Computational Study of Roll Waves in Shallow Flow over Erodible Bed

Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv

Numerical Modeling of Hyperconcentrated Turbidity Currents

Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv

Computational Study of Flooding Due to Overtopping Breach of Landslide Dams

Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv

A numerical study of the settling of non-spherical particles in quiescent water

Settling of non-spherical particles is poorly understood with previous studies having focused mainly on spherical particles. Here, a series of particle-resolved direct numerical simulations are conducted using FLOW-3D (commercial computational fluid dynamics software) for spheres and five regular, non-spherical shapes of sediment particles, i.e., prolate spheroid, oblate spheroid, cylinder, disk, and cube. The Galileo number varies from 0.248 to 360, and the particle Reynolds number Rep ranges from 0.002 77 to 562. The results show that a non-spherical particle may experience larger drag and, consequently, attain a lower terminal velocity than an equivalent sphere. If Rep is sufficiently small, the terminal velocity is less affected by particle shape as characterized by the particle aspect ratio. For relatively large Rep, the shape effect (represented by the Corey shape factor) becomes more significant. Empirical correlations are derived for the dimensionless characteristic time t95∗ and displacement s95∗ of particle settling, which show that t95∗ remains constant in the Stokes regime (Rep &amp;lt; 1) and decreases with increasing Rep in the intermediate regime (1 ≤ Rep &amp;lt; 103), whereas s95∗ increases progressively with increasing Rep over the simulated range. It is also found that in the Stokes regime, particle orientation remains essentially unchanged during settling, and so the terminal velocity is governed by the initial orientation. In the intermediate regime, a particle provisionally settling at an unstable orientation self-readjusts to a stable equilibrium state, such that the effect of initial orientation on the terminal velocity is negligible. Moreover, an unstable initial orientation can enhance the vertical displacement and may promote vortex shedding.</jats:p

Full Hydrodynamic Modeling of Flash Flooding Due to Heavy Rainfall

Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv

Numerical Modeling of Shallow Flows over Irregular Topography

Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv

Turbulent Flow Overtopping a Dam - A CFD Modeling Study

Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv

Barrier lake formation due to landslide impacting a river: A numerical study using a double layer-averaged two-phase flow model

A granular landslide impacting a river may lead to the formation of a landslide dam blocking the streamflow, and subsequently create a barrier lake. Should a barrier lake outburst, the flood may be destructive and spell disastrous consequences downstream. The last decade or so has witnessed a number of experimental and numerical investigations on barrier lake outburst flooding, whilst studies on barrier lake formation remain rare – a physically enhanced and practically viable mathematical model is still missing. Generally, barrier lake formation is characterized by multi-physical, interactive processes between water flow, multi-sized sediment transport and morphological evolution. Here, a new double layer-averaged two-phase flow model is proposed, which is an advance on existing continuum models that involve a single-phase flow assumption and presume a single sediment size, and discrete models that preclude fine grains and assume narrow grain size distributions. The proposed model is first validated against data from previous laboratory experiments of waves due to landslides impacting reservoirs and landslide dam formation over dry valleys. Then it is applied to explore the complicated mechanism and threshold for barrier lake formation. The water and grain velocities are shown to be disparate, characterizing the primary role of grains in driving water movement during subaqueous landslide motion and also demonstrating the need for a two-phase flow approach. The grain size effects are revealed, i.e., coarse grains and grain-size uniformity favour barrier lake formation. A new threshold condition is proposed for barrier lake formation, integrating the landslide-to-river momentum ratio and grain size effects. The present work facilitates a promising modelling framework for solving barrier lake formation, thereby underpinning the assessment of flood hazards due to barrier lakes