ANSYS qu from new user: help me write a "for" loop please!

Hi: I am a new ANSYS user and would really appreciate help writing a "for"-type loop to go with an example found here:

http://www.mece.ualberta.ca/tutorials/ansys/CL/CAT/BirthDeath/Print.html

 At the end of the example is the paragraph below.  I want to know how to do this!  Can anyone modify the code for me?  I don't even know where to start.  I would be very grateful!  

 This procedure can be programmed in a loop, using command line code, to more accurately model element death over time. Rather than running the analysis for a time of 60 and killing any elements above melting temperature at the end, a check can be done after each substep to see if any elements are above the specified temperature and be killed at that point. That way, the prescribed convection can then act on the elements below those killed, more accurately modelling the heating process. 


Re: For loops in ansys

Look at the help on the *do command.  The syntax is something like

*do, <index>, <start_idx>, <incr>, <end_index>

*enddo

You will have to break your solution loadstep up into a number of substeps.  Each substep will have its own solve command.

For example 

/solu
total_time = 1
time_steps = 100 
time_inc = total_time/time_steps 

*do, step_no, 1, num_step
    time, step_no*time_inc
    nsub, 1
    outres, all, all
    ... any stuff about boundary conditions ...
    solve
    finish
    /post1
    set, last
    etable,melty,temp, ! Create an element table
    esel,s,etab,melty,273 ! Select all elements from table above 273
    finish
    /solu ! Re-enter solution phase
    antype,,rest ! Restart analysis
    ekill,all ! Kill all selected elements
    esel,all
*enddo

etc.


Loops in Ansys

Hi Biswajit:

Thanks a lot for your help.  I tried your suggestion and have a couple of  questions if you have time.  Sorry--I know that this is probably really simple stuff, but I'm trying to learn!

 I got a couple of error messages (all of my code is below, with the part I got and modified from you in bold blue): First, after entering the code I got from you, I got "No DO trips needed, enter *ENDDO".  Second, after entering the postprocesser, I got: "The current database is not from a previous solution. No restart is possible with this database"; then " Cumulative iteration 1 may have been solved using different model or boundary condition data than currently stored. POST1 results may be erroneous unless you RESUME from a Jobname.DB file for this substep.

 If you have any idea what this stuff means and how to fix it, I would really appreciate hearing it!  My code is below.  

 

/title, Transient melting by element death (conduction)
/prep7                         ! Enter the preprocessor

                        ! define geometry

BLC4,0,0,20,15                     ! Create rectangle
BLC4,0,0,10,4                     ! Create smaller rectangle (magma)
ASBA,1,2                    ! Boolean Subtraction (subtracts area 2 (small) from area 1 (big))

ET,1,Plane55                     ! Element type

MP,Dens,1,2262e9                 ! Define density
mp,c,1,0.001604                 ! Define specific heat
mp,kxx,1,0.001                    ! Define heat transfer coefficient
                   
SMRT,6                    ! Mesh size 
CM,_Y,AREA 
ASEL, , , , 3
CM,_Y1,AREA
CHKMSH,'AREA'  
CMSEL,S,_Y 
 
AMESH,_Y1                   ! Mesh area                       
CMDEL,_Y                    ! Refine mesh
CMDEL,_Y1  
CMDEL,_Y2  
FLST,5,6,2,ORDE,4  
FITEM,5,6  
FITEM,5,22 
FITEM,5,-25
FITEM,5,44 
CM,_Y,ELEM 
ESEL, , , ,P51X
CM,_Y1,ELEM
CMSEL,S,_Y 
CMDEL,_Y
EREF,_Y1, , ,3,0,1,1
CMDEL,_Y1  
finish

/solu                         ! Enter solution phase
antype,4                     ! Transient analysis
nropt,full                     ! Newton Raphson - full
SOLCONTROL,ON,0
total_t = 3.1536e13
t_steps = 100 
t_inc = total_t/t_steps

*do, step_no, 1, num_step
    time, step_no*t_inc
    nsub, 1
    outres, all, all
                            !... any stuff about boundary conditions ...
TUNIF,200, 
TREF,200,
IC,all,temp,200                     ! Initial conditions, temp = 200
PRED,-1
FLST,2,628,1,ORDE,2
FITEM,2,1  
FITEM,2,-628
IC,P51X,TEMP,200,  
FLST,2,2,4,ORDE,2  
FITEM,2,6  
FITEM,2,-7 
/GO

DL,P51X, ,TEMP,1200,1            ! BC  
FLST,2,2,4,ORDE,2  
FITEM,2,2  
FITEM,2,-3 
/GO
 
DL,P51X, ,TEMP,200,1

/STAT,SOLU 
    solve
    finish
    /post1
    set, last
    etable,melty,temp,     ! Create an element table
    esel,s,etab,melty,600     ! Select all elements from table above 600 C
    finish
    /solu     ! Re-enter solution phase
    antype,,rest     ! Restart analysis
    ekill,all     ! Kill all selected elements
    esel,all
*enddo


