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1.
Introduction The 1303 Hongtong earthquake is an important earthquake in the eastern China. There is a lot of information in historical documents about the earthquake and many traces destroyed by the earthquake in the southern Shanxi Province. Many scholars have studied the earthquake from dif-ferent aspects, but mainly limited the definitions of the isoseismal and three factors of the earth-quake. Owing to being limited by the analysis technique, many useful damage information of the earthqu… 相似文献
2.
Spur dikes are river training structures that have been extensively used worldwide for towards enhancing flood control and the stability of embankments and riverbanks.However,scour around spur dikes can be a major problem affecting their stability and hydraulic performance.The precise computation of temporal scour depth at spur dikes is very important for the design of economical and safe spur dikes.This study focuses on experimentally assessing the temporal variation of scour depth around a vertical wall spur dike and identifying the parameters,which mostly influence spur dike performance for a channel bed surface comprised of sand-gravel mixtures.In the current study,the authors did physical experiments in a flume based study to obtain new data,aimed at deriving a new predictive model for spur dike scour and comparing its performance to others found in the literature.It was found that the dimensionless temporal scour depth variation increases with an increase in(i)the threshold velocity ratio,(ii)the densimetric Froude number of the bed surface sediment mixture,(iii)the flow shallowness(defined as the ratio of the approach flow depth,y,to the spur dike’s transverse length,l),and(iv)the flow depth-particle size ratio.It is also concluded that the temporal scour depth variation in the sediment mixture is influenced by the non-uniformity of sediment and decreases with an increase in the non-uniformity of the sediment mixture.A new mathematical model is derived for the estimation of temporal scour depths in sand-gravel sediment mixtures.The proposed equation has been calibrated and validated with the experimental data,demonstrating a good predictive capacity for the estimation of temporal scour depth evolution. 相似文献
3.
Experimental study on scour and flow field in a scour hole around a T-shape spur dike in a 90° bend 总被引：4，自引：1，他引：3
In this paper results of experimental study on scour and flow field around a T-shape spur dike in a 90 degree channel bend are presented. Experiments were conducted in a laboratory channel to measure the variations of bed topography under a clear water condition. The three dimensional flow field was measured by an Acoustic Doppler Velocimeter in a scour hole due to a T-shape spur dike. It was found that by increasing the Froude number and length of spur dike the amount of scour increases. Increasing the wing length of spur dike decreases the scour. The amount of scour at the upstream of spur dike is much more as compare to that at the downstream of spur dike. By increasing the wing length of spur dike the zone of flow separation expands. As a result the sizes of vortex increase. Details of flow field are also addressed in the paper. 相似文献
4.
ShixiongHU ZhaoyinWANG GangWANG XiaoyingLIU 《国际泥沙研究》2004,19(2):142-148
The Three Gorges Project is one of the largest hydro-projects in the world and has drawn many debates inside China and abroad. The major concern is that sediment load from the river basin may eventually fail the functions of the project for flood control and power generation. To reduce sedimentation in the reservoir, watershed management has been adopted. However, there is limited information regarding the effectiveness of various control measures such as terracing and afforestation on a watershed scale. The Jialing River, a main tributary of the Yangtze River, contributes approximately 25% of the total sediment load in the main river but only represents 8% of the whole basin area. There have been various land use patterns and extensive human activities for thousands of years in the Jialing River watershed. Based on analysis of the major factors affecting erosion in the Jialing River watershed, the main watershed management strategies (afforestation, farming and engineering practice) are illustrated, and their effects on the reduction of sediment and runoff are studied in detail. The sediment budget of the watershed shows that 1/3 of the sediment yield is trapped by the erosion control measures (afforestation and farming) on the slope, 1/3 is trapped by the reservoirs, ponds and dams within the watershed, and only about 1/3 is transported into the Yangtze River, which will affect the Three Gorges Project. 相似文献
5.
