Problem:

How to input field accelerometer / displacement  data at a specific node point in an AutoPIPE model?

Solution:

The measured accelerations should never be used as input unless they are boundary nodes like nozzles on pumps or supports and anchors. At other locations, the measurement is a response rather than input. You cannot enter accelerations in AutoPIPE v9.3, but you can do so in v9.4 and higher at supports and anchors only.

Remember that in AutoPIPE Impose support displacement, acceleration, and Velocity are only applied to the base of the support spring:

The stiffness factor of the support determines the amount of movement that is transferred from the base of the support to the other end of the support spring. A support with rigid stiffness should transfer 100% of base movement to the other end of the support spring, and ultimately to the pipe being supported minus direction of support restraint(s). A support with less than rigid stiffness will translate only a portion of the bas support movement.  

This is a limitation of AutoPIPE and with similar programs.  We need to input these external loads via supports as they are applied loads.  What you have is a response to some internal load source that you are trying to reverse engineer into an input load.  We could consider the internal source and model as a harmonic and predict the accelerations you are measuring, but not use them as the input.

In earlier versions we have "acceleration" input. This particular input is a uniform earthquake ground acceleration that applies to the whole model. The program should give you a warning when attempting to use it for nodal support points. In the latest version “acceleration" was renamed to "Ground Acceleration" and new "Imposed Acceleration" and "Imposed Displacement" have been added. These latter ones are valid for individual supports nodes only.

Workaround:

At the time of this posting AutoPIPE does not have a feature to explicitly displace a standard node point xxx distance in an axis direction (138612). The only suggestion is an iterative approach:

1. Confirm that all aspects of the model are correct as indicated in the field (i.e. piping layout, all pipe properties, thermal expansion for all conditions. anchor location / stiffness / movement, all support location / stiffness, etc.. anything that would affect the model's stiffness)

2. Accurately locate the node point in the model where the measurements were taken

3. Make that node point the active point

4. Insert a Concentrated Force of xxx load in some direction (Dx, Dy, Dz) per xxx load case.

5. Run the analysis

6. Look at operating condition results to compare with filed data.

7. Adjust displacements to inserted Concentrated until the analysis results match the field data within acceptable tolerances.

If you would like a feature added to be able to impose node displacement, please log a Bentley Service Request and mention this WIKI page here. 

See Also

Modeling Approaches in AutoPIPE

Bentley AutoPIPE