Predicting the morphodynamics of sedimentary landscapes due to fluvial and aeolian flows requires answering following questions: Is flow strong enough initiate sediment transport, is sustain transport once initiated, how much transported by in saturated state (i.e., what capacity)? In geomorphological related literature, widespread consensus has been that initiation, cessation, capacity initiation are controlled fluid entrainment bed caused forces overcoming local resisting forces, whereas...

We report on chute measurements of the free-surface velocity $v$ in dense flows spheres and diverse sands spheres-sand mixtures down rough inclines. These previous are inconsistent with standard flow rules, which Froude number $v/\sqrt{gh}$ scales linearly $h/h_s$ or $(\tan\theta/\mu_r)^2h/h_s$, where $\mu_r$ is dynamic friction coefficient, $h$ thickness, $h_s(\theta)$ its smallest value that permits a steady, uniform state at given inclination angle $\theta$. This because characteristic...

Here we address the old question in aeolian particle transport about role of midair collisions. We find that, surprisingly, these collisions do enhance overall flux substantially. The effect depends strongly on restitution coefficient and wind speed. can explain this observation as a consequence soft bed grains which floats above ground reflects highest flying particles. make unexpected that is maximized at an intermediate 0.7, comparable to values experimentally measured for between sand grains.

Sediment transport along the surface drives geophysical phenomena as diverse wind erosion and dune formation. The main length scale controlling dynamics of sediment deposition is saturation Ls, which characterizes flux response to a change in conditions. Here we derive, for first time, an expression predicting Ls function average velocity under different physical environments. Our accounts both characteristics entrainment particle fluid velocities, has only two parameters can be estimated...

One of the physically least understood characteristics geophysical transport sediments along sediment surfaces is well-known experimental observation that rate Q linearly dependent on fluid shear stress τ applied onto surface in air, but nonlinearly water. Using simulations for a wide range driving conditions, we show scaling depends manner which kinetic fluctuation energy transported particles dissipated: via predominantly drag and quasistatic contacts (linear) versus collisional...

We reveal that the transition in saturated flux for aeolian saltation is generically discontinuous by explicitly simulating particle motion turbulent flow. This first time a jump has been observed. The discontinuity followed coexistence interval with two metastable solutions. modification of wind profile due to momentum exchange exhibits maximum at high shear strength.

Using particle-scale simulations of non-suspended sediment transport for a large range Newtonian fluids driving transport, including air and water, we determine the bulk cessation threshold $\Theta^r_t$ by extrapolating load as function dimensionless fluid shear stress (`Shields number') $\Theta$ to vanishing limit. In this limit, simulated steady states continuous can be described simple analytical model equations relating average layer properties law wall flow velocity profile. We use...

The turbidity current (TC), a ubiquitous fluid–particle coupled phenomenon in the natural environment and engineering, can transport over long distances on an inclined terrain due to suspension mechanism. A large-eddy simulation discrete element method model is employed simulate particle-laden gravity currents slope order investigate auto-suspension mechanism from Lagrangian perspective. particle Reynolds number our TC $0.01\sim 0.1$ angle $1/20 \sim 1/5$ . influences of initial...

Dry, wet, dense, and dilute granular flows have been previously considered fundamentally different thus described by distinct, in many cases incompatible, rheologies. We carry out extensive simulations of flows, including wet dry conditions, various geometries driving mechanisms (boundary driven, fluid gravity driven), which are not captured standard rheology models. For all simulated except for fluid-driven gravity-driven close to the flow threshold, we find that Mohr-Coulomb friction...

Abstract Nonsuspended sediment transport (NST) refers to the regime in which flow turbulence is unable support weight of transported grains. It occurs fluvial environments (i.e., driven by a stream liquid) and aeolian wind‐blown) plays key role shaping sedimentary landscapes planetary bodies. NST highly fluctuating physical process because turbulence, surface inhomogeneities, variations grain size shape packing geometry. Furthermore, energy grains varies strongly due their exposure duration...

Abstract Aeolian sand transport is a major process shaping landscapes on Earth and diverse celestial bodies. Conditions favoring bimodal transport, with fine-grain saltation driving coarse-grain reptation, give rise to the evolution of megaripples characteristic composition. Here, we derive unified phase diagram for this special aeolian ensuing nonequilibrium megaripple morphodynamics by means conceptually simple quantitative model, grounded in grain-scale physics. We establish...

