×
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

Why Force is not considered by software during modal and frequency response analysis

Why Force is not considered by software during modal and frequency response analysis

Why Force is not considered by software during modal and frequency response analysis

(OP)
Is there any specific reason behind , the analysis software is not considering the force if they are applied in any specific nodes. But they consider forces in static analysis.
Is there any other way to consider that force in modal and dynamic analysis

Appreciate your comments

RE: Why Force is not considered by software during modal and frequency response analysis

(OP)
Is wish to add one more query to the discussion. I think , i can consider this force in frequency domain by creating a seperate function. If that is right, Is it possible to apply a force function at one node and acceleration function in excitation points at the same time

RE: Why Force is not considered by software during modal and frequency response analysis

A modal analysis is used to determine the modes -aka natural frequencies- (the eigenvalues) and associated mode shapes (eigenvectors). The natural frequency is a function of the mass, stiffness, and boundary conditions of an object. It is not a function of applied load. You can not recover meaningful deflection magnitudes, stress, strains, or reactions forces. Relative displacements are meaningful though (the mode shape).

In a static analysis, you may apply a load to a part/assembly and determine deflections, stress, strain, reactions forces, etc.

Brian
www.espcomposites.com

RE: Why Force is not considered by software during modal and frequency response analysis

(OP)
Thanks for your comments brain. I understand that load will not be considered in modal analysis.

But ,It is possible to make a response analysis (Frequency response for my study) in which we can make a function( force vs frequency) and input at the desired point. Right?

In brief, my case has to be excited with a vibration at component fixing point and this force has to be applied at a specific node . Stress has to be observed as output for a limited frequency range

RE: Why Force is not considered by software during modal and frequency response analysis

I think you're looking for Harmonic Response Analysis or Transient Analysis.

http://julianh72.blogspot.com

RE: Why Force is not considered by software during modal and frequency response analysis

(OP)
Jhardy, I am looking for harmonic response analysis.. Time domain is not involved..

RE: Why Force is not considered by software during modal and frequency response analysis

Basically your modal analysis creates a list of frequencies and mode shapes. You then need to provide damping estimates for each mode, and you can then synthesise the FRFs. When you apply your force spectrum to the FRFs you will get vibration spectra at each node.

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: Why Force is not considered by software during modal and frequency response analysis

You can take 'pre-stress' effects into account in most FE programs. This is a way of taking into account that loads can make a structure stiffer. Think of tightening a guitar string for example - this would alter its frequencies.

RE: Why Force is not considered by software during modal and frequency response analysis

Modes depend only on the mass and stiffness. Loads are not considered in modal analysis. On the other hand, loads can be used to describe the mass of a model (for instance super dead loads), so in that particular case they are taken in account.

Analysis and Design of arbitrary cross sections
Reinforcement design to all major codes
Moment Curvature analysis

http://www.engissol.com/cross-section-analysis-des...

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