ObjectCAD™

This is our computer-aided design (CAD) tool that is used to interactively create a 3-D geometric representation of device that is being analyzed. It is based on the ACIS® geometry kernel from Spatial Technologies, and allows parameterization of the geometry in order to support design automation and optimization. We have also developed plugins for AutoCAD® and Mechanical Desktop® from Autodesk that allow Analyst™ to treat them as servers.

ObjectCAD's tree control displays the currently loaded model(s). A model generally consists of an assembly, which is a collection of oriented and positioned parts, and also a set of part definitions (see Fig. 1). Views of the geometry are created using the context menu associated with the assembly/part/solid of interest.

Fig. 1. ObjectCAD™ tree control, showing model hierarchy.

With ObjectCAD™, users create complex geometry by combining simple solids. A solid may be a predefined shape such as a box, cylinder, or sphere (called "primitives"), or it may be an extrusion or revolution of a wireframe created using the sketching tool (see Fig. 2). New solids may also be created by performing boolean operations on existing solids, including unions, subtractions, and intersections.

2(a). Wireframe sketch used to create solid via a revolution.

2(b). Solid generated by revolving sketch 90º about axis.

ObjectCAD™ is a parametric modeling tool. Solids are defined in terms of parameters that may be modified even after the model is assembled. Parameters for solid primitives are their dimensions, such as radius and length for a cylinder. Edges and arcs may be parameterized in a sketch (Fig. 3), as well as revolution angles and extrusion depths.

Fig. 3. Parameters defined on a sketch. Values can be changed by clicking on the appropriate variable name, or via the Parameters dialog.

The parameters defining a particular solid are accessible from the context menu associated with the solid. Additionally, all parameters in a model may be accessed/modified via a single dialog (see Fig. 4), also available on the context menu.

Once geometry is defined, the user may associated attributes with volumes and surfaces. A volume attribute is a quantity that is associated with a solid volume, e.g., a material property. Surface attributes are usually boundary conditions. Attributes are applied interactively by selecting the appropriate face(s) or volume(s) with the mouse.

Fig. 4. Parameter dialog allows access to all parameters associated with the solid, part, or assembly. Parameters are edited by clicking on the value, or double clicking on the name.

When a model is complete, the user can export it in a .sat file for use in ObjectMesh™ or any other application that can read ACIS® files. When ObjectCAD™ is used from within Analyst™ exporting is handled automatically. Surface and volume attributes are contained in the .sat file as standard ACIS® attributes.