scholarly journals Estimation of Velocity Profile in a Hyper-Concentrated Flow: a Critical Analysis of Bagnold Equation

10.29007/kd81 ◽  
2018 ◽  
Author(s):  
Donatella Termini ◽  
Antonio Fichera
Keyword(s):  
Velocity Profile ◽  
Debris Flow ◽  
Flow Velocity ◽  
Critical Analysis ◽  
Sediment Concentration ◽  
Concentrated Flow ◽  
Impact Forces ◽  
The Impact ◽  
The Vertical Distribution ◽  
Distribution Of Flow

Debris flow velocity is an important factor which influences the impact forces and runup. Due to the complexity of the phenomenon, it is difficult to define predictive methodologies. The present work reports some results of an experimental run conducted in order to investigate the velocity and sediment concentration distributions. A modified Bagnold’s approach to calculate the vertical distribution of flow velocity is presented.

The Effects of Upstream Flexible Barrier on the Debris Flow Entrainment and Impact Dynamics on a Terminal Barrier

2021 ◽  
Author(s):  
Hervé Vicari ◽  
C.W.W. Ng ◽  
Steinar Nordal ◽  
Vikas Thakur ◽  
W.A. Roanga K. De Silva ◽  
...  
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Impact Force ◽  
Dynamic Pressure ◽  
Pressure Coefficient ◽  
Flexible Barrier ◽  
Impact Forces ◽  
Flexible Barriers ◽  
The Impact ◽  
Bed Entrainment

The destructive nature of debris flows is mainly caused by flow bulking from entrainment of an erodible channel bed. To arrest these flows, multiple flexible barriers are commonly installed along the predicted flow path. Despite the importance of an erodible bed, its effects are generally ignored when designing barriers. In this study, three unique experiments were carried out in a 28 m-long flume to investigate the impact of a debris flow on both single and dual flexible barriers installed in a channel with a 6 m-long erodible soil bed. Initial debris volumes of 2.5 m<sup>3</sup> and 6 m<sup>3</sup> were modelled. For the test setting adopted, a small upstream flexible barrier before the erodible bed separates the flow into several surges via overflow. The smaller surges reduce bed entrainment by 70% and impact force on the terminal barrier by 94% compared to the case without an upstream flexible barrier. However, debris overflowing the deformed flexible upstream barrier induces a centrifugal force that results in a dynamic pressure coefficient that is up to 2.2 times higher than those recommended in guidelines. This suggests that although compact upstream flexible barriers can be effective for controlling bed entrainment, they should be carefully designed to withstand higher impact forces.

scholarly journals Debris Flow Damage Assessment by Considering Debris Flow Direction and Direction Angle of Structure in South Korea

Water ◽  
2019 ◽  
Vol 11 (2) ◽  
pp. 328 ◽  
Author(s):  
Dong Nam ◽  
Man-Il Kim ◽  
Dong Kang ◽  
Byung Kim
Keyword(s):  
South Korea ◽  
Debris Flow ◽  
Debris Flows ◽  
Impact Force ◽  
Mountainous Areas ◽  
Mountainous Regions ◽  
Impact Forces ◽  
The Impact

Recently, human and property damages have often occurred due to various reasons—such as landslides, debris flow, and other sediment-related disasters—which are also caused by regional torrential rain resulting from climate change and reckless development of mountainous areas. Debris flows mainly occur in mountainous areas near urban living communities and often cause direct damages. In general, debris flows containing soil, rock fragments, and driftwood temporarily travel down to lower parts along with a mountain torrent. However, debris flows are also often reported to stream down from the point where a slope failure or a landslide occurs in a mountain directly to its lower parts. The impact of those debris flows is one of the main factors that cause serious damage to structures. To mitigate such damage of debris flows, a quantitative assessment of the impact force is thus required. Moreover, technologies to evaluate disaster prevention facilities and structures at disaster-prone regions are needed. This study developed two models to quantitatively analyze the damages caused by debris flows on structures: Type-1 model for calculating the impact force, which reflected the flow characteristics of debris flows and the Type-2 model, which calculated the impact force based on the topographical characteristics of mountainous regions. Using RAMMS a debris flow runoff model, the impact forces assessed through Type-1 and Type-2 models were compared to check reliability. Using the assessed impact forces, the damage ratio of the structures was calculated and the amount of damage caused by debris flows on the structures was ultimately assessed. The results showed that the Type-1 model overestimated the impact force by 10% and the Type-2 model by 4% for Mt. Umyeon in Seoul, compared to the RAMMS model. In addition, the Type-1 model overestimated the impact force by 3% and Type-2 by 2% for Mt. Majeok in Chuncheon, South Korea.

