Model and method to predict the turbulent kinetic energy induced by tidal currents, application to the wave-induced turbulence

A prediction model for the turbulent kinetic energy (TKE) induced by tidal-currents is proposed as a function of the barotropic velocity only, along with a robust method evaluating the different parameters involved using Acoustic Doppler Current Profiler (ADCP) measurements from Alderney Race. We find that the model is able to reproduce correctly the TKE profiles with coefficients of correlation on average higher than 0.90 and normalised root-mean-square errors (NRMSE) less than 14%. Different profiles are also tested for the mean velocity, no satisfactory prediction model is found but we are able to have decent estimates of the velocity shear and friction velocity. Two applications are then carried out. First the turbulent budget terms are estimated and discussed. We identify the turbulent production and dissipation of TKE as the most important mechanisms, then we discuss the validity of several theoretical results derived for isotropic turbulence for this application. A strong departure for the estimation of the turbulent dissipation is notably found and explained by the turbulent anisotropy. At last the prediction model for the TKE is used to infer the wave-induced TKE. We show the importance of removing the tidal component, waves can have a strong influence down to mid-depth

Confirmation of beach accretion by grain-size trend analysis: Camposoto beach, Cádiz, SW Spain

An application of the grain size trend analysis (GSTA) is used in an exploratory approach to characterize sediment transport on Camposoto beach (Cádiz, SW Spain). In May 2009 the mesotidal beach showed a well-developed swash bar on the upper foreshore, which was associated with fair-weather conditions prevailing just before and during the field survey. The results were tested by means of an autocorrelation statistical test (index I of Moran). Two sedimentological trends were recognized, i.e. development towards finer, better sorted and more negatively skewed sediment (FB–), and towards finer, better sorted and less negatively or more positively skewed sediment (FB+). Both vector fields were compared with results obtained from more classical approaches (sand tracers, microtopography and current measurements). This revealed that both trends can be considered as realistic, the FB+ trend being identified for the first time in a beach environment. The data demonstrate that, on the well-developed swash bar, sediment transported onshore becomes both finer and better sorted towards the coast. On the lower foreshore, which exhibits a steeper slope produced by breaking waves, the higherenergy processes winnow out finer particles and thereby produce negatively skewed grain-size distributions. The upper foreshore, which has a flatter and smoother slope, is controlled by lower-energy swash-backwash and overwash processes. As a result, the skewness of the grain-size distributions evolves towards less negative or more positive values. The skewness parameter appears to be distributed as a function of the beach slope and, thus, reflects variations in hydrodynamic energy. This has novel implications for coastal management

Reply to J.J. Muñoz-Perez et al. Comments on “Confirmation of beach accretion by grain-size trend analysis: Camposoto beach, Cádiz, SWSpain” by E. Poizot et al. (2013) Geo-Marine Letters 33(4)

In a novel finding for a beach environment, Poizot et al. (2013) identified an FB+ trend (sediments becoming finer, better sorted and more positively skewed upshore) on a well-developed swash bar on the upper foreshore of the Camposoto beach of Cádiz in SW Spain. In their Discussion of that paper, Muñoz-Perez et al. (2014) provide some supporting arguments and also report grain-size, beach profile and other data from nearby beaches which differ from those of Poizot and colleagues for Camposoto beach, pointing out that a trend observed on one beach may not apply to a neighbouring beach. However, even though the absolute values differ, the overall trends actually do show the same general behaviour. In our Reply to their comments, we also address some difficulties in comparing granulometric datasets generated by different analytical techniques

2021 roadmap for sodium-ion batteries

Abstract: Increasing concerns regarding the sustainability of lithium sources, due to their limited availability and consequent expected price increase, have raised awareness of the importance of developing alternative energy-storage candidates that can sustain the ever-growing energy demand. Furthermore, limitations on the availability of the transition metals used in the manufacturing of cathode materials, together with questionable mining practices, are driving development towards more sustainable elements. Given the uniformly high abundance and cost-effectiveness of sodium, as well as its very suitable redox potential (close to that of lithium), sodium-ion battery technology offers tremendous potential to be a counterpart to lithium-ion batteries (LIBs) in different application scenarios, such as stationary energy storage and low-cost vehicles. This potential is reflected by the major investments that are being made by industry in a wide variety of markets and in diverse material combinations. Despite the associated advantages of being a drop-in replacement for LIBs, there are remarkable differences in the physicochemical properties between sodium and lithium that give rise to different behaviours, for example, different coordination preferences in compounds, desolvation energies, or solubility of the solid–electrolyte interphase inorganic salt components. This demands a more detailed study of the underlying physical and chemical processes occurring in sodium-ion batteries and allows great scope for groundbreaking advances in the field, from lab-scale to scale-up. This roadmap provides an extensive review by experts in academia and industry of the current state of the art in 2021 and the different research directions and strategies currently underway to improve the performance of sodium-ion batteries. The aim is to provide an opinion with respect to the current challenges and opportunities, from the fundamental properties to the practical applications of this technology

