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.
The study aimed to examine the thermophysical properties of briquettes as an alternative to indurated iron ore pellets in the formation of an artificial bottom bed in horizontal-grate machines. The methodology included physical simulation of the drying process (circulation of a heat transfer agent at 150/300℃), dilatometric analysis, measurement of temperature profiles in briquettes, and mathematical modeling with the use of TOREX Sensible Indurating Machine software. The briquettes were made from oxidized ferruginous quartzite concentrate with organic and inorganic binders (cement; bentonite) under a load of 15 t (cylinders measuring Ø35×35 mm). It was established that excessive moisture during drying does not reduce the strength of briquettes (70.1 daN/briquette) due to their low porosity (10% as compared to 30% in pellets) that limits water absorption. The drying of briquettes was shown to proceed 30–40% slower due to their reduced specific surface area and permeability compared to iron ore pellets, thus requiring adjustments to the heating conditions. The thermal conductivity coefficient amounted to 0.12 W/(m·K). During firing, sintering occurs exclusively in the surface layers (depth of 2–3 mm) since the inner zones do not reach the sintering temperature threshold (>1000℃) due to the low thermal conductivity of the material. The integrity of the briquette is ensured by the strength of the indurated surface and the thermal stability of the binder at its core. The mathematical simulation performed for the horizontal-grate machine No. 3 at the Mikhailovsky Mining and Processing Plant showed that the replacement of a standard bed comprising indurated iron ore pellets having a temperature of 80℃ with briquettes having a temperature of 15℃ increases the capacity of this machine by 25% (up to 583 daN/pellet) and reduces the specific consumption of natural gas during iron ore pellet firing by 8.3% (up to 8.8 m3/t) while maintaining the quality of the main product – the strength index. The obtained results confirm the feasibility of using briquettes of all tested compositions as an artificial bottom bed in horizontal-grate machines, demonstrating their key thermophysical advantage – heat loss reduction in the grate zone.
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 aimed to improve the efficiency of free cutting of metals by maximizing tool performance. This was achieved through the selection of cutting parameters based on the safety factor of tools. This work employed the finite element method with a Johnson–Cook constitutive model and an Arbitrary Lagrangian–Eulerian mesh adaptation algorithm to simulate the cutting process and reveal the stress distribution in the tool. The tool material was cemented carbide VK8, while the workpieces were steel 45, aluminum alloy 6061-T6, and titanium alloy Ti-6Al-4V. Model adequacy was confirmed by the agreement between the calculated tensile–compressive stress distributions in the tool and the isochromatic lines observed during cutting of lead with an epoxy resin tool. The study established the influence of cutting regimes, workpiece mechanical properties, and tool edge geometry on tool strength. An increase in the cutting depth from 0.2 to 1.4 mm led to a linear increase in the maximum principal stress σ1макс by a factor of 2.05, thereby reducing tool tooth strength. At a depth of 1.4 mm, σ1макс reached 780 MPa, ree-sulting in tool failure. The influence of cutting speed was shown to follow an exponential relationship. An increase in the rake angle reduced tool strength; for instance, during machining with a rake angle of 20° (σ1макс = 760 МПа), the tool failed to maintain its cutting capacity. The safety factor of the tool when machining aluminum alloy 6061-T6 was found to be 3.1 times greater than during free cutting of steel 45. The computational model and analysis of the relationship between tool strength and technological factors enabled the development of a methodology for assigning free‑cutting regimes that incorporate the safety factor of a tool.
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/dm 3 , the limiting substrate is sulfate, whereas at sulfate concentrations of 0.5–1.0 g/dm 3 and ethanol concentrations of 0.1–0.3 g/dm 3 , 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/dm 3 , 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/dm 3 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.
This study examines the effects of scanning mesh resolution on the measurement accuracy and duration for parts with double curvature. The research employed a standard aircraft component, referred to as a hatch base. This component features a double curvature that conforms to the external contours of an airplane. Measurements were carried out using a portable Scantech KSCAN Magic scanner, which captures part geometry without a fixed datum using positional markers. This scanner has a linear accuracy of 0.020 mm, repeatability of 0.010 mm, volumetric accuracy of 0.015 mm + 0.030 mm/m, and resolution of 0.010 mm. Geometric inspection was performed on the external and internal surfaces of the part. The analysis involved a curve constructed along the part surface and specific datum features, namely, hole centers. For both the reference model and scanned data, the intersection points of each hole axis with the part surface were determined to construct these curves. The results demonstrate that an increase in resolution from 0.1 mm to 0.025 mm significantly extends the scanning time, thereby reducing the geometric inspection throughput by nearly a factor of four, without a corresponding improvement in accuracy. To enhance the measurement accuracy of critical features, such as holes or complex geometry zones, it is recommended to apply a combined inspection method involving scanning with locally increased resolution on concave and critical surfaces. The study established that a mesh resolution of 0.1 mm represents the most rational choice for real-world production environments, as it provides acceptable accuracy with minimal time investment. The implementation of such optimized scanning strategies can reduce the duration of quality control operations while maintaining the required quality standards for the manufactured parts.
