Relationship between sediment connectivity and debris flow in a mountain catchment

2021 ◽  
Author(s):  
Bruno Henrique Abatti ◽  
Franciele Zanandrea ◽  
Leonardo Rodolfo Paul ◽  
Gean Paulo Michel
Keyword(s):  
Sediment Transport ◽  
Debris Flow ◽  
Flow Direction ◽  
Rectangular Channel ◽  
Computational Modelling ◽  
Horizontal Resolution ◽  
Mass Movements ◽  
Channel Coupling ◽  
High Magnitude ◽  
Sediment Connectivity

<p>The hillslope-channel coupling has a fundamental role in sediment control of a catchment, especially when the catchment is prone to mass movements. Debris flow is a type of mass movements that provides an important sediment contribution to a channel, which is influenced by hillslope-channel coupling degree. This coupling can be represented by the connectivity, a concept utilized as an approach to many queries regarding water and/or sediment transport through methodologies which relates a river with its drainage area. In this regard, this study addresses the representation of debris flow in terms of connectivity. We applied a debris flow computational modelling (DFM) and an index of connectivity (IC) in Mascarada catchment, south Brazil, where hundreds of mass movements were triggered in 2017, to evaluate the potential, limitations and capacity of IC to represent patterns of mass movements’ connectivity. The IC is calculated for each cell of the catchment’s digital elevation model (DEM) (horizontal resolution of 1 m) in relation to the drainage network. Therefore, the IC represents the lateral connectivity (hillslope-channel) and its capacity to mobilize sediment to the channel. The DFM utilizes the Multiple Flow Direction to distribute volumes of a fluid with a determined kinematic viscosity through a slope, originated from initiation areas with a depth pre-determined by the user. The model utilizes uniform and steady flow solutions for Newtonian fluid, considering a rectangular channel. The DFM simulated the observed debris flow reasonably well, with an accuracy of 68%. However, since the simulation reached the channel and carried the volumes beyond the observed debris flow scar, it presented an overestimation area of 65%. When relation the simulated debris flow paths with the IC, we observed a superposition between those paths and high IC values. Also, the results showed a pixel-by-pixel positive linear correlation between high flow depths (representing convergence of flow) and IC, with values varying from 0,1 and 0,5. Only one of the nine simulated debris flow did not reach the channel and it had the lowest mean IC value along its flow path. Simulated debris flow that reached the channel showed high hillslope-channel connectivity, denoting the important role of high magnitude sediment transport events in sediment connectivity. Therefore, the IC was capable to represent and indicate patterns of debris flow that reached the channel. Though, the results also indicated that IC must be carefully interpreted when employed to understand debris flow and related processes – some areas have high fluid depth due to low connectivity, but others have high depth in response of convergence of flow due to highly connected areas. In this regard, an integration of connectivity and debris flow modelling tools can by an important step to understand sediment connectivity and to represent patterns of high magnitude mass movements events.</p>

scholarly journals Numerical Analysis of Unsteady Laminar Flow past a Pentagonal Obstacle

2021 ◽  
Vol 10 (2) ◽  
pp. 968-974
Keyword(s):  
Laminar Flow ◽  
Flow Direction ◽  
Rectangular Channel ◽  
Time Frame ◽  
Two Dimensional ◽  
Fluid Inertia ◽  
Time Step ◽  
The Face ◽  
Computational Fluid Dynamics Cfd ◽  
Current Article

