Home – Home – Jornals – Thermophysics and Aeromechanics 2025 number 4

This special issue of the journal, dedicated to the memory of Academician Nikolai Leontievich Dobretsov, features articles reflecting the development of his research and ideas in areas within his scientific interests. The diversity of N.L. Dobretsov's scientific interests determined the broad range of topics covered in the articles presented. This range encompasses tectonics, deep geodynamics, the interaction of plate tectonics and plumes, metamorphism, including ultrahigh-pressure metamorphism in subduction zones, structural patterns of geomagnetic and gravitational fields and their relationship to plume magmatism, and unique mineral deposits.

Natural diamonds are polygenic and form over a very wide range of P-T parameters, crystallization medium compositions, and oxygen fugacity. As has been demonstrated in recent years, the genesis of some diamonds is directly related to their crystallization from metal-carbon melts. Since natural mineral-forming processes are highly likely to involve various components characteristic of mantle environments, it is relevant to analyze the results of experiments on the influence of fluids of the C-O-H-N-S system on the crystallization features and indicator properties of diamond. The experimental data presented in this review demonstrate that increasing the concentration of fluid components (N, O, S, H₂O, CH₄-H₂) at constant P-T parameters inhibits diamond crystallization processes in metal-carbon melts and ultimately leads to the formation of metastable graphite instead of diamond. Increasing P and T reduces the inhibitory effect of impurities and expands the diamond crystallization region. The main patterns of specific changes in the morphology, defect-impurity composition, and internal structure of diamond crystals are revealed, depending on the type and concentration of impurity in the crystallization medium. It is demonstrated that impurity-induced specific changes in diamond morphology and trends in nitrogen concentration in diamond are indicative of crystallization conditions and provide a basis for reconstructing diamond formation processes under reducing conditions in the metal-bearing mantle.

The study of the composition and crystallization conditions of olivine in kimberlites is of great importance for understanding the processes of their petrogenesis and predicting diamond potential. The aim of this study is to investigate the origin of the least studied generation of this mineral – late high-magnesium olivine. The material for the study consisted of samples of unaltered kimberlites from the Udachnaya-East pipe, where all generations of olivine are preserved. Results from scanning electron microscopy and microprobe analysis showed that high-Mg olivine exhibits the following variations in chemical composition: Mg# (Mg/(Mg+Fe²⁺)×100, mol. %) 93.3-98.7, 0.01-0.05 wt. % NiO, 0.12-1.88 wt. % CaO, 0.18-0.94 wt. % MnO. This olivine forms a paragenetic association with late magmatic minerals of kimberlites: magnetite, perovskite, apatite, monticellite, sodalite, phlogopite, djerfisherite, and calcite. The following forms of high-Mg olivine were identified: individual grains (the first finding in kimberlites), rinds, daughter phases within melt inclusions, phases in fractures earlier olivine generations, and in the interstices of microxenoliths. It was found that its crystallization occurred from alkaline-carbonate-chloride melts. The temperatures and oxygen fugacity values of the crystallization of high-Mg olivine can be estimated semi-quantitatively at 670-780 °C and +3.6 - +7.4 log. units ΔQFM.. The obtained data indicate that such olivine crystallized from evolved kimberlitic melts, which contradicts previously proposed models suggesting the formation of this olivine from fluids or during the serpentinization of kimberlites.

The results of direct numerical simulation (DNS) of the influence of a horizontal surface temperature gradient on the dynamics of a thermal convective flux are presented. A series of simulations was performed at moderate Rayleigh numbers (10⁵ - 10⁸). The computational domain was rectangular and its two horizontal walls had a specified average temperature difference, leading to the formation of a free-convective flow. The temperature on the lower wall was nonuniformly distributed along one of the horizontal axes. Convective cells formed due to the vertical density gradient were subject to a weak horizontal temperature gradient, which led to their deformation and transfer toward the central axis of the computational domain. As a result, intense coherent horizontal oscillations in the position of the central upflow at a low frequency were observed. This frequency depended weakly on the Rayleigh number, and the oscillation amplitude increased with its increase. This low-frequency oscillation effect is not evident in two-dimensional modeling and arises from the interaction of adjacent three-dimensional convective cells entering the central upflow. The authors propose an asymptotic estimate for the period of these oscillations. It is shown that the oscillations do not disappear with increasing Rayleigh number, suggesting their influence on heat and mass transfer in natural flows.

