Oscillating Water Columns (OWCs) are some of the most-studied wave energy converters (WECs). Previous work showed that the geometric characteristics of the OWC can play a significant role in the efficiency of the device. In this study, we investigate the behaviour of different designs of OWC making geometric modifications to the classic design of OWC and the U-OWC, initially suggested by Boccotti [1]. The multi-chamber OWCs examined here are fixed on the seabed and have a slit opening at the seaward side. The physical modelling was undertaken in the COAST laboratory of the University of Plymouth. The devices were tested in regular and irregular wave conditions, with and without power take-off (PTO) mechanism, essentially also testing absorbing seawalls.The aim of the study is to present a preliminary comparison related to the geometry of OWCs under some typical wave conditions and suggest potential shape improvements towards an overall optimization of the devices that takes into account both the hydrodynamic efficiency of the OWC and other design aspects, such as the wave run-up. The present study also endeavours to highlight potential benefits from incorporating OWCs in coastal defence as absorbing seawalls.

Various studies investigated the behaviour and the performance of Oscillating Water Columns (OWCs) suggesting many alternative design concepts to improve the efficiency of the device. The OWCs examined here are fixed on the seabed and have a slit opening at the seaward side. The present study investigates the applicability of a multiphase Reynolds Averaged Navier-Stokes (RANS) numerical model for simulating the interaction between an OWC and regular and irregular waves. An initial validation of the open-source computational fluid dynamics (CFD) software package OpenFOAM with the wave generation and absorption toolbox waves2Foam is performed against experimental results obtained at the COAST laboratory of the University of Plymouth. The main aim of the study is to complement to the validation of RANS CFD models and later employ the broadly used numerical tool for further studies for better understanding the behaviour of the OWCs. A method based on mechanical damped oscillations for calculating the eigenfrequency of the device from a decay test is presented and compared with the performance curve. The strength of CFD modelling for obtaining better insight to the hydrodynamics of OWCs is also demonstrated.

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