General Mechanical

General Mechanical

Non-linear Analysis Infinite Elements

    • bcho
      Subscriber

      Hello Community,


      has anyone tried to do a non-linear, transient analysis with infinite elements (Element type: Infin257)? For my problem the solution does not converge for a non-linear analysis.


      Regards,

    • Ashish Khemka
      Ansys Employee

      This element is used for static analysis.

    • bcho
      Subscriber

      Thanks for your reply. I found the information that it could be used for transient analysis as well on this website: https://www.sharcnet.ca/Software/Ansys/17.0/en-us/help/ans_elem/elem_infindomain.html Is this wrong?
      Is there another element I could use to do my analysis? I want to simulate the behaviour of a soil in combination with a non-linear spring on top.

    • Ashish Khemka
      Ansys Employee

      Yes, you are right - my mistake: The element supports static, transient, and harmonic analyses.

    • Ashish Khemka
      Ansys Employee

      What is the error message you see in the Solver Output when the Solution does not converge?


       

    • bcho
      Subscriber

       This is the error message I get after the 4th step. The steps 1 to 3 converge.


      The value of UX at node 61017 is 131036267.  It is greater than the    
       current limit of 1000000 (which can be reset on the NCNV command).     
       This generally indicates rigid body motion as a result of an           
       unconstrained model.  Verify that your model is properly constrained. 



      I tried a static analysis before and it worked fine, so I'm not sure why there should be a rigid body motion.

    • Ashish Khemka
      Ansys Employee

      Hi,


       


      Thanks for the update. The error message indicates rigid body motion. What did change between static and transient analysis? If it is same model then I am not sure what might be causing this. Also, model may be required for debugging and I cannot d that. If you can describe more on the problem, that may help.


       


      Regards,


      Ashish Khemka

    • bcho
      Subscriber

      Hi,


      Thanks again for your reply.


      For the soil I model the quarter of a sphere with solid186 and add infin257 at the outer surface of the sphere. Additionally I apply a spring-mass-system with combin39 and mass21.


      For the static analysis I add a load in z-direction. The transient analysis is done by a loop in time with a sinusodial load or an impulse.


      So the model does not change between static and transient except for the analysis type and the load.


      I tried the following:
      linear + transient --> converges
      non-linear + static --> converges
      non-linear + transient --> does not converge


      I added a picture of step 6 when the calculation does not converge and my APDL commands although I'm not sure if it'll be helpful for you since the comments are in german.


      Thanks a lot in advance.


      Kind regards,


      Bettina Chocholaty


      APDL commands:


      finish
      /clear


      /PREP7
      RM=0.5                ! Lastradius
      RB=10              ! Bodenradius
      Gx=80000000        ! Schubmodul
      NUxy=0.33        ! Poisson Zahl
      freq=100        ! Frequenz in Hz          
      rho=2000        ! Dichte
      cs=sqrt(Gx/rho)        ! Scherwellengeschwindigkeit
      Exx=2*Gx*(1+NUxy)    ! E-Modul
      lambda=cs/freq        ! Wellenlänge
      le=lambda/8        ! maximale Elementlänge
      lnele=(RM+RB)/le        ! Elementanzahl
      lneleh=lnele/2
      lnelemh=NINT(lneleh)
      lnelem=lnelemh*2
      !lnelem=48
      dt=le/cs        ! Zeitschritt
      t=(RM+RB)/cs        ! Ankunftszeitpunkt Welle an Rand von Modell
      RGES=RM+RB


      ET,1,SOLID186           ! 3D 20 NODE STRUCTURAL SOLID


      MP,EX,1,Exx             ! Materialzuweisung
      MP,PRXY,1,NUxy
      MP,DENS,1,rho

      !---Geometrie der Platte                                                         !*!
      *SET,H,0.4                       ! Plattenhoehe [m]                                  !*!
      *set,r,5/2            ! Halbe Breite/Länge Fundament
      *set,ri,3.75/2            ! Halbe innere Breite/Länge Fundament

      ! MATERIAL
      !---Materialdaten der Platte                                                     !*!
      rho=0                          ! Dichte der Platte [kg/m^3]                        !*!
      nue=0                         ! Querkontraktionszahl der Platte                   !*!
      EModul=9710000000              ! E-Modul der Platte [N/m^2]         
      MP,EX,2,EModul                   ! E-Modul
      MP,NUXY,2,nue                    ! Querkontraktionszahl
      MP,DENS,2,rho,,,                 ! Dichte

      ! Angaben für Masseschwinger
      m=10000                ! Masse
      knl=597000000            ! Fließgrenze-Steifigkeit
      Fnl=149000000            ! Fließgrenze-Kraft


