×
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

Question on approach to solving Random Vibration

Question on approach to solving Random Vibration

Question on approach to solving Random Vibration

(OP)
I am working on a random vibration FEA analysis of an electronic housing in Mechanica. I first ran a modal analysis to extract the modes (say first 40 modes), then ran a random vibration analysis with the input profile from 20HZ to 2000Hz, levels at 0.04 g2/Hz (typical workmanship input profile). I am confused, and I hope someone can help me out here, as to how the mass participation comes in here. To determine the output response of the system, do I have to include all the modes such that the % mass participation hits 80% or a certain threshold? Or do I simply include in the analysis the modes within the input profile frequency range i.e. less than 2000Hz? The results if I include all modes such that the % participation is >80 shows peaks in the response way above 2000Hz, which I thought is counter intuitive. Do I make any sense?

RE: Question on approach to solving Random Vibration

What do you mean by % mass participation? Shouldn't the entire mass be included?

RE: Question on approach to solving Random Vibration

Ah yea. Thanks for the link. I did a bit of reading, it seems that we can define this as the amount of mass that participates with one particular eigenmode. In other words whether the mode is local or global. In most cases I think we would be more interested with the global modes and frequencies, so the closer to 100% the better.

cheers,

 

RE: Question on approach to solving Random Vibration

Have you tried direct analysis, if there are small amount of elements the results is better.

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