Home – Home – Jornals – Journal of Applied Mechanics and Technical Physics 2022 number 2

This paper presents an experimental investigation of the dependence of the shape, structure, and opening angle of a water jet on the degree of superheating. The relationship between different boiling modes and characteristic shapes of a boiling jet has been revealed. It has been found that the shape and the opening angle of a superheated liquid jet under the same thermodynamic conditions change in different ways depending on the length of the jet. The changes in the opening angle of a boiling jet are presented in the meter, decimeter, and centimeter ranges.

The problem of the motion of a sphere in an ideal incompressible infinite fluid depths under ice cover with nonuniform compression was solved using the method of multipole expansions within the framework of the linear potential theory of waves. researched The hydrodynamic loads acting on the body such as the wave resistance and the lateral and lift forces were studied, and the deflection of the ice cover was analyzed as a function of its thickness, body speed, and the depth of submersion and direction of motion.

A linearized model is presented for the scattering problem of flexural gravity waves by the bottom with a finite number of rectangular steps in the ocean. The matched eigenfunction expansion method is used to solve the boundary-value problem, and the results are expressed in terms of a set of integral equations solved by the multiterm Galerkin's approximation technique. Numerical values of the reflection and transmission coefficients are calculated and graphed to display the influence of various parameters of the problem. The accuracy of the present method is verified by using the energy balance relation for the reflection and transmission coefficients. The results are compared with those available in some earlier works.

Theoretical results obtained within the framework of the weakly nonlinear model of a developed boundary layer in a flow past a narrow flat plate are verified with the use of methods of direct numerical simulation of the Navier-Stokes equations. The mechanism of gas ejection (bursting from the surface of a thermally insulated plate in a supersonic gas flow with the Mach number M = 2 is studied within the framework of the model of complete nonlinear interaction. It is demonstrated that the transition from the laminar to turbulent flow past the plate in the case of weak external perturbations occurs due to resonant three-wave interaction. Theoretical results relating the energy redistribution between the oscillations and the process of spatial structure formation are confirmed.

The problem of current spreading across the width of thin foils (in snake-like systems) or planar current sheets is considered. For calculation the evolution of the current distribution across the width of inhomogeneous thin conductive layers or foils is calculated using an integrodifferential equation which reduces the two-dimensional problem for the magnetic field to a one-dimensional problem. An infinite periodic system of plane snake-like foils is considered. It is shown that in this foil system the current distribution corresponding to the ideal foil conductivity is first established and then relaxation of the current distribution to a uniform one occurs. If the foils are used as circuit breakers, current must have time to be distributed uniformly across the foil width during current transfer to the load, so that the corrections for the nonuniformity of the current distribution in the switches should be small.

This study is aimed at designing, optimizing, and validating a posterior lumbar interbody cage (PLIF) model based on the 3D printing method, which provides patients with a suitable customized design capable of providing proper mechanical support. In the content of this study, the CATIA software is used for modeling of three symmetrical cage models with different porosities. Then, two replicates of each cage model are assembled in the disc space of a parametric geometry of the L1-L2 vertebrae. The proposed models are meshed, and a finite element analysis is conducted through compressive and moment loadings. The overall stiffness and von Mises stress and strain of each model are determined.

A new design for continuous separation of multiple blood cells from diluted whole blood in a microfluidic device based on dielectrophoresis phenomenon is presented. Compared to the other studies, the proposed separator is designed for simultaneous separation of more types of blood cells with desirable accuracy. Using finite-element-based simulations, the device efficiency is evaluated for separation of five blood cell types. The proposed separator uses both dielectrophoretic and hydrodynamic drag forces to separate blood cells. The separator performance under different operating conditions is also evaluated.

Aorta is the largest vessel of the human circulatory system, which plays a critical role in the supply of oxygen and nutrients tp all organs of the abdominal cavity and lower limbs. The critical pathology of this vessel is aneurysm. In medical practice, an important problem is aortic aneurysm rupture prediction and surgery planning since aneurysm rupture outside the clinic, as a rule, leads to a lethal outcome. To construct adequate mathematical models that predict such an outcome, it is necessary to determine the strength characteristics of the tissues of the aorta itself, its aneurysm and iliac arteries at various stages of growth of such an aneurysm, and also taking into account patient data. The strength characteristics of tissues of the human aorta, its aneurysm, and iliac arteries have been studied. It has been experimentally proved that in samples of healthy aorta tissues, the differences between the values of the limiting relative deformations in the axial and tangential directions are statistically significant ( p = 0.033), which is not observed in the case of an aortic aneurysm. The results can also be interpreted as the fact of remodeling of the aortic aneurysm wall in comparison with the healthy aorta. These data can be used in personalized hydroelastic simulation during construction of predictive models for the rupture of such aneurysms.