Scour and flow field around a spur dike in a 90° bend 总被引：2，自引：1，他引：1
Spur dike is an important element in river training that creates rapid variations in flow field, sediment transport and bed topography. The mechanism of flow and sediment transport in a channel bend is very complex, especially when a spur dike is constructed in a bend. Most of previous investigations on flow behavior and scour around spur dike were carried out in straight channels. In this paper results of experiments on flow field and scour around a spur dike in a 90 degree channel bend are presented. Sand with uniform grain size was used as the bed material. Experiments were conducted for different locations and different lengths of spur dikes at the bend with different values of discharge. The three dimensional flow fields around a spur dike were investigated. The maximum depth of scour was correlated to the Froude numbers, lengths and the locations of spur dike in the bend. 相似文献
6.
Spur dike is an important element in fiver training that creates rapid variations in flow field, sediment transport and bed topography. The mechanism of flow and sediment transport in a channel bend is very complex, especially when a spur dike is constructed in a bend. Most of previous investigations on flow behavior and scour around spur dike were carried out in straight channels. In this paper results of experiments on flow field and scour around a spur dike in a 90 degree channel bend are presented, Sand with uniform grain size was used as the bed material, Experiments were conducted for different locations and different lengths of spur dikes at the bend with different values of discharge, The three dimensional flow fields around a spur dike were investigated, The maximum depth of scour was correlated to the Froude numbers, lengths and the locations of spur dike in the bend. 相似文献
7.
Flood control of the Yangtze River is an important part of China’s national water security.In July 2020,due to continuous heavy rainfall,the water levels along the middle-lower reaches of the Yangtze River and major lakes constantly exceeded the warning levels,in which Taihu Lake exceeded its highest safety water level and some stations of Poyang Lake reached their highest water levels in its history.In August 2020,another huge flood occurred in the Minjiang River and the Jialing River in the upper Yangtze River,and some areas of Chongqing Municipality and other cities along the rivers were inundated,resulting in great pressure on flood control and high disaster losses.The 2020 Yangtze River flood has received extensive media coverage and raised concerns on the roles of the Three Gorges Dam and other large reservoirs in flood control.Here we analyze the changes in the pattern of the Yangtze River flood control by comparing the strategies to tackle the three heavy floods occurring in 1954,1998,and 2020.We propose that the overall strategy of the Yangtze River flood control in the new era should adhere to the principle of"Integration of storage and drainage over the entire Yangtze River Basin,with draining floods downstream as the first priority"by using both engineering and non-engineering measures.On the basis of embankments,the engineering measures should use the Three Gorges Dam and other large reservoirs as the major regulatory means,promote the construction of key flood detention areas,keep the floodways clear,and maintain the ecosystem services of wetlands and shoals.In terms of non-engineering measures,we should strengthen adaptive flood risk management under climate change,standardize the use of lands in flood detention areas,give space to floods,and promote the implementation of flood risk maps and flood insurance policies.The ultimate goal of this new flood control system is to enhance the adaptability to frequent floods and increase the resilience to extreme flood disasters. 相似文献
8.
FLOW PATTERNS AND DAMAGE OF DIKE OVERTOPPING 总被引：1，自引：0，他引：1
Damage of a dike may result in severe damage and suffering. To reduce downstream damage and loss of life, it is important to study the process of breaching of the damaged dike. It is not possible to understand the damage process without a clear understanding of the flow patterns encountered. In the present study, data obtained from nine experimental runs are analyzed. The flow patterns and progressive damage of dike overtopping are investigated. Two types of phenomena at the dike surface: erosion; and erosion and sliding, are observed during the overtopping event. Four stages of dike damage can be distinguished. The degradation rate of the dike crest is found to be dependent on the downstream slope of the dike. The degradation rate is higher when the downstream slope is steeper. 相似文献
9.
South China Sea is the largest marginal sea of the Western Pacific between the Pacific Ocean and Asia Continent. It has been influenced by both the Pacific Ocean and continental climate. Its continental margins are broad in north and south, narrow in west. There are many islands in east. A large amount of siliciclastic sediments derived from peri-continents and islands were trans-ported into the sea[1], in which significant information of paleoceanography and paleoclimate and paleoenvironm… 相似文献
10.
