Hydrodynamic Performance of An Integrated System of Breakwater and A Multi-Chamber OWC Wave Energy Converter

A multi-chamber oscillating water column wave energy converter(OWC-WEC)integrated to a breakwater is investigated.The hydrodynamic characteristics of the device are analyzed using an analytical model based on the linear potential flow theory.A pneumatic model is employed to investigate the relationship between the air mass flux in the chamber and the turbine characteristics.The effects of chamber width,wall draft and wall thickness on the hydrodynamic performance of a dual-chamber OWC-WEC are investigated.The results demonstrate that the device,with a smaller front wall draft and a wider rear chamber exhibits a broader effective frequency bandwidth.The device with a chamber-width-ratio of 1:3 performs better in terms of power absorption.Additionally,results from the analysis of a triplechamber OWC-WEC demonstrate that reducing the front chamber width and increasing the rearward chamber width can improve the total performance of the device.Increasing the number of chambers from 1 to 2 or 3 can widen the effective frequency bandwidth.

Experimental Investigation of the Small-scale Fixed Multi-chamber OWC Device

Sea wave energy generators or converters(WECs)have the potential to become a viable technology for clean,renewable energy production.Among the WEC technologies,the oscillating water columns(OWCs)are the most common WEC devices studied.These have been studied and developed over many years.Multi-chamber oscillating water columns(MC-OWC)have the potential to have a higher energy conversion when extracting energy in mixed sea states than single-chamber devices.In the work reported in this paper,physical experiments are carried under regular wave conditions to test the wave power extraction of a fixed MC-OWC small-scale model.The Power Take-Off(PTO)of the device is simulated using orifice plates.The flow characteristics through these orifices are pre-calibrated such that the extracted power can be obtained only using the pressure measurement.Wave condition effects on the damping of the PTO of the device power extraction are addressed.The test results illustrate that the PTO system damping is critical and affects device performance.

Iterative analytical solution for wave reflection by a multichamber partially perforated caisson breakwater

This study examines wave reflection by a multi-chamber partially perforated caisson breakwater based on potential theory.A quadratic pressure drop boundary condition at perforated walls is adopted,which can well consider the effect of wave height on the wave dissipation by perforated walls.The matched eigenfunction expansions with iterative calculations are applied to develop an analytical solution for the present problem.The convergences of both the iterative calculations and the series solution itself are confirmed to be satisfactory.The calculation results of the present analytical solution are in excellent agreement with the numerical results of a multi-domain boundary element solution.Also,the predictions by the present solution are in reasonable agreement with experimental data in literature.Major factors that affect the reflection coefficient of the perforated caisson breakwater are examined by calculation examples.The analysis results show that the multi-chamber perforated caisson breakwater has a better wave energy dissipation function(lower reflection coefficient)than the single-chamber type over a broad range of wave frequency and may perform better if the perforated walls have larger porosities.When the porosities of the perforated walls decrease along the incident wave direction,the perforated caisson breakwater can achieve a lower reflection coefficient.The present analytical solution is simple and reliable,and it can be used as an efficient tool for analyzing the hydrodynamic performance of perforated breakwaters in preliminary engineering design.

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.