In this paper, SH-wave propagation in an initially stressed triclinic layer welded between two half-spaces is investigated. The upper half-space is considered to be transversely isotropic and elastic, while the lower one is heterogeneous, isotropic, and poroelastic. In the case of the lower half-space, the problem is reduced to the Whittaker differential equation. Frequency equations are derived for the layer as a whole and half-spaces. It is found that the phase velocity is strongly influenced by the initial stress, porosity, and heterogeneity.

Results of a series of experiments aimed at studying laser cladding of individual tracks with the use of the B4C-Ti-6Al-4V cermet powder mixture are reported. The influence of laser cladding parameters (radiation power, beam motion velocity, and focus position) on the characteristics of tracks being formed (geometric sizes, microhardness, and elemental composition) is studied. It is shown that an increase in the concentration of reinforcing particles in the initial powder mixture alters the character of mass transfer inside the melt bath, leading to changes in the shape of the single track. It is found that a complex heterogeneous structure is formed in the melt bath, including secondary phase compounds formed in chemical reactions due to in-situ synthesis. The microhardness values at various points of the single track are observed to differ by more than a factor of 2 (in the interval HV0.3 = 548-1415).

The possibility of obtaining composite coatings from a mixture of aluminum and boron carbide powders for neutron shielding by cold gas-dynamic spraying has been studied. The dependences of the deposition efficiency and the residual content of boron carbide in the coating on its initial content in the sprayed mixture of powders were derived. The obtained regularities have been analyzed, and an approach has been proposed to search for the boron carbide concentration in the powder mixture that is optimal for creating effective neutron-absorbing coatings. It has been shown that the highest productivity of the spraying process is achieved when using the optimal powder composition with (a volume fraction of boron carbide of about 0.5).

An improved Ritchie-Knott-Rice failure criterion, namely (4δ_t, σ_22c) criterion, for the A515-70 steel is studied with allowance for the specimen geometry, specimen temperature, and initial crack length. The results show that the (4δ_t, σ_22c) criterion can effectively predict the cleavage fracture. Results of studying the possibility of using a dimensionless function for determining the fracture toughness are reported.

This paper describes a numerical-analytical model of the viscoelastic-plastic behavior of flexible shallow shells with account for the dependence of plastic properties of their materials on strain rate. The inelastic behavior of materials is described by the theory of flow with isotropic hardening. Loading functions depend on the hardening parameter and strain rate intensity. Viscoelastic behavior is described by linear constitutive equations from a multiconstant body model. Lateral shears of structures during bending deformation are taken into account within the framework of the Ambartsumyan theory, and geometric nonlinearity within the von Karman approximation. A cross-type explicit scheme is used for the numerical integration of the formulated initial boundary value problem. The dynamic deformation of a cylindrical elongated panel made of a polymer material is studied. The structure is transversely loaded by a pressure generated by an air blast wave. It is shown that neglecting the dependence between the plastic properties of the material and the strain rate may cause one to significantly underestimate the maximum deflection value in absolute value and the largest strain value during oscillations and cause one to overestimate a maximum residual strain. In addition, the diagrams of residual deflections of the structure obtained by such a calculation do not agree with the diagrams obtained by a calculation that takes the mentioned dependence into account.

Main correlations in the theory of bending of thin electromagnetoelastic plates are obtained, in which complex potentials are used. Exact analytical solutions are obtained for the problems of bending an elliptical plate and an infinite plate with an elliptical hole. It is established that no electric or magnetic inductions arise in the case of a simply connected finite plate under mechanical influences, and no mechanical stresses arise under the action of inductions, despite the fact that the piezoelectric effect occurs due to deformations, displacements, and field potentials. The piezoelectric effect in the case of an infinite simply connected plate is always observed and has a significant effect on the values of bending moments. The influence of the physical and mechanical properties of materials and the geometric characteristics of holes on the values of bending moments In the case of a plate with an elliptical hole is studied.

