Prospects of Debris Flow Studies from Constitutive Relations to Governing Equations

2011 ◽  
Vol 6 (3) ◽  
pp. 313-320 ◽  
Author(s):  
Shinji Egashira ◽  
Keyword(s):  
Debris Flow ◽  
Constitutive Relations ◽  
Sediment Concentration ◽  
Phase Shifting ◽  
Flow Structures ◽  
Spatial Average ◽  
Governing Equations ◽  
Erosion And Deposition ◽  
Sediment Sorting ◽  
The Difference

The author thinks keys to debris flow studies lie in 1) sediment sorting in debris flow body, 2) phase shifting to or from fluid to solid, 3) difference between sediment concentration and flux sediment concentration, 4) constitutive relations and 5) governing equations employed in numerical simulation. In discussing 3)-5), the author stresses that 1) Eq. (1) predicts the spatial average sediment concentration of the flow body well from debris flow to bed load, and thus it should be prized, 2) researchers must be careful for the difference between sediment concentration and flux sediment concentration and for different flow structures over erodible and rigid beds, and realizes that 3) many problems associated with governing equations such as bed shear stress, erosion and deposition rates and correction parameters for sediment transport still remain to be solved.

Modulation instability in nonlinear chiral fiber

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Demissie Jobir Gelmecha ◽  
Ram Sewak Singh
Keyword(s):  
Theoretical Model ◽  
Numerical Simulations ◽  
Pulse Propagation ◽  
Modulation Instability ◽  
Constitutive Relations ◽  
Gain Spectrum ◽  
Circularly Polarized ◽  
Left Handed ◽  
Simulation Results ◽  
The Difference

AbstractIn this paper, the rigorous derivations of generalized coupled chiral nonlinear Schrödinger equations (CCNLSEs) and their modulation instability analysis have been explored theoretically and computationally. With the consideration of Maxwell’s equations and Post’s constitutive relations, a generalized CCNLSE has been derived, which describes the evolution of left-handed circularly polarized (LCP) and right-handed circularly polarized (RCP) components propagating through single-core nonlinear chiral fiber. The analysis of modulation instability in nonlinear chiral fiber has been investigated starting from CCNLSEs. Based on a theoretical model and numerical simulations, the difference on the modulation instability gain spectrum in LCP and RCP components through chiral fiber has been analyzed by considering loss and chirality into account. The obtained simulation results have shown that the loss distorts the sidebands of the modulation instability gain spectrum, while chirality modulates the gain for LCP and RCP components in a different manner. This suggests that adjusting chirality strength may control the loss, and nonlinearity simultaneously provides stable modulated pulse propagation.

Secondary Flow in Cascades: Two Simple Derivations for the Components of Vorticity

1974 ◽  
Vol 16 (6) ◽  
pp. 391-401 ◽  
Author(s):  
P. M. Came ◽  
H. Marsh
Keyword(s):  
Secondary Flow ◽  
Secondary Circulation ◽  
Governing Equations ◽  
New Approach ◽  
Simple Theories ◽  
Fluid Particles ◽  
The Difference ◽  
Downstream Flow ◽  
Three Components

By considering a many-bladed cascade, two simple theories are developed for secondary flow in cascades. Following the work of Hawthorne (1)†, three components of vorticity are identified at exit from the cascade. An expression is obtained for the difference in the time taken for fluid particles to travel over the two surfaces of the blade, and this is used to derive the governing equations for the distributed secondary, trailing filament and trailing shed vorticities. It is shown that, for a many-bladed cascade, the total secondary circulation in the downstream flow is zero. The calculation of secondary flow for a real cascade is discussed, and it is shown that earlier calculations of secondary flow at exit from cascades are consistent with this new approach.

A probabilistic model for assessing debris flow propagation at regional scale: a case study in Campania region, Italy

2021 ◽  
Author(s):  
Luca Crescenzo ◽  
Gaetano Pecoraro ◽  
Michele Calvello ◽  
Richard Guthrie
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Regional Scale ◽  
Erosion And Deposition ◽  
Campania Region ◽  
Source Areas ◽  
Model Input ◽  
Travel Path ◽  
Debris Avalanches ◽  
Modelling Approach

