The growth of primary crystals from a supercooled binary melt is modeled on the basis of the phase-field method with an approximate consideration for melt stirring. Changes in the concentration of the solute in the melt near the solidification region due to stirring are considered as the main reason for modifying the dendritic morphology of the crystals. The stirring effect results in a partial removal of the melt with an increased solute concentration from the region near the interface, which is called washout in the work. This effect is approximately modeled as a forced periodic replacement of the current high solute concentration in this region either at the initial concentration or at the averaged concentration in the melt. In this paper, we propose a new algorithm for choosing such a correction region, which can be used for a small intensity of stirring. A value is introduced to describe the washout intensity-the washout parameter. It is shown that when washed away dendritic morphology passes into a rosette morphology, depending on the intensity of stirring. A numerical analysis of the growth of perturbations on the surface of the initial embryo of a circular crystal is carried out. The main differences in the development of such perturbations are shown, which leads to a non-dendritic morphology of the crystal. The growth of additional branches is demonstrated due to a decrease in the solute concentration near the center of the crystal. Calculations have been performed for the case of crystal growth with a decrease in washout intensity with growth time. For this case, the secondary arms grow on additional branches growing from the center of the crystal. It is shown that at a constant value of the washout intensity near the surface of a growing crystal, only two types of morphology are possible from a small round embryo, dendritic and rosette. At the same time, if the crystal already has a rosette morphology, it is retained and with its further growth with a decrease in the washout intensity.

The influence of the heating mode of samples of constructional cemented steels 20ХН3А, 20ХГНР and 15ХГН2ТА on the value of austenite grain after high-temperature isothermal aging at 1000 °С is studied. It is shown that the heating of steels at a rate of 1.2–3.0 °C / min in the phase-transformation interval stabilizes the grain structure of the steels and leads to a slowing down of the kinetics of the growth of austenite grains during prolonged high-temperature aging, which makes it possible to increase the temperature of the chemical-thermal treatment of steels. It is concluded that the stabilization of the grain structure of steels is associated with the formation of segregation of impurity atoms and particles at grain boundaries with high-angle disorientation during slow heating, which prevents migration of grain boundaries in the process of prolonged high-temperature aging. A high-temperature chemical-thermal treatment of a batch of billets from steel 20ХН3А under experimental conditions with stepwise heating in the phase-transformation interval provided a qualitative fine-grained structure of the cemented layer.

Experimental studies of the structure, phase composition, physical and mechanical properties of the reaction-sintered ceramics based on silicon carbide and boron obtained by reaction sintering have been performed. It has been shown that the properties of the reaction-sintered ceramics based on carbides are largely determined by the quality of impregnation of the porous carbide frame with silicon, which depends on the total and open porosity, shape and size of the pores of the compact, the composition of the charge from the carbide powder. High-temperature sintering, followed by impregnation of the carbide frame with silicon and its interaction with the carbon constituent of the frame, largely determines the properties of the material. The main task in the implementation of this process is to create conditions that ensure the full filling of pores in the initial compact during impregnation with silicon melt and, secondly, maximum activation of chemical interaction between the melt of silicon, carbon and other components that compose the charge. A complex of studies on the effect of compacting pressure and annealing temperature of the charge based on silicon carbide and boron powders with the addition of graphite on the pore structure of the compact and the quality of its impregnation with a silicon melt has been carried out in this work. It has been shown that the density, bending strength, hardness of ceramics based on silicon carbide and boron carbide obtained by reaction sintering are increased with a rise in compacting pressure of carbide frames. The optimum porosity of the carbide frame is 25–30 %; the pore size is 1.0–1.5 μm. It has been also demonstrated that ceramics based on boron carbide and boron carbide with 50 % silicon carbide impregnated with silicon at high-temperature sintering has higher strength and hardness values than those based on silicon carbide due to higher adhesion strength at the interface of boron carbide particles and binder, caused by the dissolution of boron carbide in the silicon melt and the formation of complex carbide particles on the surface.

