The direct simulation Monte Carlo method is used to study a plane–parallel supersonic gas flow through a grid formed by a series of parallel infinite cylinders. Characteristic features of the shock disturbance formation during the interaction of a supersonic flow with a permeable grid and the effect of this disturbance on the flow parameters behind the grid are revealed. The boundaries of the domain of supersonic flow breakup ahead of the grid and the laws of the total momentum loss on the grid are obtained. Kinetic and energetic characteristics of the flow behind the grid are determined.
Within the framework of a thermodynamically equilibrium model, dynamic loading of mixtures of two and more condensed phases with different properties within the experimental error is described by using species parameters only. The behavior of alloys considered as mixtures with the same volume fractions of the species is studied. The behavior of condensed phases for solid and porous materials is described with the use of the equation of state of the Mie–Grüneisen type and with allowance for the dependence of the Grüneisen coefficient on temperature. The calculated results are compared with experimental data and available calculated results in wide ranges of parameters.
V. I. Bukreev, I. V. Sturova, A. V. Chebotnikov
Keywords: seiches, shallow water theory, natural frequencies and modes, laboratory experiment, spectral analysis
The natural frequencies and modes of seiche oscillations in a closed water reservoir consisting of a long narrow channel connected to a wide basin were investigated theoretically and experimentally. Calculations were made using linear shallow-water theory in two-dimensional and one-dimensional formulations. The spectral properties of free-surface oscillations at points lying on the nodal lines of the first four modes of seiche oscillations were studied experimentally. The one-dimensional model adequately predicts lower-mode frequencies, but the data on the positions of the nodal points of seiche oscillations obtained using this model are somewhat different from those obtained experimentally and using the two-dimensional model.
An exact solution of the magnetohydrodynamic equations is constructed which describes steady vortex flow in a stationary cylinder on the axis of which a conductor carrying a known current is located. The solution is obtained under the assumption that the fluid is viscous and has finite electrical conductivity and that the magnetic field has only the axial and azimuthal components in a cylindrical coordinate system. It is found that the action of the Lorentz force is compensated by changing the pressure. Fluid flow occurs from the periphery to the axis of the cylinder under a pressure gradient, with flow rotation and swirling. The fluid flow causes a concentration of the magnetic lines near the axis of the cylinder, providing an exponential decrease in the magnetic field strength with distance from the axis. This flow can be considered as a model of a local increase in the magnetic field strength due to the transfer of its force lines by the flow of the electrically conducting fluid.
A flow of a viscous incompressible fluid in a deformable tube is considered. Solutions of unsteady three-dimensional Navier–Stokes equations are obtained for low-Reynolds-number flows in the tube (under the condition of small deformations of the wall): generalized peristaltic flow and flow with elliptical deformations of the vessel walls. At small unsteady deformations of the tube walls, the solutions satisfy the equations and boundary conditions with an error smaller than the tube wall deformation level by an order of magnitude. In the case of elliptical deformations of the vessel, the solution agrees well with experimental data.
The flow structure and statistical features of a turbulent stable stratified boundary layer are studied by using the Reynolds-averaged Navier–Stokes (RANS) scheme of turbulence, which takes into account the influence of internal gravity waves. The possibility of the RANS description of intermittent turbulence both near the surface and above the surface in the vicinity of the low-level jet flow formed above the boundary layer is analyzed. The role of turbulent diffusion (third-order statistical moments) in intermittent turbulence generation is discussed. Numerical results are demonstrated to agree with results of LES modeling and actual observations. Intermittency of turbulent kinetic energy both near the surface and above this surface in the vicinity of the low-level jet flow is revealed.
The effect of passive porous coatings of different lengths on the second mode of disturbances in a hypersonic boundary layer is considered. The experiments are performed in a flow with a free-stream Mach number M∞ = 5,8 and five values of the unit Reynolds number around a sharp cone with an apex half-angle equal to 7°, which is aligned at a zero angle of attack. One half of the model surface along its generatrix is covered by a porous material, and the other part is a solid surface. Pressure fluctuations on the model surface are measured. It is found that application of a passive porous coating can either decrease or increase the amplitude of the second mode. The length of the passive porous coating corresponding to the maximum efficiency of its action on flow disturbances and the coating length that increases the amplitude of the second mode are found.
The problem of flutter of viscoelastic rectangular plates and cylindrical panels with concentrated masses is studied in a geometrically nonlinear formulation. In the equation of motion of the plate and panel, the effect of concentrated masses is accounted for using the δ-Dirac function. The problem is reduced to a system of nonlinear ordinary integrodifferential equations by using the Bubnov–Galerkin method. The resulting system with a weakly singular Koltunov–Rzhanitsyn kernel is solved by employing a numerical method based on quadrature formulas. The behavior of viscoelastic rectangular plates and cylindrical panels is studied and the critical flow velocities are determined for real composite materials over wide ranges of physicomechanical and geometrical parameters.
On the preliminary statistical data provided by the Goskomstat of the Russian Federation (Statistics Russia), the paper assesses how Russian regions recovered from and developed after the world financial crises (2007-2012) and considers the changes of the spatial structure which can be observed according to the economic indicators showed the largest drops such as the fixed investments and industrial output.
