Improvements to SOIL: An Eulerian hydrodynamics code Page: 6 of 20
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The use of pseudo-viscosity in SOIL differs somewhat from conventional
wisdom. Generally the q is set to zero on expansion but in SOIL it can be
used both in expansion and compression. The value for the linear contribution
of (qL - 0.1) produces fairly smooth profiles behind the shock front.
The mixed cell treatment of SOIL is also quite basic and relates to the
Simple Line Interface Calculation (SLIC) method described by B. Noh (1975)/
First a NUMF (see Johnson 1971b) array is carried that identifies the
materials in the cell. A mixed cell has a negative number for NUMF. The
volume fractions (f) are calculated from pressure iterations in the mixed
cell. Consider two materials in the cell with masses M. and Mx. Using a
simple iteration technique (secant) the volume fractions (f) and internal
energies (I) are changed until, through the EOS of each material, pressure
equilibration is attained.
In the transport of material from cell K to cell KA, the cell above, to
or from a pure cell a simple decision of flow direction and adjacent like
material is used. If both cells are mixed, the decisions are more complex as
seen in Fig. 1, where cells K ard KA are mixed and the flow is in the
direction of KA. To remove preferential treatment of the mass transport, a
look ahead feature is used based on the mass flows across boundaries of cells
KA+1. The material that is moved first is the same material as that in the
At present, SOIL is neither vectorized nor multitasked, but because of
the splitting technique used in solving the hydrodynamic equations, the
ability to improve SOIL in this regard is fairly straightforward.
III. ADVECTION SCHEMES
Generally, the problem of advection does not come up in the discussion of
Lagrangian codes except in the process of rezoning the mesh when obtuse
triangles or bow ties occur. We will not discuss this aspect of advection in
terms of the Lagrangian section of SOIL. In an Eulerian mesh, material can be
advected from cell to cell by a simple first-order upwind scheme. In the Lax-
Wendroff scheme for instance material from cell i is advected with the
velocity from cell i +1 in the combination
n + 1 n
u - ui
.n + V2
i + Va
F n + Va
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Davis, C.G. Improvements to SOIL: An Eulerian hydrodynamics code, report, April 1, 1988; New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc1064690/m1/6/: accessed April 19, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.