The current article dispenses the numerical investigation of a two dimensional unsteady laminar flow of incompressible fluid passing a regular pentagonal obstacle in an open rectangular channel. The centre of attention of this work is the comparison of drag coefficients estimated for two distinct cases based on the orientation of face and corner of an obstacle against the flow direction. The numerical results shows that the corner – oriented obstacle bring about 42% larger value of drag coefficient at Re = 500 than face – oriented obstacle. The substantial growth in the expanse of vortex behind obstacle (presented as a function of fluid inertia 25 < Re < 500) is analyzed through the contours and streamline patterns of velocity field. The two eddies in the downstream become entirely unsymmetrical at Re = 500 for both the cases, whereas; the flow separation phenomena occurs a bit earlier in the face – oriented case at Re = 250. Two dimensional Pressure – Based – Segregated solver is employed to model the governing equations written in velocity and pressure fields. The numerical simulations of unsteady flow are presented for 50 seconds time frame with time step 0.01 by using one of the best available commercial based Computational Fluid Dynamics (CFD) software, ANSYS 15.0.

scholarly journals An attempt to measure cycloidal rotor fan in a rectangular duct

2021 ◽  
Vol 345 ◽  
pp. 00029
Author(s):  
Tomasz Staśko ◽  
Mirosław Majkut ◽  
Sławomir Dykas ◽  
Krystian Smołka
Keyword(s):  
Air Conditioning ◽  
Flow Direction ◽  
Rectangular Channel ◽  
Velocity Fields ◽  
Laser Doppler ◽  
Marine Propeller ◽  
Rectangular Duct ◽  
Direct Control ◽  
Flow Rates

A fan with cycloidal rotor (CRF) becomes a popular idea in wide application such as aviation, HVAC (heat, ventilation and air conditioning) or marine propeller systems. This is due to advantages such as direct control of the flow direction, larger flow rates than in a conventional machines without cycloidal control. In the presented article, velocity fields of CRF placed in a rectangular channel was measured, using Laser Doppler Anemomentry (LDA) method and thermoanemometric probe (TA).

Viscomagnetic Heat Flux Experiments as a Test of Gas Kinetic Theory in the Burnett Regime

1978 ◽  
Vol 33 (7) ◽  
pp. 749-760 ◽  
Author(s):  
G. E. J. Eggermont ◽  
P. W. Hermans ◽  
L. J. F. Hermans ◽  
H. F. P. Knaap ◽  
J. J. M. Beenakker
Keyword(s):  
Magnetic Field ◽  
Boundary Layer ◽  
Heat Flux ◽  
External Magnetic Field ◽  
Room Temperature ◽  
Flow Direction ◽  
Rectangular Channel ◽  
Gas Kinetic Theory ◽  
The Magnetic Field ◽  
Good Agreement

In a rarefied polyatomic gas streaming through a rectangular channel, an external magnetic field produces a heat flux perpendicular to the flow direction. Experiments on this “viscom agnetic heat flux” have been performed for CO, N2, CH4 and HD at room temperature, with different orientations of the magnetic field. Such measurements enable one to separate the boundary layer contribution from the purely bulk contribution by means of the theory recently developed by Vestner. Very good agreement is found between the experimentally determined bulk contribution and the theoretical Burnett value for CO, N2 and CH4 , yet the behavior of HD is found to be anomalous.

scholarly journals Submarine Slope Stability of a Fjord Delta: Bella Coola, British Columbia

2007 ◽  
Vol 43 (1) ◽  
pp. 87-95 ◽  
Author(s):  
Ray A. Kostaschuk ◽  
S. Brian McCann
Keyword(s):  
British Columbia ◽  
High Frequency ◽  
Low Frequency ◽  
Mass Movements ◽  
Wave Loading ◽  
Gas Generation ◽  
Source Areas ◽  
High Magnitude ◽  
Pore Water Pressures ◽  
Bella Coola

ABSTRACT Recent evidence indicates that the submarine slopes of the Bella Coola Delta, a fjord delta in British Columbia, are subject to mass movements. Mass movements originate in the source areas of chutes (gullies) and transfer coarse sediment downslope. Stability analyses indicate that earthquakes, depositional loading and wave loading are capable of causing slope failures in chute source areas. Gas generation and tidal drawdown appear to reduce sediment strength by increasing pore water pressures, increasing the potential for failures initiated by other mechanisms. Failure related to slope over-steepening at distributary mouths would require much steeper slopes than those encountered. The most unstable areas are those at distributary mouths where most of the mechanisms of failure generation could occur simultaneously. With the exception of earthquakes, the failure mechanisms examined would result in high frequency, low magnitude slides that are most likely to occur in spring and summer. Earthquakes would cause high magnitude, low frequency failures.