The main goal of the study is an experimental investigation of the mechanism of weakly nonlinear interaction of low-amplitude unsteady modes of crossflow instability in the boundary layer on a 35-degree swept wing with steady vortices of crossflow instability. The dominating factor in the flow under study is crossflow instability, while the Tollmien-Schlichting instability is suppressed by the favorable pressure gradient. High-amplitude steady distur-bances (up to 20% at the end of the measurement region) are excited by a surface roughness element. Controlled low-amplitude unsteady disturbances are generated in the boundary layer by a source of disturbances located upstream from the roughness element. Their amplitude in the main interaction region does not exceed 1%. The source excites quasi-two-dimensional (spanwise-uniform) waves at low frequencies corresponding to the primary crossflow instability region. The results of hot-wire measurements show that the characteristics of the mean flow, as well as of steady and unsteady disturbances are independent of the disturbance amplitude. However, the evolution of unsteady disturbances is strongly affected by the presence of vortices. The excited quasi-two-dimensional instability waves rapidly decay in the downstream direction, while the forming and growing (in a certain range of transverse wave numbers) steady vortices transform two-dimensional waves to essentially three-dimensional waves with the transverse wave spectrum corresponding to the most rapidly growing crossflow instability modes. This transformation does not occur locally, in the near field of the surface roughness, but is distributed in the streamwise direction. The amplitudes of steady disturbances grow almost exponentially, with the growth rate depending on the transverse wave number in a manner typical for crossflow instability modes. The growth of the amplitudes of unsteady modes exhibits a more complicated, sometimes nonmonotonic character owing to their nonlinear interaction. It is found that the amplitudes of unsteady disturbances of all frequencies in the plane normal to the flow and the wall are strongly localized in regions of high values of the mean flow velocity gradient over the model span. An essentially three-dimensional physical mechanism of weakly nonlinear transformation of quasi-two-dimensional wave disturbances to three-dimensional waves by high-amplitude steady instability vortices is proposed, which is similar to the lift-up effect used previously to explain the growth of streaky structures in two-dimensional boundary layers.

The experimental results on the swirling flow structure behind a vane swirler in a smooth tube at an axial flow Reynolds number varying within Re = 240 - 1640 are presented. A change in the degree of flow swirl along the tube length is analyzed as a function of the Reynolds number. The main patterns in the evolution of the profiles of longitudinal and circumferential velocity components and the distribution of the mean square pulsations of the longitudinal velocity component with increasing distance from the swirler are determined. It is shown that at Re = 1640, flow instability develops in the tube, which is a consequence of the formation of a reverse flow region on the tube axis in the immediate vicinity of the swirler. The influence of flow swirl on the appearance of signs of a local laminar-tur-bulent transition in vicinity of the tube axis and near its wall is analyzed (a sharp increase in the mean square velocity pulsations with increasing Reynolds number and the appearance of intermittency in the flow velocity oscillograms). It has been established that in the near-wall region, local turbulence of the flow is caused by the interaction between the swirler vane wakes and the wall.

The unfluence of the mass flow rate ratio of the input flows of distilled water on the efficiency of liquid mixing within a T-shaped microchannel was studied using numerical and experimental modeling. The model was verified by comparing the calculated results with experimental data. High-resolution digital tracer visualization was used to measure the flow velocity characteristics. Computer modeling was used to obtain and describe the flow structure and the dynamics of flow pattern changes at unequal mass flow rates. The possibility of increasing the efficiency of liquid mixing by varying the mass flow rate ratio is demonstrated.

