Advanced SPA Convergence Control
During an SPA analysis, Creo Simulate stimates the error in stress that it computes throughout the model. These stress error estimates control the convergence algorithm. By default, the error of the stress in an element is computed as a percentage of the maximum stress that occurs in the model. If the maximum stress in the model is very high at any one location, such as at a stress singularity, then the stress error for all elements of the model away from that location will be very low. As a result, for an SPA analysis, stress in locations away from a high stress location may not be very accurate.
For models with stress singularities, it is recommended that you use the
Isolate for Exclusion option on the
AutoGEM Control dialog box to detect and isolate the singularities in a model as an
Isolate for Exclusion AutoGEM Control (IEAC). You must also select the
Exclude Elements and the
Ignore for normalizing stress errors check boxes on the
Excluded Elements tab on the analysis definition dialog boxes.
As another method to improve the accuracy of stresses in regions of low stress, Creo Simulate provides an advanced SPA convergence control. With this advanced convergence control you can set targets for both the globally normalized stress error (similar to the default stress error mentioned above) and a locally normalized stress error. The target for the globally normalized stress error is called the Maximum Stress Error Target because it acts to set a target error for the maximum stress in the model. The target for the locally normalized stress error is called the Local Stress Error Target because it acts to set a target for the error for local stresses everywhere in the model. Both are expressed as percentages.
For a single pass adaptive (SPA) method of convergence, select Advanced Control on the Static Analysis Definition dialog box to open the Advanced SPA Convergence Control dialog box.
This dialog box contains the following items.
• Use Advanced Controls—Select this check box to activate the remaining items in the Advanced SPA Convergence Control dialog box. If you do not select this check box, all options in this dialog box are inaccessible and Creo Simulate does not use advanced convergence controls.
• Maximum Stress Error Target—Specify a floating point value less than or equal to 100 for the target of the error of the maximum stress in the model. The default value of the maximum stress error target depends on the type of analysis. Use a smaller value to increase the accuracy of the analysis.
The following table gives the default value of maximum stress error target in terms of percentage for the different types of analysis.
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Type of Analysis
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Default Value of Maximum Stress Error in %
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Static
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8
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Modal, Pre-Stress Modal
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16
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Buckling
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12
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The following two items on the dialog box are optional.
• Local Stress Error—Use this collector to select different locations and entities on the model where you wish to specify the locally normalized stress error target. Hold down the CTRL key to select multiple points, edges, surfaces, volumes or components.
• Local Stress Error Target—Enter a positive floating point value less than 100 for the target of the locally normalized stress error you wish to specify for the selected regions on the model. Local stress error has a default value of 10%. Use a smaller value to increase the accuracy of the analysis.
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 For shells, the maximum stress in an element is the maximum stress along the shell’s edges. |