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May 1, 2012, 17:36 
convergence criteria

#1 
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ramila.h
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I am trying to write a convergence criteria for a code ans I really need your help to do so
it's like (tempnewtempold) less than 1e6 do k=1,mstep do i=0,n do j=0,n temp(0,0)=0.0 temp(i,j)=th(i,j) diff=temp(i,j)temp1(i,j) enddo enddo temp1=temp if (diff.lt.temp1e6)then stop endif enddo Last edited by afnene; May 1, 2012 at 17:40. Reason: error 

May 1, 2012, 21:48 

#2 
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Chris DeGroot
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Your logic doesn't make sense.
do k=1,mstep do i=0,n do j=0,n temp(0,0)=0.0 < Why is this inside the loop; doesn't depend on i, j, or k temp(i,j)=th(i,j) < What is "th"? It is never used diff=temp(i,j)temp1(i,j) < You calculate "diff" inside the loop and do nothing with it; it's not an array so it will be erased each time the loop is incremented enddo enddo temp1=temp < What is this supposed to do? if (diff.lt.temp1e6)then < "diff" is meaningless here since it is only that value for i=j=n stop endif enddo To check time convergence you could do something like: maxdiff=0.0 do i=0,n do j=0,n diff=abs(tempnew(i,j)tempold(i,j)) if (diff>maxdiff) then maxdiff=diff end if end do end do if (maxdiff<1.0e6) then stop end if 

May 2, 2012, 14:40 

#3 
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Thank you so much for your precious help
I am just a beginner in CFD computation, The first step I did was to try how convergence can be written in a code Please tell me how to read the old a new value of temperature inside iterrations? 

May 2, 2012, 14:47 

#4  
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Chris DeGroot
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Quote:
1. Initialize T and TO 2. According to your numerical model find a new temperature field T 3. Check convergence between T and TO (see my previous post) 3a. If converged, exit 3b. If not converged, transfer T to TO and go to step 2 

May 2, 2012, 15:05 

#5 
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Thanks again,
I will do what you explained and let you know if it works for me 

May 2, 2012, 17:36 

#6 
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Well, It sounds working,but I really want that you check that with me and of course if you don't mind
the subroutine which compute temperature is as following: subroutine tcalcu(f,temp,temp1,n,m) real f(0:8,0:n,0:m),temp(0:n,0:m),temp1(0:n,0:m) temp1=temp do j=0,m do i=0,n sum=0.0 do k=0,8 sum=sum+f(k,i,j) end do temp(i,j)=sum enddo enddo I called 'temp1' the new temperature value and insert it inside the subroutine and 'temp' as an old value......does it make sense? return end 

May 6, 2012, 22:52 

#7 
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Chris DeGroot
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Your subroutine seems to be doing what you intend, but I can't really say if it is "correct" without knowing a bit more about what sort of algorithm you are using. So you are filling in temp1 with the existing temp array, i.e. as an old value. Then you update temp as the sum of all the local elements of f. If that is what you intend, then you are good.


May 7, 2012, 18:21 

#8 
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It worked fine, I checked that by printing old and new values of temperature.
Thanks again Cdegroot, you were very helpful. Afnene 

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