Home – Home – Jornals – Journal of Applied Mechanics and Technical Physics 2018 number 4

A scheme for obtaining and detecting high-velocity compact metal elements moving with hypersonic velocities under high-intensity shock loading is developed. A light-gas ballistic device and shadow photography are used for this purpose. Application of the hemisphere - cylinder cladding makes it possible to test a cumulative charge steadily forming in a compact steel element, moving with a velocity approximately equal to 6 km/s. The results of the numerical and experimental testing of this projecting device are given.

A mathematical model for the interior ballistics of an electrothermal launcher of macrobodies has been developed which can be used to predict the projectile velocity for specified values of the mass and size of the impactor, the electrodynamic parameters of the capacitive energy storage, and launcher parameters. The problem of determining the projectile velocity was solved in a hydrodynamic formulation by numerical integration of the equations of motion, the energy conservation equation, and the caloric equation of state. It is shown that without accounting for the dynamically changing friction coefficient and erosion of the electrodes, the calculation results differ considerably from the experimental data, but the model qualitatively describes the physical processes of interior ballistics of the electrothermal launcher.

Electrophysical, hydro-gas-dynamic, and thermal characteristics of a discharge arising between liquid electrodes are considered. Spatial visualization of flow patterns in the gas discharge region is performed by using the Schlieren technique.

Two-dimensional seiche oscillations in a rectangular basin of constant depth with an open entrance are considered within the framework of the linear theory of long waves. An analytical solution is obtained for the case where a nodal level line is located at the entrance to the basin. It is shown that transverse seiches in a basin with an open entrance are two-dimensional in contrast to similar modes in a completely closed basin, which are one-dimensional. Calculation of seiche parameters is performed for model basins having dimensions and depth characteristic of a number of Sevastopol bays. Comparison of the results of the calculations are with the data of full-scale observations show that they are in satisfactory agreement.

The flow of the Casson fluid due to non-coaxial rotation of a disk and the fluid at infinity is investigated. Partial differential equations are made dimensionless and coupled. The exact solution of the resultant nonlinear initial-boundary-value problem is solved by applying the Laplace transform. The shear stresses at the disk surface and the steady state stresses are computed. The effects of dimensionless parameters on the dimensionless primary and secondary velocities are analyzed.

A new type of ducted pulse thermal actuators with a high pulse repetition frequency is proposed to control wing buffeting at transonic flight velocities. Ducted pulse thermal actuators can operate up to frequencies of about 1 kHz, which is sufficient for controlling the majority of aerodynamic processes at high subsonic flow velocities. As the use of a pulse thermal actuator in the regime of tangential injection of a jet is less efficiency from the energy viewpoint than in the regime of boundary layer suction, an ejector-type pulse thermal actuator is proposed for implementation of the suction regime.

Problems of motion of a triaxial ellipsoid in an ideal fluid and in a viscous fluid in the Stokes approximation and also equilibrium shapes of the rotating gravitating fluid mass are considered. Solutions of these problems expressed via four quadratures depending on four parameters are significantly simplified because they are expressed via the only function of two arguments. The efficiency of the proposed approach is demonstrated by means of analyzing the velocity and pressure fields in an ideal fluid, calculating the attached mass of the ellipsoid, determining the viscous friction, and studying the equilibrium shapes and stability of the rotating gravitating capillary fluid. The pressure on the triaxial ellipsoid surface is expressed via the projection of the normal to the impinging flow velocity. The shape of an ellipsoid that ensures the minimum viscous drag at a constant volume is determined analytically. A simple equation in elementary functions is derived for determining the boundary of the domains of the secular stability of the Maclaurin ellipsoids. An approximate solution of the problem of equilibrium and stability of a rotating droplet is presented in elementary functions. A bifurcation point with non-axisymmetric equilibrium shapes branching from this point is found.

Singular integral equations of the first and second kind with the Cauchy kernel on a limiting narrow closed contour are theoretically considered. The initial equations are found to degenerate on the limiting contour. This singularity of integral equations with the Cauchy kernel does not allow boundary-value problems of the flow around thin airfoils to be solved correctly; therefore, a system consisting of integral equations of the first and second kind is proposed for solving such problems. The results of the present study are tested against an exact solution of the problem of the flow past a flat plate.