The wear resistance of DI37-VI and EK80-VI steel is studied using a device for investigating friction. A sample made of high-carbon chromium-vanadium steel relative to pellets of MS221, VK3M, and VK6OM hard alloys on this device carries out reciprocating motion at a rate of 0.1 m/s. The base friction path is 50 km and the average temperatures of the samples are 100, 140, and 190oC. The effect of an average temperature of samples on the wear resistance of DI37-VI and EK80-VI steel is described.

This paper presents the results of an experimental study of the physical properties, microstructure, and phase composition of a TiC-NiCr ceramic-metallic compact obtained by hot pressing. It is shown that an increase in the volume fraction of the metal binder in the samples reduces the HRA hardness (from 55 to 25) and the HV300 microhardness (from 1000 to 350) of the material.

Coal mined from the surface or underground is rarely suitable for direct use and requires preparation based on physical and/or chemical methods of removing certain components in order to improve the quality of coal to the required level. High humidity leads to a decrease in the energy efficiency of boiler, so the process of fuel drying is a necessary step in coal preparation, and reducing energy costs for moisture removal is an urgent task. One of the ways of moisture reduction is coal treatment with microwave radiation. As compared with other methods, microwave drying has the following features and important advantages: 1) volumetric heating; 2) selective heating (there is no energy absorption in dried areas); 3) low thermal inertia. However, this method requires high power inputs and there is a need to find energy-efficient processing regimes. In the present work, a drying model has been constructed, the optimal regime of layer drying has been found using the finite element method at the example of brown coal from the Talovsky deposit, and energy costs have been determined.

This study aims to investigate the effect of gas radiation on laminar free convection flow within a square cavity with internal heat generation. The cavity walls are isothermally cooled whereas the inner body is kept constant at a higher temperature. An important finding from this analysis is that radiative contribution plays a major role in the acceleration of the vortexes, providing a homogenizing effect on temperature fields. It is also shown that the optimal level of energy efficiency is achieved if the heater is located at the center of the lower part of the enclosure and when the inclination angle of the enclosure is of π /4.

One of the promising ignition technologies is the plasma thermochemical preparation of pulverized coal for combustion using plasma-fuel systems (PFS). This technology allows increasing the efficiency of fuel application and improving the environmental performance of thermal power plants, as well as eliminating fuel oil, used traditionally to ignite boilers and stabilize combustion of a pulverized coal flame. This paper presents the numerical results on ignition of a pulverized coal flame in a PFS. The plasma-fuel system is designed for oil-free ignition of boilers and stabilization of flame combustion and this is a pulverized coal burner equipped with a plasmatron. In addition to plasmatron electric power and ash content in coal, one of the main operating parameters of PTS, which ensures fuel ignition, is concentration of coal dust in the air mixture, which can be varied over a wide range. The conditions of fuel mixture ignition in the PFS were determined for three above-mentioned operating parameters of PFS using the PlasmaKinTherm program, which combines kinetic and thermodynamic methods for calculating the processes of motion, heating, and thermochemical transformations. The calculations were performed for a cylindrical PFS with a diameter of 0.2 m and a length of 2 m. The coal consumption was 1000 kg/h. The conditions of fuel mixture ignition in the PFS were studied depending on plasmatron power (20-100 kW), coal concentration in the fuel mixture in the range from 0.4 to 1.8 kg of coal per 1 kg of air, and also for three different values of coal ash content (20, 40, and 70%). The main regularities of the process of plasma thermochemical preparation of fuel for combustion have been revealed.

Results of numerical simulation of two-dimensional flows of cellular detonation in plane channels in gas suspensions of submicron aluminum particles (0.6 and 0.3   m) in oxygen are presented. Mixtures with homogeneous and heterogeneous concentrations are considered. A previously developed model of reduced kinetics verified on the basis of the detonation velocity dependence on the particle concentration and extended to heterogeneous mixtures is used. The size and character of detonation cells are found as functions of the particle size and concentration. Problems of detonation propagation in channels with transverse concentration gradients and intermittent distributions of concentration are considered.

Results of numerical simulations of mixing, ignition, and combustion of a cold supersonic (М _jet = 1.46) hydrogen jet injected coaxially into an annular supersonic (M _air = 1.86) jet of hot vitiated air expanding into a still space are reported. The simulations are performed within the framework of the ANSYS Fluent 2020 R1 software in a transient two-dimensional axisymmetric approach based on the Reynolds-averaged Navier-Stokes equations supplemented with the k-w SST turbulence model and a detailed mechanism of hydrogen combustion in air. The geometry and simulation parameters are chosen to be those of the experiment of Cohen and Guile (1969), whose data were used for verification of the numerical algorithm. The structure of the reacting jet is studied, and the hydrogen combustion efficiency is evaluated for various values of the jet pressure ratio. The instantaneous, mean, and RMS components of the main gas-dynamic quantities and species mass fractions in the reacting mixture are obtained.