Relationships between size and velocity for particles within debris flows

2008 ◽  
Vol 45 (12) ◽  
pp. 1778-1783 ◽  
Author(s):  
Adam B. Prochaska ◽  
Paul M. Santi ◽  
Jerry D. Higgins
Keyword(s):  
Particle Size ◽  
Debris Flow ◽  
Particle Velocity ◽  
Video Analysis ◽  
Debris Flows ◽  
Impact Force ◽  
Analysis Software ◽  
Impact Forces ◽  
The Impact ◽  
Current Guidelines

Estimation of the impact forces from boulders within a debris flow is important for the design of structural mitigation elements. Boulder impact force equations are most sensitive to the inputs of particle size and particle velocity. Current guidelines recommend that a design boulder should have a size equal to the depth of flow and a velocity equal to that of the flow. This study used video analysis software to investigate the velocities of different sized particles within debris flows. Particle velocity generally decreased with increasing particle size, but the rate of decrease was found to be dependent on the abilities of particles to rearrange within debris flows.

A combined model approach for debris-flow impact forces

2021 ◽  
Author(s):  
Lukas Reider ◽  
Anna-Lisa Fuchs ◽  
Lisa Dankwerth ◽  
Susanna Wernhart ◽  
Roland Kaitna ◽  
...  
Keyword(s):  
Debris Flow ◽  
Correction Factor ◽  
Debris Flows ◽  
Flow Behaviour ◽  
Material Composition ◽  
Correction Factors ◽  
Additional Pressure ◽  
Impact Forces ◽  
Pressure Term ◽  
The Impact

&lt;p&gt;For the design of mitigation measures knowledge of debris-flow impact forces, usually estimated based on hydrostatic, hydrodynamic, or combined approaches, is essential. As these approaches are based on Newtonian fluids, they must be adjusted by empirical correction factors to account for the solid-fluid nature of debris flows. The values for the correction factors shown in the literature vary over a wide range and several studies showed a clear dependence with the Froude regime of debris flows.&lt;/p&gt;&lt;p&gt;To better understand the correction factors and to be able to calculate them using parameters that describe the flow behaviour a total of 32 experiments were conducted in the course of the project &amp;#8220;Debris flow impact forces on bridge super structures (DEFSUP)&amp;#8221;, funded by the Austrian Science Fund (FWF). Two different material compositions, different water contents as well as a total impact and a bypassing of the measuring block were tested.&lt;/p&gt;&lt;p&gt;The experimental setup designed within the project consists of a 4 m long semi-circular channel with a diameter of 300 mm and an inclination of 20&amp;#176;. The material is released from a rectangular reservoir in a dam-break scenario and accelerated with zero roughness on a length of 1.2 m and transferred to the semi-circle profile. The subsequently introduced roughness with a grain diameter of 1-2 mm generates a stationary phenomenological debris flow until it hits the measuring setup. With a starting volume of 50 kg, flow heights between 8 and 12 cm and velocities from 0.8 to 2.2 m/s were achieved according to the material composition and different water content. With these different mixtures a Froude-range from 0.6 to 3.6 was covered. In addition, normal stresses and pore water pressures were measured at the exact same point.&lt;/p&gt;&lt;p&gt;A detailed analysis of the measured impact forces together with the above mentioned measured parameters showed that the hydrodynamic correction factor is a constant mainly corresponding to the liquification ratio of the debris-flow mixture. Hence, the hydrodynamic correction factor can be regarded as a drag coefficient and seems to depend mainly on the internal friction of the flowing medium. At low Froude numbers measured impact forces exceed even a full momentum transfer if the mean bulk density is used for the calculation. This indicates that the impact forces can no longer be described by the hydrodynamic approach alone. For this reason, an additional pressure term based on a hydrostatic approach is considered in the combined concept. This additional pressure term depends on the dynamics of flow (Froude number) and can be modelled via a dynamic earth pressure coefficient.&lt;/p&gt;&lt;p&gt;The findings from these experiments contribute to a better prediction of debris-flows impact forces in terms of their material composition and flow behaviour.&lt;/p&gt;

An experimental evaluation of impact force on a fiber bragg grating (FBG)-based device for debris flow warning

2020 ◽  
Author(s):  
Shaojie Zhang
Keyword(s):  
Debris Flow ◽  
Fiber Bragg Grating ◽  
Debris Flows ◽  
Impact Force ◽  
Dynamic Strain ◽  
Bragg Grating ◽  
New Device ◽  
Impact Forces ◽  
Measured Strain ◽  
The Impact

