I have written a FEM program, with which
you can calculate technical springs numerically.
Therefore I'm using the GetFEM-MATLAB-Interface
These calculations are highly non-linear
due to self-contact issues and large deformations.
That is the reason why technical springs
have to be solved iteratively in several substeps.
The calculation by itself works very
well. But I think I have a problem with the maximum allowed residuum that
is passed to the solve command of getfem.
My theory is that the maximum allowed
residuum has to be variable during the different substeps.
By investigating these question online
I found a paper of an university in Germany that contains the following
for a equation system of
A*x=b : ||delta_x||/||x|| <= Cond(A)
Unfortunatley these _expression_ is not
leading to plausible results.
I'm also familiar using ansys. By using
this commercial software I know that the maximum allowed residuum is changing
by each iteration and by each substep.
All of the delivered getfem examples
are using a constant maximum allowed residuum, no matter of high deformation
So my question is, how am I able to
find the maximum allowed residuum and by what _expression_? And do I have
to define a variable maximum allowed residuum during the substeps to get
reliable results out of the solve command?