×
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

resonance frequency V beam

resonance frequency V beam

resonance frequency V beam

(OP)
Hi people,
I am trying to model the V shape fixed-free beam (view on attachments) with beam dimensions in order to get the resonance frequency.

[link http://files.engineering.com/getfile.aspx?folder=f8744b93-ea3f-4c8b-866e-2f21be3ea0c2&file=beam-shape.png]http://files.engineering.com/getfile.aspx?folder=f8744b93-ea3f-4c8b-866e-2f21be3ea0c2&file=beam-shape.png[/link]

I tried a 2 x (mass spring system) or beam FEA models without success.
Do you have any idea what I have to do?

RE: resonance frequency V beam

What are you comparing the FEA results to? Did the FEA analysis allow for torsional (twisting) modes, esp. for the #1 segment?

RE: resonance frequency V beam

That's quite a nice little example. There is no reason why FEA should not be able to solve it, but it would be a bit tricky to check the FEA with a handcalc, although you could check that it solves some similar configurations accurately. For example, replace the free arm with a flywheel, do you get the right modes in flex and torsuion ?

Cheers

Greg Locock


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

RE: resonance frequency V beam

(OP)
I compared results with real experimentation and comsol model. Both are coherent but not with my model.

I choose a 2 flex beam model with 3 dof by node (2 translation and 1 rotation). Then I wrote down M and K matrix and try to solve det(K-w²M)=0, with computer in the first place, but results are far away from reality??

I do not know how to "model" the bend. Should I add a extra stiffness or torsion moment on node 2 or something like that??

RE: resonance frequency V beam

I'd think in the real world the lowest frequency mode would involve rotation about the axis of the cantilevered, lower (#1?), beam. To resolve that mode would require a 3D beam model, not a 2D solution. Unless the "real world" beam was constrained against such rotation, or the beam depth was such that the torsional stiffness was much greater than the bending stiffness.

RE: resonance frequency V beam

The dominant flexure of the first mode is very much dependent on the ratio of length of the arms to the diameter of the beams they are made from.

"I do not know how to "model" the bend. Should I add a extra stiffness or torsion moment on node 2 or something like that??
"

No, and that question indicates you haven't got the physics right.

Cheers

Greg Locock


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

RE: resonance frequency V beam

(OP)
Thank you

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