  We present a Pressure-Oscillation-Free projection algorithm for
large-density-ratio multiphase fluid-structure interaction simulations,
implemented on a non-staggered Cartesian grid. The incompressible Navier-Stokes
is decoupled with an improved five-step incremental pressure correction
algorithm. Fluid-fluid interface is captured using the Cahn-Hilliard equation,
and the surface tension model is coupled with a momentum-weighted interpolation
scheme to suppress unphysical pressure oscillations, ensuring accurate
evolution of multiphase interfaces. Interaction at the fluid-structure
interface is obtained by implicitly solving for the feedback acceleration in
the Eulerian-Lagrangian system. For validation of the present method, the
comparison studies for Pressure-Oscillation-Free effect are systematically
conducted using lid driving cavity and droplet deformation cases. Moreover,
several challenging multiphase simulations are implemented and discussed. As a
demonstrating example of fluid-structure interaction, a rising bubble bypassing
an obstacle is tested.
