The hydrodynamic characteristics of a fixed Oscillating Water Column (OWC) device have been investigated using a finite volume method and compared with experimental and analytical results. The numerical model was set up using the open-source computational fluid dynamics toolbox OpenFOAM®. The solver is a finite volume method for two incompressible fluids (air and water), capturing the interface using a Volume-of Fluid (VOF) method. A series of numerical experiments on generic OWCs were conducted with a range of OWC geometries, including varying the width, front and back wall dimensions. Fourier analyses have been performed to aid the investigation into the frequencies present within the system. This knowledge is used to gain an understanding of the combined role of the natural and sloshing frequencies in tuning the wave energy device for optimal performance in a known wave climate. In this paper, the numerical model and investigation is presented for a fixed OWC and the results show good agreement with experiments, however the method will be extended in future work to develop the numerical methodology for a floating OWC.