05-11-2018 01:13 PM - edited 05-11-2018 03:52 PM
Hello All, please find below a simple shear flow test model with inertia relief, but the model fails when run with:
^^^ USER FATAL MESSAGE 9137 (SEKRRS) Linear Statics
^^^ RUN TERMINATED DUE TO EXCESSIVE PIVOT RATIOS IN MATRIX KLL.
Wondering if you have any feedback.
Model:
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
ID,NASTRAN,shear_flow_test_sim1-shear_flow_test
SOL 101
CEND
$*
$*$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$*
$* CASE CONTROL
$*
$*$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$*
ECHO = NONE
OUTPUT
DISPLACEMENT(PRINT,REAL) = ALL
FORCE(PRINT,REAL,CENTER) = ALL
GPFORCE(PRINT,REAL) = ALL
OLOAD(PRINT,REAL) = ALL
SPCFORCES(PRINT,REAL) = ALL
STRESS(PRINT,REAL,VONMISES,CENTER) = ALL
PARAM,GRDPNT,2
PARAM,INREL,-1
PARAM,AUTOSPC,NO
$* Step: Subcase - Static Loads 1
SUBCASE 1
LABEL = Subcase - Static Loads 1
LOAD = 1
$*
$*$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$*
$* BULK DATA
$*
$*$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$*
BEGIN BULK
$*
$* PARAM CARDS
$*
PARAM AUTOSPC NO
PARAM GRDPNT 2
PARAM INREL -1
PARAM K6ROT 100.0
PARAM OIBULK YES
PARAM OMACHPR YES
PARAM POST -2
PARAM POSTEXT YES
PARAM UNITSYS LBF-IN
$*
$* GRID CARDS
$*
GRID 1 0 0.0 2.0 0.0 0
GRID 2 0 0.0-1.09-15 0.0 0
GRID 3 0 2.0 0.0 0.0 0
GRID 4 0 2.0 2.0 0.0 0
$*
$* ELEMENT CARDS
$*
$* Mesh Collector: Cshear Collector(1)
$* Mesh: 2d_mesh(1)
CSHEAR 1 1 2 3 4 1
$* Mesh Collector: Crod Collector(1)
$* Mesh: 1d_mesh(1)
CROD 2 2 1 2
CROD 3 2 2 3
CROD 4 2 4 1
CROD 5 2 3 4
$*
$* PROPERTY CARDS
$*
$* Property: PSHEAR1
PSHEAR 1 2 .016 0.0 0.0 0.0
$* Property: PROD1
PROD 2 2 1.0-3 0.0
$*
$* MATERIAL CARDS
$*
$* Material: Al Alloy
MAT1 2 8.061 .33 2.59-4
$*
$* DEGREE-OF-FREEDOM SETS
$*
$* DOF Set: DOFSet(1)
SUPORT 2 123456
$*
$* LOAD AND CONSTRAINT CARDS
$*
$* Load: Force(1)
FORCE 1 1 0 10.0 1.0 0.0 0.0
ENDDATA 5d01ce25
05-11-2018 01:51 PM
Also tried to include an RBAR element and used a SUPORT entry at the new node 5, and without GRDPNT parameter, same error:
ID,NASTRAN,shear_flow_test_sim1-shear_flow_test
SOL 101
CEND
$*
$*$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$*
$* CASE CONTROL
$*
$*$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$*
ECHO = NONE
OUTPUT
DISPLACEMENT(PRINT,REAL) = ALL
FORCE(PRINT,REAL,CENTER) = ALL
GPFORCE(PRINT,REAL) = ALL
OLOAD(PRINT,REAL) = ALL
SPCFORCES(PRINT,REAL) = ALL
STRESS(PRINT,REAL,VONMISES,CENTER) = ALL
PARAM,GRDPNT,5
PARAM,INREL,-1
PARAM,AUTOSPC,NO
$* Step: Subcase - Static Loads 1
SUBCASE 1
LABEL = Subcase - Static Loads 1
LOAD = 1
$*
$*$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$*
$* BULK DATA
$*
$*$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$*
BEGIN BULK
$*
$* PARAM CARDS
$*
PARAM AUTOSPC NO
$PARAM GRDPNT 5
PARAM INREL -1
PARAM K6ROT 100.0
PARAM OIBULK YES
PARAM OMACHPR YES
PARAM POST -2
PARAM POSTEXT YES
PARAM UNITSYS LBF-IN
$*
$* GRID CARDS
$*
GRID 1 0 0.0 2.0 0.0 0
GRID 2 0 0.0-1.09-15 0.0 0
GRID 3 0 2.0 0.0 0.0 0
GRID 4 0 2.0 2.0 0.0 0
GRID 5 0 0.0 0.0 1.0 0
$*
$* ELEMENT CARDS
$*
$* Mesh Collector: Cshear Collector(1)
$* Mesh: 2d_mesh(1)
CSHEAR 1 1 2 3 4 1
$* Mesh Collector: Crod Collector(1)
$* Mesh: 1d_mesh(1)
CROD 2 2 1 2
CROD 3 2 2 3
CROD 4 2 4 1
CROD 5 2 3 4
$* Mesh Collector: Rbar Collector(1)
$* Mesh: 1d_manual_mesh(1)
RBAR 6 5 2 123456
$*
$* PROPERTY CARDS
$*
$* Property: PSHEAR1
PSHEAR 1 2 .016 0.0 0.0 0.0
$* Property: PROD1
PROD 2 2 1.0-3 0.0
$*
$* MATERIAL CARDS
$*
$* Material: Al Alloy
MAT1 2 8.061 .33 2.59-4
$*
$* DEGREE-OF-FREEDOM SETS
$*
$* DOF Set: DOFSet(2)
SUPORT 5 123456
$*
$* LOAD AND CONSTRAINT CARDS
$*
$* Load: Force(1)
FORCE 1 1 0 10.0 1.0 0.0 0.0
ENDDATA 474e92c2
05-11-2018 04:09 PM
Even with an edge member rod area of 0.1 in^2 (r = 0.18"), the model still fails with excessive pivot ratios...
