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In the case of tetrahedral or hexahedral grids, the mesh boundary corresponds to the triangulation of the surface of the computational domain, whereas for triangular or quad grids it corresponds to the boundary edges. In this case an edge is considered to be on the boundary if it has only one adjacent element or if the angle between the face normals of the two adjacent elements is larger than a specified threshold.
The result of the calculation of the boundary of a mesh is a new list of elements that will be added to the same data set as the original grid. Once the boundary mesh is computed, different plots of its can be created.
To compute the mesh boundary of a given grid:
The first image below shows a tetrahedral mesh. The boundary mesh of the tetrahedral grid is shown in the second image (triangulation of the surface). And finally the boundary mesh of the surface triangulation is shown in the third image (boundary edges). In order to create this plots the boundary of the original tetrahedral mesh was first computed and then the boundary of the resulting triangular mesh was computed.
Cut planes can be computed for volume meshes of tetrahedra or hexahedra. The result of this calculation is a new data-set composed of a list of points and triangles located on the cutting plane and a set of fields interpolated to these points from the original data-set. Note that the calculation of a cut-plane does not produce any plot by itself. Once the cut-plane is computed any kind of plot (mesh lines, shading, vectors, etc.) can be created on the new data set.
To compute a cut-plane:
The following image shows the graphical definition of a cut-plane for the particular case of a fluid flow in a 3D rectangular box:
After calculating the cut-plane, the mesh on the cut is shown as lines and uniform shading below:
A given field defined on the original data set is shown here as a shading of the surface:
The following image shows the shading of the cut-plane according to the same field as above:
A second example is shown in the following two images. The first one displays the surface of an F117 aircraft colored according to processor number (parallel distributed calculation) and the definition of a cut-plane:
And the second figure shows the cut-plane shaded according to pressure as well as some pressure contour lines on the cut.
Iso-surfaces (surfaces of constant value) can be computed for volume meshes of tetrahedra or hexahedra. The result of this calculation is a new data-set composed of a list of points and triangles located on the surface which has a constant value of a given quantity and a set of fields interpolated to these points from the original data-set. Note that the calculation of an iso-surface does not produce any plot by itself. Once the iso-surface is computed any kind of plot (mesh lines, shading, vectors, etc.) can be created on the new data set.
To compute an iso-surface:
As an example, the following image shows the surface shading of a tetrahedral mesh according to a given field:
An iso-surface of the same field is shown below, colored according to the same field:
The triangular mesh defining the iso-surface is shown below:
A much more complex example is shown below, where the iso-surface of concentration of a toxic substance is shaded according to the velocity field of the wind around a group of buildings:
Given a mesh and a vector field defined on it, a new mesh can be computed by moving the mesh points in the direction of the vector field. This new deformed mesh is stored as a new data set. The calculation of the deformed grid will not produce any plot. Once the mesh is computed any kind of plot can be created from it (mesh lines, shading, vectors, etc.). This option is very useful for Computational Structural Dynamics (CSD) where the meshes representing structures can be deformed to visualize the deformation of the structure under loading.
To compute deformation grids:
The following example shows the deformation of a 3D bar represented by a mesh of hexahedra. The figure below displays the bar and displacement vectors colored according to the magnitude of the displacement:
The following figure shows both the original mesh and the deformed mesh colored according to the magnitude of the displacement:
Filters are used to limit the plotting to a group of points passing certaing criteria. Two types of filters are currently supported: integer fields and box of interest. In the former case all the points whose values of a given integer field are in a specified range pass the filter. In the latter all the points whose coordinates are inside the box of interest pass the filter. When creating plots that involve elements (mesh lines, shading, etc) two options are available: soft (default) or hard filters. In the case of soft filters, an element pass the filter if at least one of its nodes passes the filter, whereas in the case of hard filters, it passes the filter only if all of its nodes pass the filter. Only elements and points that pass the defined filters are included in the plots.
Other filters may be included in the future.
To define a filter:
The following example shows the results of using a box of interest filter with the soft and hard options. The image below displays the definition of the box of interest (in green):
The following image shows the mesh lines and shading of the triangular elements which pass the filter with the soft option:
The image below shows the mesh lines and shading of the triangular elements which pass the filter with the hard option:
The following example shows the use of an integer field to filter points. A fish is enclosed in a rectangular box. An integer fields has values of 0 on the outer box, while 1 on the surface of the fish. The image below shows a shading of the surface of the computational domain (fish plus box) according to the fluid pressure (no filters used here):
while the following image shows the shading of only the fish surface (using a filter according to the "body number" integer field with minimum and maximum values of 1):
