共查询到20条相似文献，搜索用时 968 毫秒
1.
UGAI Keizo 《山地科学学报》2012,9(2):221-231
This paper presents a lumped mass model to describe the run-out and velocity of a series of large flume tests,which was carried out to investigate some propagation mechanisms involved in rapid,dry,dense granular flows and energy transformation when the flows encountered obstacles and reoriented their movement directions.Comparisons between predicted and measured results show that the trend of predicted velocities was basically matched with that of measured ones.Careful scrutiny of test videos reveals that subsequent particles with a higher velocity collided with slowed fronts to make them accelerate. However,this simple model cannot reflect collisions between particles because it treated released materials as a rigid block.Thus,the predicted velocity was somewhat lower than the measured velocity in most cases.When the flow changed its direction due to the variation in slope inclination,the model predicted a decrease in velocity.The predicted decrease in velocity was less than the measured one within a reasonable range of 10% or less.For some cases in which a convexity was introduced,the model also predicted the same trend of velocities as measured in the tests.The velocity increased greatly after the materials took a ballistic trajectory from the vertex of the convexity,and reduced dramatically when they finally made contact with the base of the lower slope.The difference between prediced and measured decrease in velocity was estimated to be about 5% due to the landing.Therefore,the simple lumped mass model based on the energy approach could roughly predict the run-out and velocity of granular flows,although it neglected internal deformation,intergranular collision and friction. 相似文献
2.
The deflection angle of a river bend plays an important role on behaviours of the flow within it, and a clear understanding of the angle's influence is significant in both theoretical study and engineering application. This paper presents a systematic numerical investigation on effects of deflection angles(30°, 60°, 90°, 120°, 150°, and 180°) on flow phenomena and their evolution in open-channel bends using a Re-Normalization Group(RNG) κ-ε model and a volume of fluid(VOF) method. The numerical results indicate that the deflection angle is a key factor for flows in bends. It is shown that the maximum transverse slope of water surface occurs at the middle cross section of a bend, and it increases with the deflection angle. Besides a major vortex, or, the primary circulation cell near the channel bottom, a secondary vortex, or, an outer bank cell, may also appear above the former and near the outer bank when the deflection angle is sufficiently large, and it will gradually migrate towards the inner bank and evolve into an inner bank cell. The strength of the secondary circulations increases with the deflection angle. The simulation demonstrates that there is alow-stress zone on the bed near the outer bank and a high-stress zone on the bed near the inner bank, and both of them increase in size with the deflection angle. The maximum of shear stress on the inner bank increases nonlinearly with the angle, and its maximums on the outer bank and on the bed take place when the deflection angle becomes 120°. 相似文献
3.
Debris flow can cause serious damages to roads, bridges, buildings and other infrastructures.Arranging several rows of deceleration baffles in the significant influence on the mobility and deposition characteristic of debris flow. The deposit amount first increased then decreased when the flow density rises,flow path can reduce the flow velocity and ensure better protection of life and property. In debris flow prevention projects, deceleration baffles can effectively reduce the erosion of the debris flow and prolong the running time of the drainage channel.This study investigated the degree to which a 6 m long flume and three rows of deceleration baffles reduce the debris flow velocity and affect the energy dissipation characteristics. The influential variables include channel slope, debris flow density, and spacing between baffle rows. The experimental results demonstrated that the typical flow pattern was a sudden increase in flow depth and vertical proliferation when debris flow flows through the baffles. Strong turbulence between debris flow and baffles can contribute to energy dissipation and decrease the kinematic velocity considerably. The results showed that the reduction ratio of velocity increased with the increase in debris flow density,channel slope and spacing between rows. Tests phenomena also indicated that debris flow density hasand the deposit amount of debris flow density of 1500kg/m~3 reached the maximum when the experimental flume slope is 12°. 相似文献
4.