05-14-2018 05:09 AM
reading the file I think you are using inertia releif ,-1. Am I right?. Set up to -2 "automatic" and try it
05-14-2018 01:00 PM
Thank you for your reply, yes if I use INREL -2, and no SUPORT card and GRDPNT cards parameter, it works, of course the displacement are huge as my model is only a 2.0" square for testing. But If I need a spcific location about which the INREL balancing needs to happen, then this solution will not work. Maybe I need to update the model to be a bit more realistic and try again.. below is the model that works although not realistic.
ID,NASTRAN,shear_flow_test_sim1-shear_flow_test
SOL 101
CEND
$*
$*$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$*
$* CASE CONTROL
$*
$*$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$*
ECHO = NONE
OUTPUT
DISPLACEMENT(PRINT,REAL) = ALL
FORCE(PRINT,REAL,CENTER) = ALL
GPFORCE(PRINT,REAL) = ALL
OLOAD(PRINT,REAL) = ALL
SPCFORCES(PRINT,REAL) = ALL
STRESS(PRINT,REAL,VONMISES,CENTER) = ALL
PARAM,AUTOSPC,NO
$* Step: Subcase - Static Loads 1
SUBCASE 1
LABEL = Subcase - Static Loads 1
LOAD = 1
$*
$*$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$*
$* BULK DATA
$*
$*$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
$*
BEGIN BULK
$*
$* PARAM CARDS
$*
PARAM AUTOSPC NO
PARAM INREL -2
PARAM K6ROT 100.0
PARAM OIBULK YES
PARAM OMACHPR YES
PARAM POST -2
PARAM POSTEXT YES
PARAM UNITSYS LBF-IN
$*
$* GRID CARDS
$*
GRID 1 0 0.0 2.0 0.0 0
GRID 2 0 0.0-1.09-15 0.0 0
GRID 3 0 2.0 0.0 0.0 0
GRID 4 0 2.0 2.0 0.0 0
GRID 5 0 0.0 0.0 1.0 0
$*
$* ELEMENT CARDS
$*
$* Mesh Collector: Cshear Collector(1)
$* Mesh: 2d_mesh(1)
CSHEAR 1 1 2 3 4 1
$* Mesh Collector: Crod Collector(1)
$* Mesh: 1d_mesh(1)
CROD 2 2 1 2
CROD 3 2 2 3
CROD 4 2 4 1
CROD 5 2 3 4
$* Mesh Collector: Rbar Collector(1)
$* Mesh: 1d_manual_mesh(1)
RBAR 6 5 2 123456
$*
$* PROPERTY CARDS
$*
$* Property: PSHEAR1
PSHEAR 1 2 .016 0.0 0.0 0.0
$* Property: PROD1
PROD 2 2 .01 0.0
$*
$* MATERIAL CARDS
$*
$* Material: Al Alloy
MAT1 2 8.061 .33 2.59-4
$*
$* LOAD AND CONSTRAINT CARDS
$*
$* Load: Force(1)
FORCE 1 1 0 10.0 1.0 0.0 0.0
ENDDATA 344fddd0
05-14-2018 02:24 AM
Then I guess you are not constraining properly the model. (I did not check your model).
The recomemnded method is automatic inertia relief.
"The first method is to specify the SUPORT entry explicitly by including “PARAM,INREL,-1” in the Bulk Data Section. • The second method (recommended) is to let NX Nastran select the SUPORT degrees of freedom automatically by including “PARAM,INREL,-2” in the Bulk Data Section. An optional “PARAM,GRDPNT,x”— where x is a grid point ID— can be specified in the model. If “PARAM,GRDPNT,x” is used, the loads and accelerations will be summed about this point. If “PARAM,GRDPNT,x” is not specified, then the loads and accelerations will be summed about the origin of the basic coordinate system."
With inertia relief method it does not matter where you are setting the supports. You should get the same strains/stresses once it is properly removed the six solid rigid movements.
Then with grdpnt you get the force balance at location you want.
05-15-2018 12:11 PM
OK thanks for your reply, this model is quite simple actually, the loading is also in a single plane along the top edge, although applied at a single node. In real life, there will be no constraints for an inflight load case for an aircraft though..