Home – Home – Jornals – Journal of Applied Mechanics and Technical Physics 2018 number 3

This is a synopsis of available data on the crustal structure and properties of thirteen Archean cratons of Gondwanaland (the cratons of Africa, Australia, Antarctica, South America, and the Indian subcontinent). The data include estimates of surface area, rock age and lithology, Moho depth, thickness of lithosphere and sediments, as well as elevations, all summarized in a table. The cratons differ in size from 0.05 × 106 km2 (Napier craton) to 4 × 106 km2 (Congo craton) and span almost the entire Archean period from 3.8 to 2.5 Ga. Sediments are mostly thin, though reach 7 km in the Congo and West African cratons. Elevations above sea level are from 0 to 2 km; some relatively highland cratons (Kaapvaal, Zimbabwe, and Tanzanian) rise to more than 1 km. On the basis of regional seismic data, the Moho map for cratons has been improved. The Moho diagrams for each craton are constructed. The analysis of the available new data shows that the average Moho depth varies from 33 to 44 km: Pilbara (33 km), Grunehogna (35 km), Sгo Francisco (36 km), Yilgarn (37 km), Dharwar (38 km), Tanzanian (39 km), Zimbabwe (39 km), Kaapvaal (40 km), Gawler (40 km), Napier (40 km), West Africa (40 km), Congo (42 km), and Amazon (44 km) cratons. The Moho depth within the cratons is less uniform than it was assumed before: from 28 to 52 km. The new results differ significantly from the earlier inference of a relatively flat Moho geometry beneath Archean cratons. According to the new data, early and middle Archean undeformed crust is characterized by a shallow Moho depth (28-38 km), while late Archean or deformed crust may be as thick as 52 km.

We consider geochemical features of mafic magmatism manifested during the evolution of a complex nappe-folded structure in Western Sangilen, resulted from the Cambrian-Ordovician collisional tectogenesis. There are abundant ultramafic-mafic and mafic associations of different types in this region: layered low-Ti low-alkali ultramafic-mafic intrusions, high-Ti medium-alkali gabbroids, gabbro-monzodiorite intrusions, and alkali basalts. Isotope-geochronological data showed that these complexes formed over a wide time interval, from 570 to 440 Ma. At this time, the geodynamic setting in Western Sangilen changed from an island-arc one via a collision one to an intercontinental rift setting. At the early and late stages of the evolution of Western Sangilen, the geochemical features of mafites were typical of their geodynamic settings. The properties of mafites that formed synchronously with the collision are of particular interest. The studies have shown that the chemical composition of collisional mafites of Western Sangilen changed with time. They became richer in alkalies, titanium, and incompatible elements. This fact indicates a change in the type of mantle source from suprasubductional in the Cambrian to enriched deeper-level one in the Ordovician.

The Chulym and Kargat rivers flow through chains of saucer-shaped depressions, which are swamp meadows or drainage lakes. In the past, all of them were lakes short-lived in different Holocene epochs. These depressions accumulated a significant amount of the Chulym and Kargat runoff and thus influenced the water balance of Lake Chany. Our studies reconstruct the history of these depressions. A model describing their filling with sediments is proposed. The lacustrine sediments penetrated by boreholes and pits are dated by the radiocarbon method at 6.3-2.0 ka BP. The data obtained indicate the long existence of Lake Chany as a shallow water basin and rise in its level at ~2 kyr BP.

Eutrophication processes have been recorded in many world’s freshwater reservoirs, which are sources of drinking water. More and more investigations show that global warming is the main natural factor that causes eutrophication. In recent years, signs of eutrophication have also been recorded in Lake Baikal containing 20% of the world’s freshwater reserves. Therefore, we performed the first comprehensive analysis of long-term changes in climatic parameters capable to provoke negative changes in the shallow zone. The largest number of anomalies of climatic indices has been recorded in the 21st century. Moreover, the current decade has been the most favorable for the emergence of negative processes in the lake (outbreak of the mass growth of algae and aquatic vegetation, rotting of their remains at the bottom and on the shores of the lake, changes in the structure and zoning of biocoenoses, etc.). The main natural conditions favoring the emergence of negative signs are elevated temperatures of the air and lake shore water, reduced amount of precipitation, reduced inflow of river waters into Baikal and lowering of its water level, low-water season, and weakening of wind currents, water exchange processes, and, as a result, water self-purification. In the period of continuing global warming, it is necessary to study the climate effect on the processes in the shallow zone and to carry out long-term monitoring for elucidation of recent and expected changes in the ecological state of Lake Baikal and for their valid interpretation.