矿业活动产生的渣体是不规则颗粒介质, 具有级配复杂、结构不稳定的特征, 颗粒间通过力链传递应力。以典型铜矿渣为研究对象, 借助CT扫描技术获得矿渣的颗粒结构形态, 通过开展不同粗颗粒含量的平面压缩试验和数值模拟试验, 得到宏观力学变形曲线及力链发展过程和颗粒结构变化, 讨论颗粒结构和力链发展协同作用对宏观力学性质的影响机制, 以及颗粒介质材料压缩发展规律。结果表明: 矿渣类颗粒介质材料的力链发展方向与压力方向一致; 矿渣宏观抗压性能随>5 mm粗颗粒含量的增加先增后减, 在最优粗细颗粒配比50%处达到最大抗压强度; 颗粒结构和力链间软硬结构存在显著的协同演化; 压缩过程中内部存在快速压密、颗粒破碎和稳定压缩3个阶段。在矿渣堆填过程中, 除控制其粗颗粒在最优级配外, 保持均匀填筑和合理的压实使其进入稳定压缩阶段也非常重要。 相似文献
5.
A large amount of loose debris materials were deposited on the slope of mountainous areas after the 2008 Ms 8.0 Wenchuan earthquake. During and after the earthquake, these loose debris deposits collapsed and slide into valleys or rivers, changing river sediment supply condition and channel morphology. To investigate the mechanisms of granular flow and deposition, the dynamics of slope failure and sediment transportation in typical mountainous rivers of different intersection angles were analyzed with a coupling model of Computational Fluid Dynamics and Discrete Element Method(CFD-DEM). The numerical results show that the change of intersection angle between the granular flow flume and the river channel can affect the deposit geometry and the fluid flow field significantly. As the intersection angle increases, the granular velocity perpendicular to the river channel increases, while the granular velocity parallel to the river channel decreases gradually. Compared to the test of dry granular flow, the CFD-DEM coupling tests show much higher granular velocity and larger volume of sediments entrained in the river. Due to the river flow, particles located at the edge of the deposition will move downstream gradually and the main section of sediments deposition moves from the center to the edge of the river channel. As a result, sediment supply in the downstream river will distribute unevenly. Under the erosion of fluid flow, the proportion of fine particles increases, while the proportion of coarse particles decreases gradually in the sediment deposition. The build-up of accumulated sediment mass will cause a significant increase in water level in the river channel, thus creating serious flooding hazard in mountainous rivers. 相似文献
6.
The initiation mechanism of debris flow is regarded as the key step in understanding the debris-flow processes of occurrence, development and damage. Moreover, migration, accumulation and blocking effects of fine particles in soil will lead to soil failure and then develop into debris flow. Based on this hypothesis and considering the three factors of slope gradient, rainfall duration and rainfall intensity, 16 flume experiments were designed using the method of orthogonal design and completed in a laboratory. Particle composition changes in slope toe, volumetric water content, fine particle movement characteristics and soil failure mechanism were analyzed and understood as follows: the soil has complex, random and unstable structures, which causes remarkable pore characteristics of poor connectivity, non-uniformity and easy variation. The major factors that influence fine particle migration are rainfall intensity and slope. Rainfall intensity dominates particle movement, whereby high intensity rainfall induces a large number of mass movement and sharp fluctuation, causing more fine particles to accumulate at the steep slope toe. The slope toe plays an important role in water collection and fine particle accumulation. Both fine particle migration and coarse particle movement appears similar fluctuation. Fine particle migration is interrupted in unconnected pores, causing pore blockage and fine particle accumulation, which then leads to the formation of a weak layer and further soil failure or collapses. Fine particle movement also causes debris flow formation in two ways: movement on the soil surface and migration inside the soil. The results verify the hypothesis that the function of fine particle migration in soil failure process is conducive for further understanding the formation mechanism of soil failure and debris flow initiation. 相似文献
7.
为了阐明地震滑坡的运动特性并对其进行致灾距的预测,基于遥感影像解译和野外调查数据,借助经验公式法,分析了汶川地震滑坡水平最大运移距离L与前后缘高差H之间的相关性,给出了经验公式;探讨了不同滑坡之间滑程的差异与异常。结果表明:若已知H,可用L=aH+b或L=aHb对总位移进行预测初探;将视摩擦系数H/L=0.45作为汶川地震高速远程型滑坡的上限较合适;滑坡体积、源区破裂面积与L呈正相关,与H/L呈负相关;地震滑坡易发生在山脊线平行于断裂带、垂直于地震波传播方向的山体两侧;崩塌型滑坡易发前后缘高差范围在10~100m之间,大型高速远程型滑坡易发前后缘高差大于200m;滑坡源区易发坡度分布在25°51°之间,滑床坡降变化范围为0~58°,高速远程型滑坡的滑床坡降主要在8°20°之间;分析认为滑程差异和异常是距离效应、能量传递与岩体挡板效应、滚动润滑与气垫效应、体积与破裂面积效应、地质因子、地形因子、颗粒级配与颗粒流效应等因素综合作用的结果,考虑上述因素有益于滑坡-碎屑流致灾距的预测分析。 相似文献
8.
