scholarly journals Determining the Precipitation Intensity Threshold of Debris Flood Occurrence

2021 ◽  
pp. 473-489
Author(s):  
Mohammad Ebrahim Banihabib ◽  
Mitra Tanhapour
Keyword(s):  
Layer Thickness ◽  
Flow Direction ◽  
Average Diameter ◽  
Precipitation Intensity ◽  
Sediment Layer ◽  
Intensity Threshold ◽  
Precipitation Threshold ◽  
Debris Flood ◽  
Bed Slope ◽  
Debris Floods

AbstractIn this chapter, the precipitation threshold at which debris floods occur was evaluated experimentally, and the factors that influence debris flood occurrence, including the bed slope, sediment layer thickness, sediment grain size, length of alluvial flow direction, precipitation intensity, and time of debris flood occurrence, were examined. The impacts of these factors on debris flood initiation were investigated through dimensional analysis. Then, a method was developed to estimate the precipitation intensity threshold based on a set of laboratory tests. Furthermore, different methods for determining the precipitation intensity threshold at which debris floods are initiated were assessed and discussed. The results of the experiments showed that the effect of the sediment layer thickness on debris flood occurrence can be ignored. Moreover, by independently evaluating the effect of each factor on debris flood occurrence, it was found that the sediment length and average diameter of sediments are influential to debris flood initiation. The results of this research provide a better understanding of debris flood mechanisms and occurrence thresholds of debris floods and can be employed to prepare a forecasting model.

scholarly journals Impact of Sediment Layer on Longitudinal Dispersion in Sewer Systems

Water ◽  
2021 ◽  
Vol 13 (22) ◽  
pp. 3168
Author(s):  
Marek Sokáč ◽  
Yvetta Velísková
Keyword(s):  
Reynolds Number ◽  
Layer Thickness ◽  
Dispersion Coefficient ◽  
Longitudinal Dispersion ◽  
Low Flow ◽  
Pipe Diameter ◽  
Sediment Layer ◽  
Pollution Transport ◽  
Sewer Pipes ◽  
Hydraulic Conditions

Experiments focused on pollution transport and dispersion phenomena in conditions of low flow (low water depth and velocities) in sewers with bed sediment and deposits are presented. Such conditions occur very often in sewer pipes during dry weather flows. Experiments were performed in laboratory conditions. To simulate real hydraulic conditions in sewer pipes, sand of fraction 0.6–1.2 mm was placed on the bottom of the pipe. In total, we performed 23 experiments with 4 different thicknesses of sand sediment layers. The first scenario is without sediment, the second is with sediment filling 3.4% of the pipe diameter (sediment layer thickness = 8.5 mm), the third scenario represents sediment filling 10% of the pipe diameter (sediment layer thickness = 25 mm) and sediment fills 14% of the pipe diameter (sediment layer thickness = 35 mm) in the last scenario. For each thickness of the sediment layer, a set of tracer experiments with different flow rates was performed. The discharge ranges were from (0.14–2.5)·10−3 m3·s−1, corresponding to the range of Reynolds number 500–18,000. Results show that in the hydraulic conditions of a circular sewer pipe with the occurrence of sediment and deposits, the value of the longitudinal dispersion coefficient Dx decreases almost linearly with decrease of the flow rate (also with Reynolds number) to a certain limit (inflexion point), which is individual for each particular sediment thickness. Below this limit the value of the dispersion coefficient starts to rise again, together with increasing asymmetricity of the concentration distribution in time, caused by transient (dead) storage zones.

Influence of Chord Length and Inlet Boundary Layer on the Secondary Losses of Turbine Blades

2011 ◽  
Vol 134 (1) ◽  
Author(s):  
Helmut Sauer ◽  
Robin Schmidt ◽  
Konrad Vogeler
Keyword(s):  
Boundary Layer ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Flow Direction ◽  
Velocity Ratio ◽  
Main Flow ◽  
Chord Length ◽  
Displacement Thickness ◽  
Wide Range ◽  
Main Flow Direction