/post1                    ! Enter postprocesser

set, first
etable,melty,temp,                 ! Create an element table
esel,s,etab,melty,600                ! Select all elements from table                                             ! above 600
finish

/solu                         ! Re-enter solution phase
antype,,rest                     ! Restart analysis
ekill,all                         ! Kill all selected elements
esel,all                         ! Re-select all elements

finish

/post1                         ! Re-enter postprocessor
set,first                        ! Read in last subset of data
esel,s,live                     ! Select all live elements
plnsol,temp                     ! Plot the temp contour of the live elements

!/CONT,1,10,200,100,1200
!PLNS,TEMP, 
!/REPLOT

*DO, i,1,10,1
set,i
etable,delete
etable,melty,temp,                 ! Create an element table
esel,s,etab,melty,600                ! Select all elements from table                                             ! above 600
finish

/solu                         ! Re-enter solution phase
antype,,rest                     ! Restart analysis
ekill,all                         ! Kill all selected elements
esel,all                         ! Re-select all elements

finish

/post1                         ! Re-enter postprocessor
set,i                        ! Read in last subset of data
esel,s,live                     ! Select all live elements
plnsol,temp
 /CONT,1,10,200,100,1200
PLNS,TEMP,             
/replot


*ENDDO

ANTIME,100,0.5, ,0,2,0,0.31536E+14
 


Re: Do loop in ANSYS

I just noticed that I'd written num_step instead of t_steps in the do loop.  You'll have to correct that before you proceed.

If you want an amination, you'll have to save the results at the end of each step.  I'm not sure exactly how to proceed after that.

Please let us know when you figure out the right way of getting waht you want.

-- Biswajit 


Thanks Biswajit

Thanks a lot for being so patient...I'm making progress and will let you know when I've figured it out!


ANSYS: animating element death

I just want to clarify that I still can't animate progressive element death (i.e., elements disappearing as temp evolves).  At what point (in the "DO" loop or after it) and how do I put the results from /solu into the postporcessor for animation?  Major thanks...


I am stumped!

OK, I'm stumped on how to make an animation for this example.  Thanks a lot Biswajit; your suggestion was really helpful.  The commands are posted below, not including the animation step.  I'm going to put up a new post to ask about the animation.  

 

/title, Convection Example   
/prep7                ! Enter the preprocessor

! define geometry

k,1,0,0                ! Define keypoints
k,2,0.03,0
k,3,0.03,0.03
k,4,0,0.03
a,1,2,3,4            ! Connect the keypoints to form area

! mesh 2D areas

ET,1,Plane55            ! Element type

MP,Dens,1,2262e9         ! Define density
mp,c,1,0.001604         ! Define specific heat
mp,kxx,1,1.8            ! Define heat transfer coefficient

esize,0.0025            ! Mesh size
amesh,all            ! Mesh area

finish

/solu                ! Enter solution phase

antype,4            ! Transient analysis

tot_time = 1e6
t_steps = 50
time_inc = tot_time/t_steps

time,1e6            ! Time at end of analysis

nropt,full            ! Newton Raphson - full
lumpm,0            ! Lumped mass off
nsubst,20            ! Number of substeps, 20
neqit,10                ! Max no. of iterations
autots,off            ! Auto time search off
lnsrch,on            ! Line search on

TUNIF,200,
IC,all,temp,200            ! Initial conditions, temp = 200

*do, i,1 ,t_steps, 1
/solu
    time=i*time_inc
    nsub, 1
outres,all,all            ! Output data for all substeps

                    !... any stuff about boundary conditions ...

                ! fixed temp BC's
nsel,s,ext            ! Node select all exterior nodes
sf,all,conv,1,600
NSEL,ALL            ! Reselect all nodes
kbc,1                ! Load applied in steps, not ramped
/gst,off                ! Turn off graphical convergence monitor

    solve
    finish

    /post1
    set, last
    etable,melty,temp, ! Create an element table
    esel,s,etab,melty,900 ! Select all elements from table above 500
    finish
    /solu ! Re-enter solution phase
    antype,,rest ! Restart analysis
    ekill,all ! Kill all selected elements
    esel,all

finish
*enddo

 


A question about the loop

Hi, I tried the code you posted, but it could not work correct. The problem happens here:

 
    etable,melty,temp, ! Create an element table
    esel,s,etab,melty,900 ! Select all elements from table above 500
    finish
    /solu ! Re-enter solution phase
    antype,,rest ! Restart analysis
    ekill,all ! Kill all selected elements

 It seems that the 'esel' is not valid after  'antype,,rest ', thus all the elements have been killed....

Could you please tell me how to deal with this? Thanks. 


how to transfer convection BC from deactivated elements?

sir..,

      I am a Post Graduate student of thermal engineering specialisation & i tried several times on this code...,in ANSYS APDL. but, i did not get the melting process., it seems that there might be a mistake in this., can you please give me the correct APDL Code.,