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International audience; This paper studies wave influence on two horizontal axis tidal turbines from industrial partners : Sabella and Magallanes. The trials have been performed in a wave and current flume tank where upstream flow conditions have been monitored thanks to Laser Doppler Velocimetry. Mean velocity is computed withrotor disc integration of the velocity profile. Wave amplitude and orbital amplitude are computed thanks to least mean square method.A special attention has been paid to turbine immersion depth. Performance and blade root loads analysis highlight higher fluctuations when the turbine is close to the free surface.When a turbine is close to the free surface, the edgewise moment fluctuations can reach 100 % of the mean effort under combined wave and turbulence loading. Wave is responsible for half part of these fluctuations.; Dans ce papier est étudiée expérimentalement l’influence de la houle et du courant combinés sur le comportement de deux hydroliennes à axe horizontal pré-commerciales. Les essais sont réalisés dans un bassin à houle et courant où les conditions d’essais sont obtenues par vélocimétrie laser. La vitesse moyenne de l’écoulement est calculée par intégration sur le disque rotor. Les amplitudes de houle et les orbitales de vague sont déterminées par méthode des moindre carrés.Une attention particulière est apportée sur l’influence de la profondeur d’immersion des turbines. L’analyse des performances et des efforts sur les pales met en évidence une augmentation des fluctuations d’efforts avec la diminution de la profondeur.Le moment de mise en rotation en pied de pale sur une turbine subit des fluctuations allant jusqu’à 100 % de l’effort moyen sous l’effet de la houle et de la turbulence lorsque la turbine est proche de la surface libre. La houle est responsable de la moitié de cette fluctuation.

This paper describes a new methodology to map intertidal sediment using a commercially available unmanned aerial system (UAS). A fixed-wing UAS was flown with both thermal and multispectral cameras over three study sites comprising of sandy and muddy areas. Thermal signatures of sediment type were not observable in the recorded data and therefore only the multispectral results were used in the sediment classification. The multispectral camera consisted of a Red⁻Green⁻Blue (RGB) camera and four multispectral sensors covering the green, red, red edge and near-infrared bands. Statistically significant correlations (>99%) were noted between the multispectral reflectance and both moisture content and median grain size. The best correlation against median grain size was found with the near-infrared band. Three classification methodologies were tested to split the intertidal area into sand and mud: k-means clustering, artificial neural networks, and the random forest approach. Classification methodologies were tested with nine input subsets of the available data channels, including transforming the RGB colorspace to the Hue⁻Saturation⁻Value (HSV) colorspace. The classification approach that gave the best performance, based on the j-index, was when an artificial neural network was utilized with near-infrared reflectance and HSV color as input data. Classification performance ranged from good to excellent, with values of Youden’s j-index ranging from 0.6 to 0.97 depending on flight date and site.

Flow characteristics in coastal regions are strongly influenced by the topography of the seabed and understanding the fluid dynamics is necessary before installation of tidal stream turbines (TST). In this paper, the bathymetry of a potential TST deployment site is used in the development of the a CFD (Computational Fluid Dynamics) model. The steady state k-ϵ and transient Large Eddy Simulation (LES) turbulence methods are employed and compared. The simulations are conducted with a fixed representation of the ocean surface, i.e., a rigid lid representation. In the vicinity of Horse Rock a study of the pressure difference shows that the small change in height of the water column is negligible, providing confidence in the simulation results. The stream surface method employed to visualise the results has important inherent characteristics that can enhance the visual perception of complex flow structures. The results of all cases are compared with the flow data transect gathered by an Acoustic Doppler Current Profiler (ADCP). It has been understood that the k-ϵ method can predict the flow pattern relatively well near the main features of the domain and the LES model has the ability to simulate some important flow patterns caused by the bathymetry.

We present a new numerical treatment of the vorticity-velocity form of the governing \ud equations of fluid motion, based on the application of compact finite differences. The \ud mathematical formulation of these equations is discussed, as are the techniques used to \ud discretise them. The solver thus obtained is validated against analytical solutions to model \ud problems, and against the more physical test case of developing Tollmien-Schlichting waves \ud in a parallelised Blasius boundary layer.\ud We then use this solver to examine a reduced-order model of streaks in a turbulent \ud boundary layer. The properties of the streaks produced by the solver are discussed, \ud with a particular focus on the means of their generation.\ud Following this, we examine the use of spanwise oscillation of the wall, which is known \ud to reduce drag in turbulent boundary layers. The parameters of the oscillation (specifi­\ud cally its magnitude, its frequency and the phase difference between the wall motion and \ud the streak forcing) are altered and their influence on streak development investigated. It \ud is found that in certain cases, the modification to the basis flow by wall oscillation means \ud that the perturbations can grow exponentially. We also investigate the effects of altering \ud the pattern of oscillation from sinusoidal in time to a smoothed square wave or sawtooth \ud wave. Finally, the results are reviewed and conclusions drawn, and possible extensions to \ud the research presented in the thesis are suggested.