Home – Home – Jornals – Journal of Applied Mechanics and Technical Physics 2023 number 4

The goal of this study is to develop hybrid composites to experimentally and numerically assess their behavior under a ballistic impact. The Al₂O₃ ceramic/woven fabric (Kevlar or UHMWPE) reinforced epoxy/Al-alloy multi-layered armours are developed. Simulation and ballistic test results show good agreement.

The problem of thermocapillary convection in a flat bounded region filled with liquid and gas in contact along the interfacial interface is studied under weak evaporation. To study the processes of heat and mass transfer and the parameters of phase transitions under conditions of local heating, a two-sided mathematical model based on the Oberbeck-Boussinesq equations is proposed. The characteristics of mass transfer through the thermocapillary interface due to evaporation and vapor content in the gas layer are analyzed taking into account the influence of the Soret and Dufour effects. The results of a numerical study of the evolution of the interface and unsteady flows in a cell are presented. The calculation of the main characteristics of the liquid-gas system and the position of the interface at each moment of time was carried out using a specially developed numerical algorithm. The presented model makes it possible to describe the formation of characteristic thermal and concentration structures and transient modes of cellular convection with a complex configuration of flows in layers

Activities aimed at studying stabilization of a high-speed boundary layer with the use of porous coatings are reviewed. All types of coatings used in experimental research are considered. It is demonstrated that a porous coating with optimal parameters can stabilize the second mode of disturbances to a large extent and delay the laminar-turbulent transition in a high-speed boundary layer. A review of numerical investigations of porous coatings is presented, and it is shown that special boundary conditions are imposed for porous coating modeling; otherwise, the flow has to be calculated in each pore of the coating. The major part of results obtained on the basis of the linear stability theory and in direct numerical simulations agree well with experimental data. Examples of methods of porous coating optimization and of using promising metamaterials are provided.

The results of experimental studies of the process of cooling a zirconium ball in subcooled ethanol under the action of a submerged jet are presented. During the experiments, the degree of subcooling of the cooled liquid and the distance from the nozzle exit to the cooled surface varied. Thermograms of cooling are presented and the influence of the distance between the nozzle and the surface on the duration of cooling and the transition temperature from stable film boiling to intense heat transfer is revealed.

Behavior of a transversally flowing fluid in a boundary layer on a plate and a wedge is studied using the Faulkner-Scan equation in the presence and absence of suction and blowing on the body surface. Numerical methods are used to show that, under certain conditions in the boundary layer, one may observe the formation of attraction and repulsion lines (the transverse velocity along these lines is zero) and maximum transverse velocity lines. Different transverse flow regimes in the boundary layer depending on the key parameters of the problem are considered

An algorithm for controlling submerged jets has been developed to calculate the geometry of the forming device, which provides the velocity profile and (or) the required characteristics of its linear instability in the initial section of the jet. A class of forming devices is considered, the geometry of which is similar to the geometry of the device created at the Research Institute of Mechanics of the Moscow State University. The control algorithm is based on the gradient descent method to minimize the functional relating the parametrically specified shaper geometry and the selected characteristic of the corresponding initial jet velocity profile formed by it. The operation of the algorithm was tested on the example of a functional describing deviations of the jet velocity profile from the given one

The aim of the present work is to examine the flow of electrically conducting immiscible Newtonian fluids with variable viscosity through an inclined channel under the influence of a magnetic field. The flow is generated because of a constant pressure gradient. The flow in an inclined channel is governed by the Navier-Stokes equations. Analytical expressions for the velocity, flow rate, and stress are derived. The influence of various parameters of the problem on the flow characteristics is analyzed.

Using the Navier-Stokes system of equations, rotational regimes of thermocapillary fluid flows in a semi-infinite space bounded from above by a non-deformable free boundary, on which a local temperature distribution is specified, are calculated. It is shown that in the boundary layer near the free boundary, as a result of bifurcation, rotational regimes of fluid flows arise during non-uniform cooling of this boundary. Secondary rotational modes are calculated, which form two families of solutions that depend on several parameters, and two parameters are not determined by external conditions.

The theory of the complex matrix differential operator and finite amplitude analysis are used to investigate nonlinear nanofluid convection in a porous medium saturated under gravity modulation. The finite amplitude of convection for the g-jitter is derived while applying the solvability condition of the third order. To calculate the heat and mass transfer through the porous medium, the low-amplitude analysis is performed. The Nusselt numbers are calculated at the second order as a function of the finite amplitude to evaluate the heat and mass transfer. It is found that changing the gravitational field can affect the amount of heat and mass transfer effectively. It is also found that the oscillatory mode is preferable for better heat and mass transport results than the stationary mode.

