refineMesh problem with erroneous grid
 

Hi,

I tried to use refineMesh for a 2D structured grid:

refineMesh -overwrite

to refine in all directions (x,y)

The grid size increases from 48000 to 192000. I tried to inspect the grid. Each cell is divided into 4 cells in most cases, which is correct. However, some cells divide into strange shape, as shown attached. Why is this so?

Black is the org, blue is the new mesh.

https://i.ibb.co/zsLrdNX/Capture.jpg

So how can I correct it?

Thanks!