The first experimental measurements of the cross-correlation function (CCF) of the Earth’s seismic and electrical noise were carried out in two areas of the Minusinskoe gas condensate field in 2014 and 2015, using a VPEMPZ-M1 (Shum-6) two-channel geophysical device developed at Siberian Federal University. The Earth’s seismic noise and electrical noise in the frequency range 0.1-20 Hz were received by a geophone and an electric dipole, respectively. In both cases, a productive pool at depths of 1800-2000 m had a maximum CCF value five to seven times greater than the normal background. This phenomenon indicates the occurrence of the seismoelectric effect in passive fields.

This paper presents an analysis of the development of the current seismic state of the Kuznetsk coal basin, which is characterized by an increase in technogenic seismicity of different types under the influence of prolonged intensive mining operations. The development of technogenesis led to a significant increase in technogenic seismicity in the Kuznetsk Basin in the 1970-1980s, when the number of technogenic earthquakes began to exceed the number of natural earthquakes. Among the various types of induced seismicity, special attention is paid to strong technogenic tectonic earthquakes with a regional magnitude Mb ≥ 3 and, accordingly, a seismic energy release of more than 109 J, i.e., earthquakes of energy class K > 9. These small-focus earthquakes are often accompanied by destruction of underground mines, collapse of quarries and pits, damage to surface facilities and equipment, and other adverse effects. In this paper, such earthquakes are defined as technogenic tectonic to emphasize their dual origin: technogenic impacts and the subsequent relaxation of tectonic stresses. It is also noted that the Earth’s interior in Kuzbass initially had its own natural seismicity and a developed system of tectonic faults. Natural seismotectonic activity combined with constantly increasing scales of mining and explosive consumption has led to an increase in the number of technogenic seismic events and their intensity. A striking example of such an event was the 18 June, 2013 Bachat earthquake with a regional magnitude Mb = 5.8 and a seismic intensity of 7 in the epicentral zone. It was the world’s largest man-made earthquake induced by the mining of solid minerals. We consider the possible causes of this catastrophic earthquake and discuss the conditions favoring the formation of foci of such technogenic tectonic earthquakes resulting from changes in the geodynamic and hydrogeological conditions in the Earth’s crust under man-caused impacts. These induced changes in natural processes are accompanied by a change in the stress-strain state, resulting in the concentration of tectonic stresses at heterogeneities and in fault zones, which become sources of induced technogenic seismicity. The paper discusses the current period of the occurrence and increase in such anthropogenic seismicity in the Kuzbass region with increasing scales of coal mining and blasting. Over the last 20 years, the consumption of explosives at Kuzbass enterprises increased from 100-200 to 500-600 thousand tons per year, and, accordingly, the amounts of broken and transported rock increased from several million tons per year to a billion tons per year, which disturbed the dynamic equilibrium in the Earth’s crust and changed the existing field of tectonic stresses. Moreover, the continuously increasing consumption of explosives has also increased the technogenic impact on the crust structures. The location of the epicenters of large-scale blasts inducing seismic events with regional magnitudes Mb = 3.0-4.5 has made it possible to identify regions with the greatest technogenic impact in Kuzbass. Using the data of the ISC seismological catalog, we separated seismic events with the above magnitudes into day and night ones. Since blasting work is forbidden at night, night seismic events are referred to as technogenic tectonic earthquakes (night event criterion). The maximum magnitude of seismic events induced by blasting operations in the Kuznetsk Basin was estimated at Mb ≤ 4.4. The annual number of technogenic tectonic earthquakes with 3.0 ≤ Mb ≤ 3.4, 3.5 ≤ Mb ≤ 3.9, 4.0 ≤ Mb ≤ 4.4, and Mb ≥ 4.5 was determined based on the night event criterion. The regions of their occurrence were identified from the location of the epicenters of technogenic tectonic earthquakes.