Methodical issues associated with investigations of the laminar-turbulent transition in subsonic boundary layers with the use of video filming in the infrared range are considered. A method of estimating the wall friction based on the analysis of the temperature behavior of the heated model surface is proposed. An improved method of finding the lines of transition beginning and end is proposed.

The paper considers a possibility of controlling the structure of a fluoropolymer coating by diluting the precursor gas with an inert gas during synthesis by the Hot Wire Chemical Vapor Deposition method (Hot Wire CVD). Dilution of the precursor gas significantly affects the morphology of the formed coating and alters the coating wettability and the growth rate.

The dynamics of a slug flow in immiscible liquids remains incompletely understood due to the complex effects of channel geometry and the properties of the working fluids. The presence of surfactants in the system further complicates the problem. This work deals with the effect of an water solution of Tween 20 surfactant on the dynamics of a slug flow in a curved microchannel. Situations with surfactant concentrations below and above the critical concentration of micelle formation are considered. Regime maps are plotted, and three regimes of water phase dispersion are identified. It is shown that increasing the surfactant concentration leads to stabilization of slug interfaces in straight sections, while the probability of slug disintegration in curved sections increases due to reduced interfacial tension and intense mixing of the surfactant within the slugs. The decisive influence of the surfactant concentration relative to the critical concentration of micelle formation on the dynamics of microdroplet detachment processes in straight and curved sections of the channel is revealed.

The paper describes experimental results on the action of weak shock waves on the development of controlled disturbances in a supersonic boundary layer on a flat plate at the Mach number of 2.0, which are obtained by measurements performed by a constant-temperature hot-wire anemometer. A two-dimensional surface roughness element 150×7×0.13 mm in size, mounted on the side wall of the test section of the T-325 wind tunnel based at ITAM SB RAS, generated a pair of weak shock waves in the free stream. Controlled disturbances are inserted into the flow by a high-frequency glow discharge in a chamber inside the model. Owing to interaction of the pair of weak shock waves with the leading edge of the flat plate, a steady wake is formed in the boundary layer, where the evolution of controlled disturbances occurs. A weakly nonlinear regime of evolution of controlled disturbances is studied under the conditions of a homogeneous boundary layer on the flat plate and a boundary layer distorted by the wake. The wave characteristics of disturbances are analyzed. A new method of estimating the dispersion relation is proposed. The experimental data are compared with the numerical results. Numerical simulations are performed based on the liner stability theory under the conditions of a homogeneous boundary layer.

The authors have developed the method of adapting blast designs and patterns to structurally complex mineral deposits on the basis of synthesis of theory of zonal rock fracture and theory of blast impulse. This article describes the sequence of practical adjustment of blast designs and patterns with regard to geological conditions. The method includes monitoring of rock mass, analysis of data, selection of techniques and their efficiency evaluation using an integral criterion embracing safety of blasting, quality of fragmentation and economic indicators. The authors propose classification of the techniques and their combinations, capable of reduction of seismic impact, flyrock and expenditure. Particular attention is given to the blast impulse peak pressure and duration control. The results enable adapting blast designs and patterns to nonuniform rock mass, and enhancing safety and efficiency of mining operations. The research prospects are connected with artificial intelligence technologies and digital data bases for forecasting blasting impact.

Coarse oversize fragments generated by blasting complicate loading and haulage of rocks, and this leads to the decreased productivity of labor and to the increased cost of mining. This article analyzes specific energy of roller-bit drilling as a drillability criterion as a case of the Koktaszhal deposit in Kazakhstan. Two electric drill rigs DML-1200 were additionally equipped with energy consumption recording facilities. The correlations between the powder factor, explosive fracture energy and ultimate compression strength of rocks, and between the average fragment and specific drilling energy are determined. For the blast design practice in open pit mining, it is substantiated to pass from mechanical specific energy of drilling to specific energy of explosive fracture and, further, to prediction of an average fragment of blasted rock. The experimental blasting operations at the Koktaszhal open pit mine show positive results which open prospects for the further research.

