compare the os with abaqus (brick elements)

[liushuhao]

deer all:

I have built a same cantibeam model in OS ,abaqus and ansys to validate the precision of brick element in OS.
it is acceptable of the 20 node brick elements (both TLFDD20nBrickElement and brcik20N),
while it is not perfect in 8 nodes bcrik elements model.the displacements of the 4 free nodes are all negative ( the concentrated force is -Y axial)in abaqus and ansys,
while there is a positive displacement in OS model!
I don'nt know why .actually,
the stiffness matrix of OS is better than abaqus (I get the sttiffness matrix by hand-calculation because the model is so
simple, it is a cube and only has 1 element),
which one is wrong?
can you give me some suggestions.thank you !

[liushuhao]

the codes are as follows :
wipe ;

model basic -ndm 3 -ndf 3

source LibUnits.tcl


set Econ [expr 2.55*1e4*$MPa]

set vp 0.2 ; # 泊松比

set s [expr 2.5*$ton/$m3 ] ; # 混凝土密度

set s 0; # 混凝土密度

set k [expr $Econ/(3*(1-2*$vp))] ; #体积模量

set G [expr $Econ/(2*(1+$vp))] ; # 剪切模量

set sig0 [expr 2.0*$MPa] ; #initial yield stress 初始屈服拉应力

set sigInf [expr 2.0*$MPa] ; # final saturation yield stress

set delta 1.0 ; # exponential hardening parameter

set H 1 ; #linear hardening parameter

# nDMaterial J2Plasticity 1 $k $G $sig0 $sigInf $delta $H
# nDMaterial J2Plasticity 1 228e8 128e8 2000000 2000000 0 0

nDMaterial ElasticIsotropic3D 1 $Econ $vp $s

# nDMaterial FDElastic3D 1 NeoHookean3D $k $G $s

node 1 2 2 2
node 2 0 2 2
node 3 0 0 2
node 4 2 0 2

node 5 2 2 0
node 6 0 2 0
node 7 0 0 0
node 8 2 0 0



# element TLFD8nBrick 1 1 2 3 4 5 6 7 8 1 0.0 0.0 $g

# element TLFD8nBrick 1 1 2 3 4 5 6 7 8 1 0.0 0.0 0



element Brick8N 1 1 2 3 4 5 6 7 8 1 0.0 0.0 0 0
# element Brick 1 1 2 3 4 5 6 7 8 1 0.0 0.0 0 0

set load [expr -10000*$KN]
# 自由端节点集中荷载
pattern Plain 1 "Linear" {

load 1 0.0 0.0 $load

}
#

#-----记录

# recorder Node -file cube8Node7.out -time -node 7 -dof 3 disp
# recorder Element -file brick.out -ele 1 stress
#recorder Element -file cubeGusspoint.out -time-ele 1 -gausspoint
# recorder Element -file cubeGusspoint.out -ele 1 gausspoint

recorder Element -file bigcubestiffness.out -ele 1 stiffness

fixY 0.0 1 1 1
#------------

# system BandGeneral

system ProfileSPD ; # 本例常用

# system UmfPack

# system SparseGeneral -piv

set NstepGravity 1; # apply gravity in 10 steps

set DGravity [expr 1./$NstepGravity]; # first load increment;

integrator LoadControl $DGravity; # determine the next time step for an analysis

test NormUnbalance 1.0e-4 20 1

set Tol 1.0e-5

#test NormDispIncr $Tol 6 ;

# test EnergyIncr $Tol 10

# algorithm Newton
algorithm Linear

# numberer Plain

numberer RCM

constraints Plain
# constraints Transformation
#constraints Penalty 1e12 1e12
analysis Static; # define type of analysis static or transient

analyze $NstepGravity; # apply gravity





# ----------------------------
# print node 1
# print node 2
# print node 5
# print node 6


print big8GLelement.txt

# source Bigcube.tcl

[fmk]

the brick and the brick8n have different node numbering .. the negative results suggests you are using the wrong numbering scheme .. check the node numbering of the 20n brick as well.

[liushuhao]

thank you fmk！
the node numbering and of the stdbrick and brick8N is strictly observed the usemanual.the results of them are same but different from the abaqus.
so I am puzzled

[liushuhao]

thank you fmk！
the node numbering and of the stdbrick and brick8N is strictly observed the usemanual.the results of them are same but different from the abaqus.
so I am puzzled