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-   -   FSI - Specified Mesh Displacement (http://www.cfd-online.com/Forums/cfx/79675-fsi-specified-mesh-displacement.html)

Vinzent August 31, 2010 04:32

FSI - Specified Mesh Displacement
 
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Hello,

the mesh motion over the interface produces falted parts of the mesh. Therefore I tried to support the mesh motion manually by defining additional Specified Displacement of a subdomain with expressions, e.g. like this:

dy1=dyFin1*(y1Max-y)/(y1Max-y1Min)

with:
probe(Total Mesh Displacement Y )@Fin1
y1Max=maxVal(yGlobal)@REGION:DC1

You can see, the Specified Displacement depends on the mesh motion witch comes from the interface motion.
In the steady state case with very small disp.-relaxation (e.g. 0.01) it works a few stagger iterations, then error: negative element volumes, however in the last backuped mesh the displacements look right.

Is there a option to keep more then one backup files to see the history of the motion over the stagger iterations? Or better ideas?

On the solver monitor I found something conspicuous regarding the Mesh motion. On some monitor points it thakes a few iterations (about 5), some just one. You see this on the image1. Why? Is it possible to manipulate the value of mesh motion iterations? Could this be helpful for my problem?

Another question: In the transient case, MFX solver donīt want to deform any subdomains with the displacement expressions. Itīs like stationary without reference to the time step size. How is it possible anyway?

Image1: You see the values of displacements of two adjacent nodes (at the interface) of one element. Itīs not understandable, that in every stagger step one displacement is solved by and by over 5 iterations and the other jerky just over one iteration. Except for the coordinates, there is no difference between these two nodes.

Image2: This is the displacement of one node at the interface (MonXFin1) an the running after displacement ot the subomain (xMinDC1). The solution broke after solving the interface displacements before solving the subdomain displacements.

Thanks in advance!

Vinzent

Pavelko August 31, 2010 08:13

Hi !

I have to start learning FSI . Do you have any tutorials to suggest me ?
I just don't know where to begin...

Thanks in advance ,
Pavelko.

alialibas September 17, 2010 07:09

Hi,

I think, I faced the similar problem. i received a error like "folding mesh." And then it triggers the negative volume, so run is gonna down. Actually i am not so sure but i solved this problem with changing the mesh. Firstly i had a very small boundary layer meshes. i thought those meshes becoming folded. then i used triangle and a little bigger meshes. and then it is ok, it is running. but as i said, i am not sure it is true way or not :s


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