The sound velocity of seafloor sediments from shallow seas can provide important information for harbor design, and ocean and seacoast engineering projects. In this study, in situ measurements were used to obtain accurate sediment sound velocities at 45 stations offshore of Qingdao. The relationships between the sound velocity and granular properties of the seafloor sediments were analyzed. Sound velocity showed an increase with the sand content, sand-clay ratio, and sorting coefficient; and a nonlinear decreasing trend with increasing mean grain size and clay content. We plotted a sound velocity distribution map, which shows that the sound velocity was closely related to the geological environment. Previous empirical equations suggested by Hamilton, Anderson, and Liu were used to calculate the velocity with grain size. A comparison between the measured and calculated velocities indicates that the empirical equations have territorial limitations, and extensive data are essential to establish global empirical equations. Future work includes the calibration of the laboratory acoustic measurements with an in situ technique. 相似文献
9.
At 5 am 24 th June 2017, a catastrophic landslide hit Xinmo Village, Maoxian County, Sichuan Province, China. The slide mass rushed down from an altitude of 3400 m and traveled 2700 m in a high velocity. The 13 million m~3 deposition buried the whole village and caused about 100 deaths. The source area of the landslide is located in a high steep slope, average slope angle is 40o and maximal angle is 65o. The strata are interbedded Triassic Zagunao Formation metamorphic sandstone and slate with the dip slope angle of 45°. Based on high-resolution satellite remote sensing image, UAV image, DEM data, and field investigation, failure mechanism, travel features, and deposit characteristics were analyzed. The results showed that this landslide was influenced by Songpinggou Fault zone. According to the topography before the failure, the landslide is located in the back scarp of an antecedent landslide induced by Diexi Earthquake in 1933. The bedding slope provided potential rupture surface. Historical seismic activities and long-term gravitational deformation caused rock mass accumulated damages. Weathering and precipitation weakened the rock mass and finally induced shearing and tension failure. A huge block detached from the top rock slope, pushed the past landslide deposits in the middle part, rushed out of the slope bottom in a high velocity and buried the Xinmo Village. The rapid movement entrained and brought the soil into the Songping Gully which recoiled with and bounced back from the opposite mountain. 相似文献
10.
The aim of this research is to deepen the knowledge of the role of friction on the dynamics of granular media; in particular the friction angle is taken into consideration as the physical parameter that drives stability, motion and deposition of a set of grains of any nature and size. The idea behind this work is a question: is the friction angle really that fundamental and obvious physical parameter which rules stability and motion of granular media as it seems from most works which deal with particle dynamics? The experimental study tries to answer this question with a series of laboratory tests, in which different natural and artificial granular materials have been investigated in dry condition by means of a tilting flume. The characteristic friction angles, both in deposition(repose) and stability limit(critical) conditions, were measured and checked against size, shape, density and roughness of the considered granular material. The flume tests have been preferred to "classical" geotechnical apparatuses(e.g. shear box) since the flume experimental conditions appear closer to the natural ones of many situations of slope stability interest(e.g. a scree slope). The results reveal that characteristic friction angles depend on size and shape of grains while mixtures of granules of different size show some sorting mechanism with less clear behaviour. 相似文献
11.
Rainfall is an important factor to trigger the debris flow.Numerical simulation on the responses of slopes and the initiation of debris flow under rainfall was processed by using the software FLAC2D based on the soil parameters in Weijia Gully,Beichuan County,Sichuan Province,China.The effects of the slope angle,rainfall intensity,soil parameters on the developments of the stress and pore pressure and deformation of the slope were studied.It indicates that large displacements of the slope are mainly located near the slope toe.With the increase of the rainfall intensity the stability of the slope decreases and so the debris-flow is easy to occur. 相似文献
12.
