共查询到20条相似文献，搜索用时 15 毫秒
1.
人工掏挖是黄土高原地区夏闲地翻耕时广为应用的耕作方式,为探明其坡面侵蚀过程,利用三维激光扫描仪及ArcGIS软件,阐明其在人工模拟间歇降雨下坡面微地貌、侵蚀产沙及水力学参数演变规律。结果表明:①坡面侵蚀历经溅蚀-片蚀、断续细沟、连续细沟3个阶段;降雨截止时细沟平面密度、平均沟深、最大沟长和最大沟深分别增至初始的1.42倍、2.24倍、15.5倍和2.43倍。②地表糙度随降雨历时推移从1.706呈近似线性趋势减小至1.488;累积降雨量达80 mm之前,径流量、含沙量随地表糙度的减小增加缓慢,但之后随地表糙度减小增加剧烈。③降雨过程中流速呈现波动增加趋势,水流由层流快速过渡至紊流,但始终保持为缓流,水流阻力呈波动下降,且形态阻力一直居于主导地位。人工掏挖耕作坡面在雨强1.5 mm/min、降雨量80 mm以内可起到蓄水保土作用,但在连续强降雨下也更易引起细沟侵蚀。 相似文献
2.
西北干旱地区土遗址受风化、风蚀等破坏严重,大量土质文物亟待加固抢修。加固后土遗址的各耐环境因素及加固机制研究是土遗址加固的理论基础。首次引入颗粒元程序PFC,通过改变模型中颗粒间平行连接强度