A numerical investigation of the properties of two different ion-acoustic solitons has been performed by using analytical solutions of the Schamel equation. A new type of the analytical solution of the Schamel equation that describes soliton propagation with a negative phase velocity has been found for the first time. This new type of the solution has been applied to investigate the physical properties of two different plasmas and to understand the effect of nonextensivity and the effect of trapped electrons on ion-acoustic waves in a superthermal plasma. It is shown that the soliton amplitude and width depend on the nonextensivity parameter, superthermality of the electron distribution, and characteristic trapping parameter.

A circuit of a multicascade magnetocumulative generator based on a dynamic variation of the coupling coefficient of inductively coupled circuit is proposed. Each cascade contains two circuits including two pairs of inductively coupled coils. One pair of coils is subjected to simultaneous straining, and one of the coils in the other pair is arranged with the back-to-back connection. It is shown that the energy in the load can be gradually increased (from one cascade to another) by using additional cascades. By an example of a two-cascade system, the proposed circuit is compared to the known circuits of cascade system design based on the magnetic cumulation principle (generator with a step-up transformer and dynamic transformer). Within the framework of the model that ignores the ohmic resistance of conductors, it is demonstrated that the proposed circuit allows one to obtain a greater energy in the high-inductance load than the circuits with the step-up or dynamic transformer owing to a change in the sign of the magnetic flux in the secondary circuit. It is found that the increase in energy in the new circuit is independent of the coupling coefficient (at high values of this coefficient) and become greater as the number of cascades is increased.

Rotation bifurcation in a steady axisymmetric thermocapillary flow of an incompressible fluid filling a semi-infinite space bounded by the free surface with a nonuniform distribution of temperature is studied. The fluid flow is calculated on the basis of Navier-Stokes equations under the assumption of small diffusion coefficients. It is shown that the bifurcation triggers a rotational regime in a thin Marangoni boundary layer in the case of local cooling of the free boundary near the axis of symmetry and in the presence of an external flow; there is no rotation outside this layer. In the case of local heating of the free boundary, rotation is not observed

This paper touches upon an initial-boundary-value problem that describes the unidirectional thermogravitational motion of fluid in a plane channel in the case of solid immobile upper and lower walls with temperature distribution thereon and in the case of a heat-insulated upper wall. The motion is caused by a joint effect of the longitudinal temperature gradient and given nonstationary flow rate. The initial-boundary-value problem is inverse relative to the pressure gradient along the channel. An exact stationary solution is obtained. A solution of the nonstationary problems in Laplace images is determined, and the results of numerical calculations are presented.

The problem of injection of a hydrate-forming gas (methane) into a snow block, whose pores in the initial state are saturated by the same gas. Self-similar solutions describing the temperature and pressure fields and the snow, hydrate, and gas distributions in the block are constructed. It is shown that three characteristic zones can be distinguished, depending on the initial thermobaric state of the snow-methane system and the rate of gas injection into the filtration region: a near zone, in which snow completely is converted into hydrate and, consequently, the hydrate layer is saturated with gas; an intermediate zone, in which gas, snow, and hydrate are in phase equilibrium; a far zone filled with gas and snow. It is shown that the length of the heated zone decreases with increasing initial snow content in the block and with decreasing injected gas pressure. It is also shown that the length of the region of hydrate formation increases with increasing permeability. It is also noted that the heating of the intermediate zone occurs more rapidly.

A quasi-hydrodynamic system of equations describing flows of a heat-conducting viscous compressible multiphase multicomponent fluid is constructed taking into account surface effects. The system was obtained by generalizing the methods of obtaining a single-phase quasi-hydrodynamic system and a multicomponent flow model taking into account the surface effects based on the concept of microforces and microstresses. The equations are derived using the Coleman-Noll procedure. The results of the calculations show that the constructed model is applicable for modeling multiphase multicomponent flows with allowance for surface effects on the interfaces.

The effects of the camber ratio on the hydrodynamic and structural behaviors of a NACA-based ducted marine propeller in the wake flow behind an underwater axisymmetric body are numerically studied by computational fluid dynamics methods, in particular, the finite element method. The results are presented in terms of the efficiency, deflection, pressure coefficient, and natural frequencies. It is shown that the wake flow strongly affects the performance of the selected propulsion system. It is shown that the distributions of the camber ratio over the blades of the propeller nonlinearly changes its resistance against cavitation occurrence and deflection, and also changes its hydrodynamic performance and vibrational behavior.

