Page 82 - Using ANSYS for Finite Element Analysis A Tutorial for Engineers

geometrIc modelIng • 69
you are said to be building your model from the top down. You can freely
combine bottom-up and top-down modeling techniques, as appropri-
ate, in any model. Remember that geometric primitives are built within
the working plane, while bottom-up techniques are defined against the
active coordinate system. If you are mixing techniques, you may wish to
consider using the CSYS, WP or CSYS, 4 command to force the coordinate
system to follow the working plane.
Using Boolean operators: You can sculpt your solid model using inter-
sections, subtractions, and other Boolean operations. Booleans allow you
to work directly with higher solid model entities to create complex shapes.
(Both bottom-up and top-down creations can be used in Boolean operations.)
Dragging and rotating: Boolean operators, although convenient, can
be computationally expensive. Sometimes, a model can be constructed
more efficiently by dragging or rotating.
Moving and copying solid model entities: A complicated area or vol-
ume that appears repetitively in your model needs only be constructed once;
it can then be moved, rotated, and copied to a new location on your model.
You might also find it more convenient to place geometric primitives in their
proper location by moving them, rather than by changing the working plane.

3.4 tUtorial 1: solid modeling Using
2d Primitives

In this tutorial, the bottom-up solid modeling of a retaining ring is pre-
sented. In the ring diagram shown, build a solid model of the retaining
ring using extrusion command. When you are done, save the database.
Rather than drawing two circles and subtracting one from the other, circu-
lar annulus will be used to create the main ring. A 2D cross-section of the
retaining ring will be first drawn, having the complete details (including
fillet radius) shown. Solid Boolean operations will be performed to make
a single object from the various entities. The 2D object, together with its
mesh, will be extruded to obtain the final retaining ring.