01. How to apply harmonic load case at a non-support point in AutoPIPE?


	Applies To

	Product(s):	AutoPIPE,
	Version(s):	2004, XM, & V8i
	Environment:	N/A
	Area:
	Subarea:
	Original Author:	Bentley Technical Support Group

Dec 2014, AutoPIPE V8i 09.06.01.10

Problem:

Whenever we have vibration problems in the field, we typically get velocity vs time data at the highest vibration points and usually there are no supports at these points. We were looking in to doing a harmonic analysis in AutoPIPE for the piping system, but I believe AutoPIPE requires a support if we need to specify harmonic loads in the form of displacement, velocity or acceleration. We cannot add a support at these locations just to input the velocity based harmonic loads as it would change the natural frequency of the system. Currently the only way to specify harmonic load to a point without support is to use a load based (force vs. time) forcing function in AutoPIPE, but unfortunately it is not the information that we get from the field. Is there a work around to this problem in AutoPIPE?

Answer:

Yes per the online help displacement, velocity and acceleration can only be applied at a support or anchor while harmonic forces can be defined at any unrestrained node.

Wiki article can be found here

Attached is some vibration guidelines for modeling a pump oil lift system (see d) and PDF of presentation of features for designing Oil and Gas pipeline systems