RESOLUTION... Setting Contour Resolution
RESOLUTION... Setting contour resolution
Structural elements
The output from most 2D & 3D elements in Ansys LS-DYNA is only written at element centres, implying constant stress: no values are written at nodes on elements. Therefore contouring, by displaying variations of data across elements, is an approximation used to help visualization of the data distribution.
For fully integrated SHELL elements D3PLOT can use the data to more accurately contour the variation of data across the element (provided MAXINT on the *DATABASE_EXTENT_BINARY card is negative and a ZTF file has been written from PRIMER).
Most Ansys LS-DYNA elements are constant stress, and experience has shown that the safest - if not necessarily the most accurate - method of averaging data at nodes for contouring is to use the largest magnitude of all the element results meeting at the node, the "Medium" resolution option. This tends to over-estimate the geographical extent of peak values, but this is preferable to losing these peaks by averaging data at nodes. However other more traditional methods are available, and are described Contour averaging options for structural elements.
Volume 3 elements (ICFD, CESE, EMAG, etc)
These analyses vary: some solution methods write results at element centres and others at nodes. However experience suggests that these analysis types work best with some degree of data smoothing, so it is possible to set their contour averaging method independently to "Low" resolution where results are averaged at nodes.
Thick shell contour for surface-based data
Thick shells are a special case: they use explicit nodes to define their thickness and hence are drawn as pseudo-3d elements with distinct top, bottom and sides. D3PLOT can display surface-based (stress, strain and extra) data either "simply" for a single surface on all faces of the element, just like thin shells. Alternatively it can show top surface data on the top face, bottom surface data on the bottom face, and interpolate results on the side faces. This is described in more detail Contour Display Options for Thick Shell elements.
Contour averaging options for structural elementsThree levels of contour resolution are provided for structural elements |
|
| LOW | Data are averaged at nodes, then contour bands (or lines) are drawn linearly from edge to edge across elements. The element centre values are not directly included so some smoothing of results occurs and peak values may be lost: which is potentially unsafe. |
| IUM | The value with the greatest magnitude at each node is found, then contour bands (or lines) are drawn linearly from edge to edge across elements. The element centre values are implicitly included since they will qualify as maxima at nodes: a safe overestimate. |
| HIGH | Data are averaged at nodes as before, but elements are then split into sub-areas using centre and mid-side values. This enables variations across elements to be seen, and peak centre values included. However it requires up to eight times as much computation, graphics storage and drawing effort as the other two modes. |
The default mode is (ium) resolution since this is both "safe", (peak centre values are included, albeit smeared out to element verticies), and quick (computation, graphics data storage and drawing effort are small).
To understand the effects of the three possible contour settings consider the following example:
|
The four plots below show the results plotted as unaveraged (true) data, and also using the three data averaging methods described above.
|
Two sheets are spot-welded together, and are then pulled apart.
Unaveraged dataThis shows the actual "true" results that come from Ansys LS-DYNA. It is the most accurate, if not the mostly visually appealing, way of showing results in constant stress elements. However it is by definition not "contouring".
|
|
 |
|
LOW resolution contoursIn this mode the results from all elements meeting at a node are averaged to give a nodal value, and then these nodal values are contoured.
 Note that this method always reduces peak values . If you are interested in the worst case values then you should not use low resolution contours, as they are not intrinsically safe, however they are suitable for smoothing out noisy values.
|
|
 |
|
MEDium resolutionIn this method results are not averaged, rather the element value with the greatest magnitude at a given node is used. These values are then contoured.
 This method over-estimates the geographical extent of the peak value, here you can see that the purple extends into adjoining elements, but it is safe since the worst case values will not be lost due to averaging. The method is the default in D3PLOT for constant-stress structural elements since it is fast to compute and draw, and also safe.
|
|
 |
|
HIGH resolution contoursIn this method results are averaged linearly not only at nodes, but also at element mid-side points, which allows elements to be split up into [centre], [mid-side point], [node], [mid-side] sub-elements. Contouring is then performed on these sub-elements.
 This method is both safe and accurate . It does not lose element centre values and gives the most realistic display of data variation. However it is slow to compute (for single on plan points: 9 locations per quad instead of 4, for multiple on plan points: 16 locations) and also slow to draw (for single on plan points: 4 sub-elements per quad instead of a single element, for multiple on plan points: 9 sub-elements), which is why it is not the default.
|
|
 |
Contour Display Options for Thick Shell elementsThis only affects how per-surface data is displayed on the element faces. It has no bearing on the low / medium / high resolution averaging methods described above.
|
|
|
Interpolate case In this case the data displayed on the top surface of the shell is from the topmost (outer) integration point, and that on the bottom surface is from the bottommost (inner) integration point. Data on the side faces is interpolated. |
|
|
Simple case In this case data for the same surface, here layer 1, is displayed on all faces of the element. |
|
