Hydrodynamic Study on Energy Capturing Performance of Horizontal Axis Blades Under Sub-Low Speed Tidal Current

The research on the hydrodynamics of blades is mainly focused on sea areas with high-speed current.However,the average velocity in most territorial waters of China is smaller than 1 m/s,and the lift type of airfoil blades has limited application in most of these conditions.Therefore,it is of great significance to study the tidal current energy capture of blades in sub-low speed sea areas.The effect of flow impact resistance on the blade at sub-low current speed is considered and a new type of thin-walled blade based on the lift type of blade is proposed,and then the lift-impact combined hydrodynamic model of horizontal axis blade is established.Based on this model,and considering the characteristics of tidal current and velocity in the sea area of Yushan Islands,simulation and optimization of blade design are carried out.Additionally,the horizontal axis thin-walled blade and the NACA airfoil contrast blade under the same conditions are developed.By using a synthetical experimental test system,the power,torque,rotational speed and load characteristics of these two blades are tested.The performance of the thin-walled blade and the design theory are verified.It shows that this type of blade has much better energy capture efficiency in the sub-low speed sea area.This research will promote the study and development of turbines that can be used in low-speed current sea areas in the future.

Experimental Research on A New Type of Floating Breakwater for Wave-Absorbing and Energy-Capturing

To avoid the damage caused by big wind and wave in cage culture, and to solve the problem of energy supply faced by automatic breeding equipment, a new type of floating breakwater, named as Savonius double buoy breakwater(SDBB), is proposed in the paper. The floating breakwater is composed of HDPE cylindrical double buoys and horizontal axis Savonius rotors, and has the functions of wave-absorbing and energy-capturing. Based on the linear wave theory and energy conservation law, the Fourier Transform was applied to separate the two-dimensional wave frequency domain, and the energy captured by the rotors and absorbed by the floating breakwater were calculated.Experiments were conducted in a two-dimensional wave-making flume, and the transmitted waves at different wave heights and periods, the tension of mooring lines, and the rotational torque exerted on the Savonius rotor were measured. A series of performance comparison tests were also performed on the new floating breakwater and the traditional double-floating breakwater. Results show that the new floating breakwater is better than the traditional one in terms of reducing wave transmittance, and the combination of the floating breakwater with Savonius rotors can provide for marine aquaculture equipments with green power supply to a certain degree of self-sufficiency.

Study on Performance of Savonius Rotor Type Wave Energy Converter Used in Conjunction with Floating Breakwater

In the present study,the performance characteristics of a Savonius rotor type wave energy converter used in conjunction with a conventional double-buoy floating breakwater is investigated using physical model studies.The Savonius rotor type converter is suspended under the double-buoy floating breakwater to achieve wave attenuation while generating electricity,thereby enhancing the overall wave-elimination effect of the combination.The Savonius rotor is tested with different water submergence depths,and a reasonable relative submergence depth is determined within the scope of the research parameters.The hydrodynamics and energy capture performance of the combined breakwater with four different sizes of Savonius rotor under different wave conditions are studied,and the transmission coefficient of the experimental device is analyzed.The results show that when the optimal relative submergence depth is 0.65D,where D is the impeller diameter,there is a correspondence between the optimal performance of Savonius rotor with different rotor sizes and the wave period and wave height.The optimal energy capture efficiency of the wave energy converter reaches 17%−20.5%,and the transmission coefficient is reduced by 35%−45%compared with the conventional double-buoy breakwater.

Robust nonlinear control strategy to maximize energy capture in a variable speed wind turbine with an internal induction generator

This paper proposes a control strategy to maximize the wind energy captured in a variable speed wind turbine, with an internal induction generator, at low to medium wind speeds. The proposed strategy controls the tipspeed ratio, via the rotor angular speed, to an optimum point at which the efficiency constant （or power coefficient） is maximum for a particular blade pitch angle and wind speed. This control method allows for aerodynan^c rotor power maximization without exact wind turbine model knowledge. Representative numerical results demonstrate that the wind turbine can be controlled to achieve near maximum energy capture.