Papers

We study the sedimentation of flexible fibers through arrays of obstacles in a viscous fluid, combining experiments and numerical simulations. Obstacles induce lateral dispersion of the fibers and, depending on fiber flexibility and obstacle geometry, non-trivial trapping states.

@article{makanga2023obstacle,
  title   = {{Obstacle-induced lateral dispersion and nontrivial trapping of flexible fibers settling in a viscous fluid}},
  author  = {Ursy Makanga and Mohammadreza Sepahi and Camille Duprat and Blaise Delmotte},
  year    = {2023},
  journal = {Physical Review Fluids},
  volume  = {8},
  number  = {4},
  pages   = {044303},
  doi     = {10.1103/PhysRevFluids.8.044303},
}

@inproceedings{makanga2023siam,
  title     = {{Sedimentation of Flexible Fibers in Structured Environments}},
  author    = {Ursy Makanga and Mohammadreza Sepahi and Camille Duprat and Blaise Delmotte},
  year      = {2023},
  booktitle = {SIAM Conference on Computational Science and Engineering},
  url       = {https://hal.science/hal-04438332},
}

@inproceedings{duprat2022apsdfd,
  title     = {{Sedimenting flexible fibers against obstacles in a viscous fluid}},
  author    = {Camille Duprat and Ursy Makanga and Mohammadreza Sepahi and Blaise Delmotte},
  year      = {2022},
  booktitle = {Bulletin of the American Physical Society, 75th Annual Meeting of the Division of Fluid Dynamics},
  url       = {https://meetings.aps.org/Meeting/DFD22/Session/U26.10},
}

The stably stratified atmospheric boundary layer forms over land at night as the surface cools, and the buoyant suppression of turbulence makes it one of the hardest parts of the atmosphere to observe, simulate and parameterise. This thesis uses large-eddy simulation with the Advanced Research WRF model to study how the vertical structure and intensity of boundary-layer turbulence respond to increasing surface cooling, and how that response depends on mechanical forcing. Eight idealised simulations cross two geostrophic wind speeds (16.5 and 8.25 m/s) with four surface cooling rates (0, 0.25, 0.50 and 1.00 K/h). The strongly forced cases respond monotonically, consistent with the classical quasi-steady stable boundary layer. The weakly forced cases depart from that regime: the surface heat flux saturates near 10 W/m² despite a fourfold increase in imposed cooling, the surface friction velocity collapses, and the flow aloft decouples from the surface.

@mastersthesis{sepahi2026thesis,
  title   = {{Stratification and Vertical Turbulence Structure in the Atmospheric Boundary Layer: A Large-Eddy Simulation Study}},
  author  = {Perseus Sepahi},
  year    = {2026},
  school  = {University of Waterloo},
  address = {Waterloo, Ontario, Canada},
  url     = {https://hdl.handle.net/10012/24382},
}