Home  Blog The “Constrained Displacement” Grid Deformation Feature
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The “Constrained Displacement” Grid Deformation Feature |
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When running Fluid Structure
Interaction (FSI) problems with CFD-ACE+ you may run into problems with
severe grid skewness in the fluid regions. While the CFD-ACE+
Stress module solves for the deformation of the grid for the solid
part, the CFD-ACE+ Grid Deformation module must determine how the grid
for the fluid regions is deformed. In order to perform this grid
deformation, the only "known" information is the fact that the
fluid/solid interfaces have moved. While
advanced logic is written into the grid deformation module, it cannot
cope
with deforming the volume grid for every type of grid system which
could
be presented.
The “Constrained Displacement” feature can be used to provide more
control over the grid deformation by making certain grid boundaries and
nodes follow the motion of other leader grid boundaries and nodes.
How does it work?
The concept is quite easy. There is a leader and a follower.
The leader is usually a boundary or a node that is being deformed
by the stress simulation. The follower is a boundary or node for which
you want to follow the leader's motion.
Implementation
The "Constrained Displacement" grid deformation feature is accessible
using the V2004 CFD-ACE-GUI. You will be in the General BC
setting mode and pick the "follower" boundary to get started.
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- Pick
the boundary condition that is to be the "follower".
- Go to
the Deform tab and change the subtype to "Constrained Displacement".
- Pick a
"leader" boundary condition name from the "Leader Name" list.
- Select
which node should be used as the actual leader
- minimum
displacement node - the node which moves the least on the leader
- maximum
displacement node - the node which moves the most on the leader
- select
node from list - select the exact node on the leader which you wish to
follow
- A
follower option is available to specify which direction you want to
follow (i.e., if you select x, only the x-displacement of the leader
will be followed but the y and z displacement will be as normally
calculated
by the grid deformation module)
- A
follower option is available to allow all nodes of the boundary to
follow, or only
selected nodes. (usually all nodes is desired)
Click on the image below to start an animation that shows this
feature in use. The deformation of the paddle is controlled by
the stress solution and without the use of the "Constrained
Displacement" feature the outer grid system would have no reason to
deform. With the use of this
feature we are able to make the outer grid system follow the motion of
the
paddle, therefore resulting in minimum skewness of the volume mesh.
If you
have
any questions about this feature or would like us to discuss some other
topic in the future, please let us know.
Regards,
Abhra Roy, Ph. D.
Senior Applications Engineer
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