Home – Home – Jornals – Journal of Applied Mechanics and Technical Physics 2020 number 6

This paper describes the formulation and calculation results pertaining to the Euler gas aerodynamic complex (EGAC) method of interaction between a shock wave and a turbulent mixing zone, which develops on a flat contact boundary separating air and argon. The study is carried out using both direct numerical three-dimensional modeling and a two-dimensional ( k -e) turbulence model. A comparison is made with the results of experiments in which the expansion and stratification of a shock wave is observed during its propagation after passing through a turbulent mixing zone. Calculations are carried out using the ( k -e) model and with account for the presence of a boundary layer, which make it possible to explain this effect.

A system of equations of magnetohydrodynamics for an incompressible fluid is used to study flow stability between coaxial cylinders, which arises under the action of a longitudinal pressure gradient, in the case where a uniform magnetic field is directed along the cylinder axis. The differential sweep method is applied to investigate the dependences of the critical Reynolds numbers on the value of electrical conductivity and the strength of the external magnetic field. The existence of two ranges of electrical conductivity values is established, in which the stabilizing effect of the magnetic field is most significant. An abrupt increase in the critical Reynolds numbers and the detachment of closed instability regions from neutral curves are revealed.

A mathematical model of the unsteady temperature field of an oil reservoir after well start-up at a constant bottom-hole pressure is described taking into account the throttling and adiabatic effects. Two approximate solutions are considered and compared with the results of calculations of the thermal field using Ansys numerical simulator.

A mathematical model describing thermohydrodynamic processes in an oil reservoir penetrated by a horizontal well has been developed. An inverse problem for estimating the filtration parameters of an oil reservoir is formulated. Temperature and pressure dependences obtained simultaneously using several autonomous downhole instruments placed in different sections of a horizontal wellbore are used as initial information. It is shown that the solution of the inverse problem based on numerical simulation and regularization methods can be used to construct inflow profiles along horizontal wellbores and estimate the reservoir properties of bottomhole and remote zones of the reservoir and the radii of bottomhole zones near downhole instruments.

The aerodynamic characteristics of various models of aeration ridge ventilation windows are analyzed by numerical simulation. The most effective designs of ridge ventilation windows from the point of view of the lowest aerodynamic resistance of a lantern are found.

A forced convective heat transfer problem inside a micropipe as well as inside a microchannel with parallel walls in the laminar gaseous slip flow regime, a with finite heating region and a prescribed wall heat flux, including the axial heat conduction effect, is analytically investigated. The temperature field and Nusselt number are derived under the assumption that the flow is hydrodynamically fully developed in the finite-length heating region. The solution is found by applying the functional analysis method, by decomposing the energy equation into a pair of first-order partial differential equations. The first-order slip boundary conditions are imposed at the gas-wall interface. The analytical solution is compared with available calculations. The results show that the thermal characteristics in the heating region are significantly affected by the axial heat conduction, rarefaction effects, and finite length of the heating region.

This article addresses the formulation of an exact analytical solution of a three-dimensional dual-phase-lag bioheat model in relation to living tissues of human organs subjected to regional hyperthermia treatment. The solution methodology is employed as a finite integral transform in combination with a filtered approach. A renovated initial condition with appropriate boundary conditions is imposed in the present modelling. Isotherms in different cross sections of the physical domain are generated and discussed with different thermal and geometric variables for establishing the exact temperature field. The present research output is compared with the published experimental work. The results show the necessity of a 3D analysis for an accurate prediction of the temperature response in tumour cells.

The bending vibrations of a pipeline under the influence of the variable pressure of the transported fluid and the vertical vibrational motion of the supports are studied. The first mode of vibration is considered. Nonlinear forced parametric vibrations and their interaction are studied. The results of approximate analytical and numerical solutions are compared.

This paper presents the results of an experimental study of the efficiency of constrained vibrodamping coatings comprising a thin polymer layer with a very high damping capacity and thin constraining layers of various thickness. Vibration analysis of steel plates with and without a coating on the plate surface was performed. It has been shown that the application of the studied coating significantly reduces the vibration and sound generation in plate elements of structures.

