Simulation of iron fracture caused by a blast wave

A numerical simulation is made of the fracture of iron caused by a blast wave. The numerical method is described and results of calculations using a one-dimensional formulation of three qualitatively different explosion regimes are presented. Pis’ma Zh. Tekh. Fiz. 23, 33–39 (May 12, 1997)     

Self-reproduction of multimode hermite-gaussian beams

The condition for the self-reproduction of multimode Hermite-Gaussian beams is obtained and analyzed. Partial self-reproduction planes are also considered. A numerical example is presented. Pis’ma Zh. Tekh. Fiz. 25, 62–69 (June 26, 1999)     

Calculation of the optimum parameters of a copper-vapor laser lidar for remote probing of H2

A numerical solution of the lidar equation is obtained for Raman backscattering by hydrogen molecules and the optimum radiation powers of a copper laser are determined at distances of 100–6000 m. Pis’ma Zh. Tekh. Fiz. 24, 32–35 (February 26, 1998)     

Magnetic-field control of gas flow in a supersonic intake

A numerical simulation is used to assess the potential for controlling the flow structure in the air intake of a supersonic aircraft by means of an external magnetic field. Pis’ma Zh. Tekh. Fiz. 23, 1–5 (August 26, 1997)     

Bilateral bounds for the shear and torsion factors: comments on elementary derivations

This paper proposes a new simple derivation of bilateral bounds for the strain energy–based shear and torsion factors, χ _i , of an elastic beam together with some comments about the coherence of the current formulations. A rearrangement of the definition as a mean over the cross-section and an original decomposition of the shear stress in two parts—τ _eqv that is equivalent to the external force and a residual Δτ—allow (i) to interpret (χ − 1) as the mean quadratic deviation of the shear field with respect to the distribution τ _eqv and (ii) to easily evaluate an upper bound, using minimal information about the stress field. In this formulation, the lower bound becomes trivial. Several numerical examples illustrate the accuracy and suitability of the results obtained.     

Size distribution of copper nanoclusters in amorphous carbon

A theoretical analysis is made of the formation of copper nanoclusters in a growing amorphous carbon film. The calculated size distributions of the copper clusters are compared with the experimental data. A numerical estimate is made of various kinetic parameters of copper in amorphous carbon. Pis’ma Zh. Tekh. Fiz. 25, 76–79 (March 12, 1999)     

Theory of multiple scattering in a fractal medium

An analysis is made of multiple scattering of particles whose ranges have a power-law distribution corresponding to a fractal medium. The small-angle approximation is used to derive an expression for the angular distribution of particles which have traversed a specific path. The results of numerical calculations are presented. Pis’ma Zh. Tekh. Fiz. 25, 34–40 (June 12, 1999)     

Eigenvalues of damped structures: Vectoriteration in the original space of DOF

The equations of motion in structural dynamics as well as the corresponding eigenvalue problem are governed by 3 matrices for mass, damping and stiffness of order n which equals the number of degrees of freedom. High-performance eigenvalue-solvers are developed for only pairs A, B of matrices. Nevertheless, to benefit from these solvers, the original eigenvalue problem (λ² M+λD+K)x=0 is transformed into a linear eigenvalue representation with only two hypermatrices of double order 2n. Consequently the total numerical effort depends on this order 2n. This paper presents a vectoriteration process which actually works in the original space of order n and which needs no special actions like simultaneous iteration if complex conjugate eigenvalues λ, λˉ with identical norm have to be calculated. The theoretical foundation of this process still goes back to the pair of hypermatrices.     

Chaotic oscillations in a system of coupled triggers

A circuit consisting of two triggers coupled by a capacitance is studied. The equations of motion are presented with a cubic approximation for the nonlinear terms. It is shown by numerical analysis that chaotic oscillations can be excited. A mechanism for the transition of the oscillations to chaos is described. Pis’ma Zh. Tekh. Fiz. 25, 1–6 (March 26, 1999)     

Universal nature of the instability of the thermodynamic parameters of transient processes accompanying the melting of crystalline substances in quasistatic regimes

A numerical method of differential thermal analysis was used to study transient processes accompanying the melting of germanium and antimony in quasistatic regimes at heating rates of ∼1 K/min. It is shown that the premelting initiation temperature and the melting initiation point are unstable and depend on the initial conditions. Pis’ma Zh. Tekh. Fiz. 25, 1–5 (February 26, 1999)     