      K,1
      K,2,,RM+T
      PCIRC,0,RGES,0,90               ! Kreisfläche
      !! für Plattengenerierung
      !Pcirc,RM,RM+T/2,0,90
      !PCIRC,0,RM,0,90         
      !Pcirc,RM/2,RM,0,90
      VROTAT,all,,,,,,1,2,-90,,       ! Kugelvolumen

      allsel
      vplot

      ! Unterteilung der radialen Linien
      lsel,inve
      lsel,s,length,,RGES
      lesize,all,,,lnelem,,1         ! Linienunterteilung nach elementzahl
      !lesize,all,le,,,,1        ! Linienunterteilung nach Elementgröße

      ! Unterteilung der Bogenlinien
      Csys,2
      lsel,s,loc,x,RGES
      lesize,all,,,lnelem,,1        ! Linienunterteilung nach elementzahl
      !lesize,all,le,,,,1        ! Linienunterteilung nach Elementgröße

      allsel
      csys,0

      !!!!!!!!!!!!!!!!!!!!!!!!!!!!
      !!! MASSE-SCHWINGER !!!
      !!!!!!!!!!!!!!!!!!!!!!!!!!!!

      !!! Masse-Fdeder-System
      ET,10,COMBIN39,,,,1,,1                ! ELEMENT WITH DISPLACEMENT ALONG NODAL z-AXIS
      KEYOPT,10,4,1
      ET,11,MASS21,,,0                      ! MASS WITHOUT ROTARY INERTIA
      KEYOPT,11,3,2
      R,10,-5,-Fnl,-0.5,-Fnl,0.0,0.0  ! SPRING DATA
      RMORE,0.5,Fnl,5,Fnl 
      !R,11,0,0,m,0,0,0                  ! MASS DATA
      R,11,m
      csys,0 
      NSEL,All
      !NSEL,S,LOC,X,-r+(r-ri)/2
      !NSEL,R,LOC,Y,-r+(r-ri)/2
      !NSEL,R,LOC,Z,-H
      !*GET,n_center1,NODE,,NUM,MIN
      !*GET,n_center1,NODE,1,NSEL,,
      !NSEL,S,LOC,X,+r-(r-ri)/2
      !NSEL,R,LOC,Y,-r+(r-ri)/2
      !NSEL,R,LOC,Z,-H
      !*GET,n_center2,NODE,,NUM,MIN
      !*GET,n_center2,NODE,1,NSEL,,
      *GET,knotenanzahl,NODE,,NUM,MAX
      N,knotenanzahl+1,+r-(r-ri)/2,+r-(r-ri)/2,-H
      NSEL,S,LOC,X,+r-(r-ri)/2
      NSEL,R,LOC,Y,+r-(r-ri)/2
      NSEL,R,LOC,Z,-H
      !*GET,n_center3,NODE,,NUM,MIN
      *GET,n_center3,NODE,,NUM,MIN
      !*GET,n_center3,NODE,1,NSEL,,
      !NSEL,S,LOC,X,-r+(r-ri)/2
      !NSEL,R,LOC,Y,+r-(r-ri)/2
      !NSEL,R,LOC,Z,-H
      !*GET,n_center4,NODE,,NUM,MIN
      !*GET,n_center4,NODE,1,NSEL,,
       
      NSEL,all
      *GET,n_max,NODE,,NUM,MAX
      !N,n_max+1,-r+(r-ri)/2, -r+(r-ri)/2,-5*H
      !N,n_max+2,+r-(r-ri)/2, -r+(r-ri)/2,-5*H
      N,n_max+3,+r-(r-ri)/2 , +r-(r-ri)/2,-5*H
      !N,n_max+4,-r+(r-ri)/2, +r-(r-ri)/2,-5*H
      !TYPE,10
      !REAL,10
      !E,n_center1,n_max+1   !Non-linear spring
      !TYPE,11
      !REAL,11
      !E,n_max+1 !Mass
      !nummrg,all
       
      !TYPE,10
      !REAL,10
      !E,n_center2,n_max+2   !Non-linear spring
      !TYPE,11
      !REAL,11
      !E,n_max+2 !Mass
      !nummrg,all

      TYPE,10
      REAL,10
      E,n_center3,n_max+3   !Non-linear spring
      TYPE,11
      REAL,11
      E,n_max+3 !Mass
      nummrg,all

      !TYPE,10
      !REAL,10
      !E,n_center4,n_max+4   !Non-linear spring
      !TYPE,11
      !REAL,11
      !E,n_max+4 !Mass
      !nummrg,all
      NSEL,All
      nummrg,nodes
      nummrg,all



