MYSTRANsolver
Small thickness shells go wrong with SOL 5
With my shell buckling PR, this Euler column should have proper buckling mode but it's crooked with wrong eigenvalues. Affects all shell elements, including thin shells, and both EIRGL and MGIV eigenvalue solvers. Also seems to be an existing problem for CBAR.
It happens when thickness is too low (0.0006).
EDIT: It's also a problem in static (SOL 101) for bending.
SOL 105
CEND
DISPLACEMENT = ALL
FORCE = ALL
SPC = 1
SUBCASE 1
LOAD = 1
SUBCASE 2
METHOD = 1
BEGIN BULK
GRID* 1 0 0.0046984631 -0.00171010072*
* 0. 0
GRID* 2 0 0.0046984631 0.00578989928*
* 0. 0
GRID* 3 0 0.0046984631 0.00828989928*
* 0. 0
GRID* 4 0 0.0046984631 0.0182898993*
* 0. 0
GRID* 5 0 0.0071984631 0.00578989928*
* 0. 0
GRID* 6 0 0.0046984631 0.000789899283*
* 0. 0
GRID* 7 0 0.0046984631 0.0132898993*
* 0. 0
GRID* 8 0 0.0046984631 0.0107898993*
* 0. 0
GRID* 9 0 0.0046984631 0.00328989928*
* 0. 0
GRID* 10 0 0.0071984631 0.0107898993*
* 0. 0
GRID* 11 0 0.0071984631 0.0132898993*
* 0. 0
GRID* 12 0 0.0071984631 -0.00171010072*
* 0. 0
GRID* 13 0 0.0071984631 0.0182898993*
* 0. 0
GRID* 14 0 0.0046984631 0.0157898993*
* 0. 0
GRID* 15 0 0.0071984631 0.0157898993*
* 0. 0
GRID* 16 0 0.0071984631 0.00328989928*
* 0. 0
GRID* 17 0 0.0071984631 0.000789899283*
* 0. 0
GRID* 18 0 0.0071984631 0.00828989928*
* 0. 0
PARAM* NOCOUNTS Y *
*
DEBUG* 201 1 *
*
$--1---><------2-------><------3-------><------4-------><------5-------><--6--->
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ Material $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
MAT1* 1 5.+10 0.*
* 0. 0.0006 0.
$--1---><------2-------><------3-------><------4-------><------5-------><--6--->
SPC* 1 1 1 0.*
*
SPC* 1 1 2 0.*
*
SPC* 1 1 3 0.*
*
SPC* 1 1 4 0.*
*
SPC* 1 1 5 0.*
*
SPC* 1 1 6 0.*
*
SPC* 1 12 1 0.*
*
SPC* 1 12 2 0.*
*
SPC* 1 12 3 0.*
*
SPC* 1 12 4 0.*
*
SPC* 1 12 5 0.*
*
SPC* 1 12 6 0.*
*
$--1---><------2-------><------3-------><------4-------><------5-------><--6--->
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ Default $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
PSHELL* 1 1 0.0001 1*
* 1 0.
CQUAD4* 1 1 12 17*
* 6 1 0. 0.
CQUAD4* 2 1 16 5*
* 2 9 0. 0.
CQUAD4* 3 1 3 18*
* 10 8 0. 0.
CQUAD4* 4 1 17 16*
* 9 6 0. 0.
CQUAD4* 5 1 7 11*
* 15 14 0. 0.
CQUAD4* 6 1 8 10*
* 11 7 0. 0.
CQUAD4* 7 1 5 18*
* 3 2 0. 0.
CQUAD4* 8 1 14 15*
* 13 4 0. 0.
$--1---><------2-------><------3-------><------4-------><------5-------><--6--->
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ force $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
FORCE* 1 13 0 1.*
* 0. -0.5 0.
FORCE* 1 4 0 1.*
* 0. -0.5 0.
$--1---><------2-------><------3-------><------4-------><------5-------><--6--->
EIGRL* 1 3*
* 0 0.001 MASS
ENDDATA
It works OK with PARAM,AUTOSPC,N and DOF6 constrained on all the nodes, so probably an AUTOSPC bug.
Setting AUTOSPC_RAT to 1e-9 instead of the default 1e-8 make it work OK. So there may be a problem with the default ratio or the AUTOSPC algorithm in general not recognizing that very small rotational stiffness is significant for thin shells.