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in creator/contributor: "MENIKOFF, R."

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Numerical anomalies mimicking physical effects

Numerical simulations of flows with shock waves typically use finite-difference shock-capturing algorithms. These algorithms give a shock a numerical width in order to generate the entropy increase that must occur across a shock wave. For algorithms in conservation form, steady-state shock waves are insensitive to the numerical dissipation because of the Hugoniot jump conditions. However, localized numerical errors occur when shock waves interact. Examples are the ``excess wall heating`` in the… more

Date: September 1, 1995

Creator: Menikoff, R.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Anomalous physical effects from artificial numerical length scales

Shock capturing algorithms are widely used for simulations of compressible fluid flow. Though these algorithms resolve a shock wave within a couple of grid points, the artificial length scale from the numerical shock profile can have side effects. The side effects are similar to physical effects that occur when a relaxation process gives rise to fully or partly dispersed shock waves. Two anomalies due to a non-zero shock width are discussed: (1) in one-dimension, a non-decaying entropy spike re… more

Date: September 1, 1995

Creator: Menikoff, R. & Lackner, K.S.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Compaction Waves in Granular HMX

Piston driven compaction waves in granular HMX are simulated with a two-dimensional continuum mechanics code in which individual grains are resolved. The constitutive properties of the grains are modeled with a hydrostatic pressure and a simple elastic-plastic model for the shear stress. Parameters are chosen to correspond to inert HMX. For a tightly packed random grain distribution (with initial porosity of 19%) we varied the piston velocity to obtain weak partly compacted waves and stronger f… more

Date: January 1, 1999

Creator: Kober, E. & Menikoff, R.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Modeling compaction-induced energy dissipation of granular HMX

A thermodynamically consistent model is developed for the compaction of granular solids. The model is an extension of the single phase limit of two-phase continuum models used to describe Deflagration-to-Detonation Transition (DDT) experiments. The focus is on the energetics and dissipation of the compaction process. Changes in volume fraction are partitioned into reversible and irreversible components. Unlike conventional DDT models, the model is applicable from the quasi-static to dynamic com… more

Date: December 31, 1998

Creator: Gonthier, K.A.; Menikoff, R.; Son, S.F. & Asay, B.W.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Modeling energy dissipation induced by quasi-static compaction of granular HMX

A simple extension of a conventional two-phase (inert gas and reactive solid) continuum model of Deflagration-to-Detonation Transition (DDT) in energetic granular material is given to account for energy dissipation induced by quasi-static compaction. To this end, the conventional model equations,, valid in the limit of negligible gas phase effects, are supplemented by a relaxation equation governing irreversible changes in solid volume fraction due to intergranular friction, plastic deformation… more

Date: November 1, 1997

Creator: Gonthier, K.A.; Menikoff, R.; Son, S.F. & Asay, B.W.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

COMPACTION WAVE PROFILES IN GRANULAR HMX

Meso-scale simulations of a compaction wave in a granular bed of HMX have been performed. The grains are fully resolved in order that the change in porosity across the wave front is determined by the elastic-plastic response of the grains rather than an empirical law for the porosity as a function of pressure. Numerical wave profiles of the pressure and velocity are compared with data from a gas gun experiment. The experiment used an initial porosity of 36%, and the wave had a pressure comparab… more

Date: June 1, 2001

Creator: MENIKOFF, R.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

EQUATION OF STATE AND HUGONIOT LOCUS FOR POROUS MATERIALS: P-ALPHA MODEL REVISITED

Foams, porous solids and granular materials have a characteristic Hugoniot locus that for weak shocks is concave in the (particle velocity, shock velocity)-plane. An equation of state (EOS) that has this property can be constructed implicitly from a Helmholtz free energy of the form {Psi}{sub s}(V,T,{phi}) = {Psi}{sub s}(V,T)+B({phi}) where the equilibrium volume fraction {phi}{sub eq} is determined by minimizing {Psi}, i.e., the condition {partial_derivative}{sub {psi}} {Psi} = 0. For many cas… more

Date: August 1, 1999

Creator: MENIKOFF, R. & AL, ET

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

MESO-SCALE SIMULATIONS OF COMPACTION WAVES IN A GRANULAR BED

A granular bed provides an extreme example of a heterogeneous material. Behind a moderate strength wave, the shock compression in a granular material is due to squeezing out pore space rather than an increase in the density of individual grains. This type of shock is known as a compaction wave. The key properties of compaction waves are displayed in mesomechanics simulations--continuum mechanics calculations in which individual grains are resolved. Fluctuations in hydrodynamic quantities occur … more

Date: May 1, 2001

Creator: MENIKOFF, R.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

GRANULAR EXPLOSIVES AND INITIATION SENSITIVITY

No Description Available.

Date: November 1, 1999

Creator: MENIKOFF, R.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Hamiltonian and generating functional for a non-relativistic local current algebra

No Description Available.