      ! Meshing
      Mat,1
      mshape,0,3D            ! Elementform
      vmesh,1


      ! Infinite Elements oder Feste Auflager
      *GET,NMAX,NODE,0,NUM,MAXD
      NPOLE=NMAX+1
      N,NPOLE

      CSYS,2                     
      ASEL,S,loc,x,RGES
      NSLA,S,1
      EINFIN,,NPOLE                   ! Infinite Elements
      !d,all,all            ! Feste Auflager
      ALLSEL


      ! Symmetriebedingungen
      CSYS,0
      !NSEL,S,LOC,Z,0
      !DSYM,SYMM,Z                 ! SYMMETRIC CONSTRAINTS,UZ
      ALLSEL,ALL,ALL
      NSEL,S,LOC,Y,0
      DSYM,SYMM,Y                    ! SYMMETRIC CONSTRAINTS,UY
      ALLSEL,ALL,ALL
      NSEL,S,LOC,X,0
      DSYM,SYMM,X                    ! SYMMETRIC CONSTRAINTS,UX
      ALLSEL,ALL,ALL

      !shpp,on

      !shpp,summ

      ! Knoten für Last auswählen
      NSEL,All
      nummrg,nodes

      csys,2
      !asel,s,loc,x,0,RM
      nsel,s,loc,x,0,RM
      csys,0
      !asel,r,loc,z,0
      nsel,r,loc,z,0
      CM,CM_load,node

      allsel

      !*DIM,displ,Table,17                                ! Kraftvektor
      !*TREAD,displ,'last','sis',' ',,
      !*VPLOt,displ(1,0),displ(1,1)


      !!! LAST
      NSEL,All
      nummrg,nodes

      *DIM,displ,Table,17                               ! Kraftvektor
      *TREAD,displ,'last','sis',' ',,
      *VPLOt,displ(1,0),displ(1,1)


      /SOLU
      ANTYPE,trans

      tend=dt*300
      !dt=0.9108e-5
      ntime=NINT(tend/dt)+1

      !timint,on
      !nlgeom,on
      EMATWRITE,YES

      *afun,rad

       *do,itime,1,70 !* Beginn der Zeitschleife
          zeit=itime*dt            ! Variable 'zeit' definieren
          !F,CM_load,fz,1000*sin(freq*2*3.14*zeit)
          !D,CM_load,uz,0.5*sin(2*3.14*zeit)
          !SF,CM_load,Pres,100*sin(10*2*3.14*zeit)
          !F,CM_load,fz,-sin(2*3.14*5)
          D,CM_load,uz,displ(zeit)*0.5
          *MSG,WARN, itime, ntime, zeit,
          *** Step %I von %I  Zeit %G
          TIME,%zeit%            ! Zeit des nächsten Berechnungs-Schrittes
          NSUB,10,30,1
          SOLCONTROL,On
           !NROPT,FULL
           !LNSRCH,ON
           !CNVTOL,F,,0.05 ! 5% Tolerance
           !PRED,on,,on
           !NEQIT,500
         SOLVE                  ! selbstredend
         save
       *enddo

      !*** ENDE DER ZEITSCHLEIFEN ***

       FINISH                   ! Ende des Solution-Prozesses



      /EOF


    • bcho
      Subscriber

      Update to the linear-transient analysis: If I increase the time span that is observed, the solution does not converge (as I said before) since the displacements increase strongly after step 58.displacement uz

    • Ashish Khemka
      Ansys Employee

      Hi Bettina,


       


      I may not be able to run your model at my end. May be someone from the group can run the model. 


       


      Regards,


      Ashish Khemka

    • bcho
      Subscriber

      Thanks anyway. I appreciate your help.

    • Augusto13
      Subscriber

      I'm having this same problem. But for a linear trasient analysis:


      https://forum.ansys.com/forums/topic/transient-analysis-with-infinite-element/


      Bcho, Did you solve the problem?

    • bcho
      Subscriber
      Unfortunately I have not been able to solve the problem. Now I'm using Combin14 Elements for my calculations which seem to work quite good.
    • Augusto13
      Subscriber

      I realized that your problem converged to a linear analysis with infinite element. What was the boundary condition of your problem?

    • bcho
      Subscriber
      As I stated before in a comment, the linear Analysis also did not converge as I thought before. It only took longer to diverge.
      About the boundary conditions :
      I modeled a Part of a sphere and applied symmetry conditions at the plane surfaces and the infinte elements at the spherical surface.
    • Augusto13
      Subscriber

      interesting is when I do the modal analysis before and take advantage of its results in the transient analysis ( transient analysis with modal superposition), the problem does not happen. But the results are not influenced by the infinite element.

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