Problem with an obstacle in format stl
 

DEAR EXPERTS

I am trying to simulate a weir in a channel, I prepare the STL form and I put it in the channel, but I was surprised by the resultas as the pictures shows, the barrier was crossed by the flow as if it does not exist, although it is imported as a solid, standard

The mesh is not fine enough to resolve that thin .stl. There needs to be at least 2 (preferably 3 - 4) cells across the cross-section of all solids.

thanks for explaining
I drew the STL file with Autocad and I import directly as STL file format, the mesh that I can change is the Block, I do not know how to change the mesh STL?

THANKS

plz clarify your question. what exactly do you want to do?