Heat Transfer in a Rotating Two-Pass Rectangular Channel Featuring Reduced Cross-Sectional Area After Tip Turn (Aspect Ratio = 4:1 to 2:1) With Profiled 60 deg Angled Ribs

2019 ◽  
Vol 141 (7) ◽  
Author(s):  
Andrew F Chen ◽  
Chao-Cheng Shiau ◽  
Je-Chin Han ◽  
Robert Krewinkel
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Aspect Ratio ◽  
Flow Direction ◽  
Rectangular Channel ◽  
Secondary Flows ◽  
Transfer Coefficients ◽  
First Passage ◽  
Cross Sectional ◽  
Internal Surfaces

The present study features a two-pass rectangular channel with an aspect ratio (AR) = 4:1 in the first pass and an AR = 2:1 in the second pass after a 180-deg tip turn. In addition to the smooth-wall case, ribs with a profiled cross section are placed at 60 deg to the flow direction on both the leading and trailing surfaces in both passages (P/e = 10, e/Dh ∼ 0.11, parallel and in-line). Regionally averaged heat transfer measurement method was used to obtain the heat transfer coefficients on all internal surfaces. The Reynolds number (Re) ranges from 10,000 to 70,000 in the first passage, and the rotational speed ranges from 0 to 400 rpm. Under pressurized condition (570 kPa), the highest rotation number achieved was Ro = 0.39 in the first passage and 0.16 in the second passage. The results showed that the turn-induced secondary flows are reduced in an accelerating flow. The effects of rotation on heat transfer are generally weakened in the ribbed case than the smooth case. Significant heat transfer reduction (∼30%) on the tip wall was seen in both the smooth and ribbed cases under rotating condition. Overall pressure penalty was reduced for the ribbed case under rotation. Reynolds number effect was found noticeable in the current study. The heat transfer and pressure drop characteristics are sensitive to the geometrical design of the channel and should be taken into account in the design process.

scholarly journals Bedforms in a turbulent stream: ripples, chevrons and antidunes

2011 ◽  
Vol 690 ◽  
pp. 94-128 ◽  
Author(s):  
Bruno Andreotti ◽  
Philippe Claudin ◽  
Olivier Devauchelle ◽  
Orencio Durán ◽  
Antoine Fourrière
Keyword(s):  
Free Surface ◽  
Sediment Transport ◽  
Flow Direction ◽  
Linear Instability ◽  
Physical Parameters ◽  
Flow Depth ◽  
Supercritical Regime ◽  
Free Surface Waves ◽  
Alternate Bars ◽  
Flooding Events

AbstractThe interaction between a turbulent flow and a granular bed via sediment transport produces various bedforms associated with distinct hydrodynamical regimes. In this paper, we compare ripples (downstream-propagating transverse bedforms), chevrons and bars (bedforms inclined with respect to the flow direction) and antidunes (upstream-propagating bedforms), focusing on the mechanisms involved in the early stages of their formation. Performing the linear stability analysis of a flat bed, we study the asymptotic behaviours of the dispersion relation with respect to the physical parameters of the problem. In the subcritical regime (Froude number $\mathscr{F}$ smaller than unity), we show that the same instability produces ripples or chevrons depending on the influence of the free surface. The transition from transverse to inclined bedforms is controlled by the ratio of the saturation length ${L}_{\mathit{sat}} $, which encodes the stabilizing effect of sediment transport, to the flow depth $H$, which determines the hydrodynamical regime. These results suggest that alternate bars form in rivers during flooding events, when suspended load dominates over bedload. In the supercritical regime $\mathscr{F}\gt 1$, the transition from ripples to antidunes is also controlled by the ratio ${L}_{\mathit{sat}} / H$. Antidunes appear around resonant conditions for free surface waves, a situation for which the sediment transport saturation becomes destabilizing. This resonance turns out to be fundamentally different from the inviscid prediction. Their wavelength selected by linear instability mostly scales on the flow depth $H$, which is in agreement with existing experimental data. Our results also predict the emergence, at large Froude numbers, of ‘antichevrons’ or ‘antibars’, i.e. bedforms inclined with respect to the flow and propagating upstream.

