MODELING IN ANSYS

MODEL GENERATION

The ultimate purpose of a finite element analysis is to re-create mathematically the behavior of an actual engineering system. In other words, the analysis must be an accurate mathematical model of a physical prototype. In the broadest sense, this model comprises all the nodes, elements, material properties, real constants, boundary conditions, and other features that are used to represent the physical system.

In ANSYS terminology, the term model generation usually takes on the narrower meaning of generating the nodes and elements that represent the spatial volume and connectivity of the actual system. Thus, model generation in this discussion will mean the process of defining the geometric configuration of the model's nodes and elements. The ANSYS program offers you the following approaches to model generation:

• Creating a solid model within ANSYS.
• Using direct generation.
• Importing a model created in a computer-aided design (CAD) system.

STEPS INVOLVED IN MODEL GENERATION WITHIN ANSYS

A common modeling session might follow this general outline (detailed information on italicized subjects can be found elsewhere in this guide):

• Begin by planning your approach. Determine your objectives, decide what basic form your model will take, choose appropriate element types, and consider how you will establish an appropriate mesh density. You will typically do this general planning before you initiate your ANSYS session.
• Enter the preprocessor (PREP7) to initiate your model-building session. Most often, you will build your model using solid modeling procedures.
• Establish a working plane.
• Generate basic geometric features using geometric primitives and Boolean operators.
• Activate the appropriate coordinate system.
• Generate other solid model features from the bottom up. That is, create keypoints, and then define lines, areas, and volumes as needed.
• Use more Boolean operators or number controls to join separate solid model regions together as appropriate.
• Create tables of element attributes (element types, real constants, material properties, and element coordinate systems).
• Set element attribute pointers.
• Set meshing controls to establish your desired mesh density if desired. This step is not always required because default element sizes exist when you enter the program. (If you want the program to refine the mesh automatically, exit the preprocessor at this point, and activate adaptive meshing.)
• Create nodes and elements by meshing your solid model.
• After you have generated nodes and elements, add features such as surface-to-surface contact elements, coupled degrees of freedom, and constraint equations.
• Save your model data to Jobname.DB.
• Exit the preprocessor.