Ming-li Li Yuan-jun Jiang Tao Yang Qiang-bing Huang Jian-ping Qiao Zong-ji Yang 《山地科学学报》2018,15(6):1342-1353
Early warning model of debris flow is important for providing local residents with reliable and accurate warning information to escape from debris flow hazards. This research studied the debris flow initiation in the Yindongzi gully in Dujiangyan City, Sichuan province, China with scaled-down model experiments. We set rainfall intensity and slope angle as dominating parameters and carried out 20 scaled-down model tests under artificial rainfall conditions. The experiments set four slope angles(32°, 34°, 37°, 42°) and five rainfall intensities(60 mm/h, 90 mm/h, 120 mm/h, 150 mm/h, and 180 mm/h) treatments. The characteristic variables in the experiments, such as, rainfall duration, pore water pressure, moisture content, surface inclination, and volume were monitored. The experimental results revealed the failure mode of loose slope material and the process of slope debris flow initiation, as well as the relationship between the surface deformation and the physical parameters of experimental model. A traditional rainfall intensity-duration early warning model(I-D model) was firstly established by using a mathematical regression analysis, and it was then improved into ISD model and ISM model(Here, I is rainfall Intensity, S is Slope angle, D is rainfall Duration, and M is Moisture content). The warning model can provide reliable early warning of slope debris flow initiation. 相似文献
13.
Yoshitaka Komatsu Hiroaki Kato Bo Zhu Tao Wang Fan Yang Randeep Rakwal Yuichi Onda 《山地科学学报》2018,15(4):738-751
Purple soil is highly susceptible for overland flow and surface erosion, therefore understanding surface runoff and soil erosion processes in the purple soil region are important to mitigate flooding and erosion hazards. Slope angle is an important parameter that affects the magnitude of runoff and thus surface erosion in hilly landscapes or bare land area. However, the effect of slope on runoff generation remains unclear in many different soils including Chinese purple soil. The aim of this study was to investigate the relationship between different slope gradients and surface runoff for bare-fallow purple soil, using 5 m × 1.5 m experimental plots under natural rainfall conditions. Four experimental plots(10°, 16°, 20° and 26°) were established in theYanting Agro-ecological Experimental Station of Chinese Academy of Science in central Sichuan Basin. The plot was equipped with water storage tank to monitor water level change. Field monitoring from July 1 to October 31, 2012 observed 42 rainfall events which produced surface runoff from the experimental plots. These water level changes were converted to runoff. The representative eight rainfall events were selected for further analysis, the relationship between slope and runoff coefficient were determined using ANOVA, F-test, and z-score analysis. The results indicated a strong correlation between rainfall and runoff in cumulative amount basis. The mean value of the measured runoff coefficient for four experimental plots was around 0.1. However, no statistically significant relationship was found between slope and runoff coefficient. We reviewed the relationship between slope and runoff in many previous studiesand calculated z-score to compare with our experimental results. The results of z-score analysis indicated that both positive and negative effects of slope on runoff coefficient were obtained, however a moderate gradient(16°-20° in this study) could be a threshold of runoff generation for many different soils including the Chinese purple soil. 相似文献
14.
《山地科学学报》2020,17(1):216-229
The high-density gravitational collapse of granular columns is very similar to the movements of large collapsing columns in nature. Based on the development of dangerous columnar rock mass in fields, granular column collapse boundary condition in the physical experiments of this study is a new type of boundary conditions with a single free face and a three-dimensional deposit. Physical experiments have shown that the mobility of small particles during the collapse of granular columns was greater than that of large particles. For example, when particle size was increased from 5 to 15 mm, deposit runout was decreased by about 16.4%. When a column consisted of two particle types with different sizes, these particles could mix in the vicinity of layer interfaces and small particles might increase the mobility of large particles. In the process of collapse, potential and kinetic energy conversion rate is fluctuated. By increasing initial aspect ratio a, the ratio of the initial height of column to its length along flow direction,potential and kinetic energy conversion rate is decreased. For example, as a was increased from 0.5 to 4, the ratio of maximum kinetic energy obtained and total potential energy loss was decreased from47.6% to 7.4%. After movement stopped, an almost trapezoidal body remained in the column and a fanlike or fan-shaped accumulation was formed on the periphery of column. Using multiple exponential functions of the aspect ratio a, the planar morphology of the collapse deposit of granular columns could be quantitatively characterized. The movement of pillar dangerous rock masses with collapse failure mode could be evaluated using this granular column experimental results. 相似文献
15.
