linear or non linear stress analysis

[SPLIT]

Which type of piping stress analysis to choose ? : linear or non linear ?

I nderstand that the nonlinear ( for suports and for friction ) simulates the real case more acuratelly

please your comments

SPLIT

 

[richay]

This is not something you choose. Whether a job has linear or non-linear boundary conditions is a function of how you model what you really have.

For example, if you have a guide with a 1/2" gap, you have a non-linear boundary condition (the gap).

Richard Ay
COADE, Inc.

 

[SPLIT]

Ihave the AUTOPIPE, and it has the option of doing it linear or non linear.But my question is which is more acurate


Regards,


SPLIT

 

[richay]

That doesn't make sense. A system (from a boundary condition point of view) is either linear or non-linear based on the type of restraints you define. Directional restraints (i.e. +Y), friction, gaps, and large rotation rods make a job non-linear. To assume such a system is linear, is less than correct. Accuracy isn't the issue.

Richard Ay
COADE, Inc.

 

[xhpipe]

In the real world MOST systems are non-linear, that is friction, gaps, and support lift off are all very real and common effects.

The issue is have you accounted for them in your model???





Regards,
XHPIPE

 

[SPLIT]

Actually,I have found that in general a linear analysis gives higher stresses than a non linear, but the loads results higher in a non linear .(because considers gaps and friction).These statements are based in loads combinations that include thermal+ sustained loads, and seismic loads combined with sustained loads.If the supports are of the hanging type,the loads results similar in both kind of analysis.
According the AUTOPIPE manual, the non linear is more accurate.
So , any coment?

Split

 

[xhpipe]

My first comment stands... the world is non-linear, friction is really many numbers... consider static mu will be greater than sliding mu.

If you have a non linear system it should be modeled with its non-linearities (ignoring gaps 1/16" or less of course). It should also be run with and without mu to bracket the answers.

All this of course is appropriate for critical systems as opposed to service piping.

Regards,
XHPIPE