Autodesk Robot Structural Analysis

[#1]

Hi,

I am trying to carry out a modal analysis or a simple truss bridge.

When carrying out the modal analysis I get the message: 'Number of missing eigenvalues found = 3'

If I select cancel (to search for all modes), I get the error message 'execution problem: 3240'. Then ROBOT crashes.

I have ticked the 'Sterm check' button for the modal analysis.

I have allowed a very large number of iterations (30000).

Is there anything else I can / should be doing?

Selecting 'No' on the 'Number of missing eigenvalues found = 3' message box runs the analysis fine. What is the implication for not searching for missing eigenvalues?

Thank you for your help.

Regards,

Stuart

[#2 · Accepted solution]

Turn off Sturm Check in Modal analysis.

If it does not help please send us model.

[#3]

Turning the Sterm check off worked. Thank you.

out of interest why would the Sturm check algorithm cause ROBOT to crash while checking for skipped eigenvibrations?

Regards,

Stuart

[#4]

PLease send us model to check.

It should not crash.

[#5]

Rafal,

Please find attached the ROBOT model which crashes when I have the 'Sturm Check' box ticked.

It runs fine when the 'Sturm Check' box is not ticked.

Regards,

Stuart

[#6]

With Sturm check you can caclulate 97 modes without any problems.

Why do you need more? In fact first 4 modes are global modes, I guess the most interesting ones.

[#7]

Good point!

I was trying to achieve 90% MEM participation in each direction and we are interested in frequencies upto 33Hz. Infact 97 modes should be fine.

Regards,

Stuart

[#8]

 

I was trying to achieve 90% MEM participation in each direction

33 modes is enough

and we are interested in frequencies upto 33Hz. Infact 97 modes should be fine.

101 modes with sturm check and press NO as answer for enlarging number of modes... or turn off sturm check.