Alright, that fixes it! Now I understand the reason for quasistatic! In the non-linear analyses, the time stepper is set programatically - is is possible to force solving for the first time step here as well as in:


    for ii, disp in ds:
        #my_output(dformat % (ii + 1, ds.n_step, disp))

        force0 = 0.0

        pb.ebcs['Load'].dofs['u.2'] = disp

        pb.ts.is_quasistatic = True  # <<<=========== Force quasistatic
        pb.time_update(ts)




On Wed, Jan 26, 2011 at 9:57 AM, Robert Cimrman <cimr...@ntc.zcu.cz> wrote:

So the problem is the single dot outside the linear curve, right?

What if you add

       'quasistatic' : True,

to the time-stepper options? As it is now, the first time step is not solved but taken from the initial conditions (unspecified = zero) and boundary conditions (nonzero!), so it is not in equlibrium!


r.

On Wed, 26 Jan 2011, Andre Smit wrote:

Sorry - forgot to attach the figure - your point is taken re the nodal
residual. Forces are calculated and summed on each of the nodes in the
Top region. I checked this a while back and plotted in Paraview - the
forces are zero at the other nodes within the model but equal and
opposite in direction to the Top at the corresponding Bottom nodes of the
model (as you'd expect).

a

On Wed, Jan 26, 2011 at 9:26 AM, Robert Cimrman <cimr...@ntc.zcu.cz>
wrote:
     Where can I see the line? maybe you forgot to attach a
     figure?

     As for the forces, it might be better to compute them using a
     (inner) surface integral of stress instead of the nodal
     rezidual. Btw. you look at the nodal force in the first node
     of the Top region only, right? What are the values in the
     other nodes?

     r.

     On Wed, 26 Jan 2011, Andre Smit wrote:

           Thanks Robert!

           I've attached a modification that shows the
           strain/stress output for the
           elastic case of the cylinder under compression.
           The slope of the line is
           Young's modulus as you'd expect. As with our
           non-linear analyses, the
           forces calculated after the first time step
           appear to be too high - not
           sure what the reason for this is. 

           On Wed, Jan 26, 2011 at 2:25 AM, Robert Cimrman
           <cimr...@ntc.zcu.cz>
           wrote:
                There was some old code in the
           stress_strain() function. The
                exception was caused by putting directly the
           traction
                function into the EBC definition, instead of
           its name. The
                attached file should work.

                r.


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