Pipe displacement decreases as gap size increases in AutoPIPE, why?
Example:
Given the following pipe arrangement and support (node = 120)
Support Gap settings:
Results
Notice the displacement in the Global X direction (-29.68mm)
Increase 1 gap setting as shown here:
Change _X global Gap from 32mm to 40mm
Re-analyze and review results:
Notice that the pipe displacement with lager gap has now decreased from -32.00mm to -29.68mm,
Why has displacement decreased when gap setting increased?
In short, Non-Linear analysis.
One needs to recall that a Non-Linear analysis in AutoPIPE is performed by iterations until the solution converges below set tolerance values.
In this case, when the support gap was increased the analysis took fewer / more iterations to converge than when the support gap setting was smaller. The analysis did converge to below the tolerance settings, just not to the exact same value as the previous analysis. Therefore the results may be slight different ( ~1.32mm).
One can reduce this discrepancy by making the Non-Linear tolerances smaller. However, this may significantly increase the analysis time at the expense of a minor increase in accuracy. In this model, decreasing the force tolerance from 44.40 to 1, increased the analysis time, but indicated the pipe movement increased (ex. -37.07mm).
In conclusion, when performing a Non-Linear analysis with AutoPIPE, the user should understand the significance of Non-Linear Tolerance values and set appropriately for the analysis being performed. With smaller tolerance values:
- Increases Analysis time by requiring more iterations to converge on a solution
- Increases accuracy (maybe insignificant amount)
- Chance for the analysis to not converge
"Support" sub report
Analysis Sub-reports FAQ
Bentley AutoPIPE