Please, when I run "Preview" in "Mesh Motion" option, I get the following message:

Updating mesh to time 2.00000e-06 (step = 00001)... Warning: negative volume detected --> repeat smoothing! Warning: negative volume detected --> repeat smoothing! Warning: negative volume detected --> repeat smoothing!

WARNING: non-positive volumes exist.

Dynamic Mesh Statistics: Minimum Volume =-1.42514e-006 Maximum Volume =3.04689e-007 Maximum Cell Skew =1.89024e+000 (cell zone 3) Warning: maximum cell skewness exceeds 0.95. Warning: negative cell volume detected! Error: Update dynamic mesh failed. Negative cell volume detected. Error Object: ()

What should I do?

My other question is: What is the definition of "Length Scale", I need to know it to fill "Minimum Length Scale" and "Maximum Length Scale" in "Dynamic Mesh Parameters"

Thanks

Arturo

Minimum/maximum length scales are the min/max lengths of the cell that you want to constrain. When you have moving objects and a dynamic mesh the cells often have to be re-meshed so they don't:

(1) squish up until they become 0 volume (and then 'negative volume' like you see)

or

(2) stretch out for ages, which can also cause the mesh to fail in certain circumstances

Check that the fluid zone and walls which are moving are defined as dynamic zones, and that you have smoothing and/or remeshing turned on for those dynamic zones (and that the minimum/maximum length scales are put in).

Andy

As for as dynamic mesh is concenred, u have to have mention the min scale and max. scale of the mesh and u have specify the skewness of the mesh too.. Because when u use the dynamic mesh problems, the fluent has to update the mesh automatically by remeshing option by the above parameters, suppose if u r not mentioning it correctly means it will show an error called negative volume detected.. So for proper input u click the mesh info panel, in that u can see ur mesh min scale and max scale.. Better u use that values and try it.... It will work out.. Bye.......