<p>Debris flows and debris avalanches are rapid to extremely rapid landslides that tend to travel considerable distances from their source areas. Interaction between debris flows and elements at risk along their travel path may result in potentially significant destructive consequences. One of the critical challenges to overcome with respect to debris flow risk is, therefore, the credible prediction of their size, travel path, runout distance, and depths of erosion and deposition. To these purposes, at slope or catchment scale, sophisticated physically-based models, appropriately considering several factors and phenomena controlling the slope failure mechanisms, may be used. These models, however, are computationally costly and time consuming, and that significantly hinders their applicability at regional scale. Indeed, at regional scale, debris flows hazard assessment is usually carried out by means of qualitative approaches relying on field surveys, geomorphological knowledge, geometric features, and expert judgement.</p><p>In this study, a quantitative modelling approach based on cellular automata methods, wherein individual cells move across a digital elevation model (DEM) landscape following behavioral rules defined probabilistically, is proposed and tested. The adopted model, called LABS, is able to estimate erosion and deposition soil volumes along a debris flow path by deploying at the source areas autonomous subroutines, called agents, over a 5 m spatial resolution DEM, which provides the basic information to each agent in each time-step. Rules for scour and deposition are based on mass balance considerations and independent probability distributions defined as a function of slope DEM-derived values and a series of model input parameters. The probabilistic rules defined in the model are based on data gathered for debris flows and debris avalanches that mainly occurred in western Canada. This study mainly addresses the applicability and the reliability of this modelling approach to areas in southern Italy, in Campania region, historically affected by debris flows in pyroclastic soils. To this aim, information on inventoried debris flows is used in different study areas to evaluate the effect on the predictions of the model input parameter values, as well as of different native DEM resolutions.</p>

scholarly journals Applications of simulation technique on debris-flow hazard zone delineation: a case study in Hualien County, Taiwan

2010 ◽  
Vol 10 (3) ◽  
pp. 535-545 ◽  
Author(s):  
S. M. Hsu ◽  
L. B. Chiou ◽  
G. F. Lin ◽  
C. H. Chao ◽  
H. Y. Wen ◽  
...  
Keyword(s):  
Debris Flow ◽  
Yield Stress ◽  
Empirical Model ◽  
Water Conservation ◽  
Debris Flows ◽  
Sediment Concentration ◽  
Hazard Zone ◽  
Debris Flow Hazard ◽  
Debris Flow Disaster ◽  
Soil And Water

Abstract. Debris flows pose severe hazards to communities in mountainous areas, often resulting in the loss of life and property. Helping debris-flow-prone communities delineate potential hazard zones provides local authorities with useful information for developing emergency plans and disaster management policies. In 2003, the Soil and Water Conservation Bureau of Taiwan proposed an empirical model to delineate hazard zones for all creeks (1420 in total) with potential of debris flows and utilized the model to help establish a hazard prevention system. However, the model does not fully consider hydrologic and physiographical conditions for a given creek in simulation. The objective of this study is to propose new approaches that can improve hazard zone delineation accuracy and simulate hazard zones in response to different rainfall intensity. In this study, a two-dimensional commercial model FLO-2D, physically based and taking into account the momentum and energy conservation of flow, was used to simulate debris-flow inundated areas. Sensitivity analysis with the model was conducted to determine the main influence parameters which affect debris flow simulation. Results indicate that the roughness coefficient, yield stress and volumetric sediment concentration dominate the computed results. To improve accuracy of the model, the study examined the performance of the rainfall-runoff model of FLO-2D as compared with that of the HSPF (Hydrological Simulation Program Fortran) model, and then the proper values of the significant parameters were evaluated through the calibration process. Results reveal that the HSPF model has a better performance than the FLO-2D model at peak flow and flow recession period, and the volumetric sediment concentration and yield stress can be estimated by the channel slope. The validation of the model for simulating debris-flow hazard zones has been confirmed by a comparison of field evidence from historical debris-flow disaster data. The model can successfully replicate the influence zone of the debris-flow disaster event with an acceptable error and demonstrate a better result than the empirical model adopted by the Soil and Water Conservation Bureau of Taiwan.

scholarly journals Study on the Spillover of Sediment during Typical Tidal Processes in the Yangtze Estuary Using a High-Resolution Numerical Model

2019 ◽  
Vol 7 (11) ◽  
pp. 390 ◽  
Author(s):  
Dechao Hu ◽  
Min Wang ◽  
Shiming Yao ◽  
Zhongwu Jin
Keyword(s):  
High Resolution ◽  
Numerical Model ◽  
Good Description ◽  
Sediment Concentration ◽  
Yangtze Estuary ◽  
Sediment Flux ◽  
The Yangtze Estuary ◽  
Cross Sectional ◽  
The North ◽  
The Difference

Because of special morphologies and complex runoff–tide interactions, the landward floodtide flows in Yangtze Estuary are observed to spill over from the North to the South Branches, carrying a lot of sediment. To quantitatively clarify the spillover problem, a two-dimensional numerical model using a high-resolution channel-refined unstructured grid is developed for the entire Yangtze Estuary from Datong to river mouths (620 km) and part of the East Sea. The developed model ensures a good description of the river-coast-ocean coupling, the irregular boundaries, and local river regimes in the Yangtze Estuary. In tests, the simulated histories of the tidal level, depth-averaged velocity, and sediment concentration agree well with field data. The spillover of sediment in the Yangtze Estuary is studied using the condition of a spring and a neap tide in dry seasons. For a representative cross-section in the upper reach of the North Branch (QLG), the difference of the cross-sectional sediment flux (CSSF) between floodtide and ebbtide durations is 43.85–11.26 × 104 t/day, accounting for 37.5–34.9% of the landward floodtide CSSF. The mechanics of sediment spillover in Yangtze Estuary are clarified in terms of a successive process comprising the source, transport, and drainage of the spillover sediment.