Graphene has a high tensile strength and ductility; it is an ideal choice of cementing reinforcement materials. The effect of graphene on the well cementation properties of the cement slurry and on the mechanical properties of the set cement is investigated by adding 0.02 wt.% of graphene to the cement slurry system. Addition of graphene reduces the slurry viscosity and exerts a minor effect on the filtration and thickening time of the cement slurry. A triaxial mechanical test shows that the elasticity modulus of cement with graphene addition increases from 5087.6 to 6983.2 MPa, the compressive strength increases by 60.98%, and the strain recovery ability of the cured cement is improved. The structural analysis of the set cement by means of scanning electron microscopy shows that the silicate crystals of the set cement with graphene are more regular, and there are only few inner pores in the set cement. Therefore, graphene offers broad application prospects of improving cementing quality.

We examine a range of issues related to the methodological and experimental support of a linear elastic model for an isotropic body with different moduli in tension and compression in mechanical tests of solid samples of different origin and structure. The reasons for the difference between tensile and compressive Young's moduli measured in the tests are analyzed. It is shown that using appropriate test techniques and equipment for measuring and recording deformations sustained by a homogeneous uniaxial state makes it possible to obtain statistically insignificant differences in Young's modulus for a number of materials subjected to tensile and compressive forces.

This paper presents numerical simulation results for controlling a transonic boundary layer on a supercritical wing profile of a civil aircraft using a moving section of the profile surface. The efficiency of control in the case of transonic buffeting is shown.

This paper deals with a laminar swirling flow of a viscous fluid over a stretchable rotating disk. The classical flow over a solid disk is known as the Kármán flow problem. For the first time in the literature, the combined effects of both the Coriolis force and radial stretching on the stability of the Kármán swirling flow has been carried out. The numerical investigation has been performed by using the Chebyshev spectral method. It is discovered that surface stretching produces a destabilising effect on the Kármán flow.

In this paper, we embark on analytical determination of the dynamic buckling of a statically pre-loaded elastic structure subjected to step loading. We first employ a two-timing regular perturbation procedure for asymptotic determination of a uniformly valid expansion of the displacement. The dynamic buckling load is determined nontrivially and is related to the corresponding static load. The dynamic buckling load is studied as a function of various problem parameters: degree of damping, initial imperfection, and static pre-loading.

The behavior of the 6008 aluminum alloy under impact loading with different strain rates is experimentally studied. Quasi-static compressive stress-strain curves of these materials areobtained in this study by using an RPL100 materials-testing machine and a split Hopkinson pressure bar. As the strain rate increases, the yield stress and the peak stress of the materials are found to increase significantly. The adiabatic temperature rise generated during the impact process makes the materials soften, so that the rate of the increase in the flow stress gradually decreases with an increase in the strain rate. Based on the dislocation dynamics theory, a viscoplastic dynamic constitutive model for the 6008 aluminum alloy is constructed. The model accurately describes and predicts the mechanical behavior of this material under impact compression at room temperature.

To study the explosive characteristics of improvised explosive devices (IEDs), the damage mode of cylindrical IEDs and the formation mechanism of natural fragments under blast loading are investigated by using the ANSYS/AUTODYN 3D finite element code with Mott's stochastic failure model, as well as experiments of the hydraulic burst test and explosion test. The influence of the explosive charge amount and its position is also discussed. The main damage mode of the pressure container is the shearing damage, which is obviously affected by the explosive charge amount, charge position, and its power. The ability of the instantaneous function (pressurization rate) of the self-made explosive is far smaller than that of the standard explosive. Under the action of the self-made explosive, the closer to the detonation point, the smaller the size of the fragments formed.

Based on Hill's anisotropic theory, theoretical solutions for the burst pressure and the corresponding equivalent stresses and strains for a thick-walled spherical pressure vessel made of a ductile material with plastic orthotropy are obtained. The effects of the plastic orthotropy, strain hardening, ratio of the external to internal radius of the vessel, and external pressure on the burst pressure is considered. It is found that the external pressure affects the burst pressure, while the corresponding equivalent stresses and strains have nothing to do with the external pressure.

Copper powder spraying is under study: the PMS-1 original copper, the copper that is mechanically treated in a high-energy planetary mill, and the copper that is also spheroidized in a plasma jet. High-density copper coatings are obtained using a CCDS2000 detonation complex. The microhardness of coatings HV0.1, obtained from original and mechanically treated copper powders, increases from 110 to 160 and from 150 to 185, respectively, and the microhardness of coatings from the spheroidized powder is HV0.1=165. An X-ray phase analysis is carried out, and the resulting data indicate that, during the spraying, the copper oxide is partially reduced.