In this paper, results concerning the influence of chord length and inlet boundary layer thickness on the endwall loss of a linear turbine cascade are discussed. The investigations were performed in a low speed cascade tunnel using the turbine profile T40. The turning of 90 deg and 70 deg, the velocity ratio in the cascade from 1.0 to 3.5 as well as the chord length of 100 mm, 200 mm, and 300 mm were specified. In a measurement distance of one chord behind the cascade in main flow direction, an approximate proportionality of endwall loss and chord was observed in a wide range of velocity ratios. At small measurement distances (e.g., s2/l=0.4), this proportionality does not exist. If a part of the flow path within the cascade is approximately incorporated, a proportionality to the chord at small measurement distances can be obtained, too. Then, the magnitude of the endwall loss mainly depends on the distance in main flow direction. At velocity ratios near 1.0, the influence of the chord decreases rapidly, while at a velocity ratio of 1.0, the endwall loss is independent of the chord. By varying the inlet boundary layer thickness, no correlation of displacement thickness and endwall loss was achieved. A calculation method according to the modified integral equation by van Driest delivers the wall shear stress. Its influence on the endwall loss was analyzed.

scholarly journals ANALISIS KETEBALAN LAPISAN SEDIMEN DAN INDEKS KERENTANAN SEISMIK KOTA JAMBI BAGIAN TIMUR

2020 ◽  
Vol 6 (1) ◽  
pp. 18-30
Author(s):  
Arie Satria ◽  
Ichy Lucya Resta ◽  
Nasri MZ
Keyword(s):  
Layer Thickness ◽  
Natural Frequency ◽  
Seismic Vulnerability ◽  
Amplification Factor ◽  
Vulnerability Index ◽  
Research Area ◽  
Ratio Method ◽  
Sediment Layer ◽  
Alluvial Deposits ◽  
High Zone

A Research was carried about analysis of sediment layer thickness and seismic vulnerability index in eastern Jambi City. The purpose of this research was to  determine the effect of sediment layer thickness on seismic vulnerability index in eastern Jambi City based on microtremor data. The Acquisition data of microtremor is 25 points spread in research area. Processing data was carried out using the HVSR (Horizontal to Vertical Spectra Ratio) method to obtain the H/V curve. This curve represents the value of the natural frequency (f0) and amplification factor (A0). Based on the results of data processing obtained, the range of natural frequency (f0) value is 1.04 – 3.78 Hz, the range of amplification factor (A0) value is 1.13 - 4.88 times, the range of sediment layer thickness (h) value is 16.46 – 61.45 meters, and the range of seismic vulnerability index (Kg) value is 0.70 - 20.18×10-6 cm2/s. The results showed that the distribution of seismic vulnerability index (Kg) correlated relatively well with sediment layer thickness of the research area. The high zone of seismic vulnerability index (Kg) is relatively associated with alluvial deposits and also the sediment layer thickness of more than 30 meters. The high zone of seismic vulnerability index (Kg) is concentrated in Pasir Panjang, Tanjung Raden to Olak Kemang in Danau Teluk sub-district and Tanjung Sari in Jambi Timur sub-district.

The Effects of Fuel Injection Angle and Injection Velocity on Propulsive Droplets Sizing in a Duct

2011 ◽  
Vol 110-116 ◽  
pp. 2879-2887
Author(s):  
Mohammad Mahdi Doustdar ◽  
Mohammad Mojtahedpoor
Keyword(s):  
Mass Fraction ◽  
Fuel Injection ◽  
Flow Direction ◽  
Average Diameter ◽  
Injection Velocity ◽  
Fuel Vapor ◽  
Counter Flow ◽  
Injection Angle ◽  
Fuel Droplets ◽  
Air Mixing

— The effects of fuel injection angles on the average diameter of fuel propulsive droplets sizing and efficient mass fraction in combustion chamber of a ramjet are numerically investigated in the present paper. We named the mass of fuel vapor inside the flammability limit as the efficient mass fraction. In order to investigate the effects of fuel injection angle on the mean diameter of fuel propulsive droplets sizing, there are conducted two sets of calculation. The fuel injection angle of part I is varied as 30°, 45°, and 60° in flow direction, also the fuel injection angle of part II is counter-flow and varied as 0°, 30°, 45° and 60° to examine its effects on the fuel droplets and fuel/air mixing phenomena, as well as we have increased the fuel injection velocity from 40 to 45, 50 and 55m/s respectively and we have inspected the needed data again. To fulfill the calculation we used a modified version of KIVA-3V.

