Bed particle dynamics at entrainment

Matthew J Witz (Corresponding Author), Stuart Cameron, Vladimir Ivanovich Nikora

Research output: Contribution to journalArticle

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Abstract

The paper reports a high-resolution experimental study focused on statistical properties of particle trajectories starting with detachment from the bed. This local range of particle motion can either be considered to start from a collision with the bed of an already mobile particle, or from the entrainment of a previously immobile particle. Both approaches are investigated and compared based on the particle diffusion concept. From the point of entrainment, local particle diffusion in all three coordinate directions displays an exponent significantly greater than that of ballistic diffusion. In contrast, particle motion after collision with the bed demonstrates ballistic diffusion in all three coordinate directions. The results highlight clear differences between the diffusion of an already mobile particle and one starting from a position of rest. These differences are attributed to variations in physical mechanisms acting at the initial phase of particle motion after detachment from the bed.
Original languageEnglish
Pages (from-to)464-474
Number of pages11
JournalJournal of Hydraulic Research
Volume57
Issue number4
Early online date28 Aug 2018
DOIs
Publication statusPublished - 2019

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entrainment
particle motion
Ballistics
collision
Trajectories
particle
experimental study
trajectory

Keywords

  • bedload
  • entrainment
  • particle diffusion
  • particle velocity
  • sediment transport
  • turbulence–sediment interactions
  • turbulence–sediment interactions
  • Bedload
  • TRANSPORT
  • MOTION
  • DIFFUSION
  • OPEN-CHANNEL
  • FLOWS
  • turbulence-sediment interactions

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Bed particle dynamics at entrainment. / Witz, Matthew J (Corresponding Author); Cameron, Stuart; Nikora, Vladimir Ivanovich.

In: Journal of Hydraulic Research, Vol. 57, No. 4, 2019, p. 464-474.

Research output: Contribution to journalArticle

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abstract = "The paper reports a high-resolution experimental study focused on statistical properties of particle trajectories starting with detachment from the bed. This local range of particle motion can either be considered to start from a collision with the bed of an already mobile particle, or from the entrainment of a previously immobile particle. Both approaches are investigated and compared based on the particle diffusion concept. From the point of entrainment, local particle diffusion in all three coordinate directions displays an exponent significantly greater than that of ballistic diffusion. In contrast, particle motion after collision with the bed demonstrates ballistic diffusion in all three coordinate directions. The results highlight clear differences between the diffusion of an already mobile particle and one starting from a position of rest. These differences are attributed to variations in physical mechanisms acting at the initial phase of particle motion after detachment from the bed.",
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note = "The reported work was partly supported by Engineering and Physical Sciences Research Council [EPSRC(UK)], Grant EP/G056404/1 “High resolution numerical and experimental studies of turbulence-induced sediment erosion and near-bed transport” and Grant EP/K041088/1 “Bed friction in rough-bed free-surface flows: a theoretical framework, roughness regimes, and quantification”.",
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