This paper considers methods for controlling secondary flows arising near an oscillating circular cylinder by changing two process control parameters: the dimensionless amplitude and the vibrational Reynolds number. A direct numerical modeling study is performed. It is shown that by varying the indicated parameters in a relatively small range, it is possible not only to intensify mass transfer processes, but also change the direction of the main secondary flows.

A mathematical model of blood circulation in human lower limbs is proposed. The model is based on the laws of motion (filtration) of a viscous fluid in a heterogeneous medium consisting of two or more interpenetrating continua. It is assumed that the blood system consists of a distribution network of comparatively large vessels (arterioles) connected to small capillaries and a similarly structured collection network of small capillaries united into larger veins. A system of parabolic differential equations is derived, for which a problem with no initial data is posed. A periodic (in time) solution of the system corresponding to harmonic oscillations defined by the cardiac rhythm is found. Analytical solutions for particular cases of problems following from the general model of blood circulation are obtained. Numerical calculations are performed, and a numerical solution is found for a one-dimensional problem with parameters similar to those corresponding to real conditions of blood circulation with allowance for the cross-sectional area of the muscular tissue of the lower limb.

This paper presents the results of numerical modeling of gas hydrate formation upon injection of carbon dioxide into a finite-length reservoir saturated with methane and water. It is shown that at different stages, hydrate formation can occur on both the frontal surface and in a reservoir region of finite length. The effects of pressure on the boundaries of the reservoir and the permeability and initial water saturation of the reservoir on the hydrate formation process were studied. The dependences of the time of the complete conversion of water into gas hydrate state in the entire reservoir on the injection pressure and reservoir permeability were obtained.

Analytical frequency dependences of the absorption coefficient, wavenumber, and phase velocity were constructed for filtration-wave fields in a highly permeable interlayer bounded from above and from below by layers having high permeability in the vertical direction. It is shown that as the frequency decreases, the phase velocity of the wave decreases to values below this velocity in the porous medium, and low-frequency deceleration occurs.

A reverse experiment technique is used along with the technology of measuring rods to study the impact and penetration of a steel conical shocker in frozen sandy soil. This paper presents the dependences of maximum values of the force of resistance of cones with base diameters of 10.0, 12.0, and 19.8 mm to penetration into soil on the impact velocity in the range of values 100-400 m/s. The numerical solution of the problem in an axisymmetric formulation with the use of the “Dinamika-2” software package is used to show the effect of waves reflected from the walls of the container on the contact force. A comparative analysis of the forces of resistance to penetration of the shocker into compacted dry, water-saturated, and frozen sandy soils is carried out.

Within the framework of the anisotropic theory of elasticity, a three-dimensional contact problem of interaction of two massive transversely isotropic bodies, whose dimensions substantially exceed the size of the contact region. In this case, the isotropy planes of contacting elastic bodies are mutually perpendicular. Exact and numerical solutions of the problem are determined. Calculations for various transversely isotropic materials are carried out.

A new mechanism of deformation of enclosing rocks near mine workings is presented. The developed method to calculate geomechanical behavior of rocks takes into account the weight of overlying strata in the concordant direction with the orientation of tensile stresses at the mine working boundary while these directions differ in the mine working floor. The proposed calculation method for rock deformation includes two additional parameters characterizing the ratio of displacements in the mine working roof and floor and the ratio of the ground surface movement to to the mine working roof displacements which are determined experimentally.

Physical modeling of electromagnetic response of rock mass to low-energy impacts in terms of the Tashtagol iron ore deposit shows that multiple low-energy series of impacts initially increase the amplitudes of electromagnetic signals which later on decrease to the same level. This circumstance is indicative of the fact that the slowly varying levels of electromagnetic signals recorded after large-scale blasts are conditioned by the rock mass movement along various slip planes. The change in the stress-strain state of rocks is a slow process which takes from units to tens of hours.

The uniaxial compression testing of brittle rock specimens show that the specimens fail in the form of a columnar fracture along the axis of loading. The test data are compared with the characteristic quantities of tensile strength. Failure of the specimens is modeled with regard to features of grains, which allows assessment of tensile/compressive strength ratio.

