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You will use the Patran Geometry application form for most of your geometry modeling tasks.
Using the Geometry Application Form
To use the Geometry Application form:
1. Click the Geometry button on the Patran Main form.
The Geometry Application form appears on your screen.
2. Select an Action/Object/Method combination from the drop-down menus at the top of the Geometry application form.
Several additional form fields display on the lower two thirds of the Geometry form that vary depending on the your selections for Action, Object, and Method.
Actions
The Action defines what you want to do. Actions fall into three categories: create, modify, or verify. The table that follows briefly describes the Action choices for the Geometry application.
| Action Descriptions |
| Create Actions | | |
Create | Creates points, curves, surfaces, solids, planes, vectors, and coordinate frames based on data input or cursor-selections from the viewport. |
Transform | Creates additional objects by duplicating existing entities at new locations. You may specify the new locations by offsets, rotations, scaling, mirroring about an axis, and so on. |
| Modify Actions |
Edit | Modifies geometric objects to improve the model design and correct errors, such as breaking big objects into groups of smaller ones, and deleting duplicate points. |
Delete | Eliminates objects from the database and erases them from the viewport window. |
Associate / Disassociate | Associate joins entities, such as a surface and a tangent curve, so that they are meshed together. Disassociate separates them. |
| Qualify Actions |
Verify | Identifies problem areas in your model that can then be corrected, such as gaps between edges of adjacent objects and missing surfaces. |
Show | Displays a spreadsheet form with information about geometric objects. For points, you may request data such as coordinate value locations and node IDs. |
Objects
The Object field defines the type of geometry. For example, if you specify a Create Action, the object defines what type of geometry you want to create.
Object | Description |
| Points (light blue) - a point coordinate location that has zero dimensions. Curves (yellow) - a one dimensional parametric curve. |
Surface | Simple surfaces (green) - Parametric surfaces with 3 or 4 outer edges; no inner edges, holes, or cutouts. General surfaces (magenta) - Surfaces with more than 4 outer edges, and/or with inner edges, holes, cutouts. |
Solid | Simple solids (dark blue) - Parametric solids with 5 or 6 faces. General solids (white) - Solids with more than 6 faces and/or with inner holes, edges, or cutouts. |
| Planes (pink) - a two-dimensional parametrized surface. Vectors (blue) - a one-dimensional curve with direction and magnitude. Frames (purple) - rectangular, cylindrical, or spherical frames of reference. |
Methods
The method specifies how the Action is going to be carried out. The choices for Method are so numerous that it would take many pages to list them all. An example of the Glide method is presented in the sample that follows this section. For a complete listing, please refer to the Patran Reference Manual, Volume 2, Part 3: Geometry Modeling.
Sample Geometry Form
The following illustration shows the selection of a Create action on the Geometry application form, with before and after snapshots from the viewport window. This selection, Create/Solid/Glide, creates Solid 1 using Curve 5 as the Glide path and Surface 2 as the base surface
Note: | The Geometry portion of the Patran Reference Manual provides annotated illustrations similar to this one for most of the supported Action/Object/Method choices. |
Creating Trimmed Surfaces
You must select Create/Surface/Trimmed on the Geometry application form to construct a trimmed surface in Patran. This form prompts you to define a surface in terms of its boundary curves, which are continuous closed "loops" that define both the outside boundaries of the surface, and interior holes or cutouts. This form also allows you to specify a parent surface from which the new surface is trimmed.
You can create the loops that form the outside boundaries and interior holes for the trimmed surface in one of three ways:
• The Create/Curve/Chain form prompts you to create a continuous loop from an existing set of curves that are joined from end to end. This operation defines a new, single chained curve, and prompts you to delete the original curves. The Auto-Chain option guides you visually through the process of creating a chained curve from this menu.
• The Auto-Chain button on the Create/Surface/Trimmed form allows you to create exterior and interior loops from existing sets of curves that are joined from end to end. This operation defines the new chained curves, and prompts you to delete the original curves.
• Certain curve options, such as Create/Curve/2D Circle and Create/Curve/Conic (when used to form a closed ellipse), create closed curves used directly as loops in trimmed surface creation.
The Create/Surface/Composite option allows you to create a single, composite surface from adjacent planar surfaces. This option is useful for creating a single, meshable surface from regions with complex edge boundaries or multiple adjacent regions.
Creating B-Rep Solids
A boundary representation (B-rep) solid is defined in terms of Patran surfaces which comprise the entire boundary of a solid. These solids may have an arbitrary number of boundary surfaces, so long as they comprise a closed solid region.The solids are defined using the Create/Solid/B-rep option of the Geometry menu form. However, before you use this option, the surfaces which bound the solid must be created or imported. Some guidelines for doing this properly include:
• Make sure that all surfaces are topologically congruent (e.g., they share common edges and vertices). In cases where surface edges do not align, consider options such as Edit/Surface/Sew or Edit/Surface/Match to align adjacent surfaces.
• In the case of models imported from CAD systems, make sure that its model tolerances fall within the geometric tolerance values of your database. For example, if your Patran database has a tolerance of .005 (meaning that points within this distance are at the same location), and your model is on a scale of units ranging from 0.0 to 0.1, you may find problems where points merge to form degenerate (e.g., collapsed) regions.
Conversely, a model scale which is too many orders of magnitude larger than the tolerance may mismatch adjacent surfaces. This tolerance value is database-specific and defined when you initially create the database using the File/New menu pick.
• Use the Verify/Surface/Boundary from the Geometry menu to make sure that there are no holes caused by missing surfaces in your model. Alternatively, you may wish to shrink surfaces towards their centroid using the Geometric Shrink option of the Display/Geometry utility menu, to observe their individual boundaries.
Check your B-rep solid for the following three items:
• The group of surfaces that will define the B-rep solid must fully enclose a volume.
• The surfaces must be topologically congruent. That is, the adjacent surfaces must share a common edge.
Important: | At this time, Patran can only create a B-rep solid with an exterior shell, and no interior shells. |
