which model should I use?

Hi folks, I am needing your advice so badly.

I am trying to model a inverted cup (bottom up, open down） submerged in water, there is still some air in the cup gathered at the bottom of the cup (actually on the top, because the cup is inverted), if more air is inflated through a pipe, how can I model this process?

I am planing to use the following two modules:
1. "Fluid flow/ Multiphase flow/ Two-phase flow, level set" to model the air-water interface and relative motion.
2."fluid-structure interaction" to model the interaction between the fluid (water and air) and the cup structure.

Do you think it is reasonable? or some advice?

thank you.