The aim of this study is to validate a fully non-linear finite-element model to simulate waves and wave-structure interactions. The Navier–Stokes equations are solved on an extended domain, which covers both fluid and structure. The latter is represented by a non-zero solid-concentration field, which is computed by conservatively mapping a mesh discretising the solid onto the extended mesh. In the regions of non-zero solid concentration, a penalty force is further added to the equations of motion in order to represent the effect of the structure on the fluid dynamics. The results are first shown for the interactions between a cylindrical pile and a regular train of small-amplitude gravity waves in a numerical wave tank. The pile is considered both as an immersed body and as a void in the fluid domain. In both cases, good overall agreement is obtained between the numerical and theoretical predictions of the free-surface elevation. The immersedbody approach however tends to underestimate the water elevation in the vicinity of the structure, due to additional dissipation induced by the body force. Second, the generation of focused wave events is considered. Preliminary results suggests that the present model is capable of modelling focused wave events propagating in the numerical wave tank. This is a first step towards modelling the interactions between pile and steep irregular waves.