The authors discuss a variant of shrinkage stoping in mining steeply-dipping ore bodies of limited thickness. In the context of the majority of operating mines in Russia, numerical stress-strain modeling of gravitational stress state of an ore-rock mass is performed. The stress patterns in structural elements of the discussed geotechnology are determined as function of thickness and occurrence of the ore body, and subject to the technology implementation. It is found that rock mass quality greatly influences stability of different-purpose mine openings and ore pillars. The safe mining system parameters are determined and standardized for the typical geological and geomechanical conditions of the test deposits.

The geomechanical substantiation is provided for the technology of sublevel caving in mining close-spaced ore bodies with dirt parting of a varying thickness. The parametric model of sublevel caving includes the case of maximum advance of stoping front on sublevels. The computational patterns of maximum principal and shear stresses, as well as their concentration and relaxation in the main constituents of the mining system are obtained. The rock mass areas around various exposures, including preparatory and development openings, which are most susceptible to failure in case of complex tectonics, are identified. The analysis of different depths of driving fringe drifts and a decline in hanging wall of an ore body in depth of mining proves consistency of the adopted engineering solutions and safety of mining in varying geological and geotechnical conditions for the whole period of operation. The order and sequence of extraction of close-spaced ore bodies are validated to ensure caving of enclosing rocks toward mined-out void at the proper ground control. The parameters of underhand sublevel stoping, such that ensure safety and efficiency of mineral mining, are determined.

The authors obtained an analytical time law of freeze pipe temperature which ensures the constant thickness of a frozen wall at the stage of passive freezing. The time law is established using the equation of balance of heat flows at the phase interface. The correctness of the mathematical expression is proved by numerical modeling of freezing of a siltstone layer typical of conditions of shaft sinking in potash mines. The results are applicable in planning energy-efficient operating regimes of freeze pipes during passive freezing.

Scale modeling is essential in studying underground mine fires since large-scale experimentation is impossible because of unsafety while numerical modeling has limited accuracy and features high computational input. This article addresses an understudied issue of selection and substantiation of similarity criteria for the analysis of mine fires. The review of the current methods available for scale modeling of heat convection of air under high temperature differences on the basis of investigations of fires in buildings and tunnels displays their insufficient conformity with mine conditions owing to difference in geometry and in air flow behavior. The dimensional analysis reveals that similarity in laboratory modeling is achievable through observance of equality of the dimensionless Richardson, Euler and Froude numbers. The authors describe an emergency scenario, with switching-off of fans, when the only defining criterion is the Grashof number. The proposed approach makes it possible to design low-temperature lab-scale experiments to model air flow along mine openings during fire.

The analysis of organic collector adhesion to the surface of diamonds and kimberlite minerals in an aqueous medium determined the main characteristics of physical and chemical properties of the mineral-water-collector interfaces and the collector adhesion patterns at variation of the type and concentration of different class control reagents. It is found that control reagents reduce differently adhesion of an apolar collector to diamonds and floatable kimberlite minerals. This allows expecting a positive effect of the increased selective attachment of the collector to minerals being separated. The criterion of the collector attachment selectivity is proposed to be the ratio of adhesion energies of an apolar collector at diamond, talk and phlogopite. The test results demonstrated a tight correlation between the coating of diamond and kimberlite surfaces with an organic collector and the collector adhesion to diamond and phlogopite. The applicability of the proposed criterion for the selection of the control reagents for selectivity of attachment of apolar collectors in weakly mineralized recycled water is substantiated. The visiometric process analysis of attachment of a luminophore-bearing apolar collector at minerals of a diamond-kimberlite mix shows that the use of sodium hexametaphosphate and oxyethylene diphosphonic acid reduces amount of an organic collector on the surface of kimberlite and enhances stability of the collector adsorption on the surface of diamonds.

