Pipe lift off in dynamic analysis

[alfmar]

Dear all,

This topic may have been already replied somewhere, but I cannot find it.

Since dynamic analysis is strictly linear, and the results provided for ABS combination are always positive, how can we perform a lift off check in such type of analysis?

Very grateful for your replies.

Best regards

 

[carthago]

I always understood that Caesar is a linear program. To this date and in my knowledge Caesar has no Non-Linear capabilities
So for dynamic it will:
1/- make all + Y supportS Y (e.g closed in both directions.
2/- make all gaps equal to Zero.

So after modifying the supports following some dynamic studies then run the System again in static to check if they are new unforseen thermal loads or secondary high stress.

Finally = ensure that reality reflects all the previous analysis = close all the gap (just fit). Close all +Y and make them sort of hold downs


And if in doubt ask the Coade boys ..go to their site

take care and thanks

 

[ZippyDDoodah]

Caesar II is capable of nonlinear static analysis if the nonlinearity is limited to boundary conditions. Gaps, friction, and bi-linear springs are all nonlinear boundary conditions which Caesar handles in static analysis. Caesar cannot consider material nonlinear behavior, geometric nonlinear effects (P-Delta), or any nonlinear dynamic analysis.. but it can certainly perform static nonlinear analysis of pipe supports with gaps or friction.

It's not "blaming" or "accusing" to state well known facts regarding what Caesar can and cannot do.

As evidenced by comments on this thread and personal experience, it seems that quite a number of engineers don't fully understand these limitations and the implications involved, some of which are quite problematic with no good workaround. If you want to consider liftoff or gaps closing in a dynamic analysis with Caesar, there's no good solution to that problem. You could try to fudge an equivalent static load and add it to your operating case in order to approximate dynamic loading, but that would be a dicey approach.. less dicey, however, than using modal analysis to check for liftoff.