×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Contact US

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.

Students Click Here

RBE2 and RBE3 vs natural frequency
2

RBE2 and RBE3 vs natural frequency

RBE2 and RBE3 vs natural frequency

(OP)
I have a model connected to masses with RBE3
after a normal modes analysis I observe the 1st frequency

after converting these RBE3 to RBE2 the 1st frequency is lower than before.
I expected the 1st frequency to be higher instead, since RBE2 are infinitely rigid?

RE: RBE2 and RBE3 vs natural frequency

2
Hi,
this is interesting observing. I would say the same at first sight - if RBE3 is correctly defined, then it does not add any additional stiffness to the structure.
And this is many times the advantage compared to RBE2.
I'm thinking what case could be responding to your problem...The "magic" is in distribution of mass and stiffness.
I haven't test it but it could be a good sample for validation:
let's have a cantilever beam. The end (let say 1/4 of length) is connected to the RBE3 which holds some mass element. 1th eigen mode is bending - bending of all length.
Then we have RBE2 instead of RBE3, it means 1/4 of length is rigid. 1th eigen mode is bending as well, but only 3/4 of length. Without any additional mass I would expect this frequency is higher (shorter length, stiffer), decreasing can be caused by mass of rigid part (compared to the rest).
It would be good to make some sensitive analysis and vary with the additional mass, because if this is true, there can be some boundary when 1th frequency starts to increase.

But as I said, I haven't test this, just idea.

Regards, Jan


With best regards,
Dr. Jan Vojna
Lead Engineer Development

Siemens, s.r.o.

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! Already a Member? Login


Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. 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:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close