C N
Ansys Employee

Hello,

I recommend instead of UDF for overset meshes, it is recommended that the gaps between walls are resolved by a minimum of 4 cells, in order to create a valid overset interface and prevent the creation of orphan cells. You can specify that the cells in gaps with a resolution that is less than this recommendation are marked, so that any subsequent overset adaption (manual or automatic) increases the resolution to 4 or more cells.For further understanding kindly refer this link 

3.4. Overset Gap Adaption (ansys.com)

If your not able to access this link kindly refer to this link Using Help with links (ansys.com)

Thanks