Variable Property and Temperature Ratio Effects on Nusselt Numbers in a Rectangular Channel With 45 Deg Angled Rib Turbulators

2003 ◽  
Vol 125 (5) ◽  
pp. 769-778 ◽  
Author(s):  
G. I. Mahmood ◽  
P. M. Ligrani ◽  
K. Chen
Keyword(s):  
Flow Direction ◽  
Rectangular Channel ◽  
Channel Height ◽  
Global Changes ◽  
Stagnation Temperature ◽  
Temperature Ratio ◽  
Height Range ◽  
Nusselt Numbers ◽  
Friction Factors ◽  
Rib Turbulators

Measured local and spatially-averaged Nusselt numbers and friction factors (all time-averaged) are presented which show the effects of temperature ratio and variable properties in a rectangular channel with rib turbulators, and an aspect ratio of 4. The ratio of air inlet stagnation temperature to local surface temperature Toi/Tw varies from 0.66 to 0.95, and Reynolds numbers based on channel height range from 10,000 to 83,700. The square cross-section ribs are placed on two opposite surfaces, and are oriented at angles of +45 deg and −45 deg, respectively, with respect to the bulk flow direction. The ratio of rib height to channel hydraulic diameter is 0.078, the rib pitch-to-height ratio is 10, and the ribs block 25 percent of the channel cross-sectional area. Ratios of globally-averaged rib Nusselt numbers to baseline, constant property Nusselt numbers, Nu̿/Nuo,cp, increase from 2.69 to 3.10 as the temperature ratio Toi/Tw decreases from 0.95 to 0.66 (provided Reynolds number ReH is approximately constant). Friction factor ratios f/fo,cp then decrease as Toi/Tw decreases over this same range of values. In each case, a correlation equation is given which matches the measured global variations. Such global changes are a result of local Nusselt number ratio increases with temperature ratio, which are especially pronounced on the flat surfaces just upstream and just downstream of individual ribs. Thermal performance parameters are also given, which are somewhat lower in the ribbed channel than in channels with dimples and/or protrusions mostly because of higher rib form drag and friction factors.

scholarly journals An assessment of soil loss and natural hazards in Nepal

2000 ◽  
Vol 21 ◽  
Author(s):  
Dinesh R. Shiwakoti
Keyword(s):  
Soil Erosion ◽  
Debris Flow ◽  
Soil Loss ◽  
Surface Soil ◽  
Mass Movements ◽  
Critical Factors ◽  
Outburst Flood ◽  
Paper Briefly ◽  
Grass Roots ◽  
The Status

This paper briefly reviews the status of soil erosion in Nepal, and examines the major causes and factors leading to soil erosion and mass movements. There are the following four major mechanisms associated with soil loss: a) surface soil erosion, b) landslide and debris flow, c) earthquake, and d) glacier lake outburst flood. Effective methods for investigating, analysing, identifying, and implementing the critical factors for protecting accelerated soil loss in a planned manner are essential from the grass roots to national and international levels.

scholarly journals DESAIN SABO DAM TIPE CONDUIT SEBAGAI PENGENDALI DAYA RUSAK ALIRAN DEBRIS

2020 ◽  
Vol 16 (2) ◽  
pp. 105-116
Author(s):  
Yuli Fajarwati ◽  
Teuku Faisal Fathani ◽  
Fikri Faris ◽  
Wahyu Wilopo
Keyword(s):  
Rock Mass ◽  
Debris Flow ◽  
Return Period ◽  
Mass Movements ◽  
Flow Depth ◽  
Overturning Stability ◽  
Sediment Flow ◽  
The Stability ◽  
Building Stability ◽  
Flood Condition