This paper presents the results of a study carried out using numerical simulation of flame front dynamics in a gaseous reacting mixture, including those in the presence of a suspended phase of liquid microdroplets. It is shown that the local effect on the flame front is one of the leading factors determining the development of combustion. Thus, the local dynamic effect of relatively large droplets on the flame front contributes to its curvature, which, in turn, determines the corresponding local acceleration of individual sections of the front. Further unstable growth of such perturbations leads to an integral acceleration of the flame. At the same time, local stretching by the flow in depleted compositions can lead to combustion extinction.

A numerical model for heterogeneous combustion of axisymmetric porous objects has been proposed that allows one to simulate processes under both forced filtration natural convection. The influence of the location of the ignition zone on combustion in a cylindrical porous reactor has been investigated. It has been shown that under forced filtering, the process similar to plane case: the combustion wave moves upward and sideways from the ignition source, completely burning out the solid fuel, while the gas tends to bypass hot zones and flow through colder regions. Under natural convection conditions, as in the plane case, the oxidizer flow into the reaction zone is significantly affected by vortex gas flows that arise in the vicinity of the combustion center at the initial time. In this case, the direction propagation of combustion waves in the axisymmetric case can significantly differ from thatin the plane case.

A physical and mathematical model of spark ignition and combustion of boron powder suspension in a propane-air mixture is presented. Dependences of the critical energy of spark ignition on the radius and mass concentration of particles and propane content in the boron gas suspension are obtained. Dependences between the steady flame propagation velocity in a boron powder suspension in a propane-air mixture on particle radius and particle mass concentration are obtained, and the propane content in a boron gas suspension is determined. Quantitative correspondence of the computational and theoretical values of the flame propagation velocity in a boron powder suspension in a propane-air mixture with known experimental data has been obtained.

An improved mathematical model of gasification is proposed solid porous fuel when hot gases are filtered through it. On the example of polymethyl methacrylate, the gasification regimes were studied both at constant pressure drop at the inlet and outlet of the gasifier, and at constant velocity of the gas at its inlet. In the event of a constant drop pressure gasification of combustible material takes longer and the gas temperature at the outlet increases more slowly than in the case of a constant gas velocity at input under comparable conditions.

Qualitative transformation of a low-velocity laminar flow to a turbulent state (owing to natural or artificial instability) and formation of compression waves passing ahead have been studied in much detail. A disputable issue is the nature of the emergence of a reaction site in the region between the bow compression wave and the flame front moving at a certain distance behind this wave, as well as the dynamics of interaction of this site with the main structural elements. It is the type of this site (slow or explosive combustion) that defines its subsequent interaction with the compression wave front: shockless or shock-induced expansion capable of forming a detonation wave. As a method of transforming the reaction site to an explosion site, its amplification owing to the resonance of streamwise acoustic oscillations of hot reaction products with the initial combustible mixture induced by flame propagation is discussed. It is the resonance with its multiple enhancement of the amplitude of gas-dynamic parameters that can effectively initiate the deflagration-to-detonation transition. Various stages of this transition are discussed; the corresponding estimates are made and are found to be consistent with experiments.

Interaction of homogeneous and heterogeneous detonation waves in mixtures of aluminum in oxygen and hydrogen in oxygen with a cloud of water droplets is studied by methods of mechanics of multiphase media. The main interaction mechanisms are determined: propagation of an attenuated detonation wave with a velocity smaller than the Chapman-Jouguet velocity and detonation failure. Critical conditions of detonation propagation in water sheets are determined. These critical conditions are compared with the results of modeling detonation suppression with the use of clouds of inert particles.

This paper presents the results of mathematical modeling of the propagation of air blast waves during methane explosion in mine workings taking into account their interaction with prefabricated parachute stoppings. Parachute stoppings are able to reduce the shock-wave intensity when the intensity of the incoming shock wave does not exceed the critical failure pressure of the stopping. The gas-dynamic method of calculating explosion-proof distances allows one to take into account parachute stoppings installed in various places of workings and to calculate the parameters of shock waves that have passed beyond the stopping.

