×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• 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.

Which formula for Natural Frequency?

Which formula for Natural Frequency?

(OP)
I have been designing a box. This box will see vibration and I want to make sure the  welds hold up. I went to look at the panels as rectangular plates and found that there are several formulas I can use depending on which book I open. They do not yield the same answer, so which do I put my faith in?
Rothbart's Mech Design (pg 6-62), gives
Fn=Cn x h/a^2 x 10^4 x Km
Mark's CD-rom gives
Fmn=(pi/2)x(gD/hd)^.5 x(m^2/a^2 + n^2/b^2)
Mark's hard copy (eq3.4.124 on pg 3-74) gives
Fmn=((pi^2)x((m/a)^2 + (n/b)^2)x(D/m)^.5)/2pi
finally can't you argue that a plate is a rectangular beam and use?
fn=(1/2pi)x((3EI/L^3)/(w/g))^.5
Above I use ^to raise to a power.

RE: Which formula for Natural Frequency?

Well, here are some suggestions.

1.  Make sure the formula is appropriate for your boundary conditions.

2.  Determine whether the formula is for a square or rectangular plate.

3.  Decide whether you are interested in the fundamental mode only or in several modes.

In addition, I recommend that you use a plate formula rather than a beam formula.  The comparsion of a plate to a beam is only valid for a few special cases.

Sincerely, Tom Irvine
http://www.vibrationdata.com

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.

Resources

eBook - Functional Prototyping Using Metal 3D Printing
Functional prototypes are a key step in product development â€“ they give engineers a chance to test new ideas and designs while also revealing how the product will stand up to real-world use. And when it comes to functional prototypes, 3D printing is rewriting the rules of whatâ€™s possible. Download Now

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:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!