Hi all,

I have a circular domain with quad mesh. I am using dynamic mesh smoothing parameter with a special command to enable smoothing for quad and all type of shapes. When I view the mesh, it says negative volume detected. I have tried varying the parameters but to no avail. I have a very fine mesh near my wall. Could someone help me here?

Sham.

Hi Sham. I use dynamic mesh smoothing on a fine quad mesh. Make sure the spring constant factor is 0. Also split the boundary movement in to maybe 10 small steps instead of one and then move the mesh ten times instead of one. The small steps mean the algorithm has less work to do and hence converges better without making bad cells.

Giles,

Thanks for your reply. What do you mean by

"Also split the boundary movement in to maybe 10 small steps instead of one and then move the mesh ten times instead of one "

I have not run the model yet, just trying to view the mesh motion in solve>mesh motion. Hope you can enlighten.

Sham.

Sorry if my response wasnt clear.

Suppose you have a boundary node which you want to move from y=0 to y=10. Then you could create a UDF which moves the node as y=y+10 and using one mesh motion it will move from y=0 to y=10. This could be a very large step for the mesh to move. Instead you could use y=y+1 and apply the mesh motion command ten times, which would create the same final deformation in many small steps.

I have succesfully used this to stop boundary layer cells collapsing under spring smoothing on the trailing edge of an airfoil.

Thanks a lot Giles for your resposnse. I really appreciate it. I have a cylinder that moves up and down meaning say from y=0 to y=0.1 back to y=0 then y=-0.1 and repeat the same cycle. If I got you right, you mean that we have to change the UDF? My motion is defined by vel[1] = A*OM*cos(OM*time) where A is amplitude and OM is frequency. Hope you can help here.

Once again thanks Giles.