Hi, Will
Thank you so much for your comments.
I study linear and non-linear Cosserat models using comsol. This is
highly nonlinear problem which engages the displacements as well as
the microrotations. As a matter of fact, I have a highly nonlinear
problem including coupling (microrotations and displacements).
According to the mathematical point of view, I know that the problem
has a unique solution and it is stable. So, I know perfectly what I
will obtain (The mathematical issue is completely treated).
I have verified all possibilities that you mentioned in your message.
I found out that the problem comes from boundary conditions (case
NO.3). For example, I apply a torque to the cylinderical bar and I
verify the calculated torque using comsol by boundary integration
(postprocessing). They are not the same!!!! The problem becomes worse
when I increase the torque value.
Would you please explain me about the modifications on the BCs? Should
I use Non-ideal or User-defined "Constrf"?
Best regards and thanks again
Hamidreza
Post by zimmerman_wbjHi Hamidreza,
You question is so open ended, that I thought it would engender no
(1) My usual experience with unwanted solutions is with highly
nonlinear problems which converge to solutions that did not match my
preconceptions of where the "real" solution is. I usually use the
parametric solver to "step along" the nonlinearity parameter to find
the bifurcation point.
(2) The other type of unwanted solution I get appears when the
boundary conditions are too prescriptive and kill off the desired by
say enforcing a symmetry.
(3) If I were to conjecture what type of "weak form and unwanted
solutions" you might have, my guess would be that coupling in your
boundary conditions does not get expressed. It is one of the age old
difficulties with Comsol and its predecessor femlab that coupling of
variables / modes in the subdomain settings is easy, but coupling in
the BCs is hard -- you have to explicitly "active" the coupling by
specifying weak boundary constraints are to be used.
The major complaint that users usually have is "singular matrix",
which can be caused by just about any conceptual or coding error.
Yours, unwanted solutions, is probably the exact opposite!
Regards,
Will
Post by Hamidreza Adib-RamezaniIHi,
Have anybody an experience about unwanted solutions using weak form?
Hamidreza