| Applies To | |
| Product(s): | AutoPIPE |
| Version(s): | ALL; |
| Environment: | N/A |
| Area: | Modeling |
| Original Author: | Bentley Technical Support Group |
| Date Logged & Current Version | Feb. 2017 11.00.00.22 |
Problem:
Why are AutoPIPE's Fluid transient loads different from other programs?
Example:
An in house software application was developed that address reflection, losses and phase change. But when modeling with this in house application the piping assumes the wave is reflected back. Also, small branch lines that are connected are not considered. Some folks in our organization believe this would produce erroneous and conservative results. People argue that when one includes all the branches and so forth, then the reflected waver is much weaker and the resulting load will be much smaller. Their argument is based on a study performed by another company some 35 years ago where they had decided not to consider the reflected wave in their designs. Unfortunately this study was never published.
We compared AutoPIPE generated fluid transient forces with our in-house program results and we found that our program results are 3 to 4 times higher than AutoPIPE generated values. why?
Solution:
Hard to answer questions when Bentley development cannot review / validate calculations performed by another application. AutoPIPE's Fluid Transient module has documented calculations used by the Fluid transient module. If there are differences between the two, it could indication that those limitations of our module are important in this system or that the other method is too conservative. No difinitative answer can be made with out a thorough review of the other application.
The reality is that each branch will reduce the effect of the wave 'chopping it up' into smaller waves, but each time this happens there will be a reflection that AutoPIPE does not consider. These reflections will be much smaller than the full reflection which the other software may or may not be considering, Therefore, it isn't hard to imagine that the real answer is somewhere in between.