Movement of Sand in Tunnels

Lysne, Dagfinn K.

doi:10.1061/jyceaj.0002192

Cited by 21 publications

(17 citation statements)

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“…Only the data from the upstream end of the rock traps were used. Lysne found that d = f V 2 = V 2 c with c = 130 fit well into Equation ( 8) for his results from both the lab and the measurements from tunnels [35]. Later experience apparently showed that C may vary in the range 115 to 140 [35].…”

Section: Theory Of Incipient Motionmentioning

confidence: 79%

“…where k = a constant that depends on the cross-section shape; A = cross-section area. By inserting (4) and ( 6) into (5), Lysne [3] developed the following formula for critical particle diameter as a function of velocity, cross section area, tunnel roughness, and particle Reynolds number:…”

Section: Theory Of Incipient Motionmentioning

confidence: 99%

“…where f V 2 = a function of the mean flow velocity squared. Lysne [3] did model tests to find a formula for critical particle diameter in a tunnel. In several experiments, a constant flow through a smooth-walled tunnel with sand particles on the invert was monitored.…”

Section: Theory Of Incipient Motionmentioning

confidence: 99%

“…As pressurized rock traps are designed to capture sediments that are transported as bedload, a suggested rule-of-thumb is that the weight proportion of the inflowing particles with a diameter smaller than 0.3 mm should be less than 30%. This criterion is based on grain size distribution curves from operational unlined hydropower tunnels and pressurized rock traps [3]. It should be noted that this rule-of-thumb assumes that the total amount of particles smaller than 0.3 mm is too small to cause significant damage to the turbine.…”

Section: Introductionmentioning

confidence: 99%

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Efficiency of Pressurized Rock Traps for Unlined Hydropower Tunnels

2021

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Pressurized rock traps are constructed in many hydropower plants to stop sand and gravel from being transported through the turbines. Pressurized rock traps are typically located in the downstream end of unlined headrace tunnels, where the tunnel itself may be one of the sediment sources. This state-of-the-art review presents an overview of research on pressurized rock traps from both publicly available sources and unpublished sources. Limited scientific literature exists on rock traps, and most of the existing literature has previously been unavailable for an international audience. Based on this review, it is concluded that pressurized rock traps should be built with the flow area and sediment deposition volume separated by plates or ribs. Without any separation measures, the sediments risk being re-entrained due to turbulence. This review is separated into three sections: (1) sediment problems and sources of sediments, (2) theory for pressurized rock traps, and (3) design of pressurized rock traps. The recommended design for new pressurized rock traps, including a design flow chart, is provided. Finally, a recommended solution for rebuilding existing pressurized rock traps with an open design into a closed design is also presented.

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Section: Theory Of Incipient Motionmentioning

confidence: 79%

Section: Theory Of Incipient Motionmentioning

confidence: 99%

Section: Theory Of Incipient Motionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Efficiency of Pressurized Rock Traps for Unlined Hydropower Tunnels

2021

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“…In model Proposition 1.iii) the gravity effect remains and the solid velocity is one order smaller than in the other models in Proposition 1. The importance of the gravity term was first evidenced in [14,27]. A model very similar to model Proposition 1.iii) was derived in [11] assuming a different scaling, i.e.…”

Section: Models With Local Sediment Dischargementioning

confidence: 90%

Asymptotic derivation and simulations of a non-local Exner model in large viscosity regime

2021

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The present paper deals with the modeling and numerical approximation of bed load transport under the action of water. A new shallow water type model is derived from the stratified two-fluid Navier-Stokes equations. Its novelty lies in the magnitude of a viscosity term that leads to a momentum equation of elliptic type. The full model, sediment and water, verifies a dissipative energy balance for smooth solutions. The numerical resolution of the sediment layer is not trivial since the viscosity introduces a non-local term in the model. Adding a transport threshold makes the resolution even more challenging. A schema based on a staggered discretization is proposed for the full model, sediment and water.

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Properties of a cellular braided-stream model

Murray

Paola

1997

Earth Surf. Process. Landforms

167

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We have shown in a previous paper that many of the main features of braided streams can be captured in a relatively simple cellular computer model. Here we examine some of the detailed characteristics of this model. We show the qualitative form of the braiding produced by the model is generally insensitive to changes in most of the numerical parameters used in the model. The most crucial parameter choice is the use of a non-linear exponent (>1) to describe the relation between sediment flux and local stream power. Use of water discharge instead of stream power to parameterize sediment flux produces braiding, but also unrealistically high-amplitude topography variations in the long term. Introduction of a threshold transport condition causes no noticeable change in the model's behaviour. Inclusion of lateral sediment transport due to gravitational effects on lateral slopes is not crucial to produce braiding, but is needed to provide reasonable lateral channel shifting, and to maintain a continuing dynamic behaviour. As long as lateral sediment transport is included, altering the initial topography for a run has no effect, other than a transient period of regrading. In addition, we show that there is a simple and apparently fundamental connection between braided-stream channel networks and erosional (dendritic) networks that has not been previously recognized. All that is needed to switch the model from braided to dendritic patterns is either to remove redeposition from the rules, simulating entrainment of cohesive sediment, or to add a cliff to the initial topography, making local redeposition unimportant. This result suggests that the presence or absence of significant local redeposition, which causes bar formation, channel division, and avulsion, determines whether a braided or dendritic pattern will form.

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Movement of Sand in Tunnels

Cited by 21 publications

References 0 publications

Efficiency of Pressurized Rock Traps for Unlined Hydropower Tunnels

Efficiency of Pressurized Rock Traps for Unlined Hydropower Tunnels

Asymptotic derivation and simulations of a non-local Exner model in large viscosity regime

Properties of a cellular braided-stream model

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