Study Of Hydrodynamic And Energy Conversion Characteristics Of Piled U-OWC Device Under Wave Action

In recent years,more and more scholars have started to research on the development and utilization of renewable energy.Among many renewable energy sources,ocean energy has high utilization value because it is widely distributed and does not occupy land area,and among many ocean energy sources,wave energy deserves key attention because of its wide distribution,high energy density,long development and utilization cycle,and predictability.Among the wave energy power generation devices currently studied in the academia,the OWC(Oscillating Water Column)power generation device has received a lot of attention from scholars because of its simple structure,high reliability,PTO(Power take-off Model)no direct contact with seawater,and not easy to corrode.The piled U-OWC(U-shaped Oscillating Water Column)device studied in this paper is an improvement on the traditional OWCdevice,which can achieve better efficiency in a wider frequency range than the traditional OWC device,and can adapt to different wave conditions,and the development and use cost is lower than the traditional OWC device,so it has high research value.In this paper,the variation of air chamber top plate opening size is used in the wave flume experiment to simulate the piled U-OWC device with different PTO damping,and the effect of the change of different experimental conditions such as PTO damping,wave elements,and water depth on the quadratic loss coefficient,gas chamber transducer characteristics of the device,and energy conversion characteristics of the piled U-OWC device is analyzed.After that,a 3D numerical model of the piled U-OWC device is developed based on the 3D incompressible N-S equation using the two-.phase flow solver Waves2Foam from the OpenFOAM open source package,and the feasibility of the numerical model is verified by the experimental data of the physical model.The variation law of the wave loading and overturning moment acting on the device is discussed.The experimental results from the wave flume show that the piled U-OWC device can achieve better wave energy extraction efficiency in a wider frequency range compared with the piled OWC device.In the study of piled U-OWC device,it was found that the energy extraction efficiency of the device peaked when the incident wave frequency was close to the intrinsic frequency of the piled U-OWC device;the energy extraction efficiency of the piled U-OWC device is sensitive to the PTO damping of the device,and the energy extraction efficiency shows a trend of increasing and then decreasing with the increase of the PTO damping,and the best PTO damping corresponds to a gas chamber opening rate of 11.4%;when analyzing the wave height on the energy extraction efficiency of the device,it is known that the wave energy extraction power of the device increases with the increase of the wave height and when analyzing the wave height on the energy extraction efficiency of the device,it can be seen that the wave energy extraction power of the device increases gradually with the increase of the wave height,and the energy conversion power at large wave height can be several times of that at small wave height,but the capture width ratio of the device at large wave height is smaller than that at small wave height;when studying the effect of water depth on the energy extraction efficiency of the device,it is found that the energy extraction efficiency of the device has a greater effect when the water depth is too small.From the numerical simulation results,it can be seen that the flow field in the piled U-OWC device shows a reciprocal change with the change of liquid level in the gas chamber of the device,and the peak value of the clockwise vortex pole vortex extremes in the flow field is higher than the peak value of the clockwise vortex pole vortex extremes,and the flow field in the device is most violent when the liquid level in the gas chamber moves to the vicinity of the static water level;analyzing the flow field change in the device at different incident wave frequencies,it is found that the flow field change in the device is more violent when the frequency of the incident wave is close to the inherent frequency of the device,and the extreme value of the vortex vorticity in the flow field is larger;analyzing the change of the flow field in the device at different incident wave heights,it is found that with the gradual increase of the incident wave height,the violent degree of the flow field in the device and the extreme value of the vortex vorticity in the flow field gradually increase.Finally,the variation of wave loading acting on the device is analyzed,and it is found that the peak wave force and wave overturning moment at the positive peak of vertical force(vertically upward)are larger,which will cause higher risk of slip and overturning instability,and then the dimensionless analysis of the force and moment acting on the piled U-OWC device is performed,and it is found that the force and overturning moment on the device increase simultaneously when the wave height increases,which is related to the wave climbing on piled U-OWC device.