The influence of changeability of dry magnetic separation feed characteristics on the separation process efficiency is considered at the fixed operation modes of equipment is examined as a case-study of the Olenegorsk deposit ore. It is found that the major effect is exerted by the content of total iron: its increase in the feed is independent of the maximum linear size in the size grade and of the size modulus, and is accompanied with Fe_tot content growth in the magnetic fraction. The results of dry magnetic separation of a narrow particle size range prove that for - 80 + 2 mm, the correlation of Fe_tot content of the magnetic fraction (at В = 0.16 T) has a high approximation coefficient of 0.9461, which is reflective of a weak contribution of the feed size to separation efficiency. Regarding influence exerted on separation performance by the size modulus, it is found that the absence of ore pretreatment by sifting ensures reduction in loss of Fe_tot with the nonmagnetic fraction in 70% of cases.

Hydrofluoric acid (HF) proved to be the most efficient reagent for the flotation separation of feldspar minerals from quartz. This research aimed to improve the quality of Wadi Zirib feldspar ore for industrial applications. Furthermore, the effect of HF on the feldspar separation process was studied. Laboratory scale flotation experiments were conducted with quaternary ammonium salt solution as a cationic collector for feldspar minerals. HF was used as a surface modifier for the activation of feldspar minerals and quartz depression, as well. The optimum concentration of HF varied between 1800-2000 g/ton. A 1800 g/ton HF dosage gave a feldspar assay of 89.81% with 44.20% recovery. A 2000 g/ton HF dosage gave a feldspar assay of 85.05% with a 67.78% recovery. Overall, a suitable quality feldspar concentrate was obtained with a mass recovery of 52.11%, having a composition of 69.04% SiO₂, K₂O & Na₂O combined more than 11%, 17.34% Al₂O₃ and about 0.4% Fe₂O₃. This product could fulfill the requirements of glass, porcelain, ceramic, vitreous tiles and semi-vitreous tiles industries.

The aim of this paper is to present an approach to predict the performance of tunnel boring machines (TBM) in Iranian water conveyance tunneling projects using an artificial neural network (ANN) approach. With this respect, a database, including field data and machine parameters, was primarily compiled from the excavation of top five Iranian water conveyance tunnels. The database was then analyzed through ANN to yield an optimum predictive model for the rate of penetration. The results show that there is a close equation between actual (measured) data and predicted data with correlation coefficient of 0.94, and the values of coefficient of determination and root mean square error obtained in this research are equal to 0.90 and 1.2, respectively.

The authors analyzed water quality in manmade water bodies at the used and operating tungsten, molybdenum and complex ore mines in eastern and southwestern Transbaikal. The chemical analysis of water used atomic absorption spectrometry and inductively coupled plasma mass spectrometry. The standardized cumulative pollution index is calculated. It is found that the level of the environmental hazard of the test water bodies is abnormally high, which points at the environmental emergency and ecological catastrophe. The greatest threat to surface and underground water is made by the manmade water bodies at the Pervomaiskoe, Sherlova Gora, Bukuka and Bom-Gorkhon deposits. The recreational utilization of such water by people is unhealthy and inadmissible.

The applicability of InSAR technique in stress-strain assessment and alteration prediction in rock mass is illustrated as a case-study of the Upper Kama Salt Deposit. The object of research is Berezniki Mine-1 flooded in 2006 after an accidental freshwater inrush. Because of high solubility of salt rocks, velocity of ground subsidence is yet very high within the mine field. Subsidence monitoring is carried out here using benchmark surveying along existing profile lines and TerraSAR-X-base radar survey with a period of 11 days. The InSAR data were interpreted using 3D mathematical modeling of deformation process in undermined rock mass. The computational model displayed a whole set of geological and geotechnical conditions, and a group of factors associated with the freshwater inrush. The numerical calculations used the semi-analytical finite element method. Within the framework of the developed modification of the method for variable-module deformations, InSAR data were a part of the parametric content of the geomechanical model determining deformation of undermined rock mass in time.

