Consider an assembly consisting of several hollow spheres glued together. The *Mass Properties* function provides the volume of all space confined by part boundaries; the sum of all spherical shells. Since the internal void of each spherical shell is entirely captive, when the assembly is immersed in a fluid, it will displace a volume equal to the volume confined by the *outer* surface of each sphere.

The number and geometry of spheres will change frequently. We require a simple workflow to compute the volume of fluid displaced by the assembly.

What is the best approach here?

Maybe I'm not understanding your problem but the volume displaced will be equal to the volume of the sum of the volume of the spheres. Regardless of shape, qty etc the volume displaced will be equal to the volume of the object displacing it. Archimedes in the bathtub thingy.

Edit to Add: Now that I read this again you want to figure the total volume but can't because the shell issue. Can you do two configurations? Shelled and not shelled? The unshelled version would give you the total volume and that would be total volume displaced.