Wind-Tunnel Screens: Flow Instability and its Effect on Aerofoil Boundary Layers

1964 ◽  
Vol 68 (639) ◽  
pp. 198-198 ◽  
Author(s):  
P. Bradshaw
Keyword(s):  
Boundary Layer ◽  
Wind Tunnel ◽  
Layer Thickness ◽  
Boundary Layers ◽  
Boundary Layer Thickness ◽  
Flow Instability ◽  
Flow Direction ◽  
Flat Plates ◽  
Mixing Processes ◽  
Flow Through

Morgan has described a spatial instability in the flow through screens or grids of small open-area ratio. Head and Rechenberg and others have observed large span-wise variations in the thickness and shear stress of nominally two-dimensional boundary layers on flat plates and aerofoils in wind tunnels. It now appears that these spanwise variations are caused by the instability of flow through the screens. The jets of air issuing from the pores of the screen attempt to entrain more air by the usual mixing processes, but can only entrain it from each other, so that groups of jets coalesce in rather random (steady) patterns determined by small irregularities in the weave. The resulting variations in axial velocity are virtually eliminated by the wind tunnel contraction, but variations in flow direction are not so greatly reduced: a theoretical analysis shows that the observed variations of boundary-layer thickness, which often reach ± 10 per cent of the mean, can be produced by directional variations in the working section of the order of ± 1/20 deg, with a spanwise wavelength of the same order as the boundary-layer thickness.

scholarly journals Perpendicular Giant Magnetoresistance and Magnetic Properties of Co/Cu Nanowire Arrays Affected by Period Number and Copper Layer Thickness

2016 ◽  
Vol 2016 ◽  
pp. 1-9 ◽  
Author(s):  
Juan Han ◽  
Xiufang Qin ◽  
Zhiyong Quan ◽  
Lanfang Wang ◽  
Xiaohong Xu
Keyword(s):  
Electron Microscopy ◽  
Layer Thickness ◽  
Giant Magnetoresistance ◽  
Average Diameter ◽  
Oscillatory Behavior ◽  
Nanowire Arrays ◽  
Magnetic Nanowires ◽  
Experimental Conditions ◽  
Remanence Ratio ◽  
Potential Applications

One-dimensional magnetic nanowires have attracted much attention in the last decades due to their unique physical properties and potential applications in magnetic recording and spintronics. In this work, ordered arrays of Co/Cu multilayered nanowires which can be exploited to develop magnetoresistive sensors were successfully prepared using porous anodic alumina (PAA) templates. The structure and morphology of the multilayered nanowire arrays were characterized by transmission electron microscopy and scanning electron microscopy. The nanowire arrays are highly ordered and the average diameter is about 50 nm, which is controlled by the pore diameter of the PAA templates. The influences of period number and Cu layer thickness on the magnetic and the giant magnetoresistance (GMR) properties were investigated. The coercivity and remanence ratio increase first and then gradually tend to be stable with the increase of period number and the Cu layer thickness, while the GMR ratio increases first and then decreases with the increase of the period number accompanied by an oscillatory behavior of GMR as the Cu layer thickness changes, which are ascribed to the spin dependence electron scattering in the multilayers. The optimum GMR of −13% appears at Co (50 nm)/Cu (5 nm) with 200 deposition cycles in our experimental conditions.

Some influences of sediments in aerated lagoons and waste stabilization ponds

2000 ◽  
Vol 42 (10-11) ◽  
pp. 237-246 ◽  
Author(s):  
D. Chabir ◽  
H. El Ouarghi ◽  
Y. Brostaux ◽  
J. L. Vasel
Keyword(s):  
Layer Thickness ◽  
Oxygen Demand ◽  
Suspended Sediments ◽  
Sediment Oxygen Demand ◽  
Sediment Layer ◽  
Waste Stabilization Ponds ◽  
Stabilization Ponds ◽  
Waste Stabilization ◽  
Main Factors ◽  
Process Factors

Respirometric tests have been undertaken on sediments in aerated lagoons and waste stabilization ponds to quantify their oxygen demand and to determine the main factors governing the process. Factors such as seasonal variations, temperature, substrate, sediment layer thickness, density of macro-invertebrates and suspended sediments were investigated. The results showed that temperature and substrate concentration are the main factors that influence sediment oxygen demand; followed by spatial heterogeneity and resuspension of sediments, whereas the density of macro-invertebrates could have an effect in summer (hot season). Sediment layer thickness had no effect. A model of sediment oxygen demand is developed for the two main factors (temperature and substrate) with an r2 of 0.98.

scholarly journals A Hybrid Intelligence Model for the Prediction of the Peak Flow of Debris Floods

