scholarly journals Numerical Simulation of a Debris Flow on the Basis of a Two-Dimensional Continuum Body Model

Geosciences ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 45
Author(s):  
Hiroshi Takebayashi ◽  
Masaharu Fujita
Keyword(s):  
Debris Flow ◽  
Flow Velocity ◽  
Flow Characteristics ◽  
Maximum Flow ◽  
Heavy Rain ◽  
Horizontal Distribution ◽  
Residential Area ◽  
Two Dimensional ◽  
Flow Depth ◽  
Maximum Flow Velocity

A two-dimensional debris and mud flow model that considers both laminar and turbulence flow was developed. Subsequently, the model was applied to a debris flow that occurred in Asaminami, Hiroshima, Japan in August 2014. The applicability of the model and the debris flow characteristics are discussed. The calculated horizontal distribution of sediment deposited in the Asaminami residential area was in good agreement with the horizontal distribution of the deposited large rocks and driftwood. This result indicates that the fine material in the downstream area was transported by water flow resulting from heavy rain that occurred after the debris flow. The scale of the initial debris flow was small; however, it increased with time, because eroded bed material and water were entrained to it. Therefore, it is important to reproduce the development process of debris flows to predict the amount of sediment produced, the deepest flow depth, the maximum flow velocity, and the inundation area. The averaged velocity of the simulated debris flow was about 9 m/s, and the velocity at the entrance to the residential area was about 8 m/s. This kind of information can be used to design sediment deposition dams. The travel time of the simulated debris flow from the upstream end of the main channel to the entrance of the residential area was 96 s. This kind of information can be used for making evacuation plans. Valley bed steps can suppress the deepest flow depth which is very important for the design of check dams; therefore, the high-resolution elevation data and fine numerical grids that reproduce step shapes are required to accurately calculate the deepest flow depth and maximum flow velocity.

scholarly journals Two-dimensional computational simulation flow of exhaust gases passing inside an electrostatic precipitator

2016 ◽  
Vol 10 (1) ◽  
pp. 106-112
Author(s):  
Giorgos Kouropoulos
Keyword(s):  
Fluid Mechanics ◽  
Flow Velocity ◽  
Electrostatic Precipitator ◽  
Computational Simulation ◽  
Flow Simulation ◽  
Maximum Flow ◽  
Theoretical Background ◽  
Two Dimensional ◽  
Exhaust Gases ◽  
Maximum Flow Velocity

In the present study the two-dimensional computational simulation flow of hot exhaust gases which are passed inside an electrostatic precipitator will be carried out. Initially, the theoretical background and necessary equations from fluid mechanics will be described. These equations will be used by software for flow simulation. Furthermore, are presented the design of precipitator through which the exhaust gases are passed. In the next step follows the declaration of various parameters of simulation on the software and finally the necessary images of the computational simulation for two case studies will be extracted. The general conclusions that arise are that the maximum flow velocity of exhaust gases prevails only at the beginning of the entrance of the precipitation element. There are different velocities in all other parts of precipitation element. When the exhaust gases approach the collecting electrodes within the element, their velocity is decreased.

scholarly journals Laboratory Analysis of Debris Flow Characteristics and Berm Performance

Water ◽  
2021 ◽  
Vol 13 (16) ◽  
pp. 2223
Author(s):  
Kukhyun Ryou ◽  
Hyungjoon Chang ◽  
Hojin Lee
Keyword(s):  
Debris Flow ◽  
Flow Velocity ◽  
Flow Characteristics ◽  
Flow Depth ◽  
Volumetric Concentration ◽  
Runout Distance ◽  
Deposition Area ◽  
Lateral Width ◽  
Channel Slope ◽  
Study Laboratory

In this study, laboratory tests were used to determine the deposition characteristics (runout distance, lateral width, and deposition area) of debris flow and their relationships with the flow characteristics (flow velocity and flow depth) according to the presence of a berm. An experimental flume 1.3 to 1.9 m long, 0.15 m wide, and 0.3 m high was employed to investigate the effects of channel slope and volumetric concentration of sediment with and without the berm. The runout distance (0.201–1.423 m), lateral width (0.045–0.519 m), and deposition area (0.008–0.519 m2) increased as the channel slope increased and as the volumetric concentration of sediment decreased. These quantities also increased with the flow velocity and flow depth. In addition, the maximum reductions in the runout distance, lateral width, and deposition area were 69.1%, 65.9%, and 93%, respectively, upon berm installation. The results of this study illustrate general debris flow characteristics according to berm installation; the reported relationship magnitudes are specific to the experimental conditions described herein. However, the results of this study contribute to the design of site-specific berms in the future by providing data describing the utility and function of berms in mitigating debris flow.

