Home – Home – Jornals – Journal of Applied Mechanics and Technical Physics 2023 number 1

Results of experimental studies of diffusion combustion of hydrogen microjets performed in recent years are presented. Specific features of the hydrogen flow structure and hydrogen combustion are studied for various shapes of the nozzle, jet exhaustion velocity, and gravitation. Hydrogen combustion in mixtures with other gases and periodic actions on microjets (in the case considered, by external acoustic disturbances, is also considered.

In this study, the burst pressure of thin-walled pressure vessels made of carbon steel is numerically simulated and verified by experimental results. The effect of the length-to-diameter ratio on the burst pressure is analyzed. The numerical and experimental results are compared.

The combustion of 12 composite propellants of the following composition was studied: 60% ammonium perchlorate of the sieve fraction (180-250 μ m)-20% active combustible binder- 20% titanium of different particle size and nature (with spongy particles of size d =32-71 μ m and with rolled pseudospherical particles of size d = 71-500 μ m). Burning rates and agglomeration parameters of the metal component at pressures 0.35 MPa in nitrogen and 0.1 MPa in air were determined. It has been found that agglomerates with minimal sizes are formed when using titanium powders with particles of the smallest sizes.

The process if single-stage synthesis of composite nanoparticles of titanium dioxide and silicon dioxide in the working zone of a plasmochemical reactor is modeled with the use of the chloride method based on joint oxidation of titanium and silicon tetrachlorides. The synthesis model takes into account the possibility of aggregation not only of titanium dioxide particles forming composite particle cores, but also of silicon dioxide particles, which do not participate in the formation of particle shells. The results predicted by various models (core size, shell thickness, and number of particles of various types) are compared.

An overview of laser welding methods and additive technologies used in modern mechanical engineering is given, and the main trends and aspects of these technologies are discussed. Processes of laser welding of thermally hardened aluminum alloys and problems of obtaining high-strength welded joints are considered. The additive growth of heterogeneous materials is analysis taking into account the dimensionless parameters that determine the structure of materials formed using additive technologies.

The problem of the interaction of a solitary wave with a partially immersed stationary body over an uneven bottom. This problem is solved using the nonlinear dispersion shallow-water model (Serret-Green-Naghdi) and the model of potential flows. The influence of the horizontal and vertical sizes of bottom irregularities and their location relative to the partially immersed body on the values of the total force acting on the obstacle. It is shown that the horizontal component of this force increases monotonically with increasing vertical dimension and length of the underwater obstacle. This effect is also enhanced when approaching the body The vertical component of the force is slightly affected by the obstacle, and its dependence on the obstacle size can be nonmonotonic.

Investigation of the flow behind a hydro turbine runner on a large-sized experimental rig consisting of a spiral chamber, stator columns, guide vanes, and a runner is difficult due to the high cost and labor intensity. This paper presents an approach to modeling the flow velocity distribution at the inlet to the draft tube of a hydro turbine, which can significantly reduce the cost of testing. In this approach, the flow at the inlet to the draft tube is modeled using a special swirl apparatus - a combination of two vane swirler: fixed and rotating. The results of an analytical calculation of the shape of the vanes for reproducing a specified velocity distribution corresponding to the optimal operation of the hydro turbine are given.

The velocity of bubbles in polydisperse bubbly flow in an inclined flat channel has been studied for various values of the Reynolds number (4500-22700) and gas volume fraction. The diameter of gas bubbles was studied using the shadow photography. It has been shown that for small values of the Reynolds number, the relative velocity of the bubbles is higher. For small gas volume fraction, a significant number of bubbles has a small diameter (1 mm), and at high gas flow rates, the bubble diameter increases to 3-5 mm.

Using the methods of physical and colloidal chemistry, capillary effects at the boundaries oil - ice - atmosphere and oil - ice - water are considered and it is shown that in the presence of these effects, the spreading of oil over the ice surface is limited, in contrast to the water surface. Formulas for determining the limiting thicknesses of the oil film are obtained, which can be used to assess the spatial scale of oil pollution of solid ice cover.

In this paper, a two-dimensional, steady, laminar boundary layer analysis is presented to analyze numerically the internal heat generation and Soret-Dufour effects on mixed convection flows of power-law fluids adjacent to a vertical flat plate maintained at variable heat flux and variable mass flux conditions in a Darcy porous medium. The Ostwald-de Waele power-law model is utilized here. The transformed governing equations are solved by the Keller box method. After performing comparisons with previously published results, good agreement is obtained.

