Home – Home – Jornals – Journal of Applied Mechanics and Technical Physics 2015 number 2

The effect of various models of the dynamics of the three-phase contact line on the flow characteristics during filling of a plane channel is investigated. The system of constitutive equations is solved numerically using a technique based on the combined use of the SIMPLE algorithm and the method of invariants. Different methods for calculating the motion of the contact point for slip and no-slip conditions for a dynamic contact angle θ = π, neglecting surface tension on the free boundary are considered. It is shown that in the whole computational domain, except in a small vicinity of the contact point, the kinematic characteristics of the flow and the distributions of the dissipation function and shear stress are slightly dependent on the selected calculation method of the motion of the contact point.

This paper presents a mathematical model for bubble flow in a vertical borehole under non-isothermal conditions and the results of calculations of the volume fraction and temperature of the phases. The influence of the bubble size on the formation phase of the temperature fields of the phases.

Results of calculations and experimental investigations of characteristics of a supersonic high-pressure wide-chord stage of an axial compressor are presented. The influence of surface roughness on the characteristics of this stage are analyzed. A method of identification of aerodynamic flow parameters in the compressor duct is described.

This work presents the results of experimental and numerical studies on the process of turbulent mixing ocurring at the contact boundaries of three-layer gas systems during the passage of a stationary shock wave with a Mach number M ≈ 1.3. The experiments are carried out in an air shock tube. The working gases are air, F₆, and He. The flow structure is recorded by a schlieren method with laser illumination. The data on the nature of turbulent mixing in two-dimensional flows are obtained.

A model of the process of migration of methane bubbles in water under thermobaric conditions of hydrate formation is proposed. The peculiarities of the temperature field evolution, migration rate, and changes in the radius and volume fraction of gas hydrate bubbles are studied. It is shown that, with a constant mass flow of gas from the reservoir bottom, for all parameters of the surfacing gas hydrate disperse system, there is a quasistationary pattern in the form of a "step"-like wave. Depending on the relationship of the initial gas bubble density with the average gas density in the hydrate composition determined by the depth from which bubbles rise to the surface, the final radius of hydrate particles may be larger or smaller than the initial gas bubble radii. It is established that the speed at which gas hydrate inclusions rise to the surface decreases by several times due to an increase in their weight during hydrate formation. The influence of the depth of the water reservoir whose bottom is a gas flow source on the dynamics of hydrate formation is studied.

The present work with specific objectives places a greater emphasis on measurements of the breakup lengths and phenomenological analysis of a hot water jet under reduced pumping pressures in still environment. Therefore, visual and comparative studies are conducted on full cone jet disintegration of heated water for low pumping pressures. A further analysis of the grabbed images confirms the strong influence of the input processing parameters on full cone spray patternation. It is also predicted that the heated liquids generate a dispersed spray pattern by utilizing partial evaporation of the spraying medium. The radial spray cone width and angle do not vary significantly with increasing Reynolds and Weber numbers at early injection phases, leading to enhanced macroscopic spray propagation. The discharge coefficient, mean flow rate, and mean flow velocity are significantly influenced by the load pressure, but less affected by the temperature. The fine scale image analysis also predicts toroidal-shaped vortex formation in the spray structure near the water boiling point.

This study investigates the dynamic formation process of water microdroplets in a silicon oil flow in a T-junction microchannel. Segmented water microdroplets are formed at the junction when the water flow is perpendicularly injected into the silicon oil flow in a straight rectangular microchannel. This study further presents the effects of the water flow inlet geometry on hydrodynamic characteristics of water microdroplet formation. A numerical multiphase volume of fluid (VOF) scheme is coupled to solve the unsteady three-dimensional laminar Navier-Stokes equations to depict the droplet formation phenomena at the junction. Predicted results on the length and generated frequency of the microdroplets agree well with experimental results in a T-junction microchannel with straight and flat inlets (the base model) for both fluid flows. Empirical correlations are reported between the volumetric flow ratio and the dimensionless microdroplet length or dimensionless frequency of droplet generation at a fixed capillary number of 4.7 × 10^–3. The results of this study indicate a reduction in the droplet length of approximately 21% if the straight inlet for the water flow is modified to a downstream sudden contraction inlet for the water flow.

A steady boundary layer flow and heat transfer over a radially stretching isothermal porous sheet is analyzed. Stretching is assumed to follow a radial power law, and the fluid is electrically conducting in the presence of a transverse magnetic field with a very small magnetic Reynolds number. The governing nonlinear partial differential equations are reduced to a system of nonlinear ordinary differential equations by using appropriate similarity transformations, which are solved analytically by the homotopy analysis method (HAM) and numerically by employing the shooting method with the adaptive Runge-Kutta method and Broyden's method in the domain [0, ∞). Analytical expressions for the velocity and temperature fields are derived. The influence of pertinent parameters on the velocity and temperature profiles is discussed in detail. The skin friction coefficient and the local Nusselt number are calculated as functions of several influential parameters. The results predicted by both methods are demonstrated to be in excellent agreement. Moreover, HAM results for a particular problem are also compared with exact solutions.

This article presents a numerical solution for the flow of a Newtonian fluid over an impermeable stretching sheet with a power-law surface velocity, slip velocity, and variable thickness. The flow is caused by nonlinear stretching of the sheet. The governing partial differential equations are transformed into a nonlinear ordinary differential equation with appropriate boundary conditions for various physical parameters. The remaining ordinary differential equation is solved numerically by using the Chebyshev spectral method. The effects of the slip parameter and the wall thickness parameter on the flow profile and local skin friction are presented. A comparison of obtained numerical results is made with previously published results in some special cases, and excellent agreement is noted.