scholarly journals Two-dimensional computational simulation flow of exhaust gases passing inside an electrostatic precipitator

2016 ◽  
Vol 10 (1) ◽  
pp. 106-112
Author(s):  
Giorgos Kouropoulos
Keyword(s):  
Fluid Mechanics ◽  
Flow Velocity ◽  
Electrostatic Precipitator ◽  
Computational Simulation ◽  
Flow Simulation ◽  
Maximum Flow ◽  
Theoretical Background ◽  
Two Dimensional ◽  
Exhaust Gases ◽  
Maximum Flow Velocity

In the present study the two-dimensional computational simulation flow of hot exhaust gases which are passed inside an electrostatic precipitator will be carried out. Initially, the theoretical background and necessary equations from fluid mechanics will be described. These equations will be used by software for flow simulation. Furthermore, are presented the design of precipitator through which the exhaust gases are passed. In the next step follows the declaration of various parameters of simulation on the software and finally the necessary images of the computational simulation for two case studies will be extracted. The general conclusions that arise are that the maximum flow velocity of exhaust gases prevails only at the beginning of the entrance of the precipitation element. There are different velocities in all other parts of precipitation element. When the exhaust gases approach the collecting electrodes within the element, their velocity is decreased.

scholarly journals Sensitivity and identifiability of rheological parameters in debris flow modeling

2020 ◽  
Author(s):  
Gerardo Zegers ◽  
Pablo A. Mendoza ◽  
Alex Garces ◽  
Santiago Montserrat
Keyword(s):  
Sensitivity Analysis ◽  
Debris Flow ◽  
Flow Velocity ◽  
Numerical Models ◽  
Maximum Flow ◽  
Rheological Parameters ◽  
Model Parameters ◽  
Relevant Variables ◽  
Distributed Evaluation ◽  
Maximum Flow Velocity

Abstract. Over the past decades, several numerical models have been developed to understand, simulate and predict debris flow events. Typically, these models simplify the complex interactions between water and solids using a single-phase approach and different rheological models to represent flow resistance. In this study, we perform a sensitivity analysis on the parameters of a debris flow numerical model (FLO-2D) for a suite of relevant variables (i.e., maximum flood area, maximum flow velocity, maximum flow velocity, deposit volume). Our aims are to (i) examine the degree of model overparameterization, and (ii) assess the effectiveness of observational constraints to improve parameter identifiability. We use the Distributed Evaluation of Local Sensitivity Analysis (DELSA) method, which is a hybrid local-global technique. Specifically, we analyze two creeks in northern Chile that were affected by debris flows on March 25, 2015. Our results show that SD and β1 – a parameter related to viscosity – provide the largest sensitivities. Further, our results demonstrate that equifinality is present in FLO-2D, and that final deposited volume and maximum flood area contain considerable information to identify model parameters.

scholarly journals The mechanical origin of snow avalanche dynamics and flow regime transitions

2020 ◽  
Author(s):  
Xingyue Li ◽  
Betty Sovilla ◽  
Chenfanfu Jiang ◽  
Johan Gaume
Keyword(s):  
Flow Velocity ◽  
Alpha Angle ◽  
Maximum Flow ◽  
Flow Regimes ◽  
Snow Avalanche ◽  
Snow Avalanches ◽  
Deposition Zone ◽  
Avalanche Dynamics ◽  
Maximum Flow Velocity ◽  
Deposit Height

