Investigation of influence of an obstacle on granular flows by virtue of a depth-integrated theory

Meng, Xiannan; Wang, Yongqi; Chiou, M.J.; Zhou, Yunlai

doi:10.1016/j.euromechflu.2020.06.014

Cited by 3 publications

(5 citation statements)

References 56 publications

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“…The volume fraction of water φ w can therefore take three values 0, 1 − φ c or 1, where φ c is the solids volume fraction, which is constant and uniform throughout the granular phase. This latter assumption precludes excess pore fluid pressure effects (see Kowalski & McElwaine 2013;Bouchut et al 2016;Wang et al 2017;Meng & Wang 2018;Meng et al 2020). While the local water and grain concentrations in regimes (i)-(iii) are set in stone, the water height h w and the grain height h g are independent fields that determine the local vertical structure.…”

Section: Discussionmentioning

confidence: 99%

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Formation of dry granular fronts and watery tails in debris flows

2022

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Debris flows are particle–fluid mixtures that pose a significant hazard to many communities throughout the world. Bouldery debris flows are often characterised by a deep dry granular flow front, which is followed by a progressively thinner and increasingly watery tail. The formation of highly destructive bouldery wave fronts is usually attributed to particle-size segregation. However, the moving-bed flume experiments of Davies (N. Z. J. Hydrol., vol. 29, 1990, pp. 18–46) show that discrete surges with dry fronts and watery tails also form in monodisperse particle–fluid mixtures. These observations motivate the development of a new depth-averaged mixture theory for debris flows, which explicitly takes account of the differing granular and phreatic surfaces, velocity shear, and relative motion between grains and fluid to explain these phenomena. The theory consists of four coupled conservation laws that describe the spatial and temporal evolution of the grain and water thicknesses and depth-averaged velocities. This system enables travelling wave solutions to be constructed that consist of (i) a large amplitude dry flow front that smoothly transitions to (ii) an undersaturated body, (iii) an oversaturated region and then (iv) a pure water tail. It is shown that these solutions are in good quantitative agreement with Davies’ experiments at high bed speeds and slope inclinations. At lower bed speeds and inclinations, the theory produces travelling wave solutions that connect to a steady-uniform upstream flow, and may or may not have a bulbous flow front, consistent with Davies’ observations.

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Section: Discussionmentioning

confidence: 99%

“…2017; Meng & Wang 2018; Meng et al. 2020). While the local water and grain concentrations in regimes (i)–(iii) are set in stone, the water height and the grain height are independent fields that determine the local vertical structure.…”

Section: Discussionmentioning

confidence: 99%

Formation of dry granular fronts and watery tails in debris flows

2022

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“…2016; Rocha, Johnson & Gray 2019), debris flows (Meng et al. 2018, 2020) and submarine landslides (Sun et al. 2023).…”

Section: Methodsmentioning

confidence: 99%

“…Numerical method The system of conservation laws (3.5)-(3.8) is solved numerically using the shock-capturing non-oscillatory central scheme of Kurganov & Tadmor (2000). This robust scheme has been used to successfully solve a number of closely related systems of conservation laws for dry granular flows (Edwards & Gray 2015;Baker et al 2016;Rocha, Johnson & Gray 2019), debris flows (Meng et al , 2020 and submarine landslides (Sun et al 2023). The method is a semidiscrete Riemann-free solver that maintains the non-oscillatory property by using a flux limiter.…”

Section: Numerical Methods and Physical Parametersmentioning

confidence: 99%

Granular-fluid avalanches: the role of vertical structure and velocity shear

Meng,

Taylor-Noonan,

Johnson

et al. 2024

J. Fluid Mech.

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Field observations of debris flows often show that a deep dry granular front is followed by a progressively thinner and increasingly watery tail. These features have been captured in recent laboratory flume experiments (Taylor-Noonan et al., J. Geophys. Res.: Earth Surf., vol. 127, 2022, e2022JF006622). In these experiments different initial release volumes were used to investigate the dynamics of an undersaturated monodisperse grain–water mixture as it flowed downslope onto a horizontal run-out pad. Corresponding dry granular flows, with the same particle release volumes, were also studied to show the effect of the interstitial fluid. The inclusion of water makes debris flows much more mobile than equivalent volumes of dry grains. In the wet flows, the formation of a dry front is crucially dependent on the heterogeneous vertical structure of the flow and the velocity shear. These effects are included in the depth-averaged theory of Meng et al. (J. Fluid Mech., vol. 943, 2022, A19), which is used in this paper to quantitatively simulate both the wet and dry experimental flows using a high-resolution shock-capturing scheme. The results show that velocity shear causes dry grains (located near the free surface) to migrate forwards to create a dry front. The front is more resistant to motion than the more watery material behind, which reduces the overall computed run-out distance compared with debris-flow models that assume plug flow and develop only small dry snouts. Velocity shear also implies that there is a net transport of water to the back of the flow. This creates a thin oversaturated tail that is unstable to roll waves in agreement with experimental observations.

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“…The fluid can penetrate this interface. Analogous to the model of Iverson and George (2014), the present theory does not explicitly take into account the tangential percolation of fluid through the grain skeleton in the mixture regime, but the vertical relative motion between grains and fluid is characterized using the granular dilatancy law (see Meng et al., 2020; Pailha & Pouliquen, 2009; Roux & Radjai, 1997). In this way, the form of the current depth‐averaged equations is manipulable, though nonconservative products emerge.…”

Section: Introductionmentioning

confidence: 99%

A Depth‐Averaged Description of Submarine Avalanche Flows and Induced Surface Waves

et al. 2023

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Submarine avalanche flows are very destructive to infrastructure. A devastating example is that of a December 2006 submarine avalanche flow in the southwestern sea of Taiwan, which had a major impact on submarine telecommunications cables, interrupting communication between Taiwan and Southeast Asia countries for 12 hours (see Hsu et al., 2008). Moreover, submarine landslides could induce free-surface water waves and even tsunami waves characterized by locally high amplitudes and run up, which can be extraordinarily devastative in the coastline regions and confined water bodies (Mohammed & Fritz, 2012). A typical example is the 1964 Alaska earthquake, which triggered massive subaerial and submarine landslides. These landslides generated extremely destructive tsunami waves that caused significant damage and loss of life along the Alaska coast and as far away as Hawaii and California. The tsunami caused additional damage to buildings and infrastructure, and many coastal communities were completely destroyed. In total, the earthquake and tsunami resulted in 139 deaths and caused an estimated $ 2.3 billion in property losses (in 2013 dollars) (see Brocher et al., 2014). This provides strong motivation for the study of submarine landslides and resulting water waves, in an effort to minimize damage to people and infrastructures.Seafloor observation shows that cohesionless and coarse particles, entraining ambient water, move rapidly down a steep continental slope driven by gravity, forming a layered structure. A dense particle layer develops near the bottom, above which a turbidity current forms whose density is smaller and which could travel a relatively long

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Investigation of influence of an obstacle on granular flows by virtue of a depth-integrated theory

Cited by 3 publications

References 56 publications

Formation of dry granular fronts and watery tails in debris flows

Formation of dry granular fronts and watery tails in debris flows

Granular-fluid avalanches: the role of vertical structure and velocity shear

A Depth‐Averaged Description of Submarine Avalanche Flows and Induced Surface Waves

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