One of the limitations imposed on this process of bending is the possibility of cracking on the surface of the sheet during bending. To predict this type of metal destruction, information is needed on the plastic properties of the material and the stress state in the deformation zone during the bending process. The solution of the problem of sheet bending under conditions of a flat-strained state by graphical construction of the slip line field using a rigid cylindrical mandrel has been analyzed. The material model is a perfectly plastic body. The stresses in the deformation zone and accumulated strains have been determined. The bending process is characterized as unidirectional and monotonous. It has been determined that the mean stress on the outer surface of the sheet during bending equals to 1, and it does not depend on the sheet thickness and the radius of the rigid cylindrical mandrel. Verification of the accuracy of the graphical solution is made. The resulting solution can be used as the basis for an experimental method for testing the plastic properties of metals.

A calculation of the technological process of lumber drying in convection drying chamber of periodic action is presented. For this purpose, a three-dimensional geometric model of a drying chamber with a lumber pile is developed. A physico-mathematical model describing the processes of heat and mass transfer both in the drying agent and in the stack is presented. The three-dimensional geometry of the problem was taken into account by using the Ansys Fluent package. The process of mass transfer in wood was described on the basis of User-Defined Function and User-Defined Scalar. The result of calculation of a specific technological regime of drying of stack from pine sawn timber is given, which allowed finding detailed spatial distributions and temporary changes of the temperature and humidity fields for the drying agent and wood. On their basis, graphs of the time variation of the mean values are plotted. The nonlinearity and interrelationship of the processes of heat and mass transfer in a convective drying chamber leads to unsteadiness of the drying process. So, during the warm-up stage, it is not possible to avoid moisture removal from the lumber. At the drying stages, the unsteadiness leads to an oscillatory character of changes of the temperature, the mass fraction of vapour and the relative humidity of air in the gaps between the wood boards at the intensive heat input. Therefore, it is necessary to take additional procedures to keep the drying agent parameters constant at the drying stages. The obtained results can be used for the design of drying chambers and the development of drying regimes of lumber based on the mathematical modeling and computational experiment.

An analysis of process of scanning laser processing is made. The possibility of use of program and changeable power of a laser radiation in the course of scanning is shown. A mathematical model of process of training is developed by the scanning laser radiation. The model considers parameters of reciprocation of a laser beam and headway of a detail. Calculation of the temperature profile arising at laser training with a constant power and with change of power of a laser radiation depending on the provision of a laser beam at its relative movement is executed. Implementation of laser training with a program and changeable power of radiation in the course of scanning allows lowering a metabolic cost by 25 % with preservation of the given geometry of a zone of hardening. Results of laser training of a surface of steel 45 with the gas laser and the process unit on the basis of the fiberoptic laser with power up to 2 kW are presented. The volume, hardened in unit of time, was taken for an indicator of efficiency. Use of radiation of the fiber-optic laser provides increase in efficiency of training by 3–5 times in comparison with use of radiation of CO2 laser of the same power. The gained effect is explained by change of conditions of interaction of radiation with the surface of metal at change by an order of a radiation wavelength and also by change of balance distribution of heat in a zone of influence of a laser beam. Taking into account higher efficiency of fiber-optic lasers in comparison with gas, the energy efficiency of use of fiber-optic lasers for the surface strengthening is 9–15 times higher than when using CO₂ lasers.

