Microscopic simulations of shock propagation in condensed media: comparison between real time and frequency domains Page: 2 of 9
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MICROSCOPIC SIMULATIONS OF SHOCK PROPAGATION IN CONDENSED MEDIA:
COMPARISON BETWEEN REAL TIME AND FREQUENCY DOMAINS*
A. M. Karo, J. R. Hardy,** and M. H. Mehlman
Lawrence Livermore National Laboratory
Livermore, California 94550
**Behlen Laboratory of Physics, University of Nebraska
Lincoln, Nebraska 68588
Computer molecular dynamics (CMD) is now recognized as a
very powerful technique for examining the microscopic
details of a wide variety of chemical and physical
phenomena, including the shock-induced fast decomposition
processes that characterize the shock-initiation of
energetic materials. The purpose of the present paper 1s
to describe some results obtained by new methods of post
processing of CMD data. First we present a pictorial
history of a canonical system which is bonded with
identical potentials and has identical atomic masses. We
then present Fourier transforms of the energy components of
different units judiciously chosen to show the "frequency
fingerprint" of the shock impact and passage through
specific units of the system, including, e.g., the behavior
of spalled fragments.
To complement these studies, we also display the behavior
of our canonical system when defects (point or line) are
present. In these studies we monitor the motion of diatoms
above and below a line defect consisting of heavy masses.
The Fourier transform techniques proylde optimum compromise
histories which present neither too much nor too little
Of the three/four states of matter: solid, liquid and gas/plasma, the
last differs far more radically from the first two than the first two do from
each other. The primary difference, from which all others largely spring, is
that of density or volume/particle. While this 1s essentially unchanged at
the solid-liquid transition, at the liquid (or solid)-gas transition the
volume/particle ratio increases by many orders of magnitude (at least by 10®
and often by far more). Consequently, the zero order theoretical approximation
is that of an assembly of largely non-interacting free particles (the “ideal
gas"). This has the consequence that workers dealing with shock phenomena in
gases recognize, either explicitly or implicitly, that there are fundamental
limitations on the continuum hydro-codes used to model hydrodynamic phenomena,
and that shock fronts are beyond those limits. As a consequence of this
realization, the shock is regarded as a discontinuity about which hydro-codes
can say essentially nothing and 1s simply modelled by Imposing the Hugoniot
jump conditions across the shock front.
♦Work performed under the auspices of the U. S. Department of Energy by the
Lawrence Livermore National Laboratory under contract number W-7405-ENG-48
and under the auspices of the Office of Naval Research.
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Karo, A.M.; Hardy, J.R. & Mehlman, M.H. Microscopic simulations of shock propagation in condensed media: comparison between real time and frequency domains, article, July 1, 1985; United States. (digital.library.unt.edu/ark:/67531/metadc1093724/m1/2/: accessed December 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.