Swell impact on reef sedimentary processes: A case study of the La Reunion fringing reef

Two surface-sediment sampling campaigns were carried out in November and December 2003, before and after a strong swell event, in the back-reef area of a microtidal fringing reef on the western coast of La Reunion, Indian Ocean. The spatial distributions of the mean grain size, sorting and skewness parameters are determined, and grain-size trend analysis is performed to estimate the main sediment transport pathways in the reef. The results of this analysis are compared with hydrodynamic records obtained in the same reef area during fair weather conditions and during swell events. Sediment dynamics inferred from the hydrodynamic records show that significant sediment erosion and transport occur only during swell events and under strongly agitated sea states. Under normal wave conditions, there is a potential for onshore sediment transport from the reef-flat to the back-reef, but this transport is episodic and occurs principally during high-tide stages. Sediment transport trends revealed by the grain-size trend analysis method show onshore and alongshore low-energy transport processes that are in agreement with the hydrodynamic records. The grain-size trend analysis method also provides evidence of an offshore high-energy transport trend that could be interpreted as a real physical process associated with return flow from the shore to the reef. The impact of swell on the reef sediment dynamics is clearly demonstrated by onshore and alongshore transport. Considering different combinations of the vector transport trends computed through the grain-size trend analysis approach, more realistic and pertinent results can be obtained by applying an exclusive OR operation (XOR case) on the vectors. The main results presented here highlight a trend towards the accumulation of carbonate sands in the back-reef area of the fringing reef. These sediments can only be resuspended during extreme events such as storms or tropical cyclones

Dominant updriftward sediment transport on the updrift-side of a modern deflected delta, Ishikari coast, Hokkaido, Japan

International audienceThe Ishikari coast of Hokkaido, Japan is a wave-dominated semi-enclosed coast, the sediments of which are primarily sourced from a single river (the Ishikari River), forming a northeast deflected delta. Asymmetric and deflected deltas are generally considered to be formed under net longshore sediment transport downdriftward; however, through sedimentological and grain-size trend analysis (GSTA) of seafloor sediments, along with some other observational data, we recognised dominant updriftward sediment transport on the updrift-side of the deflected delta system. GSTA showed that the most important trend in the coast is coarser, better-sorted, and more positively skewed (CB+). CB+ trends around the river mouth converge from the lower shoreface zone to the river mouth spit on the updrift side. The trends reflect the combined effects of shore-normal wave action and river sediment discharge. Wave-driven surface currents crossing over the delta lobe converge at the southwestern side of the river mouth. In the deeper zone (lower shoreface), southwest (updriftward) oriented CB+ trends prevail. These trends reflect successive re-deposition of delta front sands, with progressive mud winnowing, driven by the strong south-westerly bottom currents observed in the bay during winter storms. Although GSTA did not show any apparent trend field in the nearshore zone, gradual fining of sand fractions to the southwest, along with the chronological transition of the coastline after the construction of a large port (trap of drifted sands on the downdriftside of the port and regression of coastline on the updriftside of the port), suggest a dominant longshore sediment transport updriftward on the updrift-side of the delta. Because the growth of deflected deltas depends on dominant sediment accretion on the updrift-side, these results can be rationalised in the case of internally sourced deflected deltas. Uncertainties remain regarding the net alongshore sediment transport of the entire Ishikari coast; however, the deflected planform is controlled by deflected mouth bars and river mouth jets due to the waves approaching the river mouth at slightly oblique angle in winter, and is likely independent on the direction of dominant sediment transport

Wake of a Ducted Vertical Axis Tidal Turbine in Turbulent Flows, LBM Actuator-Line Approach

International audienceAbstract: Vertical axis tidal turbines are devices that extract the kinetic energy from tidal currents.Tidal currents can be highly turbulent. Since ambient turbulence affects the turbine hydrodynamic, itis critical to understand its influence in order to optimize tidal farms. Actuator Line Model (ALM)combined with Large Eddy Simulation (LES) is a promising way to comprehend this phenomenon.In this article, an ALM was implemented into a Lattice Boltzmann Method (LBM) LES solver.This implementation gives good results for predicting the wake of a vertical axis tidal turbineplaced into a turbulent boundary layer. The validated numerical configuration was then used tocompute the wake of a real size ducted vertical axis tidal turbine. Several upstream turbulencerates were simulated. It was found that the shape of the wake is strongly influenced by the ambientturbulence. The cost-to-precision ratio of ALM-LBM-LES compared to fully resolved LBM-LES makesit a promising way of modeling tidal farms

