Partially Immersed Surfaces

In FRED, a surface is defined as an interface between two materials. If you need to define a model where a surface is partially immersed, two surfaces - one that is immersed and one that is not - must be created. 

This is shown via the following example of a sphere (BK7) partially submerged in a block of "standard glass", all surrounded by air.

First, create a surface that represents the submerged portion, set to be an interface between BK7 and standard glass. Then, create another that represents the above portion. Assign this surface to be an interface between BK7 and air.

1. Create two copies of the original single-surface sphere.
2. If using element primitives (or lens objects), convert both to custom elements using the right-click menu.
3. On the Aperture tab for each surface, set the Surface Trimming Specification to be the top surface of the other object. In this case, select Block.Front Face. Make sure one of these settings includes the "NOT" operator. This setting trims the sphere at this plane removing the portion of the sphere that is above/below (depending on the use of the "NOT" operator and the surface orientation). The picture below shows the immersed surface after trimming.
   

   

4. Then, set the materials of each surface as you normally would.

Associated FRED file: Partially Immersed Surface Example