ABSTRAKSungai Air Kotok di Kabupaten Lebong, Bengkulu memiliki litologi batuan yang rapuh akibat pengaruh panas bumi, kondisi tersebut menyebabkan rentan mengalami pergerakan massa tanah/batuan. Oleh karena itu, diperlukan upaya mitigasi untuk mengurangi risiko bencana dengan perencanaan bangunan pengendali aliran debris berupa sabo dam. Penelitian ini bertujuan untuk merencanakan desain sabo dam tipe conduit yang dirancang secara seri dan mengevaluasi stabilitas sabo dam berdasar SNI 2851:2015. Hasil perhitungan menunjukkan debit puncak untuk kala ulang 100 tahun sebesar 171,21 m3/detik. Empat seri sabo dam memiliki dimensi lebar pelimpah rerata ± 40 m, kedalaman aliran debris sebesar 1 m, dan tinggi pelimpah ialah 2,4 m. Stabilitas sabo dam saat banjir diperoleh faktor aman untuk stabilitas geser dan guling sebesar 3,46 ; 1,62. Adapun faktor aman terhadap pengaruh aliran debris untuk stabilitas geser dan guling adalah 3,30 ; 1,58. Berdasarkan hasil analisis, empat seri sabo dam tipe conduit yang dirancang mampu mengendalikan daya rusak banjir maupun aliran debris.Kata kunci: Hidraulika sungai, aliran sedimen, bangunan sabo, stabilitas sabo ABSTRACTAir Kotok River in Lebong Regency, Bengkulu Province has the lithology of weathered rock which is a result of geothermal process, this condition causes to be susceptible to land / rock mass movements. Therefore, the mitigation efforts are needed to reduce the risk from disaster by design debris flow control such as sabo dam. This study aims to design series of conduit type sabo dam and evaluate the stability based on SNI 2851: 2015. The calculation shows that the peak discharge for the 100-year return period is 171.21 m3 / sec. The four sabo dam series have dimensions of spill width of ± 40 m, debris flow depth of 1 m, and overflow height of 2.4 m. The stability of sabo dam has safety factor in flood condition for shear and overturning stability are 3.46; 1.62, while in a debris flow condition for shear and overturning stability are 3.30; 1.58. Based on the results, the four series of conduit sabo dam are able to control the destructive power of floods and debris flows.Key word: River hydraulic, sediment flow, sabo building, stability of sabo

Investigation of a High Aspect Ratio Rectangular Channel With High Blockage Ratio Round-Corner Ribs

2004 ◽  
Author(s):  
Christophe Diette ◽  
Tony Arts ◽  
Olivier Sgarzi ◽  
Emmanuel Laroche
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
High Aspect Ratio ◽  
Large Scale ◽  
Flow Direction ◽  
Flow Behavior ◽  
Rectangular Channel ◽  
Internal Cooling ◽  
Liquid Crystal Thermography ◽  
Main Flow Direction

The flow behavior and heat transfer were measured in a large scale, high aspect ratio, turbine blade rib-roughened internal cooling channel. The ribs, installed on one wall, were inclined at 90 deg with respect to the main flow direction and generated a blockage of 20%. The rib corners were rounded to take into account manufacturing aspects. The bulk flow Reynolds number was 20,000. Pressure drop and velocity measurements were first conducted. Liquid crystal thermography was applied to quantify the heat transfer, not only along the ribbed and the smooth opposite walls but also on the rib itself. Numerical simulations were conducted with two flow solvers, IGG/FINE (Numeca) and MSD (ONERA) and compared with measurements. They also supported the analysis of the flow behavior. The influence of round-corner versus sharp edge ribs was numerically evaluated with IGG/FINE.

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