SFAM 9160

thomas.roy over 4 years ago

Running SOL111 for Structural output in NAS2019.1 with ACMS

leads to job abort with ^

*** SYSTEM FATAL MESSAGE 9160 (SUBDMAP MDACMS)

PROBLEM ENCOUNTERED IN CALCULATING DOMAINSOLVER ACMS DOMAIN MODES.

USER ACTION: IF LARGE MASS IS BEING USED FOR ENFORCED MOTION THEN REPLACE LARGE MASS METHOD WITH DIRECT METHOD

USING THE SPCD BULK DATA ENTRY.

USER INFORMATION: IF THE LARGE MASS METHOD IS NOT BEING USED THEN MASSLESS MECHANISMS MAY EXIST.

PARAM,MECHFIX,YES MAY BE USED TO IDENTIFY MASSLESS MECHANISMS.

1 SEPTEMBER 25, 2020 MSC Nastran 12/18/18 PAGE 2780

What other can be done, when the presesnt of massles mechanism where checked ?

0 Hrishikesh Phadke over 4 years ago

Can you please try running with DOMAINSOLVER ACMS(VERSION=OLD) and PARAM,MECHFIX,YES in begin bulk section?

Try checking for things that could generate massless mechanisms like cbush with stiffness only in x,y,z. No stiffness in rotational dof's could make it free to move in those directions and generate massless mechanisms..

Incorrect RBE2/RBe3...

See remark for rbe2 from QRG.

12. It can be any combination in 1, 2, 3, but must have all "456" if any rotation dof is used when there is large rotation.

For rbe3

5. We recommend that for most applications only the translation components 123 be used for Ci. An exception is the case where the Gi,j are colinear. A rotation component may then be added to one grid point to stabilize its associated rigid body mode for the element.
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0 thomas.roy over 4 years ago

Thanks for the hints hrishkesh. I thought I keept all the typical suspicious ones. I run Version=old with mech fix yes. The information of the contraint dofs isn't that much clear. The RBE3 check in ANSA was OK. But I will check the RBE2 as you said. Are there any issues known regarding CGAB Elements in context with ACMS ?
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0 Hrishikesh Phadke over 4 years ago

1. The CGAP element is intended for the nonlinear solution sequences 106, 129, 153, 159, and 400.

However, it will produce a linear stiffness matrix for the other solutions, but remains linear with the

initial stiffness. The stiffness used depends on the value for the initial gap opening (U0 field in the

PGAP entry).

So i think if you want to make sure this works well in SOL 111 and also with ACMS, make sure the U0 field in PGAP as significant values as SOL 111 being linear solution it will take only the initial stiffness..
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0 thomas.roy over 4 years ago

Hi Hrishikesh, it seems there was a insufficient definition in my hinge representation, a cbar element could rotate about the element axis. PARAM,ZROMASS,1.0e-12 didn't helped.
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0 Hrishikesh Phadke over 4 years ago

For hinge type behaviour it is best to use an RJOINT. Please refer QRG for RJOINT definition. The CBAR can create problems due to incorrect defintion or less stiffness in it creating singular matrix.
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0 thomas.roy over 4 years ago

OK, I will keep it in mind
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