&lt;p&gt;Conventional sensors for debris flow monitoring suffer from several drawbacks including low service life, low reliability in long-distance data transfer, and stability in severe weather conditions. Recently, fiber Bragg grating (FBG)-based sensors have been developed to monitor debris flows. However, they can be easily damaged by the impact forces of boulders within debris flow. This paper presents a new FBG-based device to measure the strain induced by the impact force of debris flow with high reliability and effectiveness. The effects of the impact forces of debris flows have been investigated. Then, the relationship between the strain and the debris flow energy correlating with the damage to building structures has been established. It is shown that this new FBG-based device is capable of monitoring and warning about debris flows. The impact experiment results show that the peak value of dynamic strain on the fixed end of the new device is positively correlated with the external impact force. Using an impact force, we establish a relationship between the measured strain and the potential of a debris flow resulting in damage to structures was established. This follows the general rule that a larger measured strain corresponds to a higher level of debris flow. Using this relationship, we can quantify a dangerous level of debris flow using the monitored strain data. Our new device is capable of monitoring and warning about dangerous debris flows, allowing for more effective debris flow mitigation.&lt;/p&gt;

scholarly journals Modeling Hydro-Dynamics in a Harbor Area in the Daishan Island, China

Water ◽  
2019 ◽  
Vol 11 (2) ◽  
pp. 192 ◽  
Author(s):  
Yuting Li ◽  
Zhiyao Song ◽  
Guoqiang Peng ◽  
Xuwen Fang ◽  
Ruijie Li ◽  
...  
Keyword(s):  
Sediment Transport ◽  
Flow Velocity ◽  
Suspended Sediment ◽  
Hydrodynamic Model ◽  
Transport Model ◽  
Measurement Data ◽  
Cross Flow ◽  
Sediment Concentration ◽  
Suspended Sediment Transport ◽  
The Impact

This study presents an incorporation and application of a two-dimensional, unstructured-grid hydrodynamic model with a suspended sediment transport module in Daishan, China. The model is verified with field measurement data from 2017: water level, flow velocities and suspended sediment concentration (SSC). In the application on the Daishan, the performance of the hydrodynamic model has been satisfactorily validated against observed variations of available measurement stations. Coupled with the hydrodynamic model, a sediment transport model has been developed and tested. The simulations agreed quantitatively with the observations. The validated model was applied to the construction of breakwaters and docks under a different plan. The model can calculate the flow field and siltation situation under different breakwater settings. After we have analyzed the impact of existing breakwater layout schemes and sediment transport, a reasonable plan will be selected. The results show that the sea area near the north of Yanwo Shan and Dongken Shan has a large flow velocity exceeding 2.0 m/s and the flow velocity within the isobath of 5 m is small, within 0.6 m/s. According to the sediment calculation, the dock project is feasible. However, the designed width of the fairway should be increased to ensure the navigation safety of the ship according to variation characteristics of cross flow velocity in channel.

Distribusi Kecepatan dan Konsentrasi Sedimen Suspensi pada Aliran Menikung (Studi Kasus pada Saluran Irigasi Mataram Yogyakarta)

2016 ◽  
Vol 12 (1) ◽  
pp. 11
Author(s):  
Chairul Muharis
Keyword(s):  
Velocity Distribution ◽  
Flow Velocity ◽  
Suspended Sediment ◽  
Centrifugal Force ◽  
Suspended Sediment Concentration ◽  
Sediment Concentration ◽  
Low Velocity ◽  
Distribution Profile ◽  
Bend Flow ◽  
Distribution Of Flow

The flow velocity and suspended sediment concentration are important parameters of sediment transport mechanisms, especially for agradation and degradation problems. The centrifugal force at the bend channels will increased flow velocity at the outer bank of the bend. It is of course also affects the distribution of flow velocity toward the outside and the inside of the bend channels. The change of the velocity distribution  it is very possible also changes the distribution of suspended sediment concentration. In this paper will discuss the velocity distribution profile and distribution of sediment concentration in the bend flow. This research was conducted at Mataram Irrigation Channel Yogyakarta. The channel rectangular in shape and made of masonry with angle bend 580. Measuring the flow velocity used Propeller currentmeter and  sediment concentration used Opcon Probe. Measuring flow velocity and sediment concentration conducted simultaneously for each measurement point.The results showed that due to the centrifugal force in bend flow, flow velocity distribution and sediment concentration distribution undergoing significant change the outside and the inside of the bend. In general, the distribution of flow velocity toward the outerbank of the bend has increased and the distribution suspended  sediment concentration has decrease  and the opposite occurs innerbank of the bend. A low velocity on the inner bank of the channel bend causes larger grains of sediment that settles and potentially silting.