A modified form of differential equations is proposed that describes physical processes studied in applied mathematics and mechanics. It is noted that the solutions of classical equations at singular points may experience discontinuities of the first and second kind, which have no physical nature and are not observed experimentally. When deriving new equations describing physical fields and processes, we consider not infinitely small elements of the medium, but elements with finite dimensions. As a result, the classical equations include non-local functions averaged over the volume of the element and are supplemented by the Helmholtz equations establishing the relationship between non-local and actual physical variables, which are smooth functions without singular points. Singular problems of the theory of mathematical physics and the theory of elasticity are considered. The obtained solutions are compared with the experimental results.

Based on Haddad's small crack theory, a new comprehensive fatigue life model of the TC4 titanium alloy is proposed through combining the modified Chaboche model and the crack propagation formula considering the crack closure effect. The results of model validation and comparisons show that the crack initiation life and crack propagation life predicted by the model are consistent with the test data under cyclic loading of the alloy.

In this paper, a novel modified strip yield model is proposed to evaluate the load-bearing capacity of an infinite isotropic plate containing five collinear straight cracks with coalesced yield zones. It is assumed that these yield zones are subjected to a linearly varying yield stress. The well-known complex variable method is used. To assess the results, numerical studies are carried out for different cracks lengths. Good agreement of the results obtained is observed with previously published data.

A simulation mathematical model is presented that describes the process of vitrification and devitrification of the binder. Theoretical estimates of the effective physical and mechanical parameters of the material and microstructural stresses with temperature change are obtained. A numerical scheme has been developed (in the form of a computer program) that makes it possible to implement the modeling technique. Estimates of elastic moduli and submicrostructural stresses are obtained. The results can be used to select the composition of the material and its parameters at the final stages of the technological process of creating a polymer binder.

The plastic instability of an internally impulsively loaded thin-walled end-closed cylindrical shell with plastic anisotropy is investigated. The cylindrical shell is assumed to be made of a ductile material. Based on Hill's orthogonal anisotropic yield criterion, the instability strain of a thin-walled end-closed cylinder is derived, which takes into account the effects of the plastic orthotropy and strain rate. The numerical analysis of the instability strain is conducted. The results show that the instability strain for a thin-walled end-closed cylindrical shell depends upon the deviation from isotropic plasticity and the strain rate.

The Bhatnagar-Gupta method is used to consider a solution to the problem of torsion of a rod with a circular cross section cut in the longitudinal direction from a transversally isotropic plate under creep conditions is considered. It is shown that the solution agrees satisfactorily with the lower and upper estimates of the twisting angular velocity obtained on the basis of the principles of minimum total power and additional scattering, as well as with the results of numerical simulation in the Ansys finite element program. Based on the Bhatnagar-Gupta solution, the possibility of using the method of characteristic parameters for estimating the stress-strain state and the rate of the twist angle of a rod under the action of a constant moment is shown.

Theoretical aspects of natural gas liquefaction at a high-pressure gas distribution station using the Claude open cycle are considered. Based on the thermodynamic analysis of the cycle, it is shown that there are two modes of gas liquefaction: if the initial gas pressure is higher than the critical one, the liquefaction process by throttling the production flow can be considered as isenthalpic; if the initial gas pressure is below the critical one, the process of gas throttling and liquefaction should be considered as a set of processes of isentropic expansion and subsequent adiabatic expansion and deceleration of the production flow. For both modes, mathematical models and algorithms for numerical calculation of the natural gas liquefaction process have been developed. The value of the maximum yield of liquefied gas was estimated, taking into account its real properties and existing restrictions. It is shown that the obtained calculation results are in good agreement with the known experimental data.

A novel dual-axis solar tracker (DAST) based on a super-twisting high-order sliding mode controller (STHOSMC) is proposed. The surface of the photovoltaic panel is perpendicular to the solar radiation at all times. The super-twisting algorithm due to its super-spiral curve can precipitate the convergence and reduce the chattering phenomenon. Hence, the STHOSMC can promote the tracking performance of the DAST and smooth its tracking motion without the need to obtain the sliding variable time derivative. Various scenarios of the sunlight and temperature have been considered to deal with the tracking performance of this proposed controller. The simulation results under these scenarios have validated that the proposed controller accurately extracts the maximum electrical energy from the sunlight. To further evaluate the performance of the STHOSMC-based DAST, its prototype model has been provided and tested.