This study is conducted to investigate the Bingham-Papanastasiou fluid flow driven by a rotating infinite disk. The Bingham-Papanastasiou model is a modification of the Bingham plastic model, which is developed by introducing a continuation parameter to overcome its discontinuity. The von Kármán similarity solution is used to transform the flow equations from ordinary differential equations to a nonlinear system of partial differential equations, which is solved numerically. The effect of the Bingham flow parameters on the radial, tangential, and axial velocities, pressure, and radial and tangential skin friction coefficients is discussed.

The process of airfoil icing caused by incidence of ice crystals is considered. A physicomathematical model of motion of spheroidal crystals in the gas flow and their interaction with the body is formulated. The model takes into account the non-spherical particle orientation with respect to the velocity vector of the gas flow. It is assumed that particle collision with the body surface leads to partial destruction of the particle under the action of normal and tangential stresses, and some part of the particle mass remains in the vicinity of the collision point. An inviscid flow around the airfoil with a time-dependent shape is calculated by the method of approximate conformal mapping.

This paper describes an experimental study of deformation of a droplet of an organic water-coal fuel in a gas flow. The experimental data obtained are used to develop a technique that as a basis for a numerical study of integral characteristics of deformation of the droplets of organic water-coal fuel 4.5 mm in diameter with a gas flow velocity of 2 m/s and a temperature of 298 K. The characteristic changes of the area of longitudinal and transverse cross sections of the droplets of the organic water-coal fuel during their gravitational deposition in time are revealed. It is shown that the theoretical and experimental data satisfactorily agree.

Asymptotic decomposition to small quantities of the third order for the velocity potential of a fluid of finite depth and the bending deformations of a floating elastic plate arising from the interaction of harmonics of finite-amplitude progressive surface waves were constructed using the method of many scales. An expression for the second-harmonic amplitude was obtained, and critical values of the wavenumber were determined. Oscillations of the plate for different values of its thickness and elastic modulus were analyzed. Vertical displacements of the plate under bending deformation were studied.

Hydrodynamic modes of heat and mass exchange devices with a movable nozzle are considered. Relations for the critical speed, loss of momentum in the working area, and the dynamic thickness of the layer of nozzle elements are obtained which are necessary for engineering calculations.

This paper describes a detailed numerical investigation of a stationary high-aspect-ratio rib-roughed rectangular cooling channel with longitudinal intersecting ribs near the gas turbine blade trailing edge region. In order to overcome the heat transfer performance degeneration in the high-aspect-ratio channel, longitudinal intersecting ribs are arranged on the channel bottom surface. The effect of the number of longitudinal intersecting ribs on the flow and heat transfer is systematically studied in the Reynolds number range Re=10000-30000. The results show that a heat transfer augmentation region exists just downstream the junction between the longitudinal rib and the angled rib due to additional secondary flows. With more longitudinal intersecting ribs, the heat transfer distributions on the channel surfaces are more uniform. Though the pressure loss is also enlarged with an increase in the number of longitudinal intersecting ribs, the overall thermal efficiency increases in the entire range of Reynolds numbers investigated. The configuration with two sets of longitudinal intersecting ribs shows the best overall thermal efficiency

The aim of this project is implementation of computational fluid dynamics (CFD) for numerical simulation of the ejector flow. Optimal values of the ejector geometry that ensure the maximum ejector performance and the minimum noise level are determined.

Large deformations of elastoplastic cylindrical rods and shells of different thicknesses under tension are studied. The influence of the geometry of the samples and the dependence of stresses on deformations under uniaxial tension on edge effects and the neck formation process are estimated. The applicability of the Considere criterion for determining the instance of stability loss of plastic deformation under tension is analyzed. The computational experiments confirm that the role of similarity in the processes of nonuniform deformation of samples under tension can be played by the ratio of the tangent of the slope of the true strain diagram to the stress intensity.

This paper describes an experimental study on strain and fracture of plane samples made of glass textolite and textolite with surface and inner aluminum layers. It is shown that the presence of these layers reduces the strength of glass textolite under static and low-cycle loading. This can be explained by the fact that the stretching of a hybrid composite along the layers is accompanied by the formation of localized tensile regions of glass textolite across the layers. As a result, both the hybrid composite and its glass-textolite component are stratified.