The present paper describes the effects of hydrogen addition and carbon dioxide dilution in the natural gas on the velocity profiles and on the turbulent quantities (integral scale and Kolmogorov scale) in a cylindrical burner. The hydrogen content in the fuel is varied from 0 to 20 % in volume, and the volume of carbon dioxide is varied between 0 and 50 %. The velocity fields and the root mean square value of velocity are determined by the particle image velocimetry technique in the reacting flow. The concentrations of CO and NO _x are found using the corresponding analyzers. The turbulent quantities are determined by a numerical method. The results show that the absence of hydrogen and the carbon dioxide content greater than 20 % lead to flame blow-out. Therefore, the flame is hooked to the burner if hydrogen is added. In this study, with hydrogen addition, the difference in the maximum velocity ( U _max/ U ₀) along the bio-hythane jet is less important far from the burner due to the low density and high molecular diffusivity of hydrogen. The studies of the root mean square values of two velocity components ( U'_x and U'_z ) indicate that turbulence is more important for the U'_z component.

Even a slight change in the content of impurity gases during a self-propagating high-temperature synthesis can lead to a change in the combustion regime and the characteristics of the target products. In this work, the dependence of the burning rate of Ti + C granular mixtures on a titanium particle size is determined for the first time, and the effect of impurity gas evolution when using various allotropic modifications of carbon (graphite/soot) is studied. Experimental results are analyzed using the convective-conductive combustion model, which explains the strong influence of impurity gas release on the front velocity. Interaction rate of the components becomes a key factor for granular mixtures in which the influence of impurity gases is leveled. Experiments show that the burning rates of granular mixtures of titanium with soot are noticeably higher than the burning rates of a mixture of titanium with graphite. The curves approximating the dependence of the burning rate of a granular mixture of titanium and graphite on the size of titanium particles correspond to the linear law of interaction of the initial components. The interaction in a mixture of titanium and soot occurs according to the parabolic law.

This paper presents a combustion model for a solid fuel consisting of a matrix capable of self-sustained combustion and particles of a polydisperse coolant distributed in it. Heat transfer between the exothermically decomposing matrix and coolant particles in the condensed phase and the gas phase products of their gasification. The leading reaction in the region of the matrix and the evaporation surface of the coolant are assumed to be located on the interface. The heat consumption for the evaporation of the coolant is determined by the depth of its gasification during passage through the interface, which depends on the dispersion of the coolant and the burning rate of the fuel. Parametric identification of the model was carried out using data of sieve analysis of the granulometric composition of the coolant and an experimental dependence of the burning rate on pressure. It is shown that the model can be used to predict and providing the required ballistic characteristics of the fuel at the stages of its testing and series production.

Low-temperature (1 023 K) vacuum reduction of a mixture of zirconium dioxide with calcium is used to obtain a powder with an active zirconium content of 98.4 % (wt.). Physicochemical properties that determine the thermal and ignition characteristics of the powder and pyrotechnic compositions based on it are studied.

The explosive properties of cyclodextrin nitrates with various degrees of substitution of nitrate groups for hydroxyl groups in cyclodextrins. It is shown that charges of b-cyclodextrin nitrate with 100 % substitution at a density of 1.576 g/cm³ detonate with a relative explosion momentum equal to 96.4 % of its value for the 50/50 TNT/RDX composition with a density of 1.66 g/cm³, whose momentum is taken as 100 %. In this case, the detonation velocity is 7.15 km/s. It is concluded that the substance belongs to powerful blasting explosives. The sensitivity of cyclodextrin nitrates to mechanical influences was studied as a function of the degree of substitution. The obtained values of the explosive properties and sensitivity of cyclodextrin nitrates to impact and friction are compared with the properties of nitrocellulose.

The shock-wave initiation of an emulsion explosive was studied by flash radiography. Initiation was performed by impact of a thin Duralumin plate at a small angle to a flat surface of the explosive. The parameters of the initiating shock wave in the investigated explosive were estimated, and the depth of detonation initiation was measured.

