Importing and Exporting CAD Files

VISRAD is capable of importing and exporting Target Component data from/to CAD files.

Two types of CAD file formats are supported for importing and exporting:

• STEP (or STP)
• STL

Both STL and STEP file import and export are currently supported on all platforms.¹

Importing STL- and STEP-Formatted Files

To import data from a CAD file, select the File | Import CAD File menu item.

When importing an STL-formatted CAD file, the user can specify the units for the node positions, and the file format (ascii, binary, or automatically detect). When setting the File Format to "auto detect", VISRAD attempts to automatically determine whether the file is ascii or binary using the first two lines in the file.

When importing data from a CAD file, the default name for the object is given by the CAD file name. If that name is already in use, a number is (e.g., "_2") appended to the end of the name.

Importing more than one CAD file at a time is supported.

When importing a STP-formatted CAD file as a Target Component, if the CAD file contains more than one object (or "shape"), a reference object is automatically set up, and each of the CAD objects use this reference object as their Reference Coordinate System. This allows users to easily rotate or translate the entire set of CAD objects. The reference object is a small Cone object that is hidden when set up, and it is set to be ignored in laser deposition and radiosity simulations.

After importing the data, VISRAD creates a single GENERALIZED MESH object. A GENERALIZED MESH object is composed of a series of nodes and surface elements, but is not defined using a simple geometric primative (i.e., an object characterized by parameters such as Radius or Length, as is the case for a Sphere or Cylinder). While the position and orientation of a GENERALIZED MESH object are editable, the size and grid (e.g., number of nodes) are not editable.

The object position for a GENERALIZED MESH object can be defined as the centroid of a bounding box which is determined by the minimum and maximum x, y, and z values for vertices of the object. This position is automatically determined when importing data from the CAD file. Alternatively, its position can also be defined using either one of the faces of the bounding box (+/- x,y,z) or the grid origin used by the CAD file (in the latter case, the grid origin, relative to the centroid of the bounding box, is stored by VISRAD when importing the data from the CAD file).

Selecting the position to be the Grid Origin, or one of the bounding box Faces, can be useful, as it can facilitate the positioning and orienting of the CAD object.

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.

The images below show examples of targets and target chamber components imported from CAD files by VISRAD.

Exporting STL-Formatted Files

When exporting Target Component data to a STL-formatted CAD file, right-click on the target component in the Target Components List, and select Export to CAD File. For the Save as Type, select STL File. For STL-formatted files, the unstructured triangulated surface data for the object are written to the file. This data can be exported using a variety of common units (m, cm, mm, microns, inches).

Exporting STEP-Formatted (STP-Formatted) Files

VISRAD also supports exporting Target Component data to STEP-formatted files, with limitations. To export data to a STEP-formatted CAD file, right-click on a Target Component in the Target Components List, select Export to CAD File, and select STP File.

There are a number of limitations in exporting STEP-formatted CAD data:

• Hohlraums and GENERALIZED MESH objects (i.e., object imported from CAD files) cannot be exported. (in the latter case, just use the original CAD file)
• When exporting to STEP files, 3-D objects in CAD software are sometimes considered to be solid, therefore the exported objects may appear different in the CAD software. Also, if is considered to be a solid object by the CAD software, the wall thickness used in VISRAD may not have any effect. However, the wall thickness for 2-D objects does appear to have an effect.
• Exported objects may appear slightly different in other CAD software becase of the number of grid points used in rendering the object (e.g., if only 8 azimuthal grid points are used in setting up a disk in VISRAD, it looks like an octogon instead of a disk).
• If the inner and outer radius of a Disk have exactly the same value, VISRAD will create a circle, but it cannot be exported to STEP file.
• For Cylinder objects, rounded corners are currently not supported. In cases where Cylinders have a non-zero R-corner value, it will be ignored when exporting to the STEP file.
• For Torus objects, when the minimum and maximum polar angle values are not 0 and 360 degrees, the exported geometry will be different.
• For Sphere objects, when clipped by a Box clipping volume, one can choose either Interior or Exterior. Currently only Exterior is being properly exported to STEP files. Interior gives the same result as Exterior, which appears to be due to a problem with the current version of the third-party software party being utilized.
• For Polygon objects, only regular polygons can be exported.
• For Multi-Element objects that have Clipping Volumes applied in VISRAD, the Clipping Volumes are sometimes ignored when exporting to STEP files because of crashes that can occur in the third-party software party being utilized.

LIMITATIONS and KNOWN ISSUES for GENERALIZED MESH Objects

Limitations and known issues for GENERALIZED MESH objects include:

• GENERALIZED MESH object sizes and grids are not editable. This has implications for the calculation of laser power deposition across the target. CAD objects that are imported sometimes have coarse grids that are not suitable for accurate calculation of laser power deposition or radiosities.
• Surface normal directions are not editable. This has implications for radiosity calculations (i.e., radiation temperatures and fluxes). Radiosity calculations compute fluxes by including the "reflection" of thermal radiation off surface elements in the grid. The reflection depends on whether the surfaces normals are pointed "up" or "down" for a surface element. As these are not editable, the calculation of radiation temperatures and fluxes may be inaccurate.

PLATFORM-RELATED ISSUES

VISRAD utilizes a third-party software library for importing and exporting STEP-formatted CAD files. This library may exhibit platform-dependendent behavior.

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