  In this article, we present a new unified finite element method (UFEM) for
simulation of general Fluid-Structure interaction (FSI) which has the same
generality and robustness as monolithic methods but is significantly more
computationally efficient and easier to implement. Our proposed approach has
similarities with classical immersed finite element methods (IFEMs), by
approximating a single velocity and pressure field in the entire domain (i.e.
occupied by fluid and solid) on a single mesh, but differs by treating the
corrections due to the solid deformation on the left-hand side of the modified
fluid flow equations (i.e. implicitly). The method is described in detail,
followed by the presentation of multiple computational examples in order to
validate it across a wide range of fluid and solid parameters and interactions.
