ESI Group CFD Portal - The “Constrained Displacement” Grid Deformation Feature

Resources

Request Support

Community Forums

Model Library/Tutorials

CFD Paper Library

Tips and Tricks

ESI CFD FAQ

Customer Login

Home

CFD-ACE+ User Tips

The “Constrained Displacement” Grid Deformation Feature

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.

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

How to Specify Multiple Sinusoidal Voltages in One Electrode of a CCP Reactor

In many industrial Capacitively Coupled Plasma (CCP) reactors, multiple sinusoidal frequencies (in most of the cases dual frequency) are applied to one of the capacitor electrodes.

Using Cyclic Boundaries in CFD-ACE+

There are many applications that involve rotating mechanical components that result in rotational or circumferential symmetric flows. One can model an entire 3D rotating system, but the computational resources to do so can be quite large.

Turbulence Solution on a Volume-by-Volume basis

A new option has been added to CFD-ACE+ in version 2007.2 that will allow the user to solve turbulence on a zone by zone basis, i.e. some zones can be specified as laminar while others are specified as turbulent. This is available for use with all turbulence models in CFD-ACE+.

The First User Subroutine is the Hardest

Many users are interested in using user subroutines to set special boundary conditions, do problem-specific post-processing, or try things that are not supported either by the GUI or the solver itself.