Publications

2024

• Étude hydrodynamique des courses de natation en eau libre
  
  • Bolon Baptiste
  , 2024. Ce travail présente une étude physique des courses de natation en eau libre. Deux grands sujets sont abordés. D'abord, nous étudions les interactions entre nageurs (drafting), dans des configurations de nage à 2 athlètes et en peloton. Grâce à des mesures expérimentales et des calculs numériques, nous sommes capable d'évaluer l'impact de la position relative des nageurs sur la force de traînée qu'ils subissent. Ces résultats nous permettent de proposer une trajectoire optimale de dépassement. Ensuite, nous nous intéressons à l'impact des courants de la Seine sur la stratégie à mener lors de la course des Jeux Olympiques de Paris. Nos travaux montrent qu'il existe une trajectoire optimale le long du parcours, qui permet, en profitant des courants favorables et en évitant les courants les plus défavorables, de minimiser le temps de course d'un nageur. De même, il existe aussi une stratégie optimale de dépense énergétique qui permet à un nageur de minimiser son temps de course.
• Spatial and temporal analysis of the sand dynamics in alpine rivers for 3D numerical modelling
  
  • Weit A
  • Camenen B
  • Dramais G
  • Bel C
  • Jodeau M
  • Langlais S
  • Lauters F
  , 2024. Hydraulic structures can impact the sediment continuity of the river and can create a sediment imbalance downstream of dams according to the different sediment classes (silt, sand, gravel). For operators, one important issue is the presence of sand (d>63 μm), which can lead to exploitation difficulties, issues for flushing or emptying operations as well as to ecological, in-dustrial or safety issues. It was recognized that the percentage of sand particles that is transported by suspension compared to bedload transport can often prevail. However, today it is still a real challenge to evaluate the spatial and temporal variability of these sand concentrations in gravel-bed rivers since sand dynamics are generally supply limited. Using 3D hydro-sedimentary modelling could help to better understand processes of sand transport in rivers. In this article, we will present results from experimental monitoring that will then be used for 3D numerical modelling (TELEMAC 3D + Gaia) on engineered rivers in the Northern French Alps.
• Global solutions and uniform convergence stability for compressible Navier-Stokes equations with oldroyd-type constitutive law
  
  • Wang Na
  • Boyaval Sébastien
  • Hu Yuxi
  , 2024. We consider one dimensional isentropic compressible Navier-Stokes equations with Oldroyd-type constitutive law. By establishing uniform a priori estimates (with respect to relaxation time), we show global existence of smooth solutions with small initial data. Moreover, we get global-in-time convergence of the system towards the classical isentropic compressible Navier-Stokes equations.
• Experimental and numerical modeling of flow and sediment transport in shallow reservoirs
  
  • Chagdali El Mehdi
  , 2024. Shallow reservoirs are widely used in hydraulic engineering, whether for temporary water storage, or as settling basins. Many of these reservoirs have a relatively simple geometric configuration (i.e., rectangular), but exhibit complex flow phenomena (i.e., eddies, recirculation zones, attached or oscillating jets) and even instable flow patterns. This impacts the sediment transport and sedimentation (e.g., deposition rate, location), and thus the operational efficiency of reservoirs. The objective of this thesis is to enhance our understanding of the physical hydro-sedimentary processes in shallow reservoirs through experimentation and numerical modeling. Design of the laboratory setup was inspired by real basins and was carried out based on dimensional analysis and preliminary numerical simulations using the open source two-depth averaged model TELEMAC-2D (2D) and three-dimensional (3D) model TELEMAC-3D. A series of forty-two (42) experiments with clear water and fifteen (15) experiments with inlet sediment injection were conducted. Velocity fields were measured using the LSPIV (Large Scale Particle Image Velocimetry) technique as well as intrusive probes such as the ADV (Acoustic Doppler Velocimeter) and ADVP (Acoustic Doppler Velocimeter Profiler). This later technique allowed precise and advanced evaluation of average velocities and flow turbulent characteristics. Sedimentation within the reservoir was mapped using an echosounder, while the time-evolution of deposit pattern was analyzed through image processing. These experiments helped to clarify the impact of inlet boundary conditions (open channel vs pressurized jet), geometric (short vs long reservoirs), hydraulic and sediment conditions. Using the experimental data, the software code_saturne was used to assess the capability of turbulence models, both low and high Reynolds numbers, to observed replicate stable and unstable flow patterns. Finally, a real-world case was stimulated using TELEMAC-2D coupled with its sediment transport module GAIA.