CAD & Geometric Primitives

  The CAD/Geom panel provides access to facilities which can be used to complete the development of the analysis model if such has not been fully defined.  This will typically involve the creation of one or more geometric primitives to define the enclosing domain of interest followed by a series of volume operations to incorporate the desired geometry model.  In any event, it is assumed that the configuration geometry is adequately defined and possesses no holes, gaps, or mismatched edges as the facilities available herein simply provide a means to define the domain far-field boundary and the resulting solid model.  In other words, geometry used by GridEx must be a "water-tight" valid manifold solid, and the software performs no interrogation of the model to ensure that is the case.

Geometric Primitives

Basic primitives consisting of a Box, Sphere, Cone, and Cylinder may be created to represent the domain's far-field boundary by simply providing the appropriate defining data in the appropriate dialog window.  These entities may be positioned arbitrarily in three-dimensional space as prescribed by the user via a series of dialog windows which accept the relevant input parameters.  Currently, all primitives are Cartesian aligned with the subject geometry.  As the primitives are generated, they are also listed in the Structure Tree.

  For the Box, a Corner Reference Point is first specified to anchor the entity in space.  The Box Dimensions are then specified as the coordinates of the opposite corner thus defining an appropriately sized box.  Note that each of the latter coordinates must be specified such that the resulting body has non-zero volume.

  For the Sphere, the Center Reference Point anchors the center of the sphere in space.  The radius of the Sphere completes the definition and must be greater than zero to produce a body with non-zero volume.

  For the Cone, the Apex Reference Point is first specified to anchor the apex of the cone in space.  The orientation of the Cone is then prescribed by specifying coordinates for the Base Center.  The cone angle is then specified indirectly through the specification of the Radius, which is the radius of the cone in the base plane.  Like the Box,  specification of the Apex Reference Point and Base Center must not be coincident so as to produce a body with non-zero volume.

  For the Cylinder, the First Axis Reference Point represents the coordinate along the axis at one end of the cylinder.  The orientation of the cylinder is then fixed in space by specification of the Second Axis Point which corresponds to a point on the axis at the opposite end of the cylinder.  Finally, the Radius completes the definition of the cylinder.  As for the other primitives, specification of the axis points must be unique and the radius must be greater than zero to provide a non-zero volume.

  The Torus is a surface of revolution. The first three parameters define the rotation: the Center Reference Point anchors the center of the torus in space, the Sweep Curve Radius represents the distance from the center reference point to the center of the torus cross-section, and the Rotation Axis Direction is a vector about which the cross-section is rotated. The final parameter is the Cross Section Radius which defines the radius of the circle cross-section.

Solid Operations

  Solid operations consisting of Unite, Subtract, and Intersect may be performed on the geometric entities to complete the definition of the solid model or to define intermediate entities required to build a more complex model.  In any event, each operation requires the selection of a target volume followed by a single tool volume.  If successfully executed, the resulting entity will be rendered in the Working Display and entered in the Structure Tree.  Each operation will conclude by transparently redefining the rendering mode for the target and tool volumes to off such that they are no longer visible within the Working Display. They are, however, not deleted and will remain within the Structure Tree for subsequent use.

  The Unite operation combines the target volume with the tool volume to create a third volume defined by the sum of the initial volumes.  The operation will fail if the initial volumes do not overlap.  This operation may also fail if the bodies simply abut depending on the capabilities of the underlying modeling kernel.  The Unite capability is useful for assembling simple primitives into complex volumes.

  The Subtract operation determines that portion of the target volume external to the tool volume.  This facility will frequently be employed as a last step to define the solid model as this effectively "carves" the domain occupied by the configuration out of the volume whose boundaries define the extent of the analysis domain.  It can also be viewed as imprinting the tool in a clay facsimile of the target body.

  The Intersect operation determines that portion of the target volume which is also occupied by the tool volume.  If the volumes do indeed overlap, a new volume is created and displayed within the Working Display defined by the region common to both bodies.

  The solid operations tutorial provides a graphic description of the use of the facilities described above.