General Mechanical

General Mechanical

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Transient analysis – My accelerations grow exponentially!

    • franco.donaire
      Subscriber

      Short story: Using Ansys APDL, we are trying to evaluate a seismic analysis of a wood house made with shells elements with ground made with springs COMBIN14 (simplified). We are trying to evaluate a seismic response of the house with a time-history (time vs accelerations) in a transient analysis. We put the earthquake on the ground, but, when we evaluate the acceleration in the structure, the acceleration increase to E+8. ¿Can you help us? We have at least one month searching for the error:(

      /SOLU

      ANTYPE,TRANS

      acel,0,9810,0

      TIMINT,ON

      NLGEOM,ON

      TIME,0.005

      ASEL,all

      NSLA,u,1

      LSEL,s,loc,y,0

      NSLL,u,1

      !This meant that the accelerations are applied on the nodes of the ground

      D,all,ACCX,LP_Registro(0,1)

      allsel

      !acel,%LP_Registro%,0,0


      LSWRITE

      allsel


      TIMINT,ON

      *DO,i,2,20

      TIME,i*0.005

      ASEL,all

      NSLA,u,1

      LSEL,s,loc,y,0

      NSLL,u,1

      D,all,ACCX,LP_Registro(0,i)



      allsel

      LSWRITE


      *ENDDO


      !OPCIONES PASO DE CARGA

      DELTIM,0.005,0.0001,0.005

      !AUTOTS,ON

      NEQIT,250

      !LNSRCH,ON

      KBC,1


      OUTRES,ALL,LAST


      LSSOLVE,1,20    ! Initiate multiple l.s. solution

      SAVE                    

      FINISH

    • peteroznewman
      Subscriber
      Please put your LP_Registro data in a text file for me to look at.
      What is the data in the file, is it acceleration data? What units are the data in?
      Did you double integrate the acceleration data to get displacement?
      If you have the original acceleration data, please provide that text file also.

    • franco.donaire
      Subscriber
      I don't know how to double integrate the acceleration data, maybe that's the problem.
      This is the data file, we put the file with a CSV extension with this commands:

      to_skip=0
      /INQUIRE,numlines,LINES,DLomaPrieta,csv
      to_read=numlines-to_skip
      *DEL,LP_Registro,,NOPR
      *DIM,LP_Registro,TABLE,to_read,1,1,TIME !table array to hold data
      *TREAD,LP_Registro,DLomaPrieta,csv,,to_skip
      *VPLOT,LP_Registro(0,0),LP_Registro(0,1)
    • franco.donaire
      Subscriber
      The units of the accelerations are in mm/s^2.
      This is the lomas prieta earthquake of 1989, it lasted approximately 30 seconds and has the accelerations of the text file
    • peteroznewman
      Subscriber
      You must double integrate this data to convert acceleration into displacement in mm to use in a displacement boundary condition. I have done that for you.
    • franco.donaire
      Subscriber
      Thank you very much! @peteroznewman
      I changed the acceleration to displacement but still have big deformations and big accelerations.
      should I put the displacement on the roof or on the ground (ground with restricted DOFs)?
      Again, thank you, I appreciate your help.
    • franco.donaire
      Subscriber
      Dear @peteroznewman
      We found an error in a screw stiffness snd the program id working!
      Thank you, you are the best! :)
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