STL editing/modifying
 

Hi,

I'm having some trouble with my .STL file, and since I have not used softwares such as CATIA before, I don't really know what to do (despite reading all sorts of help files I can get my hands on). So here is the problem:

I am currently uploading two .STL surfaces; one flat surface that represents water and another (above the water) representing an island. The reason I upload them separately is so that I can specify different surfaces roughnesses in CFX-Pre. While I can generate a coarse structured mesh using the blocking method, there appear to be "negative volume errors" when I try to refine the mesh around the island. I believe this is due to the gap that exists between the island and water surfaces. (BTW I can generate an unstructured mesh, but this is not what I want to do).

I can of course import the island/water as one surface and create a very fine structured mesh without any issues, but then I cannot specify different roughness values..

Is there a method to somehow import the island/water as one surface with two distinct parts, such that they can somehow be differentiated? Can something like this be done in ANSYS or rather CATIA 5 or something similar?

Help is much appreciated!