×
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

Epsilon in .f06 file - big value

Epsilon in .f06 file - big value

Epsilon in .f06 file - big value

(OP)
Hi, i have a problem when trying to run a model in Nastran ( Sol 101) and hope that someone can help me: the epsilon value that i read in the .f06 file is about 1.70E-4; now, i know that this value is big and that, normally, a good value for epsilon is 10E-9 or smaller. I know also that this value is a measure of numerical accuracy and round off error of a run (101) and that a bigger value evidences a ill-conditioning problem (small perturbations in the system can lead to large changes in the solution);

What are possible cause of this problem ? in a blog i read:
1) high difference in stiffness between adjacent elements in the model.
For istance a mistake in the application of properties ( composites) on a panel done manually ? is it possible ?

Can someone suggest me other possible cause for this type of problem ?

Thank you

RE: Epsilon in .f06 file - big value

Hello!,
EPSILON is an error measure of the "normalized value of the residual loading". Epsilon values that are greater than 0.001 are flagged for a possible loss of accuracy due to numeric conditioning.
EPSILON is generated for each loading condition. An acceptable value of EPSILON depends on the model complexity and the machine that it runs on. An epsilon value in the neighborhood of less than 10-9 is generally considered acceptable.

Some general causes for singularity can include:

• Degrees of freedom without stiffness because of missing elements.
• A 2-dimensional plate problem with the normal rotation unconstrained.
• A solid model with rotational DOFs at the corners unconstrained.
• Incorrect modeling of offset beams.
• Incorrect multipoint constraints.
• Mechanisms and free bodies, such as sloped plates, beam to plate connections, beam to solid connections, and plate-to-solid connections.
• Low stiffness in rotation.
• A stiff element adjacent to a very flexible element.


If PARAM,AUTOSPC,YES is specified (this is the default in the Structured Solution Sequences, except SOLs 106 and 129), the potential singularities are automatically constrained if possible.
Also if you have error when solving the model you can override this fatal message by inserting “PARAM,BAILOUT,–1" in your input file, but this should be use only to DEBUG the problem, not for final results.

Best regards,
Blas.

~~~~~~~~~~~~~~~~~~~~~~
Blas Molero Hidalgo
Ingeniero Industrial
Director

IBERISA
48011 BILBAO (SPAIN)
WEB: http://www.iberisa.com
Blog de FEMAP & NX Nastran: http://iberisa.wordpress.com/

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