This paper considers a stochastic modification of the Frank-Kamenetskiy problem of exothermic reaction dynamics in a plane-parallel layer with random temperature fluctuations at the outer boundary as a means of modeling the behavior of chemical reactors when operating under uncontrolled environment impacts. Unlike deterministic formulations, such approaches take into account the possibility of a thermal explosion whose probability depends on the noise intensity. Based on random process theory, the conditions for achieving ignition in the quasi-stationary approximation (i.e., when the thermal relaxation rate is much higher than the rate of temperature change) are estimated. The possibility of using such a formulation to obtain an approximate relationship between the parameters of the noise and the dynamic characteristics of ignition (expected thermal explosion time) is demonstrated. The equation of non-stationary heat transfer in the reacting medium is solved numerically for a large number of random temperature trajectories at the boundary of the region of interest using a scheme combining explicit approximation of the nonlinear source with implicit approximation of the temperature field. By comparing the two approaches, the main regularities of non-stationary development of a thermal explosion in a stochastic environment can be approximated with good accuracy. Such a comparison relies on dependencies obtained when solving the quasi-stationary problem, taking into account a small correction for the critical temperature (marking the stability boundary for the stationary problem). Distributions of ignition characteristics (ignition temperature, maximum ambient temperature, and ignition time) and their dependence on input parameters (reactivity and noise intensity) are discussed.
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.
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.
The study was aimed at developing digital models that would provide a means to accurately determine the operating parameters of electrical grids connected to traction substations in the event of complex faults. To this end, an approach was used based on a multiphase phase-coordinate representation of elements comprising the electric power system; this approach was implemented using the Fazonord AC DC software. The following types of complex faults were considered: downed power line; double line-to-ground fault at different points of the power line connected to a transformer with an isolated neutral point; two simultaneous short circuits in the grid. The modeling confirmed the need to factor in the traction network when determining operating parameters in the event of complex faults. For comparison, similar calculations were performed for the case of its disconnection. For a downed power line, the difference between the calculation results obtained with the traction network taken into account and for the case of its disconnection amounted to 11%. In the case of a double line-to-ground fault, the difference in power line currents reached 13%. For simultaneous short circuits in the grid with an isolated neutral point, the corresponding parameter was equal to 22%. Digital models of electric power systems were developed; these models enable the correct determination of operating parameters in the event of complex faults, taking the traction network into account. Their use in the design and operation of high-voltage electrical grids will enable the accurate setting of relay protection and automation devices, which, in turn, can reduce accident damage and power outage time for electricity consumers.
The study aimed to examine a technology for machining holes with an automatic drilling machine during the assembly of a large hybrid structure (polymer composite material + metal) with the use of modular equipment. In order to analyze the process of hole machining in large structures during their assembly, a wing box model measuring 17,765x3050x438 mm was assembled to simulate a civil aircraft wing box – a test wing box. The used modular equipment provides a geometric position accuracy of 0.5 mm in hole machining. In order to machine holes using an automatic drilling machine, a hole machining map was created. This map details key hole parameters such as hole diameter, hole accuracy, hole center coordinates, and hole axis direction, as well as material layers. To align the automatic drilling machine with a large structure, the map of holes to be machined should be divided into areas (in the case of long parts, into subareas). It was found that the technology for machining holes with numerically controlled automatic drilling machines using a combination tool allows holes to be machined in large hybrid structures to their final diameter in one or two passes, ensuring a geometric position accuracy of 0.5 mm. The study of hole machining in large structures revealed that in order to achieve a geometric position accuracy of 0.5 mm in automatic hole machining, long parts should be divided into subsections of no longer than 1 m. The overall length of the reference zone for the automatic drilling machine was determined. The obtained results can be used to optimize hole machining in large structures in aviation, shipbuilding, and other industries.
