  In this paper, we present a computationally efficient method for including
fluid-solid interactions into direct numerical simulations of the Navier-Stokes
equations. This method is found to be as powerful as our earlier formulation
[J. Comp. Phys., vol. 249: 243 (2015)], while outperforming the earlier method
in terms of computational efficiency. The performance and efficacy of the
presented method are demonstrated by computing contact angles of droplets at
equilibrium. Furthermore, we study the instability of films due to
destabilizing fluid-solid interactions, and discuss the influence of contact
angle and inertial effects on film breakup. In particular, direct simulation
results show an increase in the final characteristic length scales when
compared to the predictions of a linear stability analysis, suggesting
significant influence of nonlinear effects. Our results also show that emerging
length scales differ, depending on a number of physical dimensions considered.