In China,gravity retaining walls are widely used as protection structures against rockfalls,debris flows and debris avalanches along the roads in mountainous areas.In this paper,the Discrete Element Method(DEM) has been used to investigate the impact of granular avalanches and debris flows on retaining walls.The debris is modeled as two dimensional circular disks that interact through frictional sliding contacts.The basic equations that control the deformation and motion of the particles are introduced.A series of numerical experiments were conducted on an idealized debris slide impacting a retaining wall.The parametric study has been performed to examine the influences of slope geometry,travel distance of the sliding mass,wall position,and surface friction on the impact force exerted on the wall.Results show that:1) the force achieves its maximum value when slope angle is equal to 60°,as it varies from 30° to 75°;2) an approximate linear relationship between the impact force and the storage area length is determined. 相似文献
16.
Mountain hazards with large masses of rock blocks in motion – such as rock falls, avalanches and landslides – threaten human lives and structures. Dynamic fragmentation is a common phenomenon during the movement process of rock blocks in rock avalanche, due to the high velocity and impacts against obstructions. In view of the energy consumption theory for brittle rock fragmentation proposed by Bond, which relates energy to size reduction, a theoretical model is proposed to estimate the average fragment size for a moving rock block when it impacts against an obstruction. Then, different forms of motion are studied, with various drop heights and slope angles for the moving rock block. The calculated results reveal that the average fragment size decreases as the drop height increases, whether for free-fall or for a sliding or rolling rock block, and the decline in size is rapid for low heights and slow for increasing heights in the corresponding curves. Moreover, the average fragment size also decreases as the slope angle increases for a slidingrock block. In addition, a rolling rock block has a higher degree of fragmentation than a sliding rock block, even for the same slope angle and block volume. Finally, to compare with others' results, the approximate number of fragments is estimated for each calculated example, and the results show that the proposed model is applicable to a relatively isotropic moving rock block. 相似文献
17.
Characteristics of viscous debris flow in a drainage channel with an energy dissipation structure 总被引：1，自引：1，他引：0
A new type of drainage channel with an energy dissipation structure has been proposed based on previous engineering experiences and practical requirements for hazard mitigation in earthquakeaffected areas. Experimental studies were performed to determine the characteristics of viscous debris flow in a drainage channel of this type with a slope of 15%. The velocity and depth of the viscous debris flow were measured, processed, and subsequently used to characterize the viscous debris flow in the drainage channel. Observations of this experiment showed that the surface of the viscous debris flow in a smooth drainage channel was smoother than that of a similar debris flow passing through the energy dissipation section in a channel of the new type studied here. However, the flow patterns in the two types of channels were similar at other points. These experimental results show that the depth of the viscous debris flow downstream of the energy dissipation structure increased gradually with the length of the energy dissipation structure. In addition, in the smooth channel, the viscous debris-flow velocity downstream of the energy dissipation structure decreased gradually with the length of the energy dissipation structure. Furthermore, the viscous debris-flow depth and velocity were slightly affected by variations in the width of the energy dissipation structure when the channel slope was 15%. Finally, the energy dissipation ratio increased gradually as the length and width of the energy dissipation structure increased; the maximum energy dissipation ratio observed was 62.9% (where B = 0.6 m and L/w = 6.0). 相似文献
18.