Improvement of energy efficiency in comminution of rocks using various pretreatment methods is being explored worldwide. This paper presents experimental data on breakage characteristics of granite and sandstone using cryogenic pre-treatment. The samples were treated with varying duration of immersion in liquid nitrogen. Combined pretreatment using oven heating followed by quenching in liquid nitrogen were also explored. The results indicate that using cryogenic pretreatment uniaxial tensile strength of granite can be decreased by more than 40% while in uniaxial compressive strength about 28% reduction is possible. For sandstone as much as 33% reduction in uniaxial compressive strength was observed.

Design development of DTH air hammers is discussed with a view to increasing efficiency of rock drilling. The problem is handled by making hammering tool with curvilinear frees surfaces which are in no contact with the hammer body. This ensures generation of rock-breaking impact at the minimum energy input. New designs of hammering tools are developed for DTH air hammer models PP110EN and PP110NK designed at the Institute of Mining, SB RAS. Experiments prove that selection of rational shape of hammering tools allows improving performance of DTH air hammers by 15% at the average.

The issues connected with the prediction of mining machinery life are discussed. The basic index of reliability is an average life. The formulas are substantiated for calculating the average life of gear wheels, friction couple parts, shafts, and axles. The procedure proposed to calculate the life standard deviation is based on the method of linearization of functions of random variables. In this way, the life of standard parts of mining equipment can be calculated as random values with regard to operation conditions. Application of the procedure is exemplified by calculations of the life of a roller bearing. The calculation results are confirmed in the numerical experiment by the Monte Carlo method.

The results of the research aimed to substantiate parameters of loose ore and rock mass (protective cushion) formed to protect and isolate underground excavations from the open pit mine at Udachnaya kimberlite pipe under mining with the caving methods are presented. The thickness of the cushion is determined based on the effect of an impact of caved rocks and the resultant air blast, and is meant to isolate aerodynamically and thermally the open pit and underground mines. The thickness of the protective cushion is calculated with regard to an increase in the depth of mining down to a level of -680 m.

The problem connected with the mine support with metal frames in unstable rock mass subjected to stoping is analyzed. In terms of the complicated geological conditions of the Orlov Mine (East Kazakhstan), the application of phenol resin Blok-Fil in filling voids and domes after rock falls in the gap between the metal frames and roof is tested at the laboratory and pilot scale. It is found that owing to complete filling of voids with resin, no dynamic loads on the support due to rock falls and self-heating of ore and mine air are observed.

The experimental research findings on processes that take place during differently directed controlled trajectory blasting of ore and gangue in underground mining of flat-dipping veins are presented. It is found that methods for designing blast patterns should take into account both linear concentration of energy and dynamics of the increase in resistance to throw of rocks and ore in a narrow stoping area. Based on the modeling data, the throw coefficient and blasting front advance are plotted as functions of geometrical and energy characteristics of the model. It is shown that blasting and throw of ore in the stoping zone is accompanied with the effect of additional fragmentation of ore due to collision with the stope roof.

Deep sea mining was identified in the middle of last century. However, its industrialization and commercialization today are limited in the costal mining industry due to the high mining cost and technical issues. The purpose of this paper is to analyse a green transport plan of deep sea mining systems in terms of the optimal efficiency of the rigid pipe lifting system and the total energy consumption. The deep sea mining facilities considered in this paper consist of a mineral collecting machine, a flexible hose, a rigid pipe, a grinding machine, a concentrating machine and a horizontal pipe conveyor. Centrifugal pump modelling and its working principle are researched, because it is the major transport facility. The relationship between the optimal efficiency, total energy consumption, transport loss factor, and the relating mining parameters is determined by numerical simulations and fittings under Fortran and Matlab environment, and the optimization under 1stOpt environment. The research conducted in this paper is valuable for the pre-evaluation of deep sea mining transport systems and the further realization of its industrialization and commercialization process.

This study discusses the prediction of penetration rate and specific energy of button bit equipped rotary-percussion drilling machines from drill cuttings and geo-mechanical properties of rocks. The operational parameters of drilling machines measured from selected locations were utilized for the calculation of specific energy of drilling operations. For this purpose three on-going hydropower projects and four active mining quarries of Pakistan were selected. The drill cuttings were further used to determine various descriptors of the chip size distribution including the coarseness index and Rosin-Rammler’s absolute size constant. A complete set of geo-mechanical rock tests were conducted in the laboratory and includes uniaxial compressive strength, Brazilian tensile strength, point load strength, Schmidt rebound hardness, p-wave velocity, dry density, porosity and brittleness indices. Regression analyses were performed to predict the penetration rate and specific energy of drilling from geo-mechanical properties of rocks. The models so developed were also validated by adopting the t-test and the F-test statistical techniques. Moreover, statistical models were also developed to evaluate penetration rate from various descriptors of the chip size distribution. Dependence of bit size on coarseness index and mean particle size was also discussed.