Detonation overcompression during detonation convergence in a hemispherical charge of plasticized triaminobtrinitrobenzene with outer and inner radii of 75 and 20 mm after its initiation along the outer surface is studied. The experiment is numerically simulated with account for the transformation kinetics of an explosive into explosion products. The overcompressed detonation parameters in the explosive under study at a diagnosable charge radius of 20 mm are obtained via experiments and calculations: in the profile maximum, the pressure is 70 GPa, the front velocity is 9.45 km/s, and the mass velocity behind the front is 3.88 km/s. The overcompression achieved in the experiment under consideration is 2.3. The adiabatintersection point of the “nonreacting” explosive and its explosion products is revealed, which is implemented at a radius of 31 mm and a pressure of 52 GPa. The corresponding front velocity and the mass velocity behind the front at this point are 8.55 and 3.18 km/s. The resulting parameters at the adiabat intersection point are compared with the available literature data for triaminotrinitrobenzene and compositions based on it. A fairly large scatter of data is revealed. Suggestions are made about the causes of the scatter.

The studies of Scotch pine ( Pinus sylvestris L.) needles structure and chlorophylls and carotenoid contents were carried out in four districts of the city of Krasnoyarsk, differing in the level of technogenic load. It was shown, that the length of the needles decreases with an increase in technogenic impact. The width, thickness and cross-section area of the needles and the central cylinder also decrease with an increase in the degree of air pollution. It was found that the cross-section areas of the conducting bundles in the central cylinder, as a rule, are not equal, the differences are 9-12 % and are characterized by high individual variability. No significant correlation was found between the sizes of conducting bundles and the level of technogenic load. The number of resin ducts in needles decreases with an increase in technogenic impact that indicates a decrease in the protection of the assimilation apparatus from damage by pests and diseases. Determination of the content of photosynthetic pigments in pine needles in two districts of the city, differing in the level of pollution, did not show significant differences in the content of chlorophylls and carotenoids. Perhaps this is due to the peculiarities of the weather of this growing season - abundant summer rainfalls prevented the accumulation of pollutants on the surface and inside the needles. The noted changes in the size, anatomical structure and pigment composition of pine needles can be considered as a result of adaptation to growing conditions and weather factors.

Analysis of the success of reforestation after a fire is the most important task of forestry. For these purposes, in the summer of 2021, aerial photography was carried out from a Phantom 4 pro UAV (Unmanned Aerial Vehicle) of a 15-year-old burnt-out (2006) along the north-western border of the Botanical Garden of Petrozavodsk State University (Republic of Karelia). In addition to this, a full-scale survey was carried out at the registration sites. Before the forest fire, rocky Scots pine ( Pinus sylvestris L.) trees grew. The work was carried out in order to assess the state of natural renewal after a fire along rocky outcrops by combining the processing of aerial photography data with field surveys. As a result of photogrammetric processing, an orthophotomap with a spatial resolution of 4.6 cm/pix, a height map and three-dimensional point clouds were reconstructed. To analyze the quantitative distribution of the territory according to the species composition, the trees were pinned on the orthophotomap according to the registration areas of field surveys, as a result of which the quantitative distribution of tree species was determined in the ratio of 64 % Scots pine and 23 % of drooping birch ( Betula pendula Roth) (other species were not identified). Field surveys showed that after the fire, a viable young stand of mixed composition with a predominance of Scots pine (71% of the total number of tree species) was formed. In addition to Scots pine, drooping birch (22 %), aspen ( Populus tremula L.) and gray alder ( Alnus incana (L.) Moench) (3.5 % each) participate in the formation of young stands on this burned-out area. These indicators are consistent with the analysis of the orthomosaic of the area (the error is less than 10 %). When comparing the height of plants on three-dimensional clouds of points with field measurements, it was possible to reliably determine only the height of plants for a large generally accepted category (> 1.5 m). The maximum height of Scots pine trees in the study area is 6 m, and the average values varied from 3.5 to 4.5 m, which indicates the success of reforestation after burning on rocky outcrops.

