A method to characterize the different extreme waves for islands exposed to various wave regimes: a case study devoted to Reunion Island

This paper outlines a new approach devoted to the analysis of extreme waves in presence of several wave regimes. It entails discriminating the different wave regimes from offshore wave data using classification algorithms, before conducting the extreme wave analysis for each regime separately. The concept is applied to the pilot site of Reunion Island which is affected by three main wave regimes: southern waves, trade-wind waves and cyclonic waves. Several extreme wave scenarios are determined for each regime, based on real historical cases (for cyclonic waves) and extreme value analysis (for non-cyclonic waves). For each scenario, the nearshore wave characteristics are modelled all around Reunion Island and the linear theory equations are used to back calculate the equivalent deep-water wave characteristics for each portion of the coast. The relative exposure of the coastline to the extreme waves of each regime is determined by comparing the equivalent deep-water wave characteristics. <br><br> This method provides a practical framework to perform an analysis of extremes within a complex environment presenting several sources of extreme waves. First, at a particular coastal location, it allows for inter-comparison between various kinds of extreme waves that are generated by different processes and that may occur at different periods of the year. Then, it enables us to analyse the alongshore variability in wave exposition, which is a good indicator of potential runup extreme values. For the case of Reunion Island, cyclonic waves are dominant offshore around the island, with equivalent deep-water wave heights up to 18 m for the northern part. Nevertheless, due to nearshore wave refraction, southern waves may become as energetic as cyclonic waves on the western part of the island and induce similar impacts in terms of runup and submersion. This method can be easily transposed to other case studies and can be adapted, depending on the data availability

Evaluation of Model Predictions of the Unsteady Tidal Stream Resource and Turbine Fatigue Loads Relative to Multi-Point Flow Measurements at Raz Blanchard

This is the final version. Available on open access from MDPI via the DOI in this recordData Availability Statement: Measured ADCP data were gathered during the Interreg TIGER project. Further information on the deployment campaigns and underlying ADCP data can be found in T1.7.3 (https://interregtiger.com/download/tiger-tidal-test-procedure-reports/, accessed on 26 June 2023). Overview of models used is given in [36]. Underlying model data are provided in the references given. Variation in the flow properties with disk-averaged velocity as reported in this study and employed for fatigue load analysis is available from https://doi.org/10.48420/24236593 (accessed on 28 September 2023). We are grateful to the French navy SHOM (”Service Hydrographique et Océanographique de la Marine”) for providing access to bathymetric data (http://data.shom.fr/, accessed on 6 June 2023).The next stage of development of the tidal stream industry will see a focus on the deployment of tidal turbines in arrays of increasing device numbers and rated power. Successful array development requires a thorough understanding of the resource within potential deployment sites. This is predictable in terms of flow speeds, based upon tidal constituents. However, the operating environment for the turbine is more complex than the turbine experiencing a uniform flow, with turbulence, shear and wave conditions all affecting the loading on the turbine components. This study establishes the accuracy with which several alternative modelling tools predict the resource characteristics which define unsteady loading—velocity shear, turbulence and waves—and assesses the impact of the model choice on predicted damage equivalent loads. In addition, the predictions of turbulence are compared to a higher fidelity model and the occurrence of flow speeds to a Delft3D model for currents and waves. These models have been run for a specific tidal site, the Raz Blanchard, one of the major tidal stream sites in European waters. The measured resource and predicted loading are established using data collected in a recent deployment of acoustic Doppler current profilers (ADCPs) as part of the Interreg TIGER project. The conditions are measured at three locations across the site, with transverse spacing of 145.7 m and 59.3 m between each device. Turbine fatigue loading is assessed using measurements and model predictions based on an unsteady blade element momentum model applied to near-surface and near-bed deployment positions. As well as across-site spatial variation of loading, the through life loading over a 5-year period results in an 8% difference to measured loads for a near-surface turbine, using conditions purely defined from a resource model and to within 3% when using a combination of modelled shear with measured turbulence characteristics.European Regional Development Fund (ERDF

Overview of resource and turbine modelling in the Tidal Stream Industry Energiser Project: TIGER

This is the author accepted manuscript. The final version is available from EWTEC via the DOI in this recordTidal energy projects require numerical modelling for the assessment of tidal site conditions and turbine/array performance. The Interreg TIGER project has offered a unique opportunity to implement a wide range of numerical models. This paper provides an overview and comparison of the different numerical models developed by academic partners in the TIGER project. The models cover a variety of spatial and temporal scales. The largest scale models provide long-term climatic studies covering the entire English Channel region, at relatively low resolution, whilst the highest-resolution models provide detailed information about short-term and small-scale turbulent flow and its interaction with tidal turbines. The models are used for various purposes. At one end of the scale, the models have been used to inform the large-scale techno-economic assessment of tidal energy and its impact on the energy mix in the UK and France. At the other end of the scale, the numerical models provide information that feeds into detailed engineering design of tidal turbines at particular sites, and assessment of the energy yield. The models showcase the range of computational tools available to aid the development of the tidal energy industry. This paper will be useful for investors, technology developers and project stakeholders to help identify suitable numerical models to support and develop ongoing and future tidal stream projects.European Regional Development Fund (ERDF

The effects of acute tryptophan depletion on costly information sampling: impulsivity or aversive processing?

RATIONALE: The neurotransmitter serotonin (5-HT) has been implicated in both aversive processing and impulsivity. Reconciling these accounts, recent studies have demonstrated that 5-HT is important for punishment-induced behavioural inhibition. These studies focused on situations where actions lead directly to punishments. However, decision-making often involves making tradeoffs between small 'local' costs and larger 'global' losses. OBJECTIVE: We aimed to distinguish whether 5-HT promotes avoidance of local losses, global losses, or both, in contrast to an overall effect on reflection impulsivity. We further examined the influence of individual differences in sub-clinical depression, anxiety and impulsivity on global and local loss avoidance. METHODS: Healthy volunteers (N = 21) underwent an acute tryptophan depletion procedure in a double-blind, placebo-controlled crossover design. We measured global and local loss avoidance in a decision-making task where subjects could sample information at a small cost to avoid making incorrect decisions, which resulted in large losses. RESULTS: Tryptophan depletion removed the suppressive effects of small local costs on information sampling behaviour. Sub-clinical depressive symptoms produced effects on information sampling similar to (but independent from) those of tryptophan depletion. Dispositional anxiety was related to global loss avoidance. However, trait impulsivity was unrelated to information sampling. CONCLUSIONS: The current findings are consistent with recent theoretical work that characterises 5-HT as pruning a tree of potential decisions, eliminating options expected to lead to aversive outcomes. Our results extend this account by proposing that 5-HT promotes reflexive avoidance of relatively immediate aversive outcomes, potentially at the expense of more globally construed future losses

Impact environnemental d'un parc hydrolien : sensibilité des prédictions à la rugosité de fond.

National audienceThis study analyses the sensitivity of a tidal hydrodynamic model to the parameterisation of rock bottom roughess in the Fromveur Strait off western Brittany. The attention is dedicated to estimations of currents, associated kinetic energy and bottom shear stress without and with a tidal stream farm. The available predicted tidal stream power shows variations up to 30 % in relation to the bottom roughness retained. Tidal stream power extraction with a tidal farm induces noticeable reductions of tidal currents and bottom shear stresses up to 10 km from the Strait. Bottom roughness impacts the amplitude of this reduction with variations of shear stresses from 9 to 17 % over the sandbank of the Four.Cette étude analyse la sensibilité d'un modèle hydrodynamique de marée a la paramétrisation de la rugosité des fonds rocheux au niveau du Passage du Fromveur en pointe Bretagne. L'attention est portée sur les estimations des courants, de la puissance associée et de la contrainte de cisaillement de fond sans et avec la présence d'un parc hydrolien. Les prédictions de la puissance du courant disponible présentent des variations allant jusqu'à 30 % en fonction de la rugosité de fond retenue. L'extraction de cette puissance par un parc hydrolien induit une réduction substantielle des courants de marée et de la contrainte de cisaillement de fond associée à plus de 10 km du Passage du Fromveur. La rugosité de fond influe sur l'amplitude de cette réduction avec des variations de la contrainte de cisaillement comprises entre 9 et 17 % au niveau du banc sableux du Four

Impact environnemental d'un parc hydrolien : sensibilité des prédictions à la rugosité de fond.

National audienceThis study analyses the sensitivity of a tidal hydrodynamic model to the parameterisation of rock bottom roughess in the Fromveur Strait off western Brittany. The attention is dedicated to estimations of currents, associated kinetic energy and bottom shear stress without and with a tidal stream farm. The available predicted tidal stream power shows variations up to 30 % in relation to the bottom roughness retained. Tidal stream power extraction with a tidal farm induces noticeable reductions of tidal currents and bottom shear stresses up to 10 km from the Strait. Bottom roughness impacts the amplitude of this reduction with variations of shear stresses from 9 to 17 % over the sandbank of the Four.Cette étude analyse la sensibilité d'un modèle hydrodynamique de marée a la paramétrisation de la rugosité des fonds rocheux au niveau du Passage du Fromveur en pointe Bretagne. L'attention est portée sur les estimations des courants, de la puissance associée et de la contrainte de cisaillement de fond sans et avec la présence d'un parc hydrolien. Les prédictions de la puissance du courant disponible présentent des variations allant jusqu'à 30 % en fonction de la rugosité de fond retenue. L'extraction de cette puissance par un parc hydrolien induit une réduction substantielle des courants de marée et de la contrainte de cisaillement de fond associée à plus de 10 km du Passage du Fromveur. La rugosité de fond influe sur l'amplitude de cette réduction avec des variations de la contrainte de cisaillement comprises entre 9 et 17 % au niveau du banc sableux du Four

An optimisation method for determining permeability and effective stress relationships of consolidating cohesive sediment deposits

International audienceGibson's equation is widely used to describe the behaviour of consolidating soft mud soils. This equation needs to be supplied with constitutive relationships, which relate effective stress and permeability to a quantity describing the soil density (mass concentration or void ratio for instance). In this paper, a method to determine the constitutive relationships is presented. This method requires recording the height of the interface between the clear water and the mud deposit. The results compare well with the ones obtained following the conventional method, which requires pore water pressure and density measurements

A comparative study for tidal current velocity prediction using simplified and fast algorithms

International audienc