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.
? Thanks, bye.
'Ability is 10% inspiration and 90% perspiration.'





RE: PARAM SNORM in NASTRAN
cheers
RE: PARAM SNORM in NASTRAN
'Ability is 10% inspiration and 90% perspiration.'
RE: PARAM SNORM in NASTRAN
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
'Ability is 10% inspiration and 90% perspiration.'