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

DLF for Harmonic Analysis

DLF for Harmonic Analysis

(OP)
I have recently done a super-rushed analysis of shaking pipe caused by slug flow.  I used a harmonic analysis, calculating the forces at the elbows from the product of density, slug velocity squared and cross-sectional area.  In a spectral analysis, one would derive a dynamic loading factor to apply to this force.  

For a harmonic analysis, should I multiply the force calculated by a dynamic loading factor before entering it in the force field on the Harmonic Forces tab?  If so, do I just use a DLF of 2, since that is the maximum for a force applied without a 'free drop,' or does a slug that hits the elbow with a non-zero velocity actually have a free drop, which would allow the DLF to be higher?   

RE: DLF for Harmonic Analysis

That DLF of 2 is only appropriate for impulse loads.  You said it's harmonic, implying that there is some residual response from the previous hit when the current impulse occurs.

If you're activating a mode of vibration, the applied static load will be valid (only?) if the shape from the applied load is similar to the excited mode shape.  

There is a lot of gray area here.

If the forcing freq. equals a nat. freq. and damping is 1%, the associated DLF is 50 not 2.
 

Richard Ay
COADE, Inc.

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