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A tip winglet can reduce the induced drag and the load fluctuation of a blade, considerably improving the hydrodynamic performance of a tidal turbine. Up to now, there are fewer studies on the unsteady effects of winglets, which limits the application of this design scheme. In this paper, a tidal turbine model is established based on computational fluid dynamics (CFD) and verified by a flume experiment. Then, unsteady effects on the turbine blade are analyzed considering different winglet lengths and cant angles. According to the study, the blade performance is optimal when the winglet cant angle is 45°, with about 11% efficiency improvement and about 8% increase in axial force; as the winglet length increases, the performance tends to further improve. In addition, this study demonstrates that the reason why a winglet can reduce blade load fluctuations is that the winglet takes the tip vortex generation position away from the blade rotation plane, instead of reducing the tip vortex intensity. [ABSTRACT FROM AUTHOR]

In this paper, an exploratory data analysis method is employed to investigate the impact of different system parameter combinations on the magnitude and stability of power of flow-induced vibration (FIV). Firstly, orthogonal experimental design within exploratory data analysis is used to set up numerical simulations of flow-induced vibration and collect data on FIV power generation characteristics. Then range method is used to select the optimal parameters combination for flow-induced vibration power generation, and the degree of influence of different system parameters on power and stability is quantitatively described by variance and entropy weight methods. Our results reveal that the optimal parameter combination for power corresponds to m* = 1.343, K = 1200 and ζ = 0.08, and the optimal parameter combination for stability is m* = 1.343, K = 1200 and ζ = 0.04. Additionally, the weight relationship of each system parameter affecting power and stability is W K > W ζ > W m* and W ζ > W m* > W K , respectively. These weight relationships allow for the effective adjustment of the parameter levels to quickly achieve the goal of optimizing power and stability. A new parameter P value-stability is proposed to comprehensively evaluate power magnitude and power stability, and optimal parameter combinations in different vibration branches is achieved. This paper provides new ideas and guidance for the design of the FIV energy harvesting device. [ABSTRACT FROM AUTHOR]

Abstract: The progress in wave energy technologies in China during the past decade is briefly reviewed. And the description is focused on the wave energy resource and the current status of wave energy in China. The difficulties facing wave energy developments in China are summarized. The national policy of wave energy developments is outlined and perspectives of wave energy in China are discussed. [Copyright &y& Elsevier]

Wind turbines in an offshore wind farm are usually allocated in a restricted area, which will result in wake interactions for downstream turbines. In order to mitigate wake effects on power and loads, wake redirection control (WRC) has been proposed to steer wake away from downstream turbines by intentionally yawing the upstream ones. However, wake interactions in combination with yaw-misalignment would produce complex structural loading behaviours, which should be carefully evaluated in control design. In this respect, priori knowledge on fatigue load contribution from wake and yaw-offset could be beneficial for multi-objective control optimisation and its real-time implementation. Therefore, we aim to quantitatively evaluate both yaw-offset and wake induced fatigue loads on offshore wind turbines in this work. More specifically, a numerical turbulent wind-field generator is established by including the wake deficit modelling feature, so that aero-elastic simulation with parametrically controlled wake inflow becomes possible. Then, aero-elastic simulations covering a wide range of waked inflow and yaw-offset conditions are performed, establishing a comprehensive database for tower and blade damage equivalent loads, where different load trends can be observed. In addition, a load assessment model is established by polynomial regression, and correlation analysis results indicate the dominant factors on fatigue loads are wind velocity and turbulence intensity. Besides, yaw-offset is more important than wakes for rated conditions, and vice versa for below and above-rated conditions. Moreover, wind tunnel results have also shown generally consistent trends with model predictions. The established load database and regression model could be used as the load indicator for future design optimisation of wind farm WRC. [Display omitted] [ABSTRACT FROM AUTHOR]

The integration of wave energy converters (WEC) into floating offshore wind turbines (FOWT) is regarded as a promising approach for comprehensively harnessing deep-sea energy and reducing the levelized cost of energy. This study aims to investigate the WEC power take-off (PTO) control effects on the dynamic performance of a floating wind-wave combined system, wherein three heaving-type WECs are integrated into a semi-submersible FOWT. In particular, the hydraulic PTO is modelled as a Coulomb damping system to enable a more realistic analysis. The aero-hydro-servo-elastic-mooring coupled numerical simulations and 1:50 wave basin experimental data demonstrate good agreement. It is observed that wave power production varies significantly with different control settings, potentially reaching 24.0 % of the overall hybrid energy production with proper control parameters. Furthermore, platform pitch oscillation generally shows a decreasing trend with increasing damping forces under below-rated and rated conditions, while showing minimal influence when above-rated. Conversely, tower base damage equivalent load (DEL) tends to initially decrease and subsequently increase across all examined conditions. This consistent convexity indicates the potential use of DEL as a performance index for optimising PTO control. In summary, power increment, motion reduction, and load mitigation could be achieved concurrently with appropriate control design. For instance, an extra 0.48 MW wave power could be produced under the rated condition, while a 10.4 % reduction in tower base DEL and a 6.57 % mitigation in platform pitch oscillation could also be achieved at the same time. [ABSTRACT FROM AUTHOR]