×
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

ABAQUS : Effect of Pre-load on Random Response Analysis

ABAQUS : Effect of Pre-load on Random Response Analysis

ABAQUS : Effect of Pre-load on Random Response Analysis

(OP)
I am running a random response analysis on a structure which has a static load applied prior to *Frequency and *Random response analysis.

What affect, if any does the preload have on the streses obtained in the Random Response analysis step?
As preload stresses are measured in MPa but the "Maximum stress" output (S) of the Random Response analysis step is in MPa^2/Hz.

Any ideas?

RE: ABAQUS : Effect of Pre-load on Random Response Analysis

In a linear passive structure the stresses at a particular frequency can ONLY be affected by loads at that frequency. Therefore the preload will not affect stresses at a higher frequency.

Note that the total stress will be affected, obviously.

Cheers

Greg Locock

RE: ABAQUS : Effect of Pre-load on Random Response Analysis

hi,

In a linear random analysis, you can add the static load stress to the mean value stress calculated by random analysis. To a nonlinear random analysis, the frequency response approach is unusable.

RE: ABAQUS : Effect of Pre-load on Random Response Analysis

The effect of prestresses will of course change the stiffness matrix of the structure. For the random response analysis in ABAQUS, the stiffness state (due to the preloads) at the end of the previous general step (presuming nonlinear geometric effects were included) will be operated upon for the actual random response analysis.

Reported stresses are perturbation stresses about the base state (hence do not include the actual stresses which are in the base state).

As ilianhui implies, adding these (inherently linear) random stresses to the (potentially nonlinear) general stresses may result in errant answers.

I hope this makes sense.  
Brad

RE: ABAQUS : Effect of Pre-load on Random Response Analysis

(OP)
Thanks guys!

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