Solid modeling
Solid modeling defines the surfaces of an object, with the added attributes of volume and mass. This allows image data to be used in calculating the physical properties of the final product. Solid modeling software uses one of two methods: constructive solid geometry (CSG) or boundary representation (B-rep). The CSG method uses Boolean operations (union, subtraction, intersection) on two sets of objects to define composite models. For example, a cylinder can be subtracted from a cube. B-rep is a representation of a solid model that defines an object in terms of its surface boundaries: faces, edges, and vertices.
Hybrid solid modeling allows the user to represent a part with a mixture of wireframe, surface modeling, and solid geometry. The I-DEAS Master Modeler offers this representation feature.
In CAD software, certain features have been developed to minimize the ambiguity of wireframe representations. These features include using dashed lines to represent the background of a view or removing those background lines altogether. The latter method is appropriately referred to as ‘‘hidden-line removal.’’
The hidden-line removal feature makes it easier to visualize the model because the back faces are not displayed. Shading removes hidden lines and assigns flat colors to visible surfaces. Rendering adds and adjusts lights and textures to surfaces to produce realistic effects. Shading and rendering can greatly enhance
the realism of the 3D image. Figures 7 and 8 show the same object represented as a pure wireframe and a wireframe with hidden-line removal.
Engineering analysis can be performed using one of two approaches: analytical or experimental. In the analytical method, the design is subjected to simulated conditions using any number of analytical formulas. By contrast, the experimental approach to analysis requires that a prototype be constructed and subsequently subjected to various experiments to yield data that might not be available through purely analytical methods.
There are various analytical methods available to the designer using a CAD system. Finite-element analysis and static and dynamic analysis are all commonly performed analytical methods available in CAD.
Emory W. Zimmers, Jr. and Technical Staff
Enterprise Systems Center
Lehigh University
Bethlehem, Pennsylvania
Mechanical Engineers’ Handbook: Materials and Mechanical Design, Volume 1, Third Edition.
Edited by Myer Kutz
Copyright 2006 by John Wiley & Sons, Inc.