The article presents the laboratory studies on cyclic treatment of fine-pore and banded bituminous coal with liquid nitrogen. Permeability of coal cores was determined in the mode of nonstationary flow, and porosity was assessed using the methods of nuclear magnetic resonance and optical microscopy. The procedures and design solutions used in the experiments are described. The change in permeability of coal along and across its banding is examined in the conditions of hydrostatic compression. It is found that permeability of test coal grows by one-two orders of magnitude along its banding and by two-three orders of magnitude across the banding. Anisotropy of permeability decreases. This effect intensifies with the increasing hydrostatic compression and water saturation of coal. It is shown that the effect of the liquid nitrogen treatment is mostly associated with different-scale crack growth in coal at a minor change in open porosity.

The authors have theoretically substantiated and experimentally tested the method of determining permeability of discontinuities as function of stresses in rock masses and reservoirs of quasi-regular layered deformation structure when fluid flows across the strike of the discontinuities. A linear model produces an analytical solution of a problem on stationary fluid flow in media with discontinuities, which allows finding the permeability kJ of the latter by the recorded flow rate. The tests are carried out using samples of sandstone blocks and a dependence is obtained for the interblock space opening h and the normal stress s. A lab-scale testing plant is proposed for the permeability tests with the coincident directions of compression and fluid flow. As a result of the experiments on gas flow in block samples subjected to normal loading, an empirical dependence is found for the specific discontinuity permeability kJ/h and the stress s, which can be approximated by a two-parameter fractional rational function.

Fine particles, when flowing with fluids in the Earth’s crust, can settle on surfaces of pores and fractures, and form colloid barriers which drastically reduce permeability of jointed media. When seismic waves travel in fault zones, which have greatly different stiffness as compared with enclosing rocks, Biot slow-wave diffusion originates, which can cause destruction of the colloid barriers, growth of permeability, redistribution of pore pressure and change in the stress-strain condition of a fault. This article describes the studies into conditions when regular seismic impacts induced by massive blasting can lead to a drastic change in the permeability in the fault zones.

Three calculation models are developed for estimating the cross size of a main crack formed by a blasthole in perimeter blasting: a numerical model for calculating the equilibrium shapes and sizes of a flat crack in 2D elasticity, and two analytical models for estimating the cross size of a flat crack in two-dimensional and axially symmetric problems. The models are used to calculate the sizes of main cracks formed in granite in blasting of ammonite charges of different density. The comparison of the 3D numerical calculations with the 2D and axially symmetric modeling results has allowed finding the conditions when the analytical modeling produces such precision that makes the analytical models applicable in design of perimeter blast patterns.

The article presents the results of the physical modeling of hydraulic fracturing in coarse cement cubes subjected to triaxial loading. The laboratory-scale plant, hardware and software tools, as well as the methods and engineering solutions applied during the experiments are described. The pressures and the trajectories of fractures which intersect the earlier created crack, including propped fractures and fractures filled with an isolating polymer, are investigated. The possibility to control hydraulic fracturing by deformation of a close-spaced hollow cavity which models an underground opening is demonstrated experimentally.

The article reports the experimental data on the effect of sodium laureth sulfate and neonol AF 9-12 on the fracture energy of dolomite at the Internatsionalnaya pipe and limestone at the Mokhsogollokh open pit at temperatures in a range of + 20 … - 30 °C. In the positive temperature range, the fracture energy of dolomite treated with surfactants, lowers by 28% on the average. Under negative temperatures, an increase is observed in the fracture energy of dolomite samples saturated with surfactant solutions. At the temperatures below - 10 °С, the fracture energy of dolomite exceeds its fracture energy at the positive temperatures by 2.3-3.1 times. The indicators of fracture of dolomite samples saturated with surfactants totally agree with the fracture indicators of water-saturated samples. The fracture energy of limestone treated with surfactant solutions decreases by 5-10% under positive temperatures and increases by 8-15% under negative temperatures as compared with the fracture energy of air-dried samples.