ZHANG Changhou WU Ganguo WANG Genhou ZHANG Weijie & SONG Honglin . Key Laboratory of Lithospheric Tectonics Lithoprobing Technology China University of Geosciences Ministry of Education of China Beijing China . School of Earth Sciences Mineral Resources China University of Geosciences Beijing China 《中国科学D辑(英文版)》2004,47(10):896-911
1 An out-of-line northwest trending tectonic beltin the middle part of the Yanshan Orogenic Belt The tectonic framework of the intraplate YanshanOrogenic Belt is dominated by east-west and northeastextending structures as revealed by many geologists.There lies, however, a 100-km-long enigmatic out-of-line northwest extending tectonic complex in the mid-dle part of the Yanshan Orogenic Belt (fig. 1). Theresearch on the geometry, kinematics, timing of thiscomplex tectonic belt and its r… 相似文献
11.
Simulation of the Micro-physics of Rocks Using LSMearth 总被引：4，自引：0，他引：4
-- The particle-based Lattice Solid Model (LSM) was developed to provide a basis to study the physics of rocks and the nonlinear dynamics of earthquakes (M0ra and Place, 1994; Place and Mora, 1999). A new modular and flexible LSM approach has been developed that allows different micro-physics to be easily included in or removed from the model. The approach provides a virtual laboratory where numerical experiments can easily be set up and all measurable quantities visualised. The proposed approach provides a means to simulate complex phenomena such as fracturing or localisation processes, and enables the effect of different micro-physics on macroscopic behaviour to be studied. The initial 2-D model is extended to allow three-dimensional simulations to be performed and particles of different sizes to be specified. Numerical bi-axial compression experiments under different confining pressure are used to calibrate the model. By tuning the different microscopic parameters (such as coefficient of friction, microscopic strength and distribution of grain sizes), the macroscopic strength of the material and can be adjusted to be in agreement with laboratory experiments, and the orientation of fractures is consistent with the theoretical value predicted based on Mohr-Coulomb diagram. Simulations indicate that 3-D numerical models have different macroscopic properties than in 2-D and, hence, the model must be recalibrated for 3-D simulations. These numerical experiments illustrate that the new approach is capable of simulating typical rock fracture behaviour. The new model provides a basis to investigate nucleation, rupture and slip pulse propagation in complex fault zones without the previous model limitations of a regular low-level surface geometry and being restricted to two-dimensions. 相似文献
12.
Finite element modeling on a highly conceptualized 2-D model of fluid flow and heat transport is un-dertaken to simulate the paleo-hydrological system as if the Mount Isa deposits were being formed in the Mount Isa basin, Northern Australia, and to evaluate the potential of buoyancy force in driving ba-sin-scale fluid flow for the formation of sedimentary-exhalative (SEDEX) deposits. Our numerical case studies indicate that buoyancy-driven fluid flow is controlled mainly by the fault penetration depth and i... 相似文献
13.
A quasi three-dimensional (QUASI 3-D) model is presented for simulating the subsurface water flow and solute transport in the unsaturated and in the saturated zones of soil. The model is based on the assumptions of vertical flow in the unsaturated zone and essentially horizontal groundwater flow. The 1-D Richards equation for the unsaturated zone is coupled at the phreatic surface with the 2-D flow equation for the saturated zone. The latter was obtained by averaging 3-D flow equation in the saturated zone over the aquifer thickness. Unlike the Boussinesq equation for a leaky-phreatic aquifer, the developed model does not contain a storage term with specific yield and a source term for natural replenishment. Instead it includes a water flux term at the phreatic surface through which the Richards equation is linked with the groundwater flow equation. The vertical water flux in the saturated zone is evaluated on the basis of the fluid mass balance equation while the horizontal fluxes, in that equation, are prescribed by Darcy law. A 3-D transport equation is used to simulate the solute migration. A numerical algorithm to solve the problem for the general quasi 3-D case was developed. The developed methodology was exemplified for the quasi 2-D cross-sectional case (QUASI2D). Simulations for three synthetic problems demonstrate good agreement between the results obtained by QUASI2D and two fully 2-D flow and transport codes (SUTRA and 2DSOIL). Yet, simulations with the QUASI2D code were several times faster than those by the SUTRA and the 2DSOIL codes. 相似文献
14.
