Publications

2023

• Numerical Wave Tanks
  
  • Guerri Alessandro
  , 2023. The objective of the Master’s thesis is to compare different NWT in terms of efficiency and accuracy. Comparisons will be achieved on a set of experimental tests already conducted in ECN. Different types of wave fields will be studied, with an increasing degree of complexity: from regular waves to unidirectional irregular waves. In addition, the wave conditions will cover mild sea conditions up to extreme sea states, exhibiting breaking events. Each numerical model has a different methodology to take care of breaking event and it is one particular focus of the Master’s thesis.
• Energy stable and linearly well-balanced numerical schemes for the non-linear Shallow Water equations with Coriolis force
  
  • Audusse Emmanuel
  • Dubos Virgile
  • Gaveau Noémie
  • Penel Yohan
  , 2023. This work is dedicated to the analysis of a class of energy stable and linearly well-balanced numerical schemes dedicated to the non-linear Shallow Water equations with Coriolis force. The proposed algorithms rely on colocated finite volume approximations formulated on cartesian geometries. They involve appropriate diffusion terms in the numerical fluxes, expressed as discrete versions of the linear geostrophic equilibrium. We show that the resulting methods ensure semi-discrete energy estimates and numerical results show a very clear improvement around the nonlinear geostrophic equilibrium when compared to those of classic Godunov-type schemes.
• River restoration works design based on the study of early‐stage vegetation development and alternate bar dynamics
  
  • Li Jiaze
  • Claude Nicolas
  • Tassi Pablo
  • Cordier Florian
  • Crosato Alessandra
  • Rodrigues Stéphane
  River Research and Applications, Wiley, 2023, 39 (9), pp.1682-1695. Abstract Active geomorphological interventions, such as reprofiling of river bars, are often used to increase bar dynamics and prevent vegetation encroachment. River restoration management should be planned based on the knowledge of what processes will follow the intervention and on the anticipation of the consequences. However, in many cases, the associated physical processes are not clearly identified whereas their consequences on bar morphodynamics are still not fully understood. This study aims to bring new insights into the biomorphodynamics evolution of the riverbed after restoration works by using a 2D biomorphodynamic model developed in the TELEMAC‐MASCARET system. It seeks to compare and evaluate the performance of five bar reprofiling scenarios in which the bar elevation is lowered to just below the water level at specified design discharges. The study area is located in the channelized and regulated alpine gravel‐bed Isère River (France). Bar dynamics and early stages of vegetation establishment are analyzed for the first 2 years after each restoration scenario. The results indicate that plant colonization would occur in all cases. Overall, maximizing the reduction of bar height is the most effective way to improve the bar dynamics and limit future vegetation encroachment. (10.1002/rra.4188)
  DOI : 10.1002/rra.4188
• Coupling 3D hydraulic simulation and fish telemetry data to characterize the behavior of migrating smolts approaching a bypass
  
  • Ben Jebria Noor
  • Carmigniani Rémi Arthur
  • Drouineau Hilaire
  • de Oliveira Eric
  • Tétard Stéphane
  • Capra Hervé
  Journal of Ecohydraulics, 2023, 8 (2), pp.144-157. Human-induced river fragmentation is a major threat to migratory fish species. Restoringriver connectivity requires the construction of fish passage solutions, such as fishways forupstream and downstream migration. While many studies focussed on the upstream migra-tion of diadromous fishes, and especially of adult Atlantic salmons (Salmosalar), we analyzejuvenile behaviour under different hydraulic conditions at reservoir to improve the develop-ment of effective bypass systems for downstream passage of salmon smolt.Based on coupling three-dimensional (3D) computational fluid dynamics (CFD) simulationsto smolt positions tracked by two-dimensional (2D) telemetry, the present study aimed toexplore smolt behaviour in relation to hydraulic cues. More specifically, we explored howhydraulic conditions influence fish behaviour and how fish navigate depending on thisbehaviour. In 2017, 23 smolts were tracked in the reservoir of Poutes (Allier River, France),associated with different turbine discharge rates. 3D CFD simulations were performed andvalidated against field measurements in the reservoir upstream of the hydropower plant.The study of fish displacements in relation to flow conditions provided new insights withthe use of thrust force, swimming orientation and direction as means to precisely character-ize smolt behaviour, which can help in the design of downstream migration passage facili-ties. At Poutes dam, flow velocity, flow acceleration and turbulent kinetic energy are verylow and therefore can lead to fish disorientation. However, results underlined that having aminimum flow velocity of 20cm/s in reservoirs is sufficient to prevent delay and allowfish navigation; (10.1080/24705357.2021.1978345)
  DOI : 10.1080/24705357.2021.1978345
• Equilibration process of out-of-equilibrium sea-states induced by strong depth variation: Evolution of coastal wave spectrum and representative parameters
  
  • Zhang Jie
  • Benoit Michel
  • Ma Yuxiang
  , 2022, pp.104099. Recent studies showed both experimental and numerical evidence that the occurrence probability of freak waves could be significantly enhanced as results of non-equilibrium dynamics induced by strong depth variations. The sea-state is characterized by strong non-Gaussian behavior in a short spatial extent after the depth transition, covering a few wavelengths. In this work, we investigate the complete equilibration process of an out-of-equilibrium sea-state via high-fidelity numerical simulations. In the simulations, the region after the depth transition is set as long as around one hundred wavelengths, such that the spectral adaptation develops and terminates eventually. The results are analyzed with spectral, cross-spectral and statistical approaches. It is shown that there are two stages with different spatial scales in the equilibration process. In the short scale, the sea-state is characterized by significant changes in wave statistics, freak wave occurrence probability is intensified. In the long scale, the wave spectrum undergoes strong modulation, the spectral peak disintegrate into a relative broad band, and low-frequency waves are enhanced as well. We show evidence that the spectral changes in the long scale are due to interactions of free components. The wave nonlinearity is shown to be positively correlated to the magnitude of the dynamical responses, but irrelevant to the length of the spatial scales in the equilibration process. In the established shallow-water equilibrium, the freak wave occurrence probability becomes less than Gaussian expectation and the waves are asymmetric in the vertical direction and symmetric in the horizontal. (10.1016/j.coastaleng.2022.104099)
  DOI : 10.1016/j.coastaleng.2022.104099
• Migrating bars influence the formation and dynamics of their peers in large sandy‐gravel bed rivers
  
  • Le Guern Jules
  • Rodrigues Stéphane
  • Tassi Pablo
  • Cordier Florian
  • Wintenberger Coraline
  • Jugé Philippe
  Earth Surface Processes and Landforms, Wiley, 2023, 48 (8), pp.1512-1525. Abstract The present study investigates the morphodynamic interactions between migrating bars in a sandy gravel and nearly straight channel of the Loire River (France). From a large dataset collected from field campaigns performed between 2016 and 2020, we analysed the deflection power exerted by bars on flow and sediment transport that influences the dynamics of other bars present in the channel. We also investigated the role of low flows in bar formation. To this aim, the riverbed evolution has been documented using four years of bathymetrical and aDcp surveys. Flow deflection induced by the presence of bars in the channel differs for pre‐existing (first‐order) bars and bedload sediment accumulations identified as new developing bars (second‐order bars). The latter needs to reach an equilibrium size to influence flow direction. During low flows, first‐order bars emerge and create contraction/expansion zones in the channel, inducing a temporary local geometrical forcing that leads to sediment deposition at the outlet of these zones. Sediment deposited in these specific areas can constitute a nucleus for second‐order bar formation or contribute to first‐order bar aggradation. According to the linear free bar theory, the critical discharge that contributes to expressing an alternate bar pattern is exceeded during moderate flood, leading to the observation of a transitional bar pattern between alternate and central bar pattern. (10.1002/esp.5563)
  DOI : 10.1002/esp.5563
• Enhanced extreme wave statistics of irregular waves due to accelerating following current over a submerged bar
  
  • Zhang Jie
  • Ma Yuxiang
  • Tan Ting
  • Dong Guohai
  • Benoit Michel
  Journal of Fluid Mechanics, Cambridge University Press (CUP), 2023, 954, pp.A50. We present experimental results of irregular long-crested waves propagating over a submerged trapezoidal bar with the presence of a background current in a wave flume. We investigate the non-equilibrium phenomenon (NEP) induced by significant changes of water depth and mean horizontal flow velocity as wave trains pass over the bar. Using skewness and kurtosis as proxies, we show evidence that an accelerating following current could increase the sea-state non-Gaussianity and enhance both the magnitude and spatial extent of the NEP. We also find that below a ‘saturation relative water depth’ $k_p h_2 \approx 0.5$ ( $k_p$ being the peak wavenumber in the shallow area of depth $h_2$ ), although the NEP manifests, the decrease of the relative water depth does not further enhance the maximum skewness and kurtosis over the bar crest. This work highlights the nonlinear physics according to which a following current could provoke higher freak wave risk in coastal areas where modulation instability plays an insignificant role. (10.1017/jfm.2022.1022)
  DOI : 10.1017/jfm.2022.1022
• Using 17 years of beach/dune profile monitoring to characterize morphological dynamics related to significant extreme water level events in North Brittany (France)
  
  • Suanez Serge
  • Yates Marissa L.
  • Floc'H France
  • Accensi Mickaël
  Geomorphology, Elsevier, 2023, 433, pp.108709. Long-term in situ monitoring of beach morphology is crucial for understanding the physical processes of coastal changes and defining the strategies of sustainable coastal management. Monthly surveys based on the beach/dune profile measurements started in July 2004 along six transects distributed along the Vougot beach (North Brittany). The analysis of these data from 2004 to 2021 shows that the eastern part of the beach has experienced chronic erosion during the 17-year period. This erosion has led to a lowering of the beach profile by about –1 to –1.5 m, and has resulted in the removal of beach sand such that waves now impact the underlying Holocene peat and Pleistocene silts or pebbles during most of the year. Conversely, the western part of the beach has accreted. Vougot beach is thus experiencing a rotation phenomenon characterized by a longshore sediment flux from the east to the west. The multidecadal evolution of the beach/dune system is punctuated by events causing significant retreat of the dune, especially when storm waves are combined with high spring tide levels. The event causing the most significant morphological changes was associated with extreme water levels (EWL) up to 9.6 m (i.e., Anne storm in February 2014), causing 14.5 m3 l.m-1 of dune sediment loss. The analysis of 17 years of hydrodynamic conditions (waves and water levels) indicates an increase in the wave runup height (+65%) and EWL (+17%). Calculation of the water level that exceeds the dune toe position (Δzexceedance) helps to further quantify the impacts of storm events on dune volume changes. The Anne storm had an EWL with a return period of approximately 13 years, but when combined with the dune toe position, showed the largest dune toe exceedance value (3.0 m), corresponding to a return period of approximately 21 years. Lastly, the events causing the most significant dune erosion during this 17-year study period have also caused shoreline erosion and/or landward barrier migration at many other sites in North Brittany, showing the broader scale impacts of observations at individual study sites. (10.1016/j.geomorph.2023.108709)
  DOI : 10.1016/j.geomorph.2023.108709
• GAIA - a unified framework for sediment transport and bed evolution in rivers, coastal seas and transitional waters in the TELEMAC-MASCARET modelling system
  
  • Tassi Pablo
  • Benson Thomas
  • Delinares Matthieu
  • Fontaine Jacques
  • Huybrechts Nicolas
  • Kopmann Rebekka
  • Pavan Sara
  • Pham Chi-Tuan
  • Taccone Florent
  • Walther Régis
  Environmental Modelling and Software, Elsevier, 2023, 159, pp.105544. (10.1016/j.envsoft.2022.105544)
  DOI : 10.1016/j.envsoft.2022.105544
• Computations of pressure loads on an oscillating water column with experimental comparison for random waves
  
  • Batlle Martin Marc
  • Pinon Grégory
  • Barajas Gabriel
  • Lara Javier
  • Reveillon Julien
  Coastal Engineering, Elsevier, 2023, 179, pp.104228. This paper presents numerical investigations with experimental comparisons of random wave induced loads on the external walls of a large scale Oscillating Water Column (OWC) device. The objective is to investigate the capability of a numerical model that uses the Reynolds Averaged Navier–Stokes (RANS) equations to accurately reproduce extreme wave loads on an OWC. Both incompressible and compressible approximations for the RANS equations are studied in this work with the aim of investigating the limitations of both approaches. After a first characterisation of the random wave propagation processes at the numerical flume, wave loads are analysed. An OWC power take-off (PTO) and in-chamber air compressibility effects are studied using regular waves. Next, an OWC facing irregular waves is studied and compared with experimental data, putting special emphasis on the extreme loads together with the stochastic nature of random waves. The simulation of extreme wave loads on an OWC is validated and the necessity of a compressible model for correct reproduction of an OWC in-chamber flow for certain operating conditions of the PTO is pointed out from the simulations. (10.1016/j.coastaleng.2022.104228)
  DOI : 10.1016/j.coastaleng.2022.104228