Search

The unsteady aerodynamic characteristics and interference effects of floating offshore wind turbine (FOWT) are mainly affected by the pitch motion of the ocean platform. Based on computational fluid dynamics (CFD) and advanced overset grid technology, the aerodynamic performance and wake characteristics of a fully configured wind turbine with rotating blades, nacelle , and tower are studied in this paper. The effects of the amplitude and frequency of pitch motion on the wind turbine aerodynamic loads and flow field are investigated herein in detail. The power and thrust between numerical simulation and experiment are compared. The results show that the grid and simulation parameters used in this study can accurately capture the aerodynamic characteristics and the flow field around wind turbines. The influence of the pitch amplitude and frequency on the performance of wind turbines is discussed. The complex flow interaction between the tip vortex, tower shedding vortex, and the turbulent wake was observed. The present results indicate that the pitch motion amplitude and frequency have a great influence on the power, thrust, and wake characteristics. [ABSTRACT FROM AUTHOR]

A CFD numerical method is established under the wave-current condition, used to analyze the hydrodynamic performance of a horizontal-axis tidal turbine based on floating platform with rotation and pitching motion. The inflow direction load, pitch moment and power coefficients with different depths of the blade tip-immersion, the periods and amplitudes of the pitch, wave heights are obtained. The three coefficients have obvious periodically fluctuated with the pitching and wave frequencies, while the time mean of those have changed little with increasing of the depth of blade tip-immersion, wave height, pitch (wave) period and pitching amplitude. So considering damping and additional mass forces, a load fitting model is established, and the damping and additional mass coefficients are calculated by the least square method. The influence of damping coefficient on the hydrodynamic loads is obvious, while the influence of additional mass coefficient on that can be neglected, and the damping coefficient of inflow direction load coefficient is basically stable. The damping coefficients of the pitching moment and power coefficients fluctuate periodically, but the mean value of damping coefficients keep stable. The research results in this paper are important for studying the coupling motion of the turbine and the floating platform. [ABSTRACT FROM AUTHOR]

To improve the adaptability in variable wave conditions, a novel oscillating water column (OWC) wave energy converter (WEC)-bottom mounted breakwater integrated system is proposed, in which the front-wall constrained by a torsional spring can oscillate in the pitch mode. In this study, an analytical model based on the eigenfunction matching method and technique of variables separation is developed to investigate the hydrodynamic performance (including energy conversion and structural safety) of the proposed integrated system. Taking the air compressibility and linear Power Take-off (PTO) system into account, the effects of the front-wall width, draft and spring stiffness on the performance are discussed, respectively. It shows that the interaction between the pitch motion of the front-wall and the air-pressure oscillation significantly broaden the frequency bandwidth of energy conversion efficiency (i.e., capture width ratio, C w), in comparison with the traditional OWC device with the fixed front-wall. It is also found that those frequency points corresponding to the peaks of C w satisfy the condition that the real part of complex air volume flux which is induced by unit air-pressure oscillation inside the chamber, is equal to zero, after decoupling and eliminating the influence of front-wall motion. • Hydrodynamics of an OWC WEC-breakwater integrated system is theoretically investigated. • Hydrodynamic efficiency is considerably enhanced when front-wall freely pitches. • The smaller the front-wall width, the wider the high-performance frequency bandwidth. • The front-wall draft exist an optimal value for the proposed system with pitching front-wall. [ABSTRACT FROM AUTHOR]

The aerodynamic performance of floating offshore wind turbines is extremely complex due to the motions of the floating platform. The surge and pitch motions are the most influential motions among the six degrees-of-freedom motions. In view of this, the aim of this study is to investigate the unsteady aerodynamic characteristics of a floating offshore wind turbine under single (surge or pitch) and combined motions using computational fluid dynamics simulations, In addition, the coupling technique of dynamic mesh and sliding mesh is employed, as well as the unsteady Reynolds averaged Navier-Stokes method. The numerical simulation method in this paper is first validated by comparison to the results of the blade element momentum method and the vortex method. Then, the aerodynamic characteristics of the floating offshore wind turbine under harmonic platform motions with different periods and amplitudes are investigated. The results show that the increase of amplitude and frequency aggravate the fluctuation of the overall aerodynamic performance of the wind turbine. In addition, the combined surge-pitch motion reduces the average power generation indicating that complex platform motions adversely affect the power generation of floating offshore wind turbines. • The effects of wind load were analyzed by comparing the platform motions under different amplitudes and frequencies. • Two representative platform motions and the combined motion were considered for analysis. • Analyze the aerodynamic characteristics of different airfoil sections to reveal the variations of overall performance. • The detailed analysis of the wake effects showed the three-dimensional flow under the platform motions. [ABSTRACT FROM AUTHOR]