Abstract. Snow avalanches cause fatalities and economic damages. Key to their mitigation entails the understanding of snow avalanche dynamics. This study investigates the dynamic behaviors of snow avalanches, using the Material Point Method (MPM) and an elastoplastic constitutive law for porous cohesive materials. By virtue of the hybrid Eulerian-Lagrangian nature of MPM, we can handle processes involving large deformations, collisions and fractures. Meanwhile, the elastoplastic model enables us to capture the mixed-mode failure of snow, including tensile, shear and compressive failure. Using the proposed numerical approach, distinct behaviors of snow avalanches, from fluid-like to solid-like, are examined with varied snow mechanical properties. In particular, four flow regimes reported from real observations are identified, namely, cold dense, warm shear, warm plug and sliding slab regimes. Moreover, notable surges and roll-waves are observed peculiarly for flows in transition from cold dense to warm shear regimes. Each of the flow regimes shows unique flow characteristics in terms of the evolution of the avalanche front, the free surface shape, and the vertical velocity profile. We further explore the influence of slope geometry on the behaviors of snow avalanches, including the effect of slope angle and path length on the maximum flow velocity, the $\\alpha$ angle and the deposit height. Unified trends are obtained between the normalized maximum flow velocity and the scaled $\\alpha$ angle as well as the scaled deposit height, reflecting analogous rules with different geometry conditions of the slope. It is found the maximum flow velocity is mainly controlled by the friction between the bed and the flow, the geometry of the slope, and the snow properties. In addition to the flow behavior before reaching the deposition zone, which has long been regarded as the key factor governing the $\\alpha$ angle, we reveal the crucial effect of the stopping behavior in the deposition zone. Furthermore, our MPM model is benchmarked with simulations of real snow avalanches. The evolution of the avalanche front position and velocity from the MPM modeling shows reasonable agreement with the measurement data from literature. The MPM approach serves as a novel and promising tool to offer systematic and quantitative analysis for mitigation of gravitational hazards like snow avalanches.

Comparative study of transcranial color duplex sonography and transcranial Doppler sonography in adults

1993 ◽  
Vol 78 (5) ◽  
pp. 776-784 ◽  
Author(s):  
Martin Schöoning ◽  
Reiner Buchholz ◽  
Jochen Walter
Keyword(s):  
Flow Velocity ◽  
Doppler Sonography ◽  
Transcranial Doppler Sonography ◽  
Maximum Flow ◽  
Duplex Sonography ◽  
Color Duplex Sonography ◽  
Content Type ◽  
Maximum Flow Velocity ◽  
Fine Print ◽  
Flow Velocities

✓ To determine whether the frequency shift recorded in basal cerebral arteries corresponds to “true” flow velocities, a prospective comparative study of transcranial color duplex sonography (TCCD) and transcranial Doppler sonography (TCD) was performed. A 2.0-MHz transducer of a computerized TCCD system and a TCD device were used. The middle cerebral artery (MCA) and anterior cerebral artery (ACA) were examined by TCCD in 49 healthy volunteers (mean age 35 ± 12 years). In 45 of the same volunteers a comparative TCD examination was possible. The studies were carried out blindly by different examiners at separate appointments. Peak systolic flow velocity, end-diastolic maximum flow velocity, time-averaged maximum flow velocity, and the pulsatility index were measured by both techniques. Additionally, for TCCD, time-averaged flow velocity was assessed, the resistance index and a spectral broadening index were calculated, and the energy output required for reliable measurement was analyzed. The TCCD signals were recorded in 98% of both MCA's and ACA's; with TCD, signals were recorded in 98% of MCA's and 87% of ACA's. Although in both vessels the angle-corrected peak systolic and time-averaged maximum velocities were approximately 10% to 15% higher in TCCD than in TCD measurements, correlation of flow velocities between both techniques was significant (p < 0.0001); differences between sides and age-dependency of flow velocities corresponded as well. In a reproducibility study, TCCD was repeated in 27 subjects by a third examiner with significant correlation (p < 0.0001) of both TCCD examinations. It is concluded that the advantage of TCCD is associated more with a qualitative aspect than a quantitative one. The additional visual dimension of TCCD can open new diagnostic possibilities in cerebrovascular disorders.

scholarly journals Analysis of Risks Associated With Water Pipes in Rapid Flow Waterways Through Waterway Modeling Experiments

2021 ◽  
Vol 35 (5) ◽  
pp. 51-58
Author(s):  
Sin-Woong Choi ◽  
A-Young Choi ◽  
Dong-Hun Han
Keyword(s):  
Flow Velocity ◽  
Maximum Flow ◽  
Water Pipe ◽  
Lower Side ◽  
Water Pipes ◽  
Average Flow Velocity ◽  
Standard Operating ◽  
Rapid Flow ◽  
Water Rescue ◽  
Maximum Flow Velocity