Behaviour of debris flows located in a mountainous torrent on the Ohya landslide, Japan

2005 ◽  
Vol 42 (3) ◽  
pp. 919-931 ◽  
Author(s):  
Fumitoshi Imaizumi ◽  
Satoshi Tsuchiya ◽  
Okihiro Ohsaka
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Water Pressure ◽  
Pressure Sensors ◽  
Ultrasonic Sensors ◽  
Erosion And Deposition ◽  
Video Cameras ◽  
Muddy Water ◽  
Initiation Zone ◽  
Flow Type

Although information on the behaviour of debris flow in the initiation zone is important for the development of mitigative measures, field data regarding this behaviour are scarce. This research examines the behaviour of debris flow in the initiation zone, based on field observations in the upper Ichinosawa catchment of the Ohya landslide in Japan. In spring 1998, a monitoring system, consisting of video cameras, ultrasonic sensors, capacitive water depth probes, and water pressure sensors (WPS), was installed to assess the behaviour of debris flows in the initiation zone. On the basis of video image analysis, we found that main flow phases during debris-flow events consisted of flow containing largely muddy water and flow containing largely cobbles and boulders. Data obtained from ultrasonic sensors and WPS show that the former flow type (muddy flow) has large amounts of interstitial water throughout its mass, whereas the latter flow type has an unsaturated layer in the upper portion. Results indicate that the concentration of solids in debris flows differs from flow to flow. Debris flows in the upper Ichinosawa catchment cause both erosion and deposition and exhibit changes in their concentration of solids.Key words: debris flow, Ohya landslide, flow behaviour, observation, initiation zone.

Het web-model

2019 ◽  
Vol 111 (3) ◽  
pp. 419-432
Author(s):  
Annelli Janssen
Keyword(s):  
Mechanistic Model ◽  
Constitutive Relations ◽  
Causal Relations ◽  
Mapping Model ◽  
Difference Making ◽  
The Difference ◽  
And Control ◽  
The Brain ◽  
Manipulation And Control ◽  
The Web

Abstract The web-model: A new model of explanation for neuroimaging studiesWhat can neuroimaging tell us about the relation between our brain and our mind? A lot, or so I argue. But neuroscientists should update their model of explanation. Currently, many explanations are (implicitly) based on what I call the ‘mapping model’: a model of explanation which centers on mapping relations between cognition and the brain. I argue that these mappings give us very little information, and that instead, we should focus on finding causal relations. If we take a difference-making approach to causation, we can find manipulation patterns between neural and cognitive phenomena and start constructing satisfying explanations in neuroimaging studies: explanations based on what I call the web-model of explanation. This model of explanation not only contrasts with the mapping model, but is also different from Craver’s constitutive mechanistic model of explanation (2007), which takes the constitutive relation to be the main explanatory relation. Taking the difference-making idea of the importance of manipulation and control seriously, means that sometimes, causal relations are preferred over constitutive relations. If we follow the web-model of explanation, we can do justice to the central role that causation should play in neuroscientific explanations.

Quantificational Method for Analyzing the Formation of Fluid Mud on Muddy Coast

2012 ◽  
Vol 212-213 ◽  
pp. 466-476
Author(s):  
Lei Tang ◽  
Wei Zhang ◽  
Ming Xiao Xie ◽  
Zhen Yu ◽  
Fan Yang
Keyword(s):  
Sediment Concentration ◽  
Formation Condition ◽  
Hydrodynamic Condition ◽  
Density Current ◽  
Fluid Mud ◽  
Forming Process ◽  
Navigation Channel ◽  
Approach Channel ◽  
The Difference ◽  
Definition Of

In the present paper, the definition of fluid mud was reviewed in detail. The difference of fluid mud and sediment-induced density current were also discussed from several aspects, including physical characteristic, forming process and conditions. As far as the formation condition of fluid mud concerned, there are three key factors which are “weak hydrodynamic condition, high sedi-ment concentration, and obvious negative terrain”. Similarly, also three factors are very important for the formation condition of density current, which are “little velocity, large density difference and deep water depth”. Obviously, there exists a one-to-one relationship between formation conditions of fluid mud and those of density current. Thus a quantitative method for analyzing the formation condition of fluid mud was established reasonably by means of the formula describing sediment-induced density current. Consequentially the critical sediment concentration for fluid mud formation can be estimated by using the method. And the navigation channel of Lianyungang harbor in Jiangsu Province, China, was taken into account as a case study. The results show that the formation condition of fluid mud will be more easily satisfied with the increase of the approach channel depth in Lianyungang Harbor. The method and main conclusions can be used as reference for similar harbor project in muddy coast regions.

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