FEAP User Forum

FEAP => Input File Issues => Topic started by: zqzhang on June 18, 2017, 03:04:35 AM

Title: How do I output nodal displacement in the MODAl analysis
Post by: zqzhang on June 18, 2017, 03:04:35 AM

Dear all,

How do I output every nodal displacement in the MODAl analysis?

best
ZQ

Title: Re: How do I output nodal displacement in the MODAl analysis
Post by: Prof. S. Govindjee on June 18, 2017, 09:04:48 AM

Did you try

Code: [Select]

DISPlacement,ALL ?

Title: Re: How do I output nodal displacement in the MODAl analysis
Post by: zqzhang on June 18, 2017, 05:56:02 PM

Dear Professor,
     
           Thank you for your reply. I have used the command, but the values of the displacement are zeros. Please see the inputfile "Imodaltry1".

Title: Re: How do I output nodal displacement in the MODAl analysis
Post by: Prof. S. Govindjee on June 18, 2017, 07:03:34 PM

You got the solution to the problem you specified!
You have imposed no loads on your body, so your solution is zero.
Try putting a force on the system and you will see something.

Also you have a problem with 3 dofs per node so there is no need to specify boundary codes for 6 dofs.

Title: Re: How do I output nodal displacement in the MODAl analysis
Post by: Prof. R.L. Taylor on June 19, 2017, 06:52:55 AM

If you want to print the eigen-vectors see Appendix D for command EIGV.  You can also plot the eigen-vectors if the mesh is not too fine.

If you have done a modal analysis that produces a non-zero solution, then the previous descriptions apply

Title: Re: How do I output nodal displacement in the MODAl analysis
Post by: zqzhang on June 22, 2017, 03:28:46 AM

Dear Prof. Taylor and Prof. Govindjee,
         Thank you for your responses. I want to output the nodal displacement  in MODAl analysis. If I obtain the nodal displacement, I can display the modal shape using other graphic program. But now only the  eigen-vectors can be print by FEAP. Can you tell me how to output or calculate the the nodal displacement? In addition,  is the  eigen-vectors printed by FEAP normalized by displacement or mass?

Best regards

ZQ. Zhang

Title: Re: How do I output nodal displacement in the MODAl analysis
Post by: FEAP_Admin on June 22, 2017, 06:56:20 AM

Did you read reply #3?!  DISP will give you the displacements if you have any!

The vectors are probably mass orthonormalized.  Run a simple problem where you know the answer to double check.

Title: Re: How do I output nodal displacement in the MODAl analysis
Post by: Prof. R.L. Taylor on June 23, 2017, 05:17:23 PM

A simple file that uses modal integration and ouputs nodal displacements and element stresses is attached

Title: Re: How do I output nodal displacement in the MODAl analysis
Post by: Prof. R.L. Taylor on June 23, 2017, 05:18:30 PM

Sorry here is file

Title: Re: How do I output nodal displacement in the MODAl analysis
Post by: zqzhang on June 25, 2017, 05:57:50 AM

Dear Prof. Taylor,
         
         Thank you very much for your input file! In your file, the beam is subjected to a point load. When the simple supported beam is  subjected to no load, I can obtain the normal modes of free vibration. In the situation, the displacements are zero in the output file. However, I want to the nodal displacements to display the modal shape of free vibration in another graphic program. How can I do?  Could you give me some guidance?

Sorry for more requests.
Thank you very much.

Title: Re: How do I output nodal displacement in the MODAl analysis
Post by: Prof. R.L. Taylor on June 25, 2017, 07:15:31 AM

See the FEAP User Manual, Appendix D, command EIGV.

Probably what you want is: EIGV ALL 1  to get eigenvector "1".

Title: Re: How do I output nodal displacement in the MODAl analysis
Post by: FEAP_Admin on June 25, 2017, 08:06:13 AM

FEAP will also plot the eigenmodes. Try

Code: [Select]

plot,defo,,,1
plot,eigv 2
for example to see the second eigenmode.

Title: Re: How do I output nodal displacement in the MODAl analysis
Post by: zqzhang on June 26, 2017, 06:31:10 PM

Thank you very much. I understand.