A method is proposed for calculating the Darcy friction coefficient in a flat channel formed by two infinite parallel plates, depending on the values of the Reynolds number and the rarefaction parameter of the gas in the channel. Maxwell's diffuse reflection model is used as a model for the reflection of gas molecules from the channel walls. The isothermal gas flow is due to the presence of a small absolute pressure gradient directed along the channel walls. The proposed method is based on solving the linearized ellipsoidal-statistical Boltzmann kinetic equation with homogeneous boundary conditions using the Chebyshev polynomial approximation. An unknown function that interpolates the solution of this equation is represented as a partial sum of a series in Chebyshev polynomials of the first kind. Using the properties of finite sums for an orthonormal system of Chebyshev polynomials, the problem is reduced to a system of linear algebraic equations with respect to the values of the desired function at the interpolation nodes. The analysis of the obtained results was carried out

Using the results of experimental studies, a comparison is made of the space-time distributions of the amplitude of controlled pulsations in the linear and weakly nonlinear phases of the development of a wave train in homogeneous and inhomogeneous boundary layers on a flat plate at a Mach number M=2. (The inhomogeneity of the flow is caused by a longitudinal stationary perturbation generated by a pair of weak shock waves. Controlled perturbations were generated locally from the surface at a fixed power of the high-frequency glow discharge inside the model.) It is established that the inhomogeneity of the flow changes the mechanism of interaction of subharmonic perturbations. It is shown that in the center of the wave train there is a violation of the spatial synchronism of pulsations of subharmonic frequency

The transport of a two-phase multicomponent gas condensate mixture in the vicinity of a vertical production well is considered taking into account the possible nonequilibrium of the process, namely, the kinetics of the gas-condensate phase transition. Results of numerical solution of the transport problem are presented for different well production rates and different rates of relaxation to the thermodynamic equilibrium of the reservoir mixture. It is shown that the effect of nonequilibrium increases with increasing well production rate

Resolving equations describing stationary flows of an incompressible viscoelastic polymer fluid through a circular pipe are derived on the basis of the rheological mesoscopic Pokrovskii-Vinogradov model. Exact solutions of the equations are obtained, and restrictions on the values of the rheological parameters that ensure their existence are formulated. These results enable one to constructively describe the destruction of Poiseuille-type laminar flow. The size and orientation of the macromolecules of the polymer fluid play a key role in the mechanics of this process. liquids. The mathematical description of the process uses the singular points of the solutions

The paper presents an analytical solution of the problem of stress relaxation in a bended viscoelastic plate. The effect the difference in the viscous properties of the material in tension and compression on the relaxation of the bending moment is investigated. The deformation is assumed to be finite, and the multiplicative decomposition of the deformation gradient tensor into elastic and inelastic components is used. Two different material models with tension-compression asymmetry are compared

Since in modern high-performance sports, the technical component is decisive, an important element of skiing race is the sliding surface of skis. This paper presents a review of papers on sliding mechanics and discusses modern ways to improve it and prospects for the development of this area in modern energy and environmental conditions. A detailed analysis of various factors affecting the sliding mechanics, in particular, snow cover albedo, and microroughness of the sliding surface of skis is given

The efficiency of two ways to reduce vibration and sound emission of a plate made of paper-laminated plastic (high-pressure laminate) has been investigated. It has been found that the inclusion of a polymer polyvinyl acetate film in the plastic structure or using constrained damping layer treatments based on polyvinyl acetate film and aluminum foil or plastic leads to a significant improvement in its vibroacoustic characteristics. The greatest reduction in vibration and sound emission was obtained when applying a coating with aluminum foil whose thickness was six times less than that of the damped plastic plate

The solution of the system of nonlinear elasticity equations was found the described the stress-strain state of a two-layer incompressible material. The solution can be used to describe the compression of a two-layer material by rigid plates that approach each other with constant acceleration

This paper describes the use of a nonlinear viscoelastic model with material properties depending on the strains in the lengthwise fracture analysis of an inhomogeneous cantilever beam structure. The viscoelastic model is obtained by placing a~nonlinear spring and a nonlinear dashpot in parallel to a series of a linear spring and a linear dashpot. The modulus of elasticity of the nonlinear spring and the coefficient of viscosity of the nonlinear dashpot depend on strains. The strain energy release rate is determined. The balance of the energy is analyzed to prove the correctness of the strain energy release rate solution.

A method for determining the limiting expansion coefficient of cylindrical pipes using conical equipment is considered which allows a fairly accurate calculation of the moment of fracture of a workpiece taking into account the nonlinear plasticity of the material and the change in thickness. The method is based on the use of forming limit diagrams to predict the fracture of the workpiece and the method of variable elasticity parameters to determine the stress-strain state

Implementation of the Candler model of vibrational-vibrational energy transfer between diatomic molecules in an inelastic collision is discussed. An example of oxygen O₂ and nitrogen N₂ interaction is used to analyze the method of simple iterations, the Newton method, the method of bisection, and the approximate formula for calculating the equilibrium vibrational temperature, which is necessary in the Candler model. The method recommended for simulations is the Newton method or bisection. The model of vibrational-vibrational energy transfer is tested by examples of zero-dimensional vibrational relaxation, the flow around a cylinder, and the flow in a wedge-shaped nozzle. It is demonstrated that vibrational-vibrational energy transfer affects the distribution of vibrational temperatures