Abstract
In this study, we investigated the hydrodynamic and energy conversion performance of a double-float wave energy converter (WEC) based on the linear theory of water waves. The generator power take-off (PTO) system is modeled as a combination of a linear viscous damping and a linear spring. Using the frequency domain method, the optimal damping coefficient of the generator PTO system is derived to achieve the optimal conversion efficiency (capture width ratio). Based on the potential flow theory and the higher-order boundary element method (HOBEM), we constructed a three-dimensional model of double-float WEC to study its hydrodynamic performance and response in the time domain. Only the heave motion of the two-body system is considered and a virtual function is introduced to decouple the motions of the floats. The energy conversion character of the double-float WEC is also evaluated. The investigation is carried out over a wide range of incident wave frequency. By analyzing the effects of the incident wave frequency, we derive the PTO’s damping coefficient for the double-float WEC’s capture width ratio and the relationships between the capture width ratio and the natural frequencies of the lower and upper floats. In addition, it is capable to modify the natural frequencies of the two floats by changing the stiffness coefficients of the PTO and mooring systems. We found that the natural frequencies of the device can directly influence the peak frequency of the capture width, which may provide an important reference for the design of WECs.
Highlights
Wave energy is an eco-friendly energy that attracts extensive research interest due to its broad global distribution and high energy density (Isaacs and Seymour 1973; Falnes 2007).Article Highlights The optimal power take-off (PTO) damping is analytically derived for a double-float wave energy converter (WEC) system. Through actively controlled generator damping, a double-float WEC achieves larger capture width ratio. Mooring stiffness is used to tune the natural frequency of the doublefloat WEC.Energy conversion in WECs is categorized into oscillating water column (OWC) and point absorber (Falcao 2010) types
The double-float WEC, which is in the point absorber category, has high conversion efficiency and simple construction, and has become a hot spot in the study of wave energy extraction
We investigate the influence of incident wave frequency, PTO damping coefficient, stiffness coefficient, and mooring stiffness coefficient on the motion response of the floats and the conversion efficiency
Summary
Wave energy is an eco-friendly energy that attracts extensive research interest due to its broad global distribution and high energy density (Isaacs and Seymour 1973; Falnes 2007). L. Zhang et al.: Oscillation and Conversion Performance of Double-Float Wave Energy Convertery and fixed-cylinder WECs using an analytical approach and determined the relationships between efficiency, the stiffness coefficient, and the geometry of a WEC, the relationship between efficiency and the natural frequencies of floats were not clearly explained. Zhang et al (2016) used an analytical method to study the relationship between the natural frequencies of floats and the conversion efficiency of the WEC, but focused on the effects of the damping plate, PTO stiffness coefficient, and mooring stiffness coefficient. Considering the PTO damping coefficient, stiffness coefficient, and mooring stiffness, we derive the optimal damping coefficient of the double-float WEC using the frequency domain method. We investigate the influence of incident wave frequency, PTO damping coefficient, stiffness coefficient, and mooring stiffness coefficient on the motion response of the floats and the conversion efficiency
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