Disruption of Shaped‐Charge Jets by a Pulsed Current

This paper gives results from experimental studies of the effect of electricpulse parameters on the development of current instability and disruption of shapedcharge jets. A simple physical model for the development of current instability and the decrease in the cavern depth in the target is proposed. Notations are introduced and analytical expressions are obtained for the critical current (critical linear current density) and the ideal shape of the current pulse required for the disruption of shapedcharge jets. It is shown that the estimate of the final cavern depths in steel target for the proposed model is in fairly good agreement with both experimental values of cavern depths in targets and with the results of numerical calculations using quasitwodimensional unsteady models of MHD instability and volume disruption.     

Stress State of an Elastic Space with a Toroidal‐Shaped Cavity

Solutions are obtained for the stress state problem for an elastic space with an internal toroidalshaped cavity that can be expanded in a trigonometric series in the angle in cylindrical coordinates. Displacements and stresses are specified on the boundary. An analytic solution of the problem is found using generalized analytic functions. Stresses and displacements of points in the elastic space are calculated.     

Gas–Dynamic Structures in Supersonic Combustion of Hydrogen in a System of Plane Jets in a Supersonic Flow

Results of numerical and theoretical studies of supersonic diffusive combustion of a system of plane hydrogen jets in a supersonic air flow are described. It is shown that large–scale vortex structures appear in the mixing zone of the system of hydrogen jets and the cocurrent flow. These vortex structures affect the mechanism of turbulent exchange between the fuel and the oxidizer.     

Symmetry of Ground States of p‐Laplace Equations via the Moving Plane Method

. In this paper we use the moving plane method to get the radial symmetry about a point of the positive ground state solutions of the equation in , in the case . We assume f to be locally Lipschitz continuous in and nonincreasing near zero but we do not require any hypothesis on the critical set of the solution. To apply the moving plane method we first prove a weak comparison theorem for solutions of differential inequalities in unbounded domains. (Accepted September 21, 1998)     

Independent‐Stress Method for Analysis of Nonlinear Antiplane Strain

The stress field in a cylindrical body under antiplane strains is studied using the nonlinear theory of elasticity in actual variables under assumptions of the absence of body forces and weak nonlinearity of the elastic potential. The stresses are determined by solving the nonlinear boundaryvalue problem for two independent stresses in polar coordinates of the physical and stress planes. Analytical solutions of the nonlinear problems are obtained. The effect of potential nonlinearity is studied. It is shown that the nonlinear problem can be solved using the harmonicequation solution corresponding to the linear potential.     

Leray-α Regularization of the Smagorinsky-Closed Filtered Equations for Turbulent Jets at High Reynolds Numbers

The article reports on blending of the Leray-α regularization with the conventional Smagorinsky subgrid-scale closure as an option for large-eddy-simulation of turbulent flows at very high Reynolds number on coarse meshes. The model has been tested in the self-similar far-field region of a jet at a range of Reynolds numbers spanning over two decades (4×10³, 4×10⁴ and 4×10⁵) on two very coarse meshes of 2×10⁵ and 3×10⁴ mesh cells. The results are compared with the well-resolved DNS for $Re_D=4\times 10^3$ on 15 million cells and experimental data for higher Re numbers. While the pure Leray-α can fail badly at high Re numbers on very coarse meshes, a blending of the two strategies by adding a small amount of extra-dissipation performs well even at a huge jet Reynolds number of $Re_D=4\times 10^5$ on a very coarse mesh (2×10⁵ cells), despite the ratio of the typical mesh spacing to the Kolmogorov length exceeding 300. It is found that the main prerequisite for successful LES, both for the classic Smagorinsky and the blended Leray-α/Smagorinsky model, is to resolve the shear-length $L_s=\sqrt{\varepsilon/{\cal S}^3}$ (where ${\cal S}$ is the shear-rate modulus), defined by the constraint Δ/L _s ?<?1, where Δ is the typical mesh-cell size. For the mixed Leray-α/Smagorinsky model the regularization parameter should also be related to the shear-length rather than the local mesh size or Reynolds number, for which we propose a guide criterion α?=?0.15÷0.3 L _s .     

Container for Localization of an Explosion of a Compact High–Explosive Charge with an Inert Shell

Results of an experimental study of fragmentation effects in the explosion and the piercing power of the fragments of inert masses in the form of hemispherical aluminum and soft–steel shells enclosing the spherical charge of a high explosive under their action on flat steel, aluminum, steel–net, and claydite—concrete barriers are given. A design of the lightest spherical explosion–proof container with a load–carrying steel or glass–reinforced plastic shell protected by a splinter–proof layer capable of withstanding an explosion of a high–explosive charge (with a twofold safety factor) with an inert steel shell is proposed.     

Asymptotic Modeling of Nonlinear Wave Processes in Shock‐Loaded Elastoplastic Materials

Nonlinear wave processes in shockloaded elastoplastic materials are modeled. A comparison of the results obtained with experimental data and numerical solutions of exact systems of dynamic equations shows that the model equations proposed qualitatively describe the stressdistribution evolution in both the elasticflow and plasticflow regions and can be used to solve one and twodimensional problems of pulsed deformation and fracture of elastoplastic media.     