The protective forests in Karelia are concentrated mainly (80 %) around water objects. More than 50 % of these forests are presented by Scotch pine ( Pinus sylvestris L.) stands. Modern practice of forestry prefers the simplified felling types oriented on use of natural renewal potential of pine forests because artifical regeneration on stony soils are very complex. On a site of the strip-shelterwood felling (intensity of 35 %) in an uneven-age pine stand of bilberry type in 9 years after the felling three transects consisting of plots of 5 × 5 m with a total length of 1150 m across the clear-cut strips were established for an assessment of natural renewal. Under forest canopy pine undergrowth is presented poorly. At the general frequency of 15 % and average height of 1.2 m its density is less than 0.2 thousand tress per ha, and its condition does not give a hope to expect of growth improvement. The condition of spruce ( Picea A. Dietr.) undergrowth is better: its frequency - 36 %, height - 2.4 m, and density - 0.32 thousand tress per ha. On the cutted strips the pine frequency are 31 %, density and frequency of spruce and birch ( Betula L.) remained almost without changes; the participation of an aspen ( Populus tremula L.) and willow ( Salix L.) are increased sharply. The strip-roads are covered by willow weed ( Chamaenerion angustifolium (L.) Scop.), under the influence of which density and frequency of the conifers is twice lower. On the whole, the frequency and average height of a pine in the middle and at the edges of cutted strips are close. The executed felling did not provide the renewal of coniferous species sufficient for formation of a new forest stand, though emergence in recent years of the small undergrowth of a pine allows to count on his further quantitative increase. The executed assessment of increase in a radial growth of trees on cores showed his insignificance. The obtained results and literary data convince of obligatory need of a scarification of the soil surface during the strip-shelterwood felling execution.

The problem of assessing the balance of accumulated and degraded woody biomass in forest communities, the budget of C, CO₂, H₂O, and Q (energy) in primary virgin forests of different ages of spruce formations in the taiga zone of European Russia is discussed. The studies were carried out in specific biogeocenoses of different dynamic characteristics in the subzones of the northern, middle and southern taiga. The purpose of the research is to study in quantitative and volumetric terms the structural elements of the age series of primary virgin spruce biogeocenoses of different ages of different successional positions, the dynamics of the formation of the stem fraction of wood waste (deadwood), pools and flows of components deposited in the wood of the stem fraction of phytocenoses and tree waste in a single succession series. biogeocenoses of various dynamic characteristics. A cycle of studies was carried out on the trial plots, which made it possible to obtain information about the age structures of forest stands, their dynamic indicators, the volume of trees in the age generations of forest stands, the current tree waste and fallen trees. All volume values of forest stands and wood waste are converted into phytomass. The volumes of C, CO₂, H₂O and Q (energy) deposited in wood and released during its decomposition by wood-destroying fungi were calculated using the formula for mycogenic wood xylolysis. On the example of the spruce biogeocenosis of the middle taiga subzone of the climax phase of dynamics, the mass of carbon, different fractions of wood, presented in a graphic image, was calculated. It has been determined that the volumes of pools and flows of wood components in forest stands and during the decomposition of wood by fungi - destructors are determined by the structural features of the age series of forest stands, the volumes of wood waste in gradations of decomposition stages. A joint analysis of the age structures of forest stands, the structures of current tree waste and deadwood by stages of decomposition helps in a more accurate determination of the dynamic position of forest biogeocenosis in the expanded space of its successional development. In the most stable (climax) virgin spruce forests of the taiga, the values of the balance ratios of accumulation and decomposition of biomass represent an optimal budget model and can be regarded as reference values in comparison with forests of different origin and structural characteristics.

The results of long-term experiments carried out on two stationary objects of forest plantations in 1976 and 1968 in different types of forest growing conditions of the Mari Trans-Volga region are presented. The plantations of the 1967, created in a dry forest, consisted only of pine Pinus L. and birch Betula L. trees in various proportions, and the second, created on loamy soils, is of three tree species (birch, spruce Picea A. Dietr. and pine). Pure pine plantations served as a control group. The productivity of the stand, its commodity composition and tax value were estimated by calculation in terms of the average diameter, height and number of trees according to our methodology. The relevance of research is driven by the need of improving measures to optimize the species composition of forests in order to preserve biological diversity, as well as reduce the frequency and intensity of fires. It is shown that in dry and fresh pine forests, pine-birch plantations demonstrate significantly worse stand productivity and especially tax value. Until the age of 10-15 years, the height of birch trees in them is higher than that of pines, but after 25-30 years, their position changes to the opposite. On sandy loam and loamy soils, birch suppresses from the composition of the stand not only light-loving pine, but even shade-tolerant spruce, significantly exceeding them in size. It is concluded that it is impractical to create mixed pine-birch and pine-spruce-birch crops in the conditions of the Mari Volga region due to the different demands of tree species on soil fertility, as well as differences in the speed of their growth and development. These plantations also do not fulfill the functions assigned to them for increasing the biological diversity and sustainability of the functioning of plantations, as well as to reduce their fire hazard.