The paper is concerned with the use of the open source computational fluid dynamics software package, OpenFOAM® for predicting and analysing the behaviour of a semiimmersed horizontal cylinder subject to different types of ocean wave conditions. This study involves two separate cases of wave-structure interaction involving a semi-immersed horizontal cylinder, which may represent the simplified form of a cylindrical component of a wave energy converter. First, the flow around a fixed semi-immersed horizontal cylinder subject to regular waves is studied, in which the horizontal and vertical forces are computed and compared to linear wave theory and available experimental data. Further, a semiimmersed horizontal cylinder with a prescribed oscillatory vertical motion is considered to determine the surface wave elevations generated by the motion of the cylinder. The measured numerical surface elevations are also compared with theoretical predictions and experimental data. Both cases considered in this paper are simulated in a numerical wave tank where wave relaxation zones are utilised to avoid wave reflections. It is concluded that the numerical data produced by OpenFOAM® provide good overall agreement within the limitations of the relevant theory and experiment data.