In this study, waterway modeling experiments were conducted by incorporating the information obtained by analyzing accident sites to prevent frequent accidents of firefighters that occur during water rescue operations conducted near water pipes in rapid flow waterways. Based on the conducted experiments, it was observed that the flow velocity increased with decreasing distance from the water pipe. Furthermore, the maximum flow velocity was found to be 3.99 times higher at the posterior end than at the anterior end of the water pipe, and the flow velocity was found to be higher at the lower side than at the upper side of the water pipe’s anterior end. The maximum flow velocity was measured to be 1.65 m/s at a distance of 10 cm from the entrance to the pipe, 2.63 m/s at a distance of 5 cm from the entrance to the pipe, 7.12 m/s within the pipe, and 5.33 m/s at a distance of 5 cm from the pipe’s exit. The average flow velocity was measured to be 0.94 m/s at a distance of 10 cm from the entrance to the pipe, 5.53 m/s within the pipe, and 4.64 m/s at a distance of 5 cm from the pipe’s exit. Furthermore, in this study, relevant standard operating procedures and regulations were taken into consideration. Based on the results obtained from this study, recommendations and guidelines were then accordingly devised for preventing accidents of firefighters that occur during water rescue operations.

The Effects of Particle Segregation on Debris Flow Fluidity Over a Rigid Bed

2020 ◽  
Vol 27 (1) ◽  
pp. 139-149
Author(s):  
Norifumi Hotta ◽  
Tomoyuki Iwata ◽  
Takuro Suzuki ◽  
Yuichi Sakai
Keyword(s):  
Shear Stress ◽  
Debris Flow ◽  
Debris Flows ◽  
High Speed ◽  
Particle Diameter ◽  
Flow Characteristics ◽  
Video Camera ◽  
Front Velocity ◽  
Flow Depth ◽  
Particle Segregation

ABSTRACT It is essential to consider the fluidity of a debris flow front when calculating its impact. Here we flume-tested mono-granular and bi-granular debris flows and compared the results to those of numerical simulations. We used sand particles with diameters of 0.29 and 0.14 cm at two mixing ratios of 1:1 and 3:7. Particle segregation was recorded with a high-speed video camera. We evaluated the fronts of debris flows at 0.5-second intervals. Then we numerically simulated one-dimensional debris flows under the same conditions and used the mean particle diameter when simulating mixed-diameter flows. For the mono-granular debris flows, the experimental and simulated results showed good agreement in terms of flow depth, front velocity, and flux. However, for the bi-granular debris flows, the simulated flow depth was less, and both the front velocity and flux were greater than those found experimentally. These differences may be attributable to the fact that the dominant shear stress was caused by the concentration of smaller sediment particles in the lower flow layers; such inverse gradations were detected in the debris flow bodies. Under these conditions, most shear stress is supported by smaller particles in the lower layers; the debris flow characteristics become similar to those of mono-granular flows, in contrast to the numerical simulation, which incorporated particle segregation with gradually decreasing mean diameter from the front to the flow body. Consequently, the calculated front velocities were underestimated; particle segregation at the front of the bi-granular debris flows did not affect fluidity either initially or over time.

Physiological assessment of augmented vascularity induced by VEGF in ischemic rabbit hindlimb

1994 ◽  
Vol 267 (4) ◽  
pp. H1263-H1271 ◽  
Author(s):  
C. Bauters ◽  
T. Asahara ◽  
L. P. Zheng ◽  
S. Takeshita ◽  
S. Bunting ◽  
...  
Keyword(s):  
Flow Velocity ◽  
Iliac Artery ◽  
Internal Iliac Artery ◽  
Guide Wire ◽  
Rabbit Model ◽  
Maximum Flow ◽  
Treated Group ◽  
Saline Control ◽  
Internal Iliac ◽  
Maximum Flow Velocity

This study was designed to assess the physiological consequences of augmented vascularity induced by administration of vascular endothelial growth factor (VEGF), an endothelial cell-specific mitogen, in a rabbit model of hindlimb ischemia. Ten days after excision of the common and superficial femoral arteries from one hindlimb of 24 New Zealand White rabbits, VEGF (n = 15) or saline (control; n = 9) was selectively injected into the ipsilateral internal iliac artery. Limb perfusion was evaluated immediately pre-VEGF (baseline) and again at days 10 and 30. A Doppler guide wire was advanced to the internal iliac artery to record flow velocity at rest and at maximum flow velocity provoked by intra-arterial injection of papaverine. At baseline and at day 10, no differences in flow parameters were observed between the control and the VEGF-treated animals. By day 30, however, flow at rest (P < 0.05), maximum flow velocity (P < 0.001), and maximum blood flow (P < 0.001) were all significantly higher in the VEGF-treated group. These physiological findings complement previous-anatomic studies by providing evidence that a single intra-arterial bolus of VEGF augments flow, particularly maximum flow, in the rabbit ischemic hindlimb. These data thus support the notion that VEGF administration represents a potential treatment strategy for certain patients with lower extremity ischemia.

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