Setting Object Size and Grid Parameters

Parameters used to specify the size and gridding of an object can be specified on an object-by-object basis. Editing the size/grid parameters of multiple objects simultaneously is also supported.

Parameters in the Size/Gridding tab are used to:

• Set the size of the object
• Set the number of grid points used in each dimension
• Set the thickness of the object
• Specify the direction of the surface normals

Quantities in the Size/Gridding tab are dependent on the type of object being edited (e.g., cylinder, rectangle, cylindrical hohlraum, ...).

Objects are composed of surface elements, which have a "preferred direction". The emission (or reemission) of surface radiation for each surface element depends on the direction of its surface normal. For object types that are hohlraums, Surface Normals are automatically set to In.

Objects created during the import of data from CAD files are GENERALIZED MESH objects. In this case, the size and grid parameters are not editable. Bounding boxes for GENERALIZED_MESH objects, which are based on the minimum and maximum x-, y-, and z-values of the nodes in their grid, can be displayed using the Show | Bounding Boxes (GM objects) menu item. The colors of the edges of the bounding boxes are red, green, and blue for the edges that are parallel to that object's x-, y-, and z-axes, respectively.

For objects of non-zero thickness, the object is constructed with:

• outer (or top) wall surface elements
• inner (or bottom) wall surface elements
• side surface elements

These objects have surface normals automatically set so that they are directed away from the opposing walls; e.g., the normals of surface elements on the top wall are directed upward, and those for the bottom wall are directed downward.

The images below show a solid, non-zero thickness cylinder display as filled polygons (left) and wireframe (right).

For parameters defining the object's size, VISRAD supports specifying either:

• a constant, time-independent value
• time-dependent values (except for Polygon shapes)

To specify time-dependent parameters, check the Time-Dep. box, and enter values into the time-dependent two-column tables.

Size values are typically entered in units of cm or mm (or degrees in the case of angles). To change the default units used to specify object sizes, go to the User Interface tab of the Preferences dialog.

Surfaces of Revolution

For Surface of Revolution objects, the radius (i.e., distance from the axis of symmetry, or z-axis) is specified as a function of z. This can be done using either an analytic function, or a tabular r(z) grid. In the latter case, the radius is computed by interpolating using the node's z-position.

Note that in the case of using analytic functions, when evaluating the radius, the value of z is always assumed to be in units of cm .

Polygons

Polygon shapes represent a special case for target component items in that:

• they can have an arbitrary number of nodes (up to 10 for the polygon base)
• their node positions can be adjusted interactively with the mouse (in the Setup Polygon Nodes window).
• time-dependent size parameters cannot be specified.

Polygons must be convex, but can be regular (equal length sides and angles) or irregular. If regular, the node center-to-corner length is specified.

Polygons can be extruded to provide 3-D shapes. They are 2-D when Polygon Height = 0, and 3-D when Polygon Height > 0.

The polygon surface (top and bottom in 3-D case) is sub-divided using grid refinement algorithms. The Subdivision Depth specifies the number of triangular subdivisions that will be applied.

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