Velocity Measurements in a One‐Dimensional Steady Flow by Methods of Emission Tomography

A new method for velocityfield measurements in a onedimensional steady flow is proposed. The method is based on principles of laserinduced fluorescence combined with emission tomography. Results of a numerical experiment are presented.     

Re‐Entering of Bodies with a Positive Lift‐to‐Drag Ratio into the Earth's Atmosphere

The problem of gliding descent of a smooth blunted body with a positive lifttodrag ratio in the Earth's atmosphere is solved within the framework of the parabolized viscous shock layer model.     

Viscosity of a Dilute Suspension in a High‐Frequency Electromagnetic Field

The action of a highfrequency electromagnetic field on a dilute suspension of spherical particles with a constant dipole moment is studied using statistical mechanics. An expression for effective viscosity is obtained. It is shown that the shear viscosity of the dilute suspension depends on the frequency, magnitude, and direction of the highfrequency electromagnetic field. Depending on the frequency of the highfrequency electromagnetic field, the rotation of the suspension particles is decelerated or accelerated, with the viscosity increasing or decreasing, respectively. It is shown that the acceleration of the suspension particles by a highfrequency electromagnetic field and, hence, the decrease in shear viscosity has a resonant nature.     

Behavior of Nonaqueous Phase Liquids in Fractured Porous Media under Two‐Phase Flow Conditions

After dense nonaqueous phase liquids (DNAPLs) travel downward through the subsurface, they typically come to rest on fractured bedrock or tight clay layers, which become additional pathways for DNAPL migration. DNAPLs trapped in fractures are continuous sources of groundwater contamination. To decide whether they can be left in place to dissolve or volatilize, or must be removed with active treatment, the movement of DNAPLs in fractured media must be understood at a fundamental level. This work presents numerical simulations of the movements of DNAPLs in naturally fractured media under twophase flow conditions. The flow is modeled using a multiphase network flow model, used to develop predictive capabilities for DNAPL flow in fractures. Capillary pressure–saturation–relative permeability curves are developed for twophase flow in fractures. Comparisons are made between the behavior in crystalline, almost impermeable rocks (e.g. granite) and more permeable rocks like sandstone, to understand the effects of the rock matrix on the displacement of the DNAPLs in the fracture. For capillarydominated flow, displacements occur as a sequence of jumps, as the invading phase overcomes the capillary pressure at downgradient apertures. Preferential channels for the displacement of nonaqueous phase are formed due to high fracture aperture in some regions.     

Penetration of shaped charge jets with tungsten–copper and copper liners at the same explosive-to-liner mass ratio into water

Jets from shaped charges with the liners made of tungsten–copper and copper and having the same mass ratio of explosive to liner are compared. They are found to have the same tip velocities in air, before reaching a steel target. When water target layers are added in front of the same steel target, it is observed in experiments and in numerical simulations that the tip velocity of the tungsten–copper jet diminishes less rapidly than that of the copper jet, so that the tungsten–copper jet velocity upon encountering the steel is higher. These phenomena are also explained by theoretical analysis.     

Propagation of Linear Waves in Gas‐Saturated Porous Media with Allowance for Interphase Heat Transfer

The effect of gas–skeleton heattransfer processes on propagation of fast and slow waves in a porous medium is examined. Frequency intervals are identified, in which attenuation of waves in a gassaturated porous medium is mainly controlled by the heattransfer processes.     

High‐Frequency Changes in the Orientation of Nematic Liquid Crystals in Radio Frequency Crossed Electric Fields

The orientational dynamics of the director of a nematic liquid crystal located in radio frequency crossed electric fields were studied by numerical calculations and experimentally. This system is shown to be a physical object of nonlinear dynamics. Depending on the parameters of the problem, the following types of states of the director were observed: stationary (an analog of the nonthreshold Freedericksz transition), periodic, quasiperiodic (multimode), and stochastic of the strange attractor type. In the calculations, all states were obtained by solving a deterministic system of two timedependent nonlinear differential equations of the first order with no electrohydrodynamic terms. All types of solutions obtained, including stochastic ones, were observed experimentally.     

Entrance of a body with a lifting force and a heat‐conducting surface into the earth's atmosphere

The problem of gliding descent of a smooth blunted body possessing a lifting force and a heatconducting surface in the Earth's atmosphere is solved. The descent trajectory is represented not only by the altitude and velocity as functions of the flight time but also by angles of attack and sideslip varying with time. Threedimensional equations of a parabolized viscous shock layer for a multispecies mixture of gases are solved jointly with a threedimensional equation of unsteady heat conduction in the solid phase.     

Application of the Carman–Kozeny Correlation to a High‐Porosity and Anisotropic Consolidated Medium: The Compressed Expanded Natural Graphite

The Carman–Kozeny correlation is applied to a medium which is consolidated, highly porous and anisotropic: the expanded then compressed natural graphite. The effective textural properties (i.e. the mean pore diameter, porosity and tortuosity) have been measured by a mercury porosimeter and a heterogeneous diffusion cell. The texture and the permeability (according to the Darcy's law) measured for the two main directions of these orthotropic porous media change over a very wide range depending on their apparent mass densities. Experimental data show that only a part of the total porosity participates in the gas flow in steady state conditions.