and economic efficiency. The objective functions included maximizing total electricity output, minimizing the overall rate of power change, minimizing total power increments, and maximizing base power, subject to constraints on installed capacity and the number of units per site. A test system was designed with six potential sites for wind power plants and two sites for solar power plants, with a combined installed capacity of 600 MW. The study proposed an algorithm integrating daily power profile simulations for a single wind turbine and a photovoltaic module group across candidate sites with varying topography and daylight duration. Optimization of installed capacity distribution among sites was then performed. Application of the model to the test system showed that the type of objective function significantly affects the configuration of the optimal system and the allocation of capacity among sites. Transitioning from the criterion of maximum electricity output to criteria related to power dynamics reduces generation by 6–7%, while decreasing the total rate of power change and total power increments by 19–39% and increasing base power by up to 38%. The proposed optimization algorithm provides a systematic framework for decision-making in the design of renewable energy systems with minimal internal volatility of generation. The selection of the objective function depends on the flexibility characteristics of a given power system and can be applied at early stages of planning renewable energy facilities.

The study was aimed at developing a technology for regenerating cyanide and precipitating copper from copper cyanide solutions through the sulfate reduction process. To this end, a mixture of strains of anaerobic sulfate-reducing bacteria was used: Desulfonatronum zhilinae, Desulfonatronum cooperativum, and Desulfonatronobacter acetoxidans from the S.N. Vinogradsky Institute of Microbiology of the Russian Academy of Sciences (Moscow). The sulfate reduction was carried out at temperatures of 20–40℃ and at pH>9.5. Ethanol was used as the electron donor, and sulfate ions were used as the acceptor. In order to ascertain the limiting substrate (ethanol or sulfate) and establish the optimal concentrations of the acceptor and the electron donor, a mathematical microbial growth model was used– the Monod equation. The calculation results indicate substrate competition for the right to limit the process. Thus, at concentrations of <0.3 g/dm3, the limiting substrate is sulfate, whereas at sulfate concentrations of 0.5–1.0 g/dm3 and ethanol concentrations of 0.1–0.3 g/dm3, the limiting substrate is ethanol. The co-limitation point of the process was determined; at this point, the concentrations of sulfate and ethanol are 0.8 and 0.3 g/dm3, respectively. In order to ascertain the hydraulic retention time of the liquid phase in a bioreactor, the Monod equation was used, taking inhibition by hydrogen sulfide into account. The presence of 0.1–0.5 g/dm3 hydrogen sulfide in bacterial solution was found to reduce the bacterial growth rate by 27–65%. The hydraulic retention time of the liquid phase in the bioreactor at the co-limitation point, taking the inhibition by hydrogen sulfide into account, should be equal to approximately 90 hours. Laboratory tests show the calculated hydraulic retention time to be sufficient to obtain 0.25–0.27 g/dm3 hydrogen sulfide for 99% copper precipitation and over 99% cyanide regeneration. The obtained copper precipitates contained copper and sulfur (65% and 35%, respectively). Thus, the examined microorganisms allow hydrogen sulfide to be obtained directly in copper cyanide solutions with different copper concentrations, which eliminates the need for a bioreactor and all auxiliary communications for transporting hydrogen sulfide.