This paper presents an experimental study of the influence of the main initial parameters (characteristic size, temperature, velocity) of droplets of an atomized liquid (water) on the process of their evaporation in gases at temperatures up to 1000 K. The limiting values of the initial parameters of liquid droplets at which the rate of evaporation reaches maximum and minimum values were determined.

In the present study, a finite volume computational procedure and a full multigrid technique are used to investigate laminar natural convection in partially heated cubic enclosures. Effects of heated strip disposition in the enclosure on the heat transfer rate are studied. Results are presented in the form of flow lines, isotherms plots, average Nusselt numbers, and average temperature on the heat source surface. Statistical distributions of temperature and average velocity fields and their root-mean-square values are presented and discussed.

A nonlinear thermal analysis of a hollow functionally graded cylinder is performed in the present paper. A power function distribution is used for simulation of non-homogeneity of the material used. A temperature dependence is employed for the thermal conductivity. These simulations reduce the problem to a nonlinear differential equation with a variable coefficient. A semi-analytical method of successive approximations is employed for solving this equation. The convergence of the method is studied for different parameters of the problem by checking two criteria: convergence of the sum of the infinite series and condition of smallness of the residual of the responses. An exponentially function is used for simulation of the nonlinear dependence of cylinder material properties on temperature.

The object of analysis is a heat conduction problem within the framework of tolerance modelling in laminated media with a functional gradation of effective properties. In contrast to the known asymptotic models (based on the homogenization technique), the characteristic feature of the tolerance model equations is that they make it possible to analyze the effect of the microstructure size on the overall behavior of the laminate. The proposed model equations describe heat conduction in laminates by mean of partial differential equations with smooth and slowly varying functions. This paper describes a certain extension of the unified tolerance modelling procedure, which makes it possible to analyze specific problems of heat conduction in laminates with a transversal gradation of effective properties.

This paper presents a review of studies of delayed fracture and fracture mechanics problems in which the hypotheses and ideas of Yu. N. Rabotnov and L. M. Kachanov on the mechanisms of delayed fracture under creep conditions are extended to describe fracture processes using scalar and tensor measures of damage. The results of current research in the theory of elasticity, the mathematical theory of plasticity and creep, the mechanics of composites, and linear and nonlinear fracture mechanics, with material damage taken into account.

The theory of large deformations is used to construct exact solutions of a sequence of one-dimensional boundary-value problems of the occurrence, development, and subsequent deceleration of viscometric flow of an elastoviscoplastic incompressible material located in the gap between rotating rigid coaxial cylindrical surfaces. In the quasistatic approximation allowing for slip of the material on its solid boundaries, the flow initiation conditions in the deformed material and the laws of motion of the boundary surfaces of the flow of this material both during its development and deceleration are determined. The parameters of the stress-strain states in the regions of reversible deformation and flow in all stages of the process, including the cessation of the flow and the complete unloading by rotation of the solid boundary in the opposite direction, are calculated.

This paper exhibits the effect of the amplitude of vibrations on the pull-in instability and nonlinear natural frequency of a double-sided actuated microswitch by using a nonlinear frequency-amplitude relationship. The nonlinear governing equation of the microswitch pre-deformed by an electric field includes even and odd nonlinearities with a quintic nonlinear term. The study is performed by a new analytical method called the Hamiltonian approach (HA). It is demonstrated that the first term in series expansions is sufficient to produce an acceptable solution. Results obtained by numerical methods validate the soundness of the asymptotic procedure.

This paper presents an experimental and theoretical study of the influence of a tensile load on the relaxation of residual stresses in a hardened cylindrical specimen of ZhS6KP alloy under creep conditions at 800 ^oC. An experimental study was conducted to investigate the distribution of the axial residual stress tensor component across the thickness of the hardened layer after hardening by air shot blasting using microbeads and after creep loading for 50 and 200 h under a tensile load of 150 and 250 MPa. A detailed theoretical analysis of the problem was performed. In all loading regimes, the calculated and experimental values of the residual stresses were found to be in good agreement. It was shown that at low tensile load, the relaxation rate decreased in comparison with the case of thermal exposure in the absence of a tensile load and, with increasing load intensity, it increased.

The optimal control problem for a three-dimensional elastic body containing a thin rigid inclusion as a surface is studied. It is assumed that the inclusion delaminates, which is why there is a crack between the elastic domain and the inclusion. The boundary conditions on the crack faces that exclude mutual penetration of the points of the body and inclusion are considered. The cost functional that characterizes the deviation of the surface force vector from the function prescribed on the external boundary is used; in this case, the inclusion shape is considered as a control function. It is proven that a solution of the described problem exists.

Stress-strain curves of dynamic loading of VT6, OT4, and OT4-0 titanium-based alloys are constructed on the basis of experimental data, and the Johnson-Cook model parameters are determined. Results of LS-DYNA simulations of the processes of deformation and fracture of the fan casing after its high-velocity impact with a fan blade simulator are presented.

Vibrations in an elastic beam supported by nonlinear supports at both ends under the influence of harmonic forces are analyzed in this study. It is hypothesized that the elastic Bernoulli-Euler beam is supported by cubic springs to simulate nonlinear boundary conditions. The dynamic behavior of the beam is described by using the Fourier expansion and the Bessel functions. The Hankel transform is then applied to obtain particular (nonhomogeneous) solutions. This study succeeds in describing the ``jump" phenomenon (instantaneous transition of the system from one position to another) of the vibrating system at certain frequencies. Models based on linear boundary conditions are unable to capture this phenomenon. A larger modulus of elasticity in nonlinear supports increases the frequency of unstable vibrations in the first mode and also widens the frequency region of system instability. This influence is less prominent in the second mode, in which the largest amplitude is smaller than those observed in the first mode.