Elements with History Variables in Programmer Manual

[Shilmin]

Dear All,

I am still not very cleared about “Section 5.6 Elements with History Variables” of Programmer Manual.
As we know, the data located at hr(nh1), hr(nh2) is for t(n), t(n+1), respectively; and in user element, we should update the data at hr(nh2). What I am not cleared is: When will the data at hr(nh1) is updated? I did some simple examples, it seems the data at hr(nh1) is not updated during the iteration. I guess, the data at hr(nh1) is updated by command TIME, but I am not sure. If so, the data at hr(nh1) can not be used to update the data at hr(nh2) during the iteration, because it contains the data at t(n), not t(k)(n+1). So, what is the right thing to correctly update these history variables? If I want to use command AUTO or BACK, how to make sure history variables are right?
P.S., Can AUTO, TIME, IMIN, IMAX,MAXR and AUTO, DT, DTMIN,DTMAX be used at the same time?

Thank you!

Xiaomin

[Prof. R.L. Taylor]

The data in nh1 does contain the data a t_n and the information in nh2 should contain the values of the last iteration at t_n+1.  Yes, the data is updated with the TIME command so at the beginning of a time step the data in nh1 and nh2 are the same.

[Shilmin]

Dear Prof.  R.L. Taylor

Thank you for your timely reply!
So, during the iteration, the data in nh1 has no change, and the data in nh2 is constantly updating based on the data in itself. When command BACK or AUTO is used, the data in nh2 is recovered by data in nh2. Am I right?
Thank you!

Xiaomin

[Prof. R.L. Taylor]

When BACK is used the information in nh1 is copied to nh2.  You will have to experiment with a small problem to follow what AUTO does.

[Shilmin]

Dear Prof. R.L. Taylor,

I try to use AUTO to solve a problem, the solve part of the input file is attaced.
If only “AUTO,TIME,300,400,3” or “AUTO,DT,1.0e-4,3.0e-3” is used, the dt keeps constant, even though the number of iterations is 1200 for over 100 steps. If these two commands are both used, the dt will increase to 3.0e-3 very soon, then keeps constant even though the number of iterations has reached 1200 sevel times. After 20 steps, the dt is reduced. This insensitivity of dt results the program works not very well.

Thank you!
Xiaomin

Batch
  DT,,2e-3
  AUTO,TIME,300,400,3
  AUTO,DT,1.0e-4,3.0e-3
  TOL,,1.e-9
  LOOP,print,100
   LOOP,time,40
    TIME,,5.2
    TANG
    LOOP,iter,1200
     FORM
     SOLV
    NEXT,iter
    ECKC
   NEXT,time
   REAC,node, 0  h1+h2         
   REAC,node, wd h1+h2           
   REAC,node, 0  h1+h2+0.91/3   
   REAC,node, wd h1+h2+0.91/3   
   REAC,node, 0  h1+h2+2*0.91/3
   REAC,node, wd h1+h2+2*0.91/3 
   REAC,node, 0  h1+h2+0.91     
   REAC,node, wd h1+h2+0.91   
   STRE,,19, 360
  NEXT,print
plot,defo,10
plot,mesh
plot,disp
end

[Prof. S. Govindjee]

From my reading of program/pmacr2.f, I think you need to place your auto,time,300,400,3 just before the loop you are trying to control.

So perhaps just before the loop,iter,1200