General Mechanical

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 :)

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