Water ◽  
2020 ◽  
Vol 12 (8) ◽  
pp. 2246
Author(s):  
Mohammad Ebrahim Banihabib ◽  
Lubos Jurik ◽  
Mahsa Sheikh Kazemi ◽  
Jaber Soltani ◽  
Mitra Tanhapour
Keyword(s):  
Artificial Intelligence ◽  
Hybrid Model ◽  
Sediment Concentration ◽  
Peak Flows ◽  
Flood Peak ◽  
Flood Warning ◽  
Intelligence Models ◽  
Artificial Intelligence Models ◽  
Debris Flood ◽  
Debris Floods

Debris floods, as one of the most significant natural hazards, often threaten the lives and property of many people worldwide. Predicting models are essential for flood warning systems to minimize casualties of debris floods. Since HEC-HMS (Hydrologic Engineering Center’s Hydrological Modelling System) cannot simulate debris flow, this study proposes a new hybrid model that uses artificial intelligence models to overcome HEC-HMS’s insufficiency in reflecting the sediment concentration effect on the debris floods. A sediment concentration is an effective factor for evaluating debris flood peak flows. This led to the proposal of new hybrid models for predicting the debris flood peak flows on the basis of hybridization of the artificial intelligence models (Bayesian Network (BN) and Support Vector Regression–Particle Swarm Optimization (SVR-PSO)) and HEC-HMS. To estimate the sediment concentration of floods by using the proposed artificial intelligence models, we nominated an average basin elevation, an average basin slope, a basin area, the current day rainfall, the antecedent rainfall of the past 3 days, and the streamflow of the previous day the previous day as the effective variables. In the validation stage, the average of the Mean Absolute Relative Error (MARE) of the estimated values were 0.024, 0.038, and 0.024 for the typical floods that occurred in the Navrood, Kasilian, and the Amameh basins in the north of Iran, respectively. Similarly, we obtained values of 0.038, 0.073, and 0.040 for the debris flood events for the three respective locations. After predicting the debris flood peak flows by the proposed hybrid HMS-BN and HMS-SVR-PSO models, the average of the MAREs for all debris flood events was reduced to 0.013 and 0.014, respectively. The comparison of MAREs of the examined hybrid models shows that the HMS-BN model results in higher accuracy than the HMS-SVR-PSO model in the prediction of the debris flood peak flows. Generally, the absolute error of prediction by the proposed hybrid model is reduced to one-third of the HEC-HMS. The prediction of the debris flood peak flows using the proposed hybrid model can be examined in the debris flood warning systems to reduce the potential damages and casualties in similar basins.

Linear analysis of the stability of particle-laden stratified shear layers

2014 ◽  
Vol 92 (2) ◽  
pp. 103-115 ◽  
Author(s):  
Ehsan Khavasi ◽  
Bahar Firoozabadi ◽  
Hossein Afshin
Keyword(s):  
Layer Thickness ◽  
Piecewise Linear ◽  
Stability Boundary ◽  
Shear Layers ◽  
Unstable Flow ◽  
Density Profiles ◽  
Background Density ◽  
Layer Flow ◽  
Bed Slope ◽  
The Stability

Hydrodynamic instabilities at the interface of stratified shear layers could occur in various modes and have an important role in the mixing process. In this work, the linear stability analysis in the temporal framework is used to study the stability characteristics of a particle-laden stratified two-layer flow for two different background density profiles: smooth (hyperbolic tangent) and piecewise linear. The effect of parameters, such as bed slope, viscosity, and particle size, on the stability is also considered. The pseudospectral collocation method employing Chebyshev polynomials is used to solve two coupled eigenvalue equations. Based on the results, there are some differences in the stability characteristics of the two density profiles. In the case of R = 1 (R is the ratio of the shear layer thickness to the density layer thickness), the stability boundary in smooth profile is the transition from the unstable flow (where the dominant unstable mode is Kelvin–Helmholtz) to the stable one where in the piecewise linear profile this boundary is the transition from Kelvin–Helmholtz to the Holmboe mode. It is also shown that the unstable region increases with the bed slope and unstable modes amplify as the bed slope increases. For R = 5 the flow does not become stable by increasing the stratification in nonzero bed slope, and in some wavenumbers the Kelvin–Helmholtz and Holmboe modes coexist. In addition, by increasing the bed slope the growth rate of the Holmboe mode and the range of its existence decrease. As expected, the viscosity makes the current more stable, and for large values of the viscosity (small Reynolds number) the flow becomes stable at long waves (small wave numbers) for all bulk Richardson numbers. Existence of small particles does not change the instability characteristics so much, however, large particles make the flow more unstable.

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