| Applies To | |||
| Product(s): | AutoPIPE | ||
| Version(s): | All | ||
| Environment: | N/A | ||
| Area: | Error Message; Dynamic Analysis | ||
| Original Author: | Bentley Technical Support Group |
Problem:
When performing a modal analysis the following error message is displayed by the program.
Why and how to avoid it?
Solution:
This message is not so much an error message as it is a warning but should be displayed regardless. This message is self explanatory; the program was instructed by the settings to find all frequencies up to and including a predetermined number, but was not able to reach that value. Hence the message is being displayed. It is Ok not to find the next frequency as the program was only able to calculate so many.
Workaround:
The only options are to change the Stiffness and / or Mass matrix of the calculations. In order to do this modify one or more of the following:
-
- Support Stiffness - open Support input grid and change stiffness values on applicable supports
- Tools> Model Options> Edit> Mass points per span - Change from A (Auto) to value 1 - 9. Note, this can be an iterative operation for which value works best for a particular model.
- Load> Dynamic> modal> modal settings - change settings as needed
- Support Stiffness - open Support input grid and change stiffness values on applicable supports
Suggestion for new Users:
For new user of modal analysis, be sure not to analyze a system to such high frequencies as it may not affect the results very much. Review the Frequency output report for "Total captured modal mass (%)". On average, anything above is 70% will provide sufficient results but better to attain closer to 100%. As an iterative approach adjust some modal settings and review the results to see how sensitive a model is to increased values of frequency.