The work of the CDI salt water distiller based on the principle of bulk deionization by creating a double electric layer on the porous structure of the electrode was investigated. The possibility of increasing the efficiency of desalination by reducing the time of discharge diffusion processes in high-porous electrodes is studied. In the experiments, a flow-through type was used, the pumping of the solution in which is carried out through porous electrodes separated from each other by a permeable separator, without the use of ion-exchange membranes. The analysis of possible pore sizes for various sorbing materials is carried out and estimates of the duration of the corresponding pulses of the control voltage are performed. Preliminary experiments carried out on a model CDI cell allowed us to optimize the choice of electrophysical parameters for carbon felt electrodes of the “Carbopon-Active” type and the “AUT-M-2” fabric produced by OJSC “SvetlogorskKhimvolokno”. A method is proposed for reducing the discharge cycle time by supplying a series of pulses of reverse polarity voltage to the electrodes of a desalter. When matching the characteristics of the porosity of the electrode material and the duration of the pulses, it is possible to achieve accelerated removal of salt ions by increasing the electric field strength from the depth of the pores to the outside, into the interelectrode gap. The estimated pore size was ~ 100 μm; therefore, in a relatively long interelectrode gap of ~ 1 mm, the main mass of ions during the pulse does not have time to reach the surface of the electrodes. This made it possible to maintain the high efficiency of the CDI desalination process. Experiments on a model cell and a full-scale CDI-desalter demonstrated a 2.5-fold decrease in the discharge cycle time in the regime of superposition of control pulses in comparison with the short-circuit mode of electrodes.

The autonomous power supply system (APSS) from synchronous magnetoelectric generator and active voltage rectifier (AVR) maximally meets the requirements of the minimum specific mass and the complete coordination of the primary electric power source with the load. With multiphase (m > 3) execution of the electric machine, it is possible to obtain a trapezoidal electromotive force (EMF) and increase the specific power conversion provided that the EMF and the current at the output of the m-phase generator are fully matched. Therefore, the aim of the work is to synthesize the space-vector modulation (SVM) algorithm of the active voltage rectifier to fully match the primary source of electrical energy with the load under the condition of a trapezoidal EMF of the generator. Synthesis of the PVM algorithm for the m-phase AVR is based on the use of a vector-matrix mathematical apparatus. Using the example of a nine-phase system, a SVM algorithm has been developed, the feature of which is the transformation of the generalized voltage vector m-phase coordinate system into (m – 1)/2 voltage vectors with different angular velocities in two-phase orthogonal stationary αβ coordinate systems. At the same time, based on the developed PVM algorithm, it is possible to independently control the (m – 1)/2 voltage vectors in the corresponding αβ planes, providing a signal similar to the EMF of the generator at the input terminals of the AVR. In order to confirm the theoretical propositions, an imitation model of the space-vector modulation unit for the realization of trapezoidal signals at the terminals of a nine-phase AVR has been developed. The efficiency of the developed algorithm is confirmed by the results of simulation modelling. As a result of the evaluation of the energy parameters (operating power) of the phase of power supply system direct current, it is established that the application of the developed space-vector modulation algorithm for the active voltage rectifier in order to fully match the trapezoidal shape of the EMF and the current at the output of the m-phase generator will increase the power of the APSS by 14 % compared to a power supply system of direct current with a sinusoidal form of the EMF and the current of the generator phase. It is established that the developed measuring device can be used to establish the presence of defects like “delamination”. The influence of the depth of the defect placement on the measured parameters is shown.

The problems of measurement the physical and mechanical properties of carbon materials by the dynamic microindentation method are considered. The description of the gage design for measurements is given. This gage allows creating different initial energy for straining of the material tested. It is shown that the design of the gage and the device allows testing both integral (in a large volume of straining) values of the hardness and the elastic modulus, and values of these characteristics for different structural components of the carbon-carbon composites materials: carbon rods and pitch. The obtained data confirms the possibility of using the accepted elastoplastic model of straining of the materials tested for the determination of the elastic modulus and hardness. The ratio between the dynamic and static characteristics is derived. Samples from such carbon materials as pyrolitic graphite, silicified graphite, graphite PPG, coal-filled PTFE and polyamide have been certified. Using these samples it was shown that the dynamic indentation method allows determining the elastic modulus in the range from 0.5 to 100 GPa and the hardness of indentation in the range from 20 to 550 MPa with an error not exceeding 10 %. It is established that the developed measuring device can be used to establish the presence of defects like "delamination". The influence of the depth of the defect placement on the measured parameters is shown.