Three-dimensional modeling of bank erosion and morphological changes in the Shishou bend of the middle Yangtze River 总被引：1，自引：0，他引：1
This paper presents a three-dimensional (3-D) numerical model to simulate morphological changes in alluvial channels due to bank erosion. A method for the simulation of bank erosion is established. This is incorporated into a 3-D mathematical model for turbulent flow and non-uniform, non-equilibrium sediment transport. This model is applied to simulate morphological changes in the Shishou bend of the middle Yangtze River in China, where serious bank erosions occurred during the last two decades. The double-layer sediment structure of the riverbank on the middle Yangtze River is taken into account in the bank erosion module. Both cohesive and non-cohesive bank material in the different layers are considered. The bank erosion module also includes other factors affecting the rate of bank erosion, such as the longitudinal length of failed bank, the thickness of each layer in the double-layer structure, and the erosion-resisting effect of cohesive material from the top layer of failed bank. A locally-adaptive grid system is proposed to efficiently simulate the lateral migration of alluvial channel due to bank erosion. The predictive capability of the 3-D model is examined by laboratory data. Simulated processes of bank erosion agree with field observations in the Shishou bend during the period of October 1996–October 1998, and the bank erosion module plays a significant role in simulating morphological changes of the study reach. In addition, the equivalent channel-forming discharge, which is defined as a constant discharge that can create the same amount of bank erosion in an alluvial channel as that created by natural runoff processes during the same period of time, is proposed to improve calculation efficiency for feasibility studies. 相似文献
15.
青藏高原存在柔性下地壳流动被越来越多的学者接受, 但是关于下地壳流动方式及速度存在争议。 地表运动有GPS等直接测量, 上地幔运动有S波分裂间接反映, 下地壳运动目前没有直接观测手段, 使得开展数值分析非常重要。 本文利用三维球壳黏弹性有限元模型研究了青藏高原下地壳柔性流动方式和流动速度。 本文通过对地表GPS观测资料的拟合与不同数值模型的对比分析, 认为青藏高原柔性下地壳东向流动遇到四川盆地的抵阻, 下地壳物质可能仅在高原东南方向存在物质外溢通道, 而在高原东北方向不存在类似的物质通道; 下地壳的流动速度比地表运动速率每年快几毫米至十几毫米, 对应的黏滞系数为1018~1019 Pa·s。 相似文献
16.
青藏高原的高精度人工源深部地震探测发现：壳-幔边界（Moho）并非是一物理学上的“刚性”界面,它不仅起伏变化强烈,极为凹凸不平,而且被一系列规模不一,产状各异的深大断裂所切割,故必然会导致复杂的地表和深部物质运移动力学响应的复杂化.在常见的通道流模型中,一般均设定下地壳与上地幔之间为一平缓界面,在数值模拟工作中亦常简化为平滑的约束界面.为此,基于青藏高原实际资料提取的壳、幔介质平均速度模型,采用黏弹性数值模型讨论Moho界面起伏变换样式对通道流模型产生的响应.研究结果表明：（1）通道流效应的影响仅限于小区域内,当Moho面存在起伏样式变化时,确会对通道流产生影响,Moho界面的起伏增强了下地壳和岩石圈地幔的同步运动效应,但是其影响范围是有限的;（2）Moho界面起伏形态变化对地表和Moho界面水平位移产生的影响各异,在Moho界面发生错断的地方,呈现为地表水平位移开始发生明显加速减小的地方,即地表与深部介质水平位移解耦,模型深部动力学效应与地表的响应并非为局部性效应,而至少体现出区域性的响应. 相似文献
17.
