Learning Forum

[Mathijs Verbist]

Hi, I'm working on a transient analysis in (Py)MAPDL and I would like to read data inbetween loadsteps and continue after with a new loadstep. But when I go from /POST26 (to read the output) to /SOLU again and solve a new loadstep, the states (speed and displacement) of the previous loadstep are deleted and the simulation is started from 0. How can I make sure that the previous timestep is taken into account after exiting /POST26 to /SOLU?
Do I have to use initial conditions for the next step, or is there an option to keep the previous step?

/SOLU

!D, 20, ALL
D, 20, ROTY
D, 20, ROTZ
D, 20, ROTX

F, 20, MX, 0
ANTYPE, TRANS

NSUBST, 10,10,10
OUTRES, ALL, ALL
KBC, 1

F, 1, MX, 10
time, 1
lswrite, 1
solve

/POST26 !this step is needed for external processing and updating the loads in the next step

NSOL, 2, 1, ROT, X, ROTX
NSOL, 3, 1, OMG, X, ROTVELX

/SOLU
F, 1, MX, 100 !value here is dependant on the previous solutions
time, 2
lswrite, 2
solve

[Erik Kostson]

Hi

Perhaps use restart option.

Example

end_time = arg1 ! WB parameters

step = arg2

substep = arg3

limpres = arg4

delta_t = end_time/step                                                ! time increment

save,model,db                                                                  ! (database saved for diagnosing purpose)

 

/solu

antype,4                                                                              ! transient analysis

autots,off                 ! User turned off automatic time stepping

timint,on

time,1e-5                                                                            ! a very small initial time

alls

solve

*do,i,1,step,1                                                    ! loop substep number

  fini

  /post1

  set,i                                                                     ! read ith step

  !do something here

  allsel,all

  fini

  parsav,all,my_par,txt                                    ! save paramters

 

  /solu

  antype,4,rest                                                   ! restart from last step

  timint,on

  autots,off                 ! User turned off automatic time stepping

  parres,new,my_par,txt                                 ! resume parameter

  time,i*delta_t

  nsubst,substep

  !do something here

  /solu

 

  alls

  solve

*enddo

Hope this helps

Erik

[Mathijs Verbist]

Hi Erik, thank you for responding. 
It think it works in MAPDL itself, but when tested with PyMAPDL, it now only solves the first loadstep. Figure 1 is what the codes returns, while it is supposed to look like figure 2 after the second load step. (Figure 2 is created without going into POST26 and without restarting the solution)

 

This is the code I run now:

mapdl.slashsolu()

mapdl.keep(1)

#mapdl.d(20, "ALL")

mapdl.d(20, "ROTY")

mapdl.d(20, "ROTZ")

#mapdl.d(20, "ROTX")

timesteps = 2

substeps = 10

substeps_max = 10

substeps_min = 10

mapdl.run("ANTYPE, TRANS")

mapdl.timint("ON")

mapdl.autots("OFF")

mapdl.nsubst(substeps, substeps_max, substeps_min)

mapdl.outres("ALL", "ALL")

mapdl.kbc(1)

#mapdl.d(20, "ALL")

mapdl.d(20, "ROTY")

mapdl.d(20, "ROTZ")

#mapdl.d(20, "ROTX")

mapdl.f(1, "MX", 10)

mapdl.time(1)

mapdl.lswrite(1)

mapdl.solve()

mapdl.post26()

rot_displ = mapdl.nsol(2, 1, "ROT", "X", "ROTX")

#print(rot_displ)

mapdl.allsel("all")

mapdl.finish

mapdl.parsav("all","my_par","txt")

mapdl.slashsolu()

mapdl.antype(4,"REST")

mapdl.timint("ON")

mapdl.autots("OFF")

mapdl.parres("new","my_par","txt")

mapdl.f(1, "MX", -10)

mapdl.slashsolu()

mapdl.time(2)

mapdl.lswrite(2)  

mapdl.solve()

mapdl.post26()

rot_displ = mapdl.nsol(2, 1, "ROT", "X", "ROTX")

#print(rot_displ)

# Plot nodal displacement against time

plt.plot( rot_displ, marker='o', linestyle='-')

plt.xlabel('Time (seconds)')

plt.ylabel('Nodal rotation')

plt.title('Nodal rotation vs. Time')

plt.grid(True)

plt.show()

mapdl.exit()

[Mathijs Verbist]

I got is working by using the restart in combination with lssolve, i ,i ,1 instead of just using solve. Now all the steps get solved while getting the data inbewteen the steps