  In this paper, we develop a novel phase-field model for fluid-structure
interaction (FSI), that is capable to handle very large deformations as well as
topology changes like contact of the solid to the domain boundary. The model is
based on a fully Eulerian description of the velocity field in both, the fluid
and the elastic domain. Viscous and elastic stresses in the Navier-Stokes
equations are restricted to the corresponding domains by multiplication with
their characteristic functions. To obtain the elastic stress, an additional
Oldroyd-B - like equation is solved. Thermodynamically consistent forces are
derived by energy variation. The convergence of the derived equations to the
traditional sharp interface formulation of fluid-structure interaction is shown
by matched asymptotic analysis. The model is evaluated in a challenging
benchmark scenario of an elastic body traversing a fluid channel. A comparison
to reference values from Arbitrary Lagrangian Eulerian (ALE) simulations shows
very good agreement. We highlight some distinct advantages of the new model,
like the avoidance of re-triangulations and the stable inclusion of surface
tension. Further, we demonstrate how simple it is to include contact dynamics
into the model, by simulating a ball bouncing off a wall. We extend this
scenario to include adhesion of the ball, which to our knowledge, cannot be
simulated with any other FSI model. While we have restricted simulations to
fluid-structure interaction, the model is capable to simulate any combination
of viscous fluids, visco-elastic fluids and elastic solids.
