Occasionally, there are discrepancies among displacement
contour plots, depending on /GRAPH and /EFACET settings. For one representative
model, the following discrepancies could be observed from a modal analysis
of a SOLID95 mesh:
Max USUM contour values:
Full graphics : .1266
Power graph w/ /EFACET,1: .1235
Power graph w/ /EFACET,2: .1270
Power graph w/ /EFACET,4: .1272
It is possible that /GRAPH and /EFACET settings can affect
contour plots of displacement values. Here is the explanation:
1. Full graphics:
Even though Full graphics plots only the corner nodes of
elements, it uses the full set of nodal results at all nodes (including midside
nodes) when calculating the contour range. For this model, the maximum nodal
displacement occurred at a midside node, and this maximum value therefore
affects the DMX and maximum contour value reported in the plot.
2a. Power graphics, /EFACET,1:
Power graphics uses only the values for the specified
subgrid level when reporting DMX and when calculating the contour range. For
/EFACET,1, only results at the corner nodes are included. For this model, then,
the maximum contour value is based on corner-node values only. The maximum value
at a midside node is not considered, leading to a discrepancy between this plot
and the Full graphics plot.
2b. Power graphics, /EFACET,2:
For /EFACET,2, subgrid points include the midside nodes,
and the centroid of each element face. For this model, the displacement was
greatest at the centroid of one face, causing a further discrepancy.
2c. Power graphics, /EFACET,4:
For /EFACET,4, subgrid points include the midside nodes,
quarter points along each edge, the centroid of each element face, and the
quarter points of each element face. For this model, the displacement was
greatest at a quarter point on a face, causing a further discrepancy.
If you zoom in on the element having maximum
displacements, turn on /PNUM,SVAL,1, and plot contour values with these various
settings of /GRAPH and /EFACET, you should readily observe these effects.
For this model, the most accurate displacement value will
be obtained with /GRAPH,POWER and /EFACET,4. If a significant discrepancy is
found between /GRAPH,FULL and PowerGraphics with /EFACET,2 or 4, then this would
give a quick indication that the mesh might be too coarse. For this model, the
discrepancy appears to be relatively small, indicating that the mesh was
probably fine enough.