Dynamic mesh udf for oscillating wall
Dear forum users,
I'm working on a case involving flow in a rectangular channel (3D geometry) with the bottom wall oscillating in the normal direction according to a law of the form: dz0=amp*sin(omega*time). After reading the udf manual section on dynamic mesh, I browsed the threads for a while and I picked up a DEFINE_GRID_MOTION udf that I modified: Code:
#include "udf.h" Is it a problem with the code or the hooking ? I noticed when accessing /dynamic mesh/zones panel the availability of all the geometric entities (walls, inlet, outlet, default interior, fluid continuum entity) does this mean that all of the entities affected by the oscillation of the bottom wall needs to be explicitly set? In /dynamic mesh/zones there is cell height values to set. Could you, please, explain what it is exactly about? Help greatly appreciated, thanks in advance. best regards 
update
since I posted the issue, I decided to move to tet/tri elements, I meshed a new 3d rectangular channel using triangular elements with no boundary layer refinement (to get things simpler).
when I try to preview mesh motion under solve menu I get systematically negative volumes even contours cells volume show no negative value. help please here is a sample output from fluent TUI: Updating mesh to time 1.10000e02 (step = 00011)... Dynamic Mesh Statistics: Minimum Volume = 2.04203e11 Maximum Volume = 4.24008e10 Maximum Cell Skew = 8.75574e01 (cell zone 2) Maximum Face Skew = 5.45587e01 (face zone 5) done. Updating mesh to time 1.20000e02 (step = 00012)... Dynamic Mesh Statistics: Minimum Volume = 1.96455e11 Maximum Volume = 4.24008e10 Maximum Cell Skew = 9.49990e01 (cell zone 2) Maximum Face Skew = 6.84857e01 (face zone 5) done. Updating mesh to time 1.30000e02 (step = 00013)... Dynamic Mesh Statistics: Minimum Volume = 1.50486e11 Maximum Volume = 4.24008e10 Maximum Cell Skew = 9.89213e01 (cell zone 2) Warning: maximum cell skewness exceeds 0.95. Maximum Face Skew = 8.24055e01 (face zone 5) done. Updating mesh to time 1.40000e02 (step = 00014)... Dynamic Mesh Statistics: Minimum Volume = 8.05291e12 Maximum Volume = 4.24008e10 Maximum Cell Skew = 9.99583e01 (cell zone 2) Warning: maximum cell skewness exceeds 0.95. Maximum Face Skew = 9.35066e01 (face zone 5) done. Updating mesh to time 1.50000e02 (step = 00015)... WARNING: nonpositive volumes exist. Dynamic Mesh Statistics: Minimum Volume =3.28737e12 Maximum Volume = 4.24008e10 Maximum Cell Skew = 1.00113e+00 (cell zone 2) Warning: maximum cell skewness exceeds 0.95. Maximum Face Skew = 9.91551e01 (face zone 5) Warning: maximum face skewness exceeds 0.95. Warning: negative cell volume detected! Error: Update dynamic mesh failed. Negative cell volume detected. Error Object: #f 
1 Attachment(s)
Hi, I've attached the figure I'm getting after few steps of mesh preview. I don't know why the surfaces are shrinking and expanding at top and bottom. Can someone please help me with this.

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