×
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

PARAM SNORM in NASTRAN
2

PARAM SNORM in NASTRAN

PARAM SNORM in NASTRAN

(OP)
Good morning everybody. Anyone can give me a clear explaination of why MSC guys have changed the default value of SNORM parameter from 0.0 to 20.0 switching from release 70.7 to 2001 ? Thanks, bye.


'Ability is 10% inspiration and 90% perspiration.'

RE: PARAM SNORM in NASTRAN

2
Hi, MSC's trying to get analysts weaned from the old K6ROT "crutch". You can obtain futhere information about this in the v2001 release notes.

cheers

RE: PARAM SNORM in NASTRAN

(OP)
OK, but it is strange that the SNORM parameter set to 20 also corrects an error in the calculation of shell structures modelled with QUAD elements with offset (the torsional stiffness was in fact underestimated in this situation)... I think they could have given more emphasis to this changes.


'Ability is 10% inspiration and 90% perspiration.'

RE: PARAM SNORM in NASTRAN

Spirit, i have forwarded your question to MSC and get following comments :
1. In Version 70.7 the default is 0.0.  If param,snorm,0.0 is used for version 2001, it yields the same result as 70.7.  However, 70.7 has a larger matrix to factor diagonal ratio of 2.8E+07.  If you want and like the results of 70.7 but wants to run 2001, then I suggest using the parameter snorm set to 0.0.
2. The reason for using SNORM is that we are modelling smooth curved surfaces as facets.
This means that the drilling direction on one element couples with bending in adjacent elements on a curved plate.  This causes the stiffness ratio problems.  (which
is a bad thing)  SNORM takes these elements and rotates the stiffnesses so that they use a common average normal.  The drilling direction is then removed by AUTOSPC with no problems and no large stiffness ratios.  In crude engineering terms this is like smoothing out the facets.
In a model where you have significant differences between 70.7 and 2001 it implies that you have significant loads being reacted through the plate normal rotation direction,
which is bad.  Check your constraint forces for poor Autospc constraints and use the GROUNDCHECK case control request to verify your rigid body conditioning.
Switching SNORM to 0.0 will probably give more inaccurate results and worse rigid body behaviour so is not a good approach.

RE: PARAM SNORM in NASTRAN

(OP)
Wow man, I am impressed, thanks!!!


'Ability is 10% inspiration and 90% perspiration.'

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