scholarly journals Effects of Barrier Stiffness on Debris Flow Dynamic Impact—I: Laboratory Flume Test

Water ◽  
2022 ◽  
Vol 14 (2) ◽  
pp. 177
Author(s):  
Yu Huang ◽  
Xiaoyan Jin ◽  
Junji Ji
Keyword(s):  
Debris Flow ◽  
Dead Zone ◽  
Peak Load ◽  
Buffer Effect ◽  
Engineering Structures ◽  
Impact Forces ◽  
Flume Tests ◽  
Run Up ◽  
The Impact

Debris flows often cause local damage to engineering structures by exerting destructive impact forces. The debris-flow–deformable-barrier interaction is a significant issue in engineering design. In this study, a large physical flume model test device was independently designed to repeatedly reproduce the flow and impact process of debris flow. Three physical flume tests were performed to investigate the effect of barrier stiffness on the debris flow impact. The flow kinematics of debris flow with three barrier stiffness values are essentially consistent with the process of impact–run-up–falling–pile-up. The development of a dead zone provided a cushion to diminish the impact of the follow-up debris flow on the barrier. The peak impact forces were attenuated as the barrier stiffness decreased. The slight deflections of a deformable barrier were sufficiently effective for peak load attenuation by up to 30%. It showed that the decrease of the barrier stiffness had a buffer effect on the debris flow impact and attenuated the peak impact force. And with the decrease of the barrier stiffness, when the barrier was impacted by the same soil types, the recoverable elastic strain will be larger, and the strain peak will be more obvious.

Impact of Flow Velocity Profile on Ultrasonic Measurement Accuracy for Feedwater Flow in Nuclear Power Plants

2002 ◽  
Author(s):  
E. Hauser ◽  
J. Regan ◽  
H. Estrada
Keyword(s):  
Velocity Profile ◽  
Flow Velocity ◽  
Power Plants ◽  
Velocity Profiles ◽  
Nuclear Plant ◽  
Flow Profile ◽  
Practical Applications ◽  
Flow Velocity Profile ◽  
The Impact ◽  
Profile Development

This paper discusses the nature of flow velocity profiles in nuclear plant feedwater system piping, and the impact of flow profile development on flow measurement. The mechanism for flow velocity profile development is described, and the influence of upstream pipe fittings and the relative roughness of the piping inside diameter on flow development is illustrated. The paper defines fully developed flow profiles and illustrates, using several practical applications, how velocity profiles in nuclear plant feedwater piping are rarely fully developed.

scholarly journals Exploiting LSPIV to assess debris-flow velocities in the field

2018 ◽  
Vol 18 (1) ◽  
pp. 1-13 ◽  
Author(s):  
Joshua I. Theule ◽  
Stefano Crema ◽  
Lorenzo Marchi ◽  
Marco Cavalli ◽  
Francesco Comiti
Keyword(s):  
Debris Flow ◽  
Flow Velocity ◽  
Sediment Trap ◽  
Debris Flows ◽  
Large Scale ◽  
Sediment Concentration ◽  
Surface Velocity ◽  
Preliminary Treatment ◽  
Flow Surface ◽  
Scale Particle

Abstract. The assessment of flow velocity has a central role in quantitative analysis of debris flows, both for the characterization of the phenomenology of these processes and for the assessment of related hazards. Large-scale particle image velocimetry (LSPIV) can contribute to the assessment of surface velocity of debris flows, provided that the specific features of these processes (e.g. fast stage variations and particles up to boulder size on the flow surface) are taken into account. Three debris-flow events, each of them consisting of several surges featuring different sediment concentrations, flow stages, and velocities, have been analysed at the inlet of a sediment trap in a stream in the eastern Italian Alps (Gadria Creek). Free software has been employed for preliminary treatment (orthorectification and format conversion) of video-recorded images as well as for LSPIV application. Results show that LSPIV velocities are consistent with manual measurements of the orthorectified imagery and with front velocity measured from the hydrographs in a channel recorded approximately 70 m upstream of the sediment trap. Horizontal turbulence, computed as the standard deviation of the flow directions at a given cross section for a given surge, proved to be correlated with surface velocity and with visually estimated sediment concentration. The study demonstrates the effectiveness of LSPIV in the assessment of surface velocity of debris flows and permit the most crucial aspects to be identified in order to improve the accuracy of debris-flow velocity measurements.

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