| Applies To | |
| Product(s): | AutoPIPE |
| Version(s): | ALL; |
| Environment: | N/A |
| Area: | |
| Original Author: | Bentley Technical Support Group |
| Date Logged & Current Version | Jan. 2017 10.01.00.09 |
Problem:
Is it possible to extract ‘modal stress amplitudes’ from a modal analysis report using AutoPIPE?
Example:
While performing a fatigue analysis of a pipe system subject to ‘Vortex Induced Vibration’ (VIV), and have extracted the natural frequency of piping spans. Then applying uniform loading to the spans under consideration, and extracting maximum deflections and bending moments for conversion into ‘Unit Diameter Stress Amplitude’.
The verification body, DNV, has suggesting that instead recommend using ‘modal stress amplitude’ and converting that into a ‘unit diameter stress amplitude’. The logic here is that the mode shape may have a different deflection profile than that generated by uniform loading.
AutoPIPE can extract a mode shape and normalized nodal displacements, but can it also extract ‘modal stress amplitude’ as requested?
Solution:
At this time (AutoPIPE CONNECT 10.01.xx.xx and lower), AutoPIPE does not have a formal VIV analysis. SSD has wrote a processor that reads AutoPIPE output data in order to perform rigorous VIV analysis. There is a way to output the mode shapes and element modal forces and moments to an external file. However, we do not output the stresses as there is no input forcing function assumed. Please note that the mode shapes in AutoPIPE are mass normalized.
One can enable such output by editing the file autopipe.ini in the AutoPIPE folder. Then use the command Result/Export Eigen values (*.txt) to generate the file Modelname_EIG.txt.
The headers should help you see the type of data being printed. Unfortunately we do not have any documentation or guidance on how to use such data. We also do not offer any support on this feature at this time. We hope to incorporate and improve this feature in the future.