《Advances in water resources》2004,27(5):547-562
This study proposes the use of several problems of unstable steady state convection with variable fluid density in a porous layer of infinite horizontal extent as two-dimensional (2-D) test cases for density-dependent groundwater flow and solute transport simulators. Unlike existing density-dependent model benchmarks, these problems have well-defined stability criteria that are determined analytically. These analytical stability indicators can be compared with numerical model results to test the ability of a code to accurately simulate buoyancy driven flow and diffusion. The basic analytical solution is for a horizontally infinite fluid-filled porous layer in which fluid density decreases with depth. The proposed test problems include unstable convection in an infinite horizontal box, in a finite horizontal box, and in an infinite inclined box. A dimensionless Rayleigh number incorporating properties of the fluid and the porous media determines the stability of the layer in each case. Testing the ability of numerical codes to match both the critical Rayleigh number at which convection occurs and the wavelength of convection cells is an addition to the benchmark problems currently in use. The proposed test problems are modelled in 2-D using the SUTRA [SUTRA––A model for saturated–unsaturated variable-density ground-water flow with solute or energy transport. US Geological Survey Water-Resources Investigations Report, 02-4231, 2002. 250 p] density-dependent groundwater flow and solute transport code. For the case of an infinite horizontal box, SUTRA results show a distinct change from stable to unstable behaviour around the theoretical critical Rayleigh number of 4π2 and the simulated wavelength of unstable convection agrees with that predicted by the analytical solution. The effects of finite layer aspect ratio and inclination on stability indicators are also tested and numerical results are in excellent agreement with theoretical stability criteria and with numerical results previously reported in traditional fluid mechanics literature. 相似文献
18.
2.5-D直流电阻率有限元数值模拟中,模型的剖分及加密主要通过手动实现.另外,采用的单元类型比较规则如矩形单元等,不易实现复杂模型的模拟.为解决上述问题,文中提出了一种自适应有限元算法.算法中采用稳健的后验误差估计来自动预测下一次网格的单元尺寸,直到设定的迭代条件满足为止.另外,采用非结构化三角形单元实现了任意复杂模型的灵活剖分.基于此,利用垂直接触面模型分析和对比了不同自适应策略的效率.通过对比发现,点源附近的单元得到了加密以消除源的奇异性.另外,对于任意一种策略,有限元结果均能最终收敛到精确解.最后,模拟了两个模型：2-D单个异常体模型和2-D地形模型. 相似文献
19.
The purpose of geophysical electrical surveys is to determine the subsurface resistivity distribution by making measurements on the ground surface. From these measurements, the true resistivity of the subsurface can be estimated. The ground resistivity is related to various geological parameters, such as the mineral and fluid content, porosity and degree of water saturation in the rock. Electrical resistivity surveys have been used for many decades in hydrogeological, mining and geotechnical investigations. More recently, they have been used for environmental surveys. To obtain a more accurate subsurface model than is possible with a simple 1-D model, a more complex model must be used. In a 2-D model, the resistivity values are allowed to vary in one horizontal direction (usually referred to as the x direction) but are assumed to be constant in the other horizontal (the y) direction. A more realistic model would be a fully 3-D model where the resistivity values are allowed to change in all three directions. In this research, a simulation of the cone penetration test and 2D imaging resistivity are used as tools to simulate the distribution of hydrocarbons in soil. 相似文献
20.
1 INTRODUCTIONUnderstanding the flow characters in open channel or other water area, whether natufal water bodies(such as rivers and estuaries) or man-made strUctures (such as navigational channels, harbors), isimportant for addressing numerous hydraulic engineering problems. These include the selechons ofsuitable waste disposal sites, contndnant transport, sediment transport and other ecological problems.The major difficulty for solving these problems is that it often requires an optimal… 相似文献