×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Random Vibration - Very Long Solution Times
2

Random Vibration - Very Long Solution Times

Random Vibration - Very Long Solution Times

(OP)
I've been working on a random vibration model that has the following:

#Nodes = 37K, #Elements = 17K, DOF=158K

It's a model of a power supply and the problem is that the solution takes DAYS to solve.  There are 116 resonant frequences.  If I just try to solve the random vibration with just using the first 40 resonant frequencies, I can get a solution in about 4 hours.  But anything longer the computer (Quad Core, 3 MB RAM) takes very, very long.

Any ideas?  Being pointed in the right direction would help.  Are there any resources that would help in how to handle large problems like this?  (Actually I didn't think it was a large problem considering the stats above).

 

RE: Random Vibration - Very Long Solution Times

I agree it isn't a large problem, by itself, but suspect that it is trying to store 116*158k results in memory. Which still doesn't seem much.

try solving with 10 20 30 resonances and you've already done 40, to see how long they take.  

Cheers

Greg Locock

SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

RE: Random Vibration - Very Long Solution Times

(OP)
I was also thinking that maybe it's trying to write out to memory.  Most of my computational background is in CFD, but I've done some FEA mostly static analysis, which runs fine.  I'm wondering if it's got to do with contact definitions or the lack thereof.  

I'm also looking for any resources on running random vibration, more than just the basics like I have with Schroff (good book nonetheless).
 

RE: Random Vibration - Very Long Solution Times

Ah, you can't do random FEA with contacts in the frequency domain

Cheers

Greg Locock

SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

RE: Random Vibration - Very Long Solution Times

(OP)
Wow, that's an eye opener - thanks!  How does one do a vibration analysis of an assembly where many of the parts are in contact - just turn off all contact sets?

 

RE: Random Vibration - Very Long Solution Times

(OP)
Greg,  I just wanted to make sure we're talking about the same thing when it comes to contacts.  I'm talking about contact sets, that is, defining that two surfaces are bonded.  I'm having a hard time understanding why Solidworks Simulation wouldn't allow for the analysis of two (or more) pieces bonded together.

Were you talking about contact analysis above?  Thanks for the help.

Dave

RE: Random Vibration - Very Long Solution Times

Random vibration is still a linear type analysis. One of the ways you can linearize a non-linear structure is to put springs in the areas of contact. You then have to tune the stiffness and damping of the springs to realistically behave like the joint.

Sounds like you are doing an out of core solution. Cosmos doesn't always use all the RAM so the fact that you are going out of core so soon doesn't surprise me. Task manager can tell you if this is in fact happening if you turn on the VM, page fault and IO data columns. Cosmos also doesn't use multiple cpu cores.

 

TOP
CSWP, BSSE
www.engtran.com  www.niswug.org

"Node news is good news."

RE: Random Vibration - Very Long Solution Times

re contacts -yes I was assuming you meant contact bcs, not glue between components.

In that case you are on the right track.

 

Cheers

Greg Locock

SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources