Experimental and numerical analysis of multi-chamber oscillating water column devices

A review of multi-chamber oscillating water column(OWC)device designs is presented.Two significant variations of these devices are discussed,onshore OWC(OOWC)and a floating OWC(FOWC).The efficiency results of several theoretical studies based on low-and high-fidelity numerical models are presented and compared with the model scale results.Generally,low-fidelity numerical models are very fast to run,but their accuracy is limited compared with high-fidelity numerical models.Scaled model experiments usually give results much more accurate than numerical models,but they need adequate facilities and are very expensive.In the case of the OOWC,all models show a similar trend of total efficiency,but while the analytical model shows a maximum value of around 90%efficiency,the CFD model shows 60%,and the experiments only go up to 40%.The main reason is connected with the mathematical simplifications and assumptions that do not represent all the hydrodynamic and aerodynamic processes between the water,air,and structure.For the case of the FOWC,interestingly,the experimental results show a maximum efficiency of almost 100%,while the analytical model only predicts a maximum of 80%.The efficiency seems highly dependent on the heave motion resonance of the entire device,where the analytical model fails to predict this natural frequency.