Influence of Pocket Geometry on the Incipient Entrainment of Coarse Particles in Turbulent Flows

The incipient motion of coarse particles critically governs bed stability, sediment transport dynamics, and geomorphic evolution in turbulent flows, with profound implications for riverbed destabilization, flood risk, and the integrity of hydraulic infrastructure. Despite extensive research, the ways under which microtopographic pocket arrangements—clusters or depressions formed by particle packing— modulate entrainment thresholds remains relatively underexplored. 
This presentation aims to outline the effects of varied pocket configurations on the critical hydraulic conditions required for particle entrainment under turbulent flow fields. Utilizing instrumented particles equipped with inertial measurement units (IMUs) [1, 2] to record high-fidelity particle accelerations and angular velocities, we probe both particle kinematics and dynamics, at the onset of motion. Novel flow-particle interaction metrics, derived from these measurements, reveal the underlying physical mechanisms—such as torque imbalances and lift generation—that drive or resist entrainment.
We hypothesize that subtle differences in pocket geometry and orientation can substantially elevate or lower the entrainment threshold, necessitating distinct flow field characteristics (e.g., shear stress and turbulence intensity) for motion initiation [3, 4]. Preliminary results from controlled flume experiments demonstrate threshold shifts across configurations, underscoring the sensitivity of bed stability to local topography. 
These insights aim to highlight the transformative potential of IMU-based instrumentation for real-time risk assessment of riverbed and bank destabilization in natural streams, as well as scour development in engineered channels, for sustainable river management and infrastructure resilience.
 
References
1. Al-Obaidi K, Xu Y, Valyrakis M. The design and calibration of instrumented particles for assessing water infrastructure hazards. J Sens Actuator Netw. 2020;9(3):36. doi:10.3390/jsan9030036.
2. Al-Obaidi K, Valyrakis M. A sensory instrumented particle for environmental monitoring applications: development and calibration. IEEE Sens J. 2021;21(8):10153-10166. doi:10.1109/JSEN.2021.3053080.
3. Al-Obaidi K, Valyrakis M. Linking the explicit probability of entrainment of instrumented particles to flow hydrodynamics. Earth Surf Process Landf. 2021;46(12):2448-2465. doi:10.1002/esp.5178.
4. Al-Obaidi K, Valyrakis M. Coherent flow structures linked to the impulse criterion for incipient motion of coarse sediment. Appl Sci (Basel). 2023;13(19):10656. doi:10.3390/app131910656.