The spectral and energy characteristics of two planar dielectric resonators (DRs), open and shielded from the curvilinear surface, excited in higher-order modes as whispering gallery modes (WGMs) in Ka-waveband are investigated. These resonators are formed by a thin (compared to the operating wavelength) disk dielectric structure, located between two conducting planes. Thus, the E-field of the resonator was limited along the height of the planar disk by two conducting surfaces. The resonance properties of such a structure are determined by the condition of total internal reflection of waves from the internal curvilinear surface of a dielectric disk. The carried out investigations shown that the unloaded Q-factor is increased at the arrangement of planar dielectric disk inside the ring metal shield at the certain ratio of the radiuses of the shield and dielectric disk. The Q-factor of the shielded resonant structure at the high-frequency edge increases to 40 %. The partial displacement of the resonant field of the WGMs modes from the dielectric to the air gap is the cause of this effect. It leads to decrease in losses in the dielectric material. A computer simulation of the WGMs fields in the planar DR was carried out using the CST Microwave Studio 2013 software to confirm this effect. In addition, computer simulation results shown that these WGMs in the planar DR are characterized by a homogeneous distribution of the resonant field along the axial coordinate. The perspectives of using planar DR in solid-state Ka-band oscillators are shown.

When forming the design parameters of an unmanned aerial vehicle (UAV) on solar energy, it is important to consider the peculiarities of energy supply not only when performing horizontal flight, but also at other stages (take-off, landing, maneuver, etc.), which ultimately form a common flight trajectory the implementation of which ensures the implementation of the specific task assigned to the UAV. However, the flight should be considered taking into account the actual operating conditions, including atmospheric factors. Determining the features of planning the trajectories and stages of flight of a UAV on solar energy during the implementation of a long flight, considering energy, design constraints and actual operating conditions, is the goal of this work. The possible trajectories of flight of UAVs on solar cells are determined in accordance with the typical tasks of its practical application. A discrete model is proposed for planning a trajectory of a route for a UAV on solar cells. The principles of the implementation of the stages of takeoff and landing of UAVs on solar energy are described, the dependencies between the energy consumption and the main parameters of each stage are determined. The dependences are obtained for determining the main components of the energy balance of UAVs on solar energy on the parameters of curvilinear flight. Verification of the obtained dependences was carried out by comparing the calculated and experimental (flight) data for a particular UAV on solar energy, which is of the mini class by mass. The convergence of the results of calculation and experiment is in the range of 15–20 %. The factors acting on an aircraft in a restless atmosphere, their effect on operational and design constraints are established. A generalized analytical model was obtained to determine the conditions for the implementation of a long flight (4–6 hours) of a solar-powered UAV, considering: mass, aerodynamic, energy characteristics; trajectory, atmospheric and operational conditions. The results of the study can be used at forming the shape of a UAV on solar energy at the stage of its preliminary design.

The scope of this work are electric circuits or electronic devices with chaotic regimes, in particular the Chua’s circuit. A nonlinear analysis of chaotic attractors based on the Krot’s method of matrix decomposition of vector functions in state-space of complex systems has been used to investigate the Chua’s circuit with smooth nonlinearity. It includes an analysis of linear term of the matrix series as well as an estimation of influence of high order terms of this series on stability of complex system under investigation. Here the method of matrix decomposition has been applied to analysis of the Chua’s attractor. The terms of matrix series have been used to create a simulation model and to reconstruct an attractor of chaotic modes. The proposed simulation model makes it possible to separate an influence of nonlinearities on forming a chaotic regime of the Chua’s circuit. Usage of both the matrix decomposition method and computational experiment has allowed us to find out that the initial turbulence model proposed by L. D. Landau is suitable for set-up description of the chaotic regime of the Chua’s circuit. It is shown that a mode of hard self-excitation in the Chua’s circuit leads to its chaotic regime operating with a double-scroll attractor in the state-space. The results might be used to generate of chaotic oscillations or data encryption.