The investigation of influence exerted by ultrasound exposure on recovery of zirconium and rare earth elements in pregnant solution of acid leaching of eudialyte concentrate is described. The methods of X-ray photoelectron spectroscopy and analytical scanning electron microscopy are used to study structural, chemical and morphological characteristics as well as elemental composition of minerals in eudialyte concentrate before and after the acid leaching.

The mathematical model of treatment of mineralized mine wastewater by pressure flotation is described. The model provides information on concentration of metal substrates in each state of the process at any arbitrary time. The numerical experiments based on the model prove its reliability and accuracy.

The results of the thermodynamic modeling are presented for oxidizing roasting of refractory molybdenite (MoS₂) with magnesite (MgCO₃). The phase and chemical compositions of the MoS₂-MgCO₃-O₂ system and its changes are determined depending on the temperature and quantity of the additive agent. The modeling reveals feasibility of thermochemical decomposition of molybdenite with the formation of water- and soda-soluble compounds MgMoO₄ and MgSO₄, which is an evidence of efficiency of magnesium carbonate in the capacity of an additive agent. The optimal conditions of the thermochemical decomposition of molybdenite determined theoretically from thermodynamic calculations are proved experimentally.

The processes of physicochemical treatment of nepheline concentrates are studied theoretically and experimentally, and the optimal conditions are determined for the integrated fluoride-ammonium recovery of different useful components. The enabling innovative technology is proposed for the production of amorphous silica, alumina, red iron oxide, calcium fluoride and other marketable products.

Applicability of local and regional scale satellite images in evaluation of vegetation in tundra in the zones of mining in permafrost area is proved. The research findings on the environmental impact of the Valkumei Mine, Chukotka Autonomous Okrug, after its closure are described and analyzed.

The spotlight is on the use of Earth remote sensing data in geoecological assessment of the Malyi Khingan Ridge area in the Russian Far East. Based on the analysis of satellite observations over the Sutara gold placer mining range, the time variation of the disturbed land is determined. It is found that natural recovery of bio-geo-cenosis takes an active part in the process. Using the normalized difference vegetation index (NDVI), the behavior and rates of self-healing of the disturbed lands are assessed. Complete recovery of vegetation in gold placer mining areas up to a level comparable with the adjacent territories takes 7 to 10 years.

The methods of deactivation and reclamation of tailings ponds are studied. The engineering-geological investigations of apatite-nepheline ore flotation tailings in the sites applied with chemicals at ANOF2 processing plant of Apatit Company are carried out. The monitoring of the bonding surface generated by dust suppression agents Alcotact DSI, Dustbind and Dloset S44 is performed. The physical properties and the aggressive action resistance, as well as the effect of suppression agent feed in recycling water on the apatite-nepheline ore flotation performance are tested on a laboratory scale. The Dustbind is recommended as the optimal suppression.

Stationary-state combustion of fine dispersed dust-gas-air mixtures in underground excavations is analyzed. Under the assumption that the single source of heat emission is the carbon oxidation reaction, the second-order nonlinear differential equation is obtained for the determination of temperature and the initial conditions are formulated. The analysis of the solution shows that there exist critical values of the dust-gas-air mixture flow velocity, and the excess over these critical values may result in the mixture combustion. The cross section of an underground excavation is related with the temperature reached in this cross section.

The structure diagram and operation of a hybrid unit for drilling and initiating slotting are presented. The loads on the cutting tool during initiating slotting are calculated, and the rational operating mode of the hybrid unit is determined.

The variant of the gamma albedo method is proposed for the radioisotope express control of coal ash content, which ensures the satisfactory accuracy in the conditions of variable elementary composition of coal. It is shown that the integral intensity of secondary (scattered and fluorescent) radiation weakened using a certain thickness filter is a univocal index of coal ash content. The analytical model for the optimization of the secondary radiation filtration parameters is developed. The utility value of the weakening filter is determined as function of ash content and composition of coal.