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.

Prediction of regular wave loads on a fixed offshore oscillating water column-wave energy converter using CFD

In this paper,hydrodynamic wave loads on an offshore stationary-floating oscillating water column(OWC)are investigated via a 2D and 3D computational fluid dynamics(CFD)modeling based on the RANS equations and the VOF surface capturing scheme.The CFD model is validated against previous experiments for nonlinear regular wave interactions with a surface-piercing stationary barge.Following the validation stage,the numerical model is modified to consider the pneumatic damping effect,and an extensive campaign of numerical tests is carried out to study the wave-OWC interactions for different wave periods,wave heights and pneumatic damping factors.It is found that the horizontal wave force is usually larger than the vertical one.Also,there a direct relationship between the pneumatic and hydrodynamic vertical forces with a maximum vertical force almost at the device natural frequency,whereas the pneumatic damping has a little effect on the horizontal force.Additionally,simulating the turbine damping with an orifice plate induces higher vertical loads than utilizing a slot opening.Furthermore,3D modeling significantly escalates and declines the predicted hydrodynamic vertical and horizontal wave loads,respectively.