| Applies To | |
| Product(s): | AutoPIPE |
| Version(s): | ALL; |
| Area: | Results |
| Original Author: | Bentley Technical Support Group |
| Date Logged & Current Version | Feb. 2017 10.01.00.09 |
Problem:
Why does AutoPIPE state that the frequency sub-report for all the pipe runs are the same?
Example:
Modeling large runs of overland piping on multiple disconnected systems. Performed a Dynamic analysis with a modal analysis to find out the frequency of the piping.
Result: The frequency for the whole pipeline is said to be the same!
Practically the pipe runs between different anchors and different segments should have a different frequency due to the different stiffness and weight plus the pipelines should not interact with each other across anchors and for completely different segments?
Solution:
The natural frequency formula assume a uniformly distributed weight. In AutoPIPE the weight is lumped at the nodes. So ½ the weight is placed on each end.
In order to simulate the natural frequency, additional mass points can be added. Either actual or automatic points can be added. When the automatic mass point option is used (Tools> Model Options> Edit) with cut-off frequency set, for example, at 200 Hz, the first mode frequency will be then be calculated, for example, to 44.5 hz. When the cut-off frequency is higher, for example, 2000 Hz, the frequency would than be calculated, for example, to 46.4 Hz.