Modeling initial imperfections

Typically, when you create an FE model, the model geometry has:

• Perfect form where planar surfaces are flat, cylinders are free of runout, and so on.

• Dimensions at their nominal values, or at the maximum or least material condition.

For many engineering applications of FEM, using such ideal geometry as the basis of the FE model is acceptable because the slight dimensional differences between the actual structure and the model of the structure have little consequence on the analysis results. However, in engineering applications of FEM such as buckling analysis, the analysis results can be sensitive to these slight dimensional differences.

To account for dimensional differences between the actual structure and the model of the structure in SOL 401, you can use the Initial Imperfection command. With the Initial Imperfection command, you can offset nodal locations for:

• Individual nodes

• All the nodes associated with a geometric feature like a polygon edge or face

• All the nodes in a mesh or group

When the software solves the model, it formulates the stiffness using the offset nodal locations.

The Initial Imperfection command is available only when SOL 401 Multi-Step Nonlinear is the solution type.

In the Initial Imperfection dialog box, two options are available for specifying nodal offsets:

• To apply offsets to nodes on an individual basis, from the Type list, select Node ID Table. You can then construct a table field or select an existing table field with node ID as the independent domain, and nodal offsets as the dependent domain.

• To apply offsets to nodes on a collective basis, in the Initial Imperfection dialog box, from the Type list, select Components. After selecting the nodes to offset, you can then construct a table field or select an existing table or formula field that defines the offsets as a function of spatial coordinates.

Where do I find it?

Application	Pre/Post
Prerequisite	An active SOL 401 Multi-Step Nonlinear solution
Command Finder	Initial Imperfection

How do I

Model an initial imperfection

Graph load factor vs. displacement

Learn more

Post-buckling analysis (SOL 401)

Post-buckling analysis workflow (SOL 401)

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Command reference

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Modeling initial imperfections, Simcenter 3D 2021.1 Series

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