## General Mechanical

#### Combin39 – requirements – Mechanical APDL

• Rajesh
Subscriber

Good Morning, Community:

I need help and preceise information about using COMBIN39 elements when plane strain is assumed. I am sure, that there is problem with connection. I imagined that I need to only create two nodes for each spring -> for begin and end part of spring and then that i have to use COMBIN39 elements next. My connection does not work however and I need some clues.

Case is very simple: ET,1 is PLANE183 with KEYO that are set for plane strain. Also linear and nonlinear springs at the bottom. I want to control UY displacement of springs via real constants. Springs are defined as ET,2 (linear springs) and ET,3 (nonlinear springs).

I am definitely missing something about COMBIN39 and I dont understand the idea of coincidence when using springs.

You see, a professional help is needed... I think someone who know how it works can say: oh you didnt apply RBE3 or sth like that, but need some help and clear instructions.

Here is my code (i marked part that is not necessary to check and can be skipped):

FINISH
/CLEAR,START
/UNITS,MKS !m,kg,s,C

/PREP7

!some parameters
a=0.008 ![m]
b=0.05 ![m]
h=0.163 ![m]
t=0.004 ![m]
p=1000 ![Pa]
v=0.3
E=2e11 ![Pa]

!-geometry-!

K,1,0,0
K,2,b-a,0
K,3,b-a,b
K,4,-a,b
K,5,-a,0

L,1,2
L,2,3
LESIZE,2,,,16

L,3,4
LESIZE,3,,,16

L,4,5,
LESIZE,4,,,24,.2
lplot

L,5,1
AL,1,2,3,4,5

MP,EX,1,E
MP,NUXY,1,v
ET,1,PLANE183,,,2    ! KOP3 = 2 so plane strain

AMESH,1

!--------------- YOU CAN SKIP THIS it works OKAY, next section indicates where problems arise ------------------------
NSEL,S,LOC,Y,0

CM,nodbott,nodes
CMSEL,S,nodbott,node
*GET,NodbottQty,NODE,0,COUNT

!*STATUS,NodbottQty

*DIM,InitialTable,ARRAY,NodbottQty,8

prevnode=0
*DO,i,1,NodbottQty,1
ni=NDNEXT(prevnode)
InitialTable(i,1)=ni
prevnode=ni
*ENDDO

*DO,i,1,NodbottQty,1
n1=InitialTable(i)
xpos_bottnodes=NX(n1)
ypos_bottnodes=NY(n1)
zpos_bottnodes=NZ(n1)
*VFILL,InitialTable(i,2),DATA,xpos_bottnodes
*VFILL,InitialTable(i,3),DATA,ypos_bottnodes
*VFILL,InitialTable(i,4),DATA,zpos_bottnodes
*ENDDO

ALLSEL,ALL
*get,maxnodeno,node,0,num,max

*DO,i,1,NodbottQty,1
N,maxnodeno+i,InitialTable(i,2),InitialTable(i,3)-0.001,InitialTable(i,4)
*ENDDO

ALLSEL,ALL
*get,maxnodeno2,node,0,num,max
NSEL,S,NODE,,maxnodeno+1,maxnodeno2
CM,nodspringends,nodes

*GET,nseQty,NODE,0,COUNT

prevnode=0
*DO,i,1,nseQty,1
ni=NDNEXT(prevnode)
InitialTable(i,5)=ni
prevnode=ni
*ENDDO

*DO,i,1,NodbottQty,1
n1=InitialTable(i,5)
xpos_nse=NX(n1)
ypos_nse=NY(n1)
zpos_nse=NZ(n1)
*VFILL,InitialTable(i,6),DATA,xpos_nse
*VFILL,InitialTable(i,7),DATA,ypos_nse
*VFILL,InitialTable(i,8),DATA,zpos_nse
*ENDDO

ALLSEL,ALL

eplot

!--------------- I THINK THIS SECTION INDICATES THE PART WHEN PROBLEM OCCURS ------------------------

*GET,MAXetypeid,ELEM,0,TYPM
ET,MAXetypeid+1,39
MP,BETD,MAXetypeid+1,1
ET,MAXetypeid+2,39
MP,BETD,MAXetypeid+2,1

KEYOPT,MAXetypeid+1,1,0
KEYOPT,MAXetypeid+1,2,0
KEYOPT,MAXetypeid+1,3,2
KEYOPT,MAXetypeid+2,1,0
KEYOPT,MAXetypeid+2,2,0
KEYOPT,MAXetypeid+2,3,2

!real constants for linear springs
R,1,-0.1,-10000,0,0,0.1,10000

!real constants for nonlinear springs
R,2,-0.1,-10000,0,0,0.5,0

!pointers

MAT,2
TYPE,2
REAL,1
allsel,all
nplot
/pnum,node,1
nplot
!COMBIN39 creation (linear behavior of springs)
E,74,670
E,122,671
E,123,672
E,124,673
E,1,661

MAT,3
TYPE,3
REAL,2
allsel,all
nplot
/pnum,node,1
nplot
!COMBIN39 elements creation (nonlinear behavior of springs)
E,3,663
E,4,664
E,5,665
E,6,666
E,7,667
E,8,668
E,9,669
E,2,662

/pnum,node,0
eplot,all

NSEL,S,LOC,Y,0.05
NPLOT
CM,nodtop,nodes
F,ALL,FY,10000

ALLSEL,ALL
CMSEL,S,nodspringends
D,ALL,ALL,0

allsel,all
eplot

antype,0
NLGEOM,ON
AUTOTS,ON
TIME,1
NSUBST,10,50,5
OUTRES,ALL,ALL
/SOLU
solve

! AND NOTHIN' HAPPENS probably because i cannot combine springs with the rest of the system

• Mike Rife
Ansys Employee

Hi Rajesh

The body is not constrained in X as the springs only act in Y.  Try constraining the lower left node of the body in X and solve just as a test.  Then decide how to constrain the model in X...maybe some weak springs that act in X direction.  Mike

• Rajesh
Subscriber

Thank you for reply i will test it soon :)