High resolution characteristics of turbulence tied of a fish farm structure in a tidal environment

International audienceCharacterization of tidal flow variations and turbulence levels surrounding aquaculture infrastructures contribute to optimal fish production management and to a good environmental quality assessment. Such flow characterization was performed in Cherbourg Roadstead, France. An acoustic Doppler current profiler was used to measure flow velocities and a vertical microstructure profiler to assess turbulence levels and length scales in the vicinity of a commercial fish farm. Flow measurement results show that fish nets increase local turbulence level, impacting the flow and vorticity produced by the nets, contributing to more scouring of the ocean floor. A wavelet analysis allows to evaluate vortex sizes and where they are localized along the water column. Flow characterization shows these vortices are produced in the vicinity of fish nets and in their wake. Larger and more energetic turbulent structures are produced below aquaculture cages, which extend into the wake and onto the ocean floor

Les gradients géochimiques : une nouvelle approche géostatistique d'interprétation du transport sédimentaire

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Transfert de la charge du fond en période de crue dans une embouchure microtidale et bilan sédimentaire associé pour le littoral limitrophe (Grand Rhône, France)

Transfer of fluvial bedload during flood events in a microtidal river mouth and associated beach nourishments (Rhône River mouth, France) We perform a Sediment Trend Analysis (STA) to investigate sediment transport mechanisms in a microtidal mouth during different hydroclimatic conditions. The aims is to determine the directions of residual transport and mode of distribution of the fluvial sediment input in an environment that is very difficult to equip with instrumentation during flood and storm periods. The modelling results and grain-size distributions of surface sediments clearly show three vector fields during periods of low river discharge. The first vector field corresponds to an upstream zone under fluvial influence. The second field is characteristic of an intermediate zone, confined inside the river mouth and marked by heterogeneous sedimentation. This sector is interpreted as the confrontation zone between fluvial and marine dynamics. Farther offshore, on the delta front, the vectors are oriented towards the river and at counter slope. In this deeper zone (bathymetry from -5 m to -20 m), the vectors are interpreted as representing a lag deposit. During medium and extreme flood events, sediments transfers are similar, apart from an increase in the vector length. Consequently, the STA method shows that, even during flood events, the river solid discharge is not particularly transferred towards the adjoining upper shoreface. And in the context of a wave-dominated delta, the distribution of surface sedimentation in a microtidal mouth remains controlled mainly by the swell, even in periods of flood when the intensity of river dynamics is exacerbated.Pour déterminer les modalités du transport sédimentaire dans une embouchure microtidale en période de crue, nous appliquons la procédure de Gao et Collins (1992) basée sur l'analyse de la répartition des paramètres sédimentométriques. L'objectif est de déterminer les directions de transport résiduel et les modalités de répartition des apports solides fluviaux dans un milieu très difficile à instrumenter en période de crue et de tempête. Durant les périodes de basse énergie, les résultats de la modélisation et des observations des spectres granulométriques des sédiments de surface montrent un transit sédimentaire organisé en trois champs de vecteurs. Le premier champ correspond à la zone amont influencée directement par les dynamiques fluviales (chenal). Le second secteur se situe au coeur de la barre d’embouchure et constitue une zone d’interface entre les dynamiques marines et fluviales, caractérisée par une couverture sédimentologique multimodale. Enfin, un troisième faisceau de vecteurs est observé sur le front du lobe prodeltaïque. Il s’oriente en direction du centre de l’embouchure même en période de crue. Ce type de transport à contre pente semblant improbable, nous interprétons ces vecteurs comme des « lag deposits » . En période de crue extrême ou moyenne, les transferts sédimentaires dans la zone d’embouchure ne semblent pas s’organiser différemment. De manière remarquable, seule l’intensité du transport est accrue. Finalement, on ne note donc pas de transfert sédimentaire particulier vers les plages adjacentes en période de crue. Quant à la distribution des sédiments de surface dans une embouchure microtidale, en contexte de delta dominé par les houles, elle semble principalement contrôlée par les houles, même en période de crue lorsque les dynamiques fluviales sont exacerbées.Maillet Grégoire, Vella Claude, Sabatier François, Poizot Emmanuel, Mear Yann. Transfert de la charge du fond en période de crue dans une embouchure microtidale et bilan sédimentaire associé pour le littoral limitrophe (Grand Rhône, France). In: 31èmes Journées de l’Hydraulique de la Société Hydrotechnique de France. Morphodynamique et gestion des sédiments dans les estuaires, les baies et les deltas. 22 et 23 SEPTEMBRE 2009. 2009