Flow in a turbulent supersonic boundary layer with a heat source

A numerical analysis is made of a turbulent supersonic boundary layer with a heat source for a wide range of heat supplied to the gas. It is shown that the frictional resistance may be reduced appreciably and the efficiency of using a heat conductor to achieve such a reduction is estimated. Pis’ma Zh. Tekh. Fiz. 25, 38–42 (April 12, 1999)     

Method of determining dynamic adiabatic compression curves of powders

A method is described for investigating the dynamic adiabatic compression curves of powders by measuring of the pulsed pressure in a powder pressed uniaxially by an elastic instrument. The instantaneous powder density is determined by numerical solution of a pulsed spectral problem using the pressing pressure pulse and the known characteristics of the pressing instrument and the external force. Pis’ma Zh. Tekh. Fiz. 23, 76–80 (July 12, 1997)     

Mutual synchronization of switching processes in coupled Lorenz systems

A numerical analysis is made of the synchronization of the mean switching frequencies in two symmetrically coupled Lorenz systems functioning in a chaotic regime. The observed effect on the coupling-mismatch parameter plane corresponds to a region of synchronization of the switching processes, within which the mean switching frequencies coincide to a given accuracy. Pis’ma Zh. Tekh. Fiz. 23, 14–19 (April 26, 1997)     

Self-consistent model of a low-pressure rf capacitive discharge

A simple self-consistent model of a low-pressure rf capacitive discharge is formulated. Effects associated with stochastic heating of the electrons and the nonlocal nature of the electric field are taken into account. The relations obtained can be used for a qualitative analysis of the main features of these low-pressure discharges. The results of the numerical calculations show good agreement with available experimental data. Pis’ma Zh. Tekh. Fiz. 23, 39–45 (January 12, 1997)     

Coherent state of a chain of Josephson tunnel junctions

The regions of stability of coherent Josephson oscillation in a chain of Josephson tunnel junctions with nonlocal electrodynamic coupling were studied by means of a numerical simulation of the dynamics of this structure using the Wertheimer macroscopic theory of Josephson junctions. The possibility of using these systems to develop generators of narrow-band electromagnetic radiation at frequencies of 1 THz is discussed. Pis’ma Zh. Tekh. Fiz. 24, 1–7 (August 12, 1998)     

Modeling of positive streamers in liquid argon

A numerical simulation is used to investigate the dynamics of positive streamers in liquid argon. It is shown that as in gases, the nature of the streamer propagation depends on the field strength in the discharge gap. It is established that electron-ion recombination in the streamer channel plays a significant role compared with streamers in gases. Pis’ma Zh. Tekh. Fiz. 25, 19–27 (February 12, 1999)     

Boundary Conditions at the Bulk–Aerogel Interface of Superfluid 3He-B

We study the interface between bulk and aerogel impregnated with ³ He-B. The magnetic susceptibility at the interface determines a boundary condition for the texture, which can be parameterized by the orbital vector L. We use Ginzburg–Landau theory to calculate the boundary condition assuming homogeneous aerogel and a sharp interface. Recent NMR measurements give reason to conjecture that L tends to be parallel to interface. Our numerical calculations confirm this conjecture in the Ginzburg–Landau (GL) regime. However, the orienting energy is one order of magnitude smaller than at a solid wall, and therefore can easily be overshadowed by a nearby wall.     

Influence of feedback on the complex dynamics of an electron beam with a virtual cathode in a virtode

Results are presented of a numerical simulation of the nonlinear dynamics of a relativistic electron beam with a virtual cathode in a drift relativistic-electron-beam vircator system with and without external feedback. Pis’ma Zh. Tekh. Fiz. 24, 51–57 (March 12, 1998)     

Influence of electrode commutation on magnetohydrodynamic flow in a supersonic diffuser

The slowing of an ionized gas in a supersonic diffuser operating as a magnetohydrodynamic (MHD) generator is investigated by numerical simulation. The calculation results, which reveal a significant dependence of the static pressure level and the Mach number distribution in the exit cross section of the diffuser on the design of the electrode system, are presented. Pis’ma Zh. Tekh. Fiz. 25, 1–8 (May 12, 1999)     

The “zero” current and self-sustaining electron bunches in M-type devices

When the processes occurring in the entire interaction space of a magnetron device are included simultaneously in a numerical simulation it is possible to observe the onset and behavior of stable solitary electron bunches. It is shown that these self-sustaining electron bunches may be responsible for the existence of an anode current in the absence of rf interaction. Pis’ma Zh. Tekh. Fiz. 24, 57–62 (June 26, 1998)