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!

*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.

Jobs

fundamental frequency

fundamental frequency

(OP)
Good morning all,
I have been focusing only on the first (lowest) frequency and calculate stress and deflection results based on that value as Steinberg indicates that this is where the highest deflection takes place. Why is this the case? If I wanted to calculate the results for higher modes, how would I take the higher frequency value into account? Is the energy dissipated (into heat?) as the frequency is increased? I have not found anything in his book (or others) that addresses this aspect.

Thanks,
Bob

RE: fundamental frequency

That is, in a general sense, a really good question. Tom Irvine's paper is excellent. This is my answer:

The response of a linear structure to a given transient excitation (which is the most common damage problem) is the sum of the modeshapes. When you hit something most of the response is at the lowest frequency mode, unless you happen to hit the structure at a node for that modeshape. The lower the frequency the greater the displacement and hence strain for a given acceleration.

However, if you are looking at strongly periodic environments, such as I4 engines, where the excitation actually increases with frequency(up to a point), the first few modes may be completely irrelevant, the mode only really matters if it gets excited, so we use what is called a modal alignment chart that maps mode shapes and excitations.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

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


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close