Publications

2024

• Statistical distributions of free surface elevation and wave height for out-of-equilibrium sea-states provoked by strong depth variations
  
  • Zhang Jie
  • Ma Yuxiang
  • Benoit Michel
  Ocean Engineering, Elsevier, 2024, 293, pp.116645. As unidirectional irregular wave trains propagate over a steep shoal, the sea-state becomes out-of-equilibrium and is continuously affected by the non-equilibrium dynamics (NED) over dozens of characteristic wavelengths. Using the set of accurate numerical simulations of Zhang et al. (2022), the NED effects on the probability distributions of free surface elevation and wave height, the statistical moments and maximum wave statistics are investigated, in both near-field and far-field regions after the water depth transition. The primary contribution of this work is to assess the applicability and limitations of several popular statistical distribution models in describing non-equilibrium statistics. In addition, a new distribution of the free surface elevation in a lognormal shape is proposed, which predicts the non-equilibrium free surface statistics with satisfactory performance and characterizes well the skewness–kurtosis relationship in the short scale. It is shown that the statistics in the far-field region are significantly influenced by the near-field wave-wave interaction, and beyond the capability of all statistical models considered here. Despite this complexity, the sea-state in the far-field region exhibits lower freak wave probability than a Gaussian sea-state. Implications of these findings for engineering practices are discussed. (10.1016/j.oceaneng.2023.116645)
  DOI : 10.1016/j.oceaneng.2023.116645
• Experimental study of particle lift initiation on roller-compacted sand-clay mixtures
  
  • Le Vern Mickael
  • Sediki Ouardia
  • Razakamanantsoa Andry
  • Murzyn Frédéric
  • Larrarte Frédérique
  Environmental Geotechnics, ICE-Publishing, 2024, 11 (1), pp.3-14. Civil engineering works are sources of dust emissions, which can cause severe security, health and environmental damages to workers and neighbourhoods. This is particularly significant for implementation of earthwork sites. The present paper reports a study conducted to characterise the soil–atmosphere interaction above compacted soils where particle lift is initiated. Mixtures of kaolin clay and sand have been compacted using a laboratory roller compactor that reproduces near-field compaction conditions. Shear testing conducted at the interface confirms that the sand content affects the friction angle between the soil and the compaction roller. The experimental velocity profiles above the compacted samples have been obtained in a wind tunnel using a non-intrusive measurement technique (laser Doppler velocimetry). Results show that the sand fraction affects velocity profiles. Compaction, therefore, may not fully reduce the roughness of the soil surface. The airflow friction velocities at the sample surfaces have been determined from the boundary layer profiles. The results achieved demonstrate that all tested soils reach the threshold friction velocity required to initiate particle lift, and the higher the sand content of the soil, the more likely it is that particle lift occurs. (10.1680/jenge.19.00172)
  DOI : 10.1680/jenge.19.00172
• 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.
• A CFD Study on Different Configurations of Spacer-Filled Membrane Distillation System Using OpenFOAM
  
  • Tizchang Atefeh
  • Morgan Abily
  • Delestre Olivier
  • Gernjak Wolfgang
  , 2024, Volume 2, pp.333-344. Circular economy initiatives like the EC funded iWAYS project (grant agreement: 958274) promote the reuse of waste heat in industrial sites. This presents opportunities and challenges for technological adaptation. Membrane distillation (MD) is a thermally driven process for water treatment that can use waste heat. However, effectively treating complex industrial wastewater requires adapting MD units to achieve reliable and efficient performance. Filament spacers within the MD units play a key role in structural maintenance and flow mixing. CFD simulations can help to characterize filament spacer configuration impacts on the hydrodynamic of feed and permeate channels, which affects both trans-membrane temperature gradient and membrane fouling control. Here, we performed a CFD study on a direct contact membrane distillation (DCMD) sub-unit with the goal of evaluating impact on robustness and performance of a set of designed filament spacer configurations. The modeled membrane distillation system has an overall length of 200 mm, width of 10 mm and height of 4.1 mm, containing two layers of filaments in each of the feed and permeate channels. The diameter of the filaments was 1 mm, and they had a 45• degree angle to the flow direction in the channels.<p>Variations of this standard filament configuration were also tested and simulated to optimize their mixing performance.</p><p>The numerical simulations to approximate in a 3D solution of Navier-stokes equations for steady state conditions were performed using OpenFOAM code. The computational domains were meshed using OpenFOAM snappyHexMesh utility, and finite-volume based simulation relying on the chtMultiRegionFoam solver was executed in parallel over 40 CPU cores. Comparing the CFD analysis of different filaments´ configurations lead to an assessment of an improved spacer structure. The selected configuration is to be 3D printed for laboratory-scale experimental confirmation of the validity of the CFD model and the optimal configuration finding.</p> (10.1007/978-981-97-4076-5_24)
  DOI : 10.1007/978-981-97-4076-5_24