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Subject: Re: Ansys FSI nightmare
Author: Y Y Tan
Date: 2008-04-26 00:03:26
Hi again,
For the past couple of hours, i've ran another 5 simulations. One thing I
realize is that lowering the under-relaxation factor for the displacement from
Ansys cures the negative volume better than lowering the pseudo timestep or
incresing the mesh stiffness and increasing the mesh quality. However the bad
news is i'm still stuck. :(
Peter, the thing i want to validate the capability of Ansys in simulating the
FSI of a collapsible tube flow. I'm using the exact boundary conditions from
another paper to do this in Ansys and i'm only interested in the final result
since this is a steady solution anyway. I've tried solving the structural part
first but the thing is if I solve the structural part first, the external
pressure would cause the pipe to buckle so much that it will prevent any fluid
from flowing through and the analysis would just crash.
I really think that the problem now is with my Solsh190, I've been reading alot
about hourglassing and volumetric locking. I'm very confused about this. In
Ansys, I could only set the keyopt to change between using a pure displacement
formulation or a mixed u-p formulation. However as i'm working on Workbench,
the only option I can change is the brick integration scheme which is either
full or reduced. Does full means mixed u-p and reduced means pure displacement?
or its a completely different thing. So please can someone tell me when error
message is element turning inside out, does it mean its hourglassing or there's
volumetric locking because I don't know how to explain the shape of the
element. Anyway how do I specify a mixed u-p formulation for solsh190 in
workbench?
Anyway does anyone know how to use shell 181 in workbench? I could only get the
mesher to mesh shell 181 when I import a surface body and when I do that, there
seems to be only 1 face and I cant specify if my loadings are on which side of
the face.
Peter, its not a fun problem. :( ... I have not been able to sleep properly for
the past few months.
Fern, I really wish my supervisor understands what i'm facing but the thing is,
people would only think of this problem as a fluid flowing through an elastic
pipe..how difficult can this be compared to people who are modelling flow past
an airplane or stuff like that. I have tried to talk to my supervisor before
but she can't help me and she wouldn't allow me to change the way I approach my
project. Everytime I tell her that my project is difficult, she'll just think
that i'm lazy and i'm not trying hard enough. Anyway what u suggested cant be
done as I've already mention it earlier but thank you so so much.
Regards,
Tan Yi Yong
The University of Sheffield
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