Date: January 1, 1974

Creator: Menikoff, R.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Sharp shock model for propagating detonation waves

Recent analyses of the reactive Euler equations have led to an understanding of the effect of curvature on an underdriven detonation wave. This advance can be incorporated into an improved sharp shock model for propagating detonation waves in hydrodynamic calculations. We illustrate the model with two simple examples: time dependent propagation of a diverging detonation wave in 1-D, and the steady 2-D propagation of a detonation wave in a rate stick. Incorporating this model into a 2-D front tr… more

Date: January 1, 1989

Creator: Bukiet, B. & Menikoff, R.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Quantized vortex filaments in incompressible fluids

Among the solutions A/sub t/(x) to the Euler equations for a classical incompressible fluid are those describing vortex filaments. Here we discuss quantum analogues of such solutions in 2 and 3 dimensions.

Date: January 1, 1986

Creator: Goldin, G. A.; Menikoff, R. & Sharp, D. H.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Generating strong shock waves with a supersonic peristaltic pump

An axially phased implosion of a cylindrical tube with a phase velocity exceeding the sound speed of the fill material acts as a peristaltic pump which drives a shock wave along the axis. The region behind the onset of the phased implosion forms a converging-diverging nozzle. When appropriately designed the flow approaches a steady state in which the shock is planar and propagates near the nozzle entrance. The steady-state flow and the approach toward it have been derived in a one-dimensional m… more

Date: January 1, 1991

Creator: Menikoff, R. & Lackner, K.S.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Understanding curved detonation waves

The reaction zone of a detonation wave is very small compared to the dynamic length scale for a typical application. Consequently, it is impractical for numerical calculations to fully resolve the reaction zone. A non-zero reaction zone width is critical to describe curved detonation waves because it affects the wave speed. The curvature effect is the result of an the interaction between the rate of energy release and geometric source terms within the reaction zone. When the reaction zone width… more

Date: January 1, 1993

Creator: Bukiet, B.G. (New Jersey Inst. of Tech., Newark, NJ (United States)); Lackner, K.S. & Menikoff, R. (Los Alamos National Lab., NM (United States))

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Understanding curved detonation waves

A wave curve is the set of final states to which an initial state may be connected by a traveling wave. In gas dynamics, for example, the wave curve consists of the shock Hugoniot curve for compressive waves and the rarefaction curve for expansive waves. In this paper, we discuss the wave curve for an undriven planar detonation and for general planar detonations. We then extend the wave curve concept to detonations in converging and diverging geometry. We also discuss the application of these w… more

Date: January 1, 1992

Creator: Bukiet, B.G. (New Jersey Inst. of Tech., Newark, NJ (United States). Dept. of Mathematics) & Menikoff, R. (Los Alamos National Lab., NM (United States))

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Statistical theories of Rayleigh-Taylor instability for compressible fluids

Statistical theories for the outer envelope of the Rayleigh-Taylor mixing layer refer to a simplified dynamics of fundamental modes and their interactions. These modes are bubbles of light fluid entrained in the mixing layer between the undisturbed light and heavy fluids. The dynamics can be understood in terms of the motion of a single mode and the interactions between modes. The single mode dynamics has to be solved self-consistently in a background field of random bubbles. The dominant inter… more

Date: January 1, 1988

Creator: Glimm, J.; Li, X. L.; Zhang, Q.; Menikoff, R. & Sharp, D. H.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Errors when shock waves interact due to numerical shock width

A simple test problem proposed by Noh, a strong shock reflecting from a rigid wall, demonstrates a generic problem with numerical shock capturing algorithms at boundaries that Noh called excess wall heating.'' We show that the same type of numerical error occurs in general when shock waves interact. The underlying cause is the non-uniform convergence to the hyperbolic solution of the inviscid limit of the solution to the PDEs with viscosity. The error can be understood from an analysis of the a… more

Date: March 4, 1993

Creator: Menikoff, R.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Numerical implication of Riemann problem theory for fluid dynamics

The Riemann problem plays an important role in understanding the wave structure of fluid flow. It is also crucial step in some numerical algorithms for accurately and efficiently computing fluid flow; Godunov method, random choice method, and from tracking method. The standard wave structure consists of shock and rarefaction waves. Due to physical effects such as phase transitions, which often are indistinguishable from numerical errors in an equation of state, anomalkous waves may occur, ''rar… more

Date: January 1, 1988

Creator: Menikoff, R.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Equilibrium ignition for ICF capsules

There are two fundamentally different approaches to igniting DT fuel in an ICF capsule which can be described as equilibrium and hot spot ignition. In both cases, a capsule which can be thought of as a pusher containing the DT fuel is imploded until the fuel reaches ignition conditions. In comparing high-gain ICF targets using cryogenic DT for a pusher with equilibrium ignition targets using high-Z pushers which contain the radiation. The authors point to the intrinsic advantages of the latter.… more

Date: December 31, 1993

Creator: Lackner, K. S.; Colgate, S. A.; Johnson, N. L.; Kirkpatrick, R. C.; Menikoff, R. & Petschek, A. G.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Errors when shock waves interact due to numerical shock width

A simple test problem proposed by Noh, a strong shock reflecting from a rigid wall, demonstrates a generic problem with numerical shock capturing algorithms at boundaries that Noh called ``excess wall heating.`` We show that the same type of numerical error occurs in general when shock waves interact. The underlying cause is the non-uniform convergence to the hyperbolic solution of the inviscid limit of the solution to the PDEs with viscosity. The error can be understood from an analysis of the… more

Date: March 4, 1993

Creator: Menikoff, R.

Item Type: Article

Partner: UNT Libraries Government Documents Department