Answer:
The easiest way, of course, would be to insert an opening for the area that should be reinforced, and to include this opening in a thicker surface again (surface thickness + reinforcement thickness). To do this, proceed as follows:
1. First, create all boundary lines (Image 01).
2. Create the first surface with external boundary lines, if this does not already exist (Image 02).
3. Create an opening where the inner surface will be located later (Image 03).
4. Create the inner surface (Image 04).
5. If necessary, create further openings within the inner surface (Image 05).
However, this modeling does not consider the contact between the surface and the reinforcement (possible failure at tension). A consideration closer to reality would be, for example, using contact solids, but this modeling would be more time-consuming, depending on the model. However, this provides more accurate results. For this, you can find a link to the article about modeling contact solids below.