Rockburst disaster is a kind of typical dynamic disaster phenomenon. In this work, the risk level of the rockburst disaster was predicted based on the convolutional neural networks and long short-term memory (CNN-LSTM), and particle swarm optimization and general regression neural network (PSO-GRNN) models. A CNN-LSTM deep learning model based on rockburst chaotic time series was proposed to predict the characteristic variables of rockburst state, with a method to quantitatively distinguish and predict the risk level of the rockburst disaster in the future, and thus the dynamic prediction of the rockburst activity was realized. As an example, the microseismic monitoring variables (i.e., indexes of the daily cumulative microseismic energies and daily maximum microseismic energy, angular frequency and concave-convex radius) and electromagnetic radiation signals (i.e., indexes of the daily average amplitude and daily maximum pulse) were used to predict the rockburst. The CNN-LSTM and PSO-GRNN models were confirmed to be the most suitable to predict the risk level of the rockburst. This work provides an important basis for timely mastering the future state of rockburst activities.

The article focuses on placer gold mining as an important factor of social and economic development in the Far Eastern Arctic Zone of Russia. The structure of unmined placer reserves and man-made placers in the permafrost area is examined as these objects are an important source of minerals in the region. The authors point at the expediency of stage-wise evaluation of geological and geotechnical potential of the unmined and man-made placer reserves to develop a resource-saving technology for mining identified clusters. The authors also discuss the approaches applicable in additional exploration and production management at such placers to transfer them to a category of the investment-attractive mineral sources. The database of the mining-altered areas in the Ust-Yana district is collected, the maps of such areas are drawn, and the mining conditions at some of the specified placers are discussed.

The article reports testing results of a hydraulic hammering tool with independently controllable energy and frequency of blows. The blow frequency is adjustable via the fluid flow rate, and the blow energy-via the pressure at the onset of a working cycle. The hydraulic hammering tool and its performance measurement procedures are described, including the pre-blow velocity-using an original piston position sensor composed of two pairs of light-emitting and photo diodes arranged in front of the collision plane of the piston and the breaking tool. The approach allows changing the blow frequency of the tool by 4 times, its blow energy by 5 times and the impact power by 20 times. The authors present the experimental oscillograms of the dynamic characteristics of working cycles and the experimental curves of the integral output characteristics, cycle start pressure, and fluid flow rate. An experimental-and-analytical estimation method is developed for the pre-blow piston velocity using the theorem of a kinetic energy of a material point.

The article offers a substantiation for the simulation model of a pneumatic hammering tool with an elastic element used as an air distributor. The working cycle of the pneumatic hammering tool with the elastic valve is modeled as the fluid-solid interaction. The comparison of these results with the one-dimensional simulation shows that the proposed model is preferable in this multi-physical problem. The parameters of the elastic valve to perform the function of sealing the back-stroke chamber to ensure operation of the hammering tool are determined. The time dependences of the basic physical parameters of air in the hammering tool within its working cycle, as well as the piston travels and velocities are found. The prospects of the proposed method in the design and analysis of hammering machines are assessed.

The authors discuss application conditions of the casing-while-drilling method and present a layout of a compound rock-breaking tool. An advantage of such tool is the coupling of the central and annular bits by spring jaws, owing to which the inner passage section of a casing pipe experiences no reduction. Computer modeling assisted in the strength analysis of the components of the tool during transfer of the impact load from the central to annular bit via the spring jaws. The operational reliability of such components is evaluated, and a method is proposed for enhancing their strength by way of improving quality of their surface finish and optimizing geometry of the surface areas exposed to the highest load. On the basis of the implemented research, a developmental prototype of the compound rock-breaking tool is designed and manufactured.