It has been a great challenge to develop robots that are able perform complex movement patterns with high speed and, simultaneously, accuracy. Copepods animals found in freshwater and saltwater habitats can have extremely fast escape responses when predator is sensed by performing explosive curved jumps. In this study, we present design build prototypes of combustion-driven underwater soft robot, the "copebot," which, similar copepods, accurately reach nearby predefined locations space...

Landslide deposits often exhibit surface features, such as transverse ridges and X-shaped conjugate troughs, whose physical formation origins are not well understood. To study the deposit morphology, laboratory studies typically focus on simplest landslide geometry: an inclined plane accelerating sliding mass immediately followed by its deceleration a horizontal plane. However, existing experiments have been conducted only for limited range of slope angle θ. Here, we effect θ kinematics...

We experimentally and computationally analyze impact-shock-induced stress wave propagation in packings of disordered flexible fibers. find that dispersive propagation, associated with large attenuation, occurs much more prevalently systems larger fiber aspect ratios moderate flexibility. trace these features to the microstructural properties contact chains energy-trapping abilities deformable These findings provide insights into physics shock-impacted open way toward an improved...

We report on chute measurements of the free-surface velocity $v$ in dense flows spheres and diverse sands spheres-sand mixtures down rough inclines. These previous are inconsistent with standard flow rules, which Froude number $v/\sqrt{gh}$ scales linearly $h/h_s$ or $(\tan\theta/\mu_r)^2h/h_s$, where $\mu_r$ is dynamic friction coefficient, $h$ thickness, $h_s(\theta)$ its smallest value that permits a steady, uniform state at given inclination angle $\theta$. This because characteristic...

We present a comprehensive analytical model of aeolian sand transport in saltation.It quantifies the momentum transfer from wind to transported by providing expressions for thickness saltation layer and apparent surface roughness.These are first time entirely derived basic physical principles.The further predicts rate (mass flux) impact threshold shear velocity.We show that predictions very good agreement with experiments numerical state art simulations saltation.

The transport of sediment by a fluid along the surface is responsible for dune formation, dust entrainment, and rich diversity patterns on bottom oceans, rivers, planetary surfaces. Most previous models have focused equilibrium (or saturated) particle flux. However, morphodynamics landscapes emerging due to controlled situations out equilibrium. In particular, it saturation length characterizing distance takes flux reach new after change in flow conditions. mass density particles entrained...

In steady sediment transport, deposition is balanced by entrainment of bed particles fluid forces or particle-bed impacts. Here we propose a proxy to determine the role impact relative mean turbulent flow: "bed velocity" $V_b$, which an effective near-bed-surface value average horizontal particle velocity that generalizes classical slip velocity, used in studies aeolian saltation transport arbitrary Newtonian fluid. We study $V_b$ for wide range particle-fluid-density ratio $s$, Galileo...

The role of coherent airflow structures capable setting gravel-size particles in motion is studied theoretically and experimentally. Specifically, a micromechanical model based on energy conservation proposed to describe the incipient large ranging from rocking (incomplete entrainment) rolling (full entrainment). Wind tunnel experiments were conducted an aerodynamically rough bed surface under near-threshold conditions. Synchronous signals velocities upwind test particle displacement are...

Granular materials transition between unjammed (deformable) and jammed (rigid) states when adjusting their packing density. Here, we report on experiments demonstrating that the same kind of phase can be alternatively achieved through temperature-controlled particle shape change. Using a confined system randomly-packed rod-like particles made memory alloy (SMA), exploit recovery these bent rods with rising temperature at constant density leads to state. The responsible physical processes are...

Avalanches of dry granular materials, such as rocks, snow, and ice, are chief contributors to hazardous geophysical flows in nature. A key problem hampering progress predicting the destructiveness hazards is poorly understood dependence flow velocity on physical properties grains constituting a given material. In particular, their usually irregular, non-spherical shapes prevent application rigorous theories, which were derived for spherical grains. addition, we do not have good empirical...

Here, we study the old problem of why identical insulators can charge one another on contact. We perform several experiments showing that, if driven by a preexisting electric field, is transferred between contacting insulators. This happens because insulator surfaces adsorb small amounts water from humid atmosphere. believe field then separates positively negatively charged ions prevailing within water, which to be hydronium and hydroxide ions, such that at point contact, positive neutralize...

We find that the granular friction coefficient and other local quantities controlling scaling behavior of sediment transport vary only little across all simulated conditions when evaluated at interface between solid-like bed gas-like layer.