cell skew for dynamic meshing
 

A case using dynamic mesh was set up. However, it's found that the cell skew kept increasing till stopping due to negative volume when I previewed mesh motion. I already set the maximum cell skewness to 0.8. Any idea to sort it out?

I had the same problem. Luckily, I was only playing around with fluent settings and didn't rely on the results...
What helped was to decrease the time step. But still, fluent just didn't seem to care about the "maximum skewness" settings and kept the distorted cells much above that value. I don't know why...