2D numerical modeling and physical simulation are carried out for a flow of a granular material in an elbow of a pipeline with a view to reducing erosion wear owing to a novel design solution. Protective plate ribs are installed on the inner surface of the elbow at an angle to lines tangent to the fixing points of the ribs. It is found that the optimal choice of the size, number and arrangement of the ribs can reduce the wear of the elbow in the areas of its maximal loading.

Spotlight of the analysis is on bending vibrations of axial fan rotor of main ventilation fans in mines. Their feature is two impellers that act interchangeably as directing and guide vanes, and one impeller only rotates in an active mode. Such design allows attaining high capacity in the reverse mode which preserves 90-95% of the straight flow mode. The presence of two impellers in the rotor influences the frequency behavior of the fan, which can vary in a wide range depending on some parameters that govern the mass and geometry of the rotor. The article describes the analysis of the rotor frequency characteristics obtained from solving a system of differential equations of bend. The curves of free bending vibrations of main shafts and masses of impellers are plotted for different values of added mass of transmission shaft and for different lengths of the main shaft areas. It is shown that in the test range of the main shaft lengths, impeller masses and added masses of the transmission shaft, the operation of rotors of fans with two impellers is safe and reliable in terms of vibrations.

A promising approach to air dedusting in tunnel ventilation in subways is inertia filters which have low air drag and can efficiently catch coarse and medium-size dust particles without addition of sophisticated equipment as dust-laden air flow through the filters is assisted by piston effect in train tunnels. An approach to the numerical modeling of a multi-phase flow in an inertia filter is substantiated. The validation of the approach is proved by the qualitative and quantitative coincidence of the numerical modeling results and lab-scale inertia filter test data. The numerical research findings helped determine the influence exerted by air velocity, dust size and filter surface characteristics on the dust catching efficiency. The design of the filter to be installed at an air connection in a single-track subway tunnel is developed.

The article describes a pilot plant generator of high-voltage nanosecond pulses for energy treatment of ore at the pretreatment stage at the capacity of up to 1 t/h of mineral raw materials. The mineralogical and chemical analyses of ferruginous quartzite are carried out. The distribution of aggregates per size grades is described, and the lab-scale and larger scale bench testing data of the equipment are reported. The experiments have proved efficiency of preliminary treatment of the first and second stage milling sands by strong electromagnetic pulses for the ferruginous quartzite softening and for the magnetic separation intensification. The interconnection is found between the impregnation of ore and rock-forming minerals, efficiency of disintegration of mineral aggregates, their release and the treatment dose. The main effect of treatment of ferruginous quartzite by strong electromagnetic pulses, with the increase in the yield of the final size grade of - 45 µm by 1.4-4.8% at the increased recovery of iron in magnetic concentrate by 2.65%, is conditioned by the decrease in the number of ore and barren rock aggregates and by the increase in the content of free magnetite grains in the size grade of - 0.16 + 0.04 mm after milling by 14.2%.

The authors analyze extra recoverability of zinc from complex ore flotation tailings. The material constitution of the manmade mineral resource is studied and the expediency of its hydrometallurgical processing is substantiated. The influence of the reagent regime on the efficiency of sulfuric-acid leaching of zinc is discussed. The sulfuric acid concentration is optimized, and the efficiency of electric processing of the leaching solution is determined. The efficiency of different oxidizers during leaching is evaluated. Ozonizing of leaching solutions and introduction of sodium chloride in them have a beneficial effect on zinc recovery.

The full-scale testing results of fixed-site recorders of electromagnetic radiation preceding failure in rocks in a mine after installation of the recorders on mobile mining equipment are presented. The threshold values of the recorded signals, coincident with failure of roof areas in mine openings are found, and the frequencies of electromagnetic noise at the totally de-energized electric equipment of working faces, and at the dead and live production equipment are estimated. The recommendations on the improvement of the recorder design and recorded data processing are given.