Numerical simulation of the hydrodynamics within octagonal tanks in recirculating aquaculture systems 总被引：2，自引：0，他引：2
A three-dimensional numerical model was established to simulate the hydrodynamics within an octagonal tank of a recirculating aquaculture system.The realizable k-s turbulence model was applied to describe the flow,the discrete phase model(DPM) was applied to generate particle trajectories,and the governing equations are solved using the finite volume method.To validate this model,the numerical results were compared with data obtained from a full-scale physical model.The results show that:(1) the realizable k-e model applied for turbulence modeling describes well the flow pattern in octagonal tanks,giving an average relative error of velocities between simulated and measured values of 18%from contour maps of velocity magnitudes;(2) the DPM was applied to obtain particle trajectories and to simulate the rate of particle removal from the tank.The average relative error of the removal rates between simulated and measured values was 11%.The DPM can be used to assess the self-cleaning capability of an octagonal tank;(3) a comprehensive account of the hydrodynamics within an octagonal tank can be assessed from simulations.The velocity distribution was uniform with an average velocity of 15 cm/s;the velocity reached0.8 m/s near the inlet pipe,which can result in energy losses and cause wall abrasion;the velocity in tank corners was more than 15 cm/s,which suggests good water mixing,and there was no particle sedimentation.The percentage of particle removal for octagonal tanks was 90%with the exception of a little accumulation of 5 mm particle in the area between the inlet pipe and the wall.This study demonstrated a consistent numerical model of the hydrodynamics within octagonal tanks that can be further used in their design and optimization as well as promote the wide use of computational fluid dynamics in aquaculture engineering. 相似文献
19.
CHEN Meixiang) ZUO Juncheng) LI Peiliang) DU Ling) and LI Lei)) Oceanography Department Ocean University of China Qingdao P. R. China ) Key Laboratory of Coastal Disaster Defence Ministry of Education Hohai University Nanjing P. R. China 《中国海洋大学学报(英文版)》2007,6(2):117-124
Based on a ship survey during January 1998, the characteristics of the flow, the thermohaline properties and the volume transport of the Arabian Sea are discussed. A strong westward flow exists between 10.5?N and 11?N, part of which turns to the south as the Somali current near the coast at about 10?N and the rest turns north. At the passage between the African continent and the So- cotra Island, the northern branch separates into two flows: the left one enters the passage and the right one flows eastward along the southern slope of the island. Off the island the flow separates once more, most of it meandering northeast and a small fraction flow- ing southeast. Volume transport calculation suggests that the tidal transport is one or two orders of magnitude smaller than the total transport in this region and it becomes more important near the coast. The average velocity of the flow in the upper layer (0-150 m) is about 20 cm s-1, with a maximum of 53 cm s-1 appearing east of the Socotra Island, and the subsurface layer (200-800 m) has an aver- age velocity of 8.6 cm s-1; the velocity becomes smaller at greater depths. The depth of the seasonal thermocline is about 100 m, above which there is a layer with well mixed temperature and dissolved oxygen. High-salinity and oxygen-rich water appears near the surface of the northern Arabian Sea; a salinity maximum and oxygen minimum at 100 m depth along 8?N testifies the subduction of surface water from the northern Arabian Sea. Waters from the Red Sea and the Persian Gulf also influence the salinity of the area. 相似文献
20.
Particle Image Velocimetry(PIV) technique was used to test the analogues of hyperconcentrated flow and dilute debris flow in an open flume. Flow fields, velocity profiles and turbulent parameters were obtained under different conditions. Results show that the flow regime depends on coarse grain concentration. Slurry with high fine grain concentration but lacking of coarse grains behaves as a laminar flow. Dilute debris flows containing coarse grains are generally turbulent flows. Streamlines are parallel and velocity values are large in laminar flows. However, in turbulent flows the velocity diminishes in line with the intense mixing of liquid and eddies occurring. The velocity profiles of laminar flow accord with the parabolic distribution law. When the flow is in a transitional regime, velocity profiles deviate slightly from the parabolic law. Turbulent flow has an approximately uniform distribution of velocity and turbulent kinetic energy. The ratio of turbulent kinetic energy to the kinetic energy of time-averaged flow is the internal cause determining the flow regime: laminar flow(k/K0.1); transitional flow(0.1 k/K1); and turbulent flow(k/K1). Turbulent kinetic energy firstly increases with increasing coarse grain concentration and then decreases owing to the suppression of turbulence by the high concentration of coarse grains. This variation is also influenced by coarse grain size and channel slope. The results contribute to the modeling of debris flow and hyperconcentrated flow. 相似文献