Results of experiments on indentation of steel balls of various diameters into glass samples shaped as rectangular parallelepipeds are reported. The limiting load of formation of a ring-shaped crack near the contact region and the radius of this crack are experimentally determined. The field of the contact stresses in the fracture region is found by using the Huber solution of the Hertz problem of pressing a ball into an elastic half-space. Modeling fracture caused by contact interaction is based on using the local criterion of the maximum stresses and several non-local criteria: criterion of mean stresses, Nuizmer criterion, and gradient criterion. For calculating the parameter that has the length dimension and is included into the nonlocal fracture criteria, the limiting tensile stress and the critical stress intensity factor of glass are experimentally determined for beams without and with a notch. It is demonstrated that the experimental data on the ring-shaped crack radius are most adequately predicted by the gradient criterion among all criteria considered in the study. However, this criterion overpredicts the limiting tensile stress in the course of beam bending, which is caused by the scale factor.

Problems of the stability of a rod of shape memory alloy during direct martensitic phase transformation under the action of constant compressive loading are solved taking into account the effect of stresses on the phase transition and the effect of the phase transition on the temperature regime using various statements. A comparison of the results of the solutions is made.

The dynamics of a pulsed signal propagating in an underground pipeline with a damaged section is investigated. Pressure waves propagating along a linear pipeline filled with a fluid are considered. Due to viscous friction and thermal conductivity, dissipation is taken into account in a thin liquid or gas layer near the wall. It is assumed that the pipeline section with damage is a reflective surface. Conditions on this surfaces were obtained under the assumption that the rate of liquid leakage during wave propagation through the damaged area is determined by the permeability of the soil. It is shown that in weakly permeable soils, the signal does not provide full information on damage, and in well-permeable soils, only short (high-frequency) pulsed signals can be used to detect damage.

The problem of the propagation of a stationary acoustic wave through an infinite thin plate stiffened on two sides by a system of absolutely rigid, crossed ribs and between two absolutely rigid barriers. It is assumed that the plate and the ribs evenly distributed along rectangular Cartesian axes are connected through elastic interlayers (foundations) without sliding. The dynamic deformation of the plate is described by the linearized Kirchhoff-Love equations of the classical theory of plates, the dynamic deformation of the interlayers is described by two-dimensional and one-dimensional relations based on linear approximations of displacements of points of the coating and interlayers along the thickness and taking into account only transverse compression and transverse shear, and the motion of acoustic media by the well-known wave equations. The solution of the problem is obtained using the Ritz method. The constructed solution was used to investigate how the physico-mechanical and geometric parameters of the mechanical system and the frequency of an acoustic wave incident on the plate influence the sound insulation parameters and the stress-strain state of the plate.

Using the variational principle in a geometrically nonlinear formulation The problem of parametric vibrations of a longitudinally stiffened orthotropic cylindrical shell in contact with an elastic medium and under internal pressure is solved in a geometrically nonlinear formulation using the variational principle. The influence of the external medium is taken into account using the Pasternak model. Amplitude-frequency dependences are constructed for parametric vibrations of a stiffened orthotropic cylindrical shell filled the medium.

This paper considers the inverse problem of identifying boundary conditions for the problem of vibrations of a string in an elastic external medium, whose elasticity coefficient is described by an asymmetric potential. It is shown that, in contrast to the case of a symmetric potential, the boundary conditions can be uniquely identified, but this requires the use of three, rather than two, vibration eigenfrequencies. Cases are considered in which unique identification using two eigenfrequencies is possible. Methods for determining boundary conditions from two and three eigenfrequencies are proposed. The error of the methods is analyzed.

This paper describes an experimental study of the strain rate of DP780, DP980, and T=240 high-strength sheet steels on an increase in their plasticity under uniaxial and biaxial tension. The strain rates of the steels vary in the range from 10-4 to 17 х 103 s-1.

Fractal analysis methods are used to construct a model describing the effect of a nanofiller structure (carbon nanotubes) on the structure of a nanocomposite as a whole and its mechanical properties. It is shown that an increase in the fractal dimension of carbon nanotubes, which are ring-like formations in a polymer matrix, or their compaction can increase the elasticity modulus of the nanocomposites. It is determined that a significant effect on the mentioned properties of nanocomposites is produced by the spatial structure of carbon nanotubes.