Home – Home – Jornals – Journal of Applied Mechanics and Technical Physics 2023 number 2

This paper describes how the method of preparing a composite TiC - n Ni mixture (n = 40, 50, 75% is the volume fraction of nickel) affects the carbide content in the coating material obtained by cold spraying. It is shown that, when coatings are obtained from a powder mixture prepared in a V-shaped mixer, the titanium carbide content is lower than in coatings obtained from powders mechanically processed in a high-energy planetary mill. In the case of mixing the powder mixture in a V-shaped mixer, fine titanium carbide particles do not reach the substrate surface during spraying because they are decelerated in a shock-compressed gas layer when a supersonic jet accumulates on an obstacle. Thus, these particles do not participate in the formation of the coating. Spraying a mechanically treated powder consisting of composite agglomerated TiC-Ni particles allows for a significant (approximately 1.8-fold) increase in the carbide content in the coating

The impact of vibrating manipulation on arterial hemodynamics and mechanical properties is explored by using the finite element method for the fluid-structure interaction. Numerical simulation results show that massage greatly changes the flow behavior of blood within the artery. Under the massage manipulation, the mean blood flow increases by more than 5.34% at a frequency of 2ʄ₀ and by smaller values at frequencies of f0 and 4ʄ₀. The blood flow has obvious disorder characteristics and an obvious wall shear stress concentration in the mixed flow area. The von Mises stress of the artery wall increases, reaching a peak value at the maximum deformation.

This paper describes an approach to modeling the flow velocity distribution at the inlet of a hydro turbine draft tube that can significantly reduce test costs. The flow is modeled using a special apparatus consisting of a combination of two swirlers: fixed and rotating. A previously proposed method for designing swirlers to generate velocity fields corresponding to the velocity distributions behind real hydro turbines was used to design eight blade arrays modeling the velocity distributions in optimal operating modes of hydro turbines of various types. This paper presents a test numerical calculation of flow parameters using the Ansys program and a comparison of the designed velocity distributions with experimental velocity profiles obtained on an aerodynamic rig using a laser Doppler anemometer. The design, calculated, and experimental velocity profiles at the draft tube inlet are in satisfactory agreement. Thus, the promising approach to the experimental modeling of the hydro turbine flow was successfully tested.

Results of experimental and numerical investigations of the flow around an elongated axisymmetric body or revolution in a low-velocity wind tunnel with a closed test section and in a free flow are reported. The Reynolds number based on the body length is varied in the interval 2,75x10⁶ ÷ 9,40x10⁶. The problem is solved numerically under the assumption of an axisymmetric steady incompressible flow with the use of the ANSYS Fluent software. It is demonstrated that the test section walls produce a significant effect on the flow character and aerodynamic characteristics of the body of revolution for the case where the blockage FACTOR of the test section by the body of revolution is formally within 2%.

New analytical solutions for the calculation temperature changes in the liquid flow and in the metal casing string due to induction heating of the string section. The solutions are based on a one-dimensional analytical model, in which convective heat transfer by fluid flow is taken into account, heat transfer between the liquid and the casing string, heat generation in the metal column when the inductor is turned on and losses in cement and rock due to thermal conductivity. To obtain a solution, the integral method was used. Laplace transform in time, inverse transform carried out using the numerical Stefest algorithm. Features explored temperature field during heating and after shutdown inductor, it is shown that the rate of decrease in temperature anomalies increases with increasing liquid flow in the column. Comparison of the results of calculations by the analytical model with numerical simulation results in the Ansys software package Fluent, as well as with experimental data. It is shown that the received analytical solutions can be used in forecasting temperature anomalies caused by induction heating of the casing columns.

The properties of the dispersion relations for two new fully nonlinear weakly dispersive shallow water models are studied, for which, with certain parameters, it is possible to obtain the fourth, sixth, or eighth order of accuracy of the approximation of the phase velocity of the three-dimensional potential current model. For the hierarchy of shallow water models, under the assumption of a slightly changing shape of the bottom, formulas are obtained that establish the relationship between the rate of change in the wave amplitude and the rate of change in the thickness of the liquid layer, and the dependences of the amplitude and length of the incident wave on the depth of the water area are also derived. It is shown that the new model of the fourth order long-wavelength approximation with the eighth order of accuracy of the dispersion relation provides the best approximation of the considered characteristics in the case of both a horizontal bottom and a variable-shaped bottom

A system of the Euler equations that describe two-dimensional steady flows of an ideal fluid is considered. This system is reduced to a nonlinear Laplace equation for the stream function. With the use of the Hirota τ-function, solutions of three elliptical equations (sin-Gordon, sinh-Gordon, and Titeica equations) are found. A simple method of deriving solutions in the form of rational expressions in elliptical functions is proposed. The resultant solutions describe sources in a swirled fluid, jet flows, chains of sources and sinks, and vortex structures. It is shown that the fluid flow rate over a closed curve is quantized in the case of the elliptical sin-Gordon equation.

Based on the turbulence model and the Ffowcs Williams-Hawkings (FW-H) acoustic model, numerical simulations of acoustic characteristics in the Hartmann whistle with the Helmholtz resonator are carried out. The important parameters that control the flow oscillation features of the Hartmann whistle are the stand-off distance, cavity geometry, nozzle pressure ratio, etc. The computational results are compared to experimental data. Under the condition that the jet exit diameter, cavity diameter, nozzle pressure ratio, and stand-off distance remain constant, the mass flow rate and the sound pressure level are calculated as functions of the diameter and length of the Helmholtz resonator. The results show that the sound directivity is similar in the conventional Hartmann whistle and the Hartmann whistle with the Helmholtz resonator, while the sound intensity is higher in the conventional Hartmann whistle. Also, the sound intensity reaches the maximum in the direction perpendicular to the jet. The magnitude of the sound intensity decreases gradually with an increase in the diameter of the Helmholtz resonator, and the decreasing trend in the fundamental resonance frequency is clearly visible. Next, as the length of the Helmholtz resonator increases, the sound intensity first decreases and then increases again. The effect of the resonator length on the fundamental resonance frequency is not large as compared to the resonator diameter.

The flow in a nonuniformly rotating (librating) cylinder with ends symmetrically inclined relative to the cross section is experimentally investigated. Due to librations, inertial waves are supported; at certain frequencies, they are focused on a closed path, called a wave attractor. The velocity of the pulsation flow changes nonmonotonically with frequency and reaches its maximum value when the attractor takes a square shape. With an increase in the oscillation amplitude, new vorticity centers appear in a threshold way, corresponding to inertial waves with a frequency different from the libration frequency. The Fourier analysis of perturbations in the supercritical regime shows that, in addition to the fundamental frequency, the spectrum contains two additional harmonics that satisfy the triadic resonance condition.

The interaction of a step-like pressure wave with a spherical gas-liquid cluster in a cylindrical channel filled with a liquid has been studied numerically. It has been shown that the cluster generates a solitary pressure wave of large amplitude. The influence of a bubble cluster on the dynamics of multiple reflection of a pressure wave from the boundaries of the cylindrical channel has been investigated. The results of numerical calculations are in good agreement with experimental data

The paper reports the results of liquid-fuel model combustor calculations based on different numerical approaches to develop a verified simulation method of combustor operation. Both steady and transient studies were carried using different RANS turbulent models and the detached eddy simulation (DES) method, and their results were compared with experimental data obtained by optical methods. RANS and hybrid eddy-resolving DES approach. Conducted comparison of the obtained results with the data of the non-contact optical experiment. The results show that the the greatest differences experiment and calculations are observed for the near-axial flow field where recirlulation backflow is formed. This vortex structure can be properly resolved in a DES solution as well as in transient calculations based on the SAS SST model. The use of the above-mentioned approaches in combination with the flamelet combustion model provides maximum accuracy in predicting the parameters of a reacting swirling flow including velocity and temperature distributions in the combustion chamber

Results of simulations of supersonic turbulent flows in a channel with due allowance for conjugate heat transfer between the air flow and a copper plate modeling the sensitive element of a thermocouple are reported. Numerical simulations are performed for free-stream Mach numbers M_∞ 3, 4, and 5. It is shown that the simulation results agree well with experimental data obtained in a hotshot wind tunnel. It is found that the conjugate heat transfer with the model walls made of steel can be ignored at times of the order of 100 ms.

A generalized mathematical model for the non-isothermal filtration of natural gas in a porous medium and a modified quasi-stationary model of gas hydrate formation (deposition) in pipelines were used to solve a conjugated problem for the case of joint operation of the “gas-bearing reservoir-well” system and predict the changes in temperature, pressure, gas moisture content, and well flow area. It is found that the presence of a thick permafrost layer accelerates hydrate formation inside the well. It is shown that when taking into account the salinity of formation waters, the duration of complete plugging of the well with hydrates increases

In this study, nonlinear forced vibrations of a bimorph piezoelectric nanobeam are investigated by using the nonlocal elasticity theory. This nanoactuator is modeled using the Euler-Bernoulli beam theory. The Hamilton principle is used to obtain the equations of motion. The derived equations are discretized by applying the mode shapes of multi-span beams as test functions in the Galerkin decomposition method. The discretized equations are then solved using the perturbation method. A parametric study is conducted to show the significance of size effects on the dynamic behavior of nanoactuators. The results show that an increase in the nonlocal parameter leads to a decrease in the fundamental natural frequency of the nanobeam and to an increase in the response amplitude.

By solving the plane problem of the mechanics of a rod strip having a fixed finite-length section on one of its front surfaces, it has been shown that when studying deformation processes with consideration of the compliance of the fixed section, it is necessary to take into account the change in the stress-strain state parameters and the mathematical models used for their description. This change occurs across the boundary between the unfixed and fixed sections. Within the framework of the classical Kirchhoff-Love model, it is impossible to take into account the compliance of the fixed section of the rod. However, within the framework of the simplest refined Timoshenko shear model, this is possible if the section is fixed only on one of the front surfaces. Exact analytical solutions of two simplest linear problems of static transverse bending of a flat rod with fixed sections of finite length on one of the front surfaces are found. One-dimensional finite elements for modeling unfixed sections of flat rods and sections on one of the front surfaces were constructed using the refined Timoshenko shear model. Numerical experiments were performed, showing the necessity of taking into account the change in the rod strain-stress parameters across the boundary between the fixed and unfixed sections.

The boron nitride nanosheet (BNNS), a graphene-like structure with excellent mechanical properties, is one of the most promising candidates for a reinforcement element to design innovative nanocomposites. Herein, we have investigated the BNNS, which serves for surface enhancement of the aluminum matrix via molecular dynamics simulations. The results show that the boron nitride nanosheet coating enlarges the critical yield strength, hardness, and modulus of elasticity. With an increase in the number of boron nitride layers, the strengthening effect is more significant. Meanwhile, a higher system temperature degrades the interfacial energy and weakens the mechanical properties of the BNNS/Al systems.

The problem of stability of cylindrical shells made of composite material, taking into account momentum and nonlinearity of their subcritical stress-strain state. Geometrically non-linear the stability problem is solved by finite element methods and linearization of Newton -Kantorovich. Critical loads are determined in the process of solving a nonlinear problem using Sylvester's criterion. Hypothesized Timoshenko finite elements of composite cylindrical shells natural curvature, in the approximation of displacements of which in explicit form, rigid displacements are highlighted, which significantly affects solution convergence. The stability of the circular cylindrical shell made of polymer composite material, under combined loading by torsional and bending moments and internal pressure. Studied the influence of the laying method monolayers, non-linearity of deformation, internal pressure on critical loads at which buckling occurs shells

This paper proposes a model of static transverse elastic deformations of a magnetic gel sample shaped as a strongly elongated cylinder, which is under the action of a transverse uniform magnetic field and the force of gravity. Theoretical results obtained within the framework of the proposed model are in qualitative agreement with the results of laboratory experiments

The flows of incompressible media with tensor-linear defining relations, including an arbitrary scalar nonlinearity in the form of a monotonically increasing hardening function. There are two types of media: without yield strength (nonlinear-viscous liquids) and with a yield strength (viscoplastic bodies), and the media of the second type are interpreted as finite perturbations of the corresponding media the first type. On the example of the problem of one-dimensional stationary shear flow in round pipe shows the influence of the method of perturbing the limit fluidity at maximum speed and flow. The values of these quantities depend on the sign of the second derivative of the hardening function, i.e. on what material the unperturbed medium is: pseudoplastic or hardening