ComputerAided_Design_Engineering_amp_Manufactur.pdf

2. Specification of analysis-specific information—providing all details that are required for performing
an effective and efficient analysis of the given design problem;
3. FEM model discretization—discretizing the entire FEM model into a properly connected mesh
of suitably sized and shaped elements;
4. Specifying design conditions—specifying loads and boundary conditions at appropriate nodes
and elements of the FEM model;
5. FEM Analysis—conducting the FEM analysis using specialized codes (in-house software programs)
or commercial codes such as NASTRAN, ANSYS, etc.;
6. Interpretation of FEA results—assessing the validity of the results for the specified design requirements;
7. Repeating the steps until acceptable results are obtained. 12 In the recent past, most of the research
efforts5–7
© 2001 by CRC Press LLC
were directed toward automation of Step 3. In order to achieve complete automation of
design analysis tasks, one would need to address issues pertaining to the individual requirements
of all of the above steps.
Since the FEA procedure would have to be integrated and driven by a CAD system, the most obvious
requirement relates to modeling the object in the CAD system and transferring geometric as well
functional requirements information from the CAD system to the finite element preprocessor. ‘‘The more
complete the geometric information passed to the preprocessor, the more automated the finite element
analysis process can be made.’’ 5 Current CAD systems that are developed based on conventional
information processing technology rely mostly on procedural representation of 3-D objects (solid
models) and do not have the capability to undertake tasks such as automatic FEA. In order to break
this barrier for integration, steps should be undertaken for developing a ‘‘complete’’ representation of
the design object and the corresponding object model which should include: (a) geometric information
to represent the shape and form of the design structure; (b) design-specific functional information to
represent attributes, properties, behaviors, and functions of the design artifact; and (c) information
management attributes and directives in order to ensure the smooth integration between the CAD and
FEM systems. Moreover, the object model cannot be a static entity (e.g., data base data structure), and
it needs to adopt flexible object and attribute representation schemes to aid in the FEA process. The
system should attempt to utilize as much design-specific knowledge as possible in order to obtain a
successful CAD-FEM interface.
Based on the above mentioned list of requirements, the object-oriented approach for object model
definition has been adopted for modeling the FEM analysis attribute information. 12 Frames have been
selected as the means of knowledge representation in the object-oriented programming (OOP) environment.
In OOP, self-contained pieces of code called ‘‘classes’’ (at the information concept level) and
‘‘objects’’ (at the implementation level) represent the informational attributes of an artifact associated
with an application or function. For instance, the Design-Information class shown in Table 1.1 represents
a class template that contains information pertinent to the specified loading and boundary conditions
on the design component, as well as the stated design requirements for FEA. Since the modeling of the
original geometric model to an appropriate FEM model is necessary for reducing the computation time,
a considerable amount of knowledge needs to be represented and consulted with in order to reason
about: (a) simplified geometric representation of the object—submodeling the object model based on
the inherent symmetry of the component geometry and design loads and restraints, and (b) removing
subcritical geometric features (e.g., small holes, fillets, etc.) from the FEM model. Once the task of model
building is complete, the geometrical, topological, and material data needs to be transferred from the
CAD package to a standard FEA package such as ANSYS, etc., and package-specific knowledge is required
for creating the appropriate data set for running the object model in the specific analysis package. The
analysis of FEA results obtained is then assessed. Similar to FE modeling, the analysis of FEA results is
also a knowledge intensive task, and often the designer’s judgment and past experience play a critical
role in successful execution of these tasks. Furthermore, based on the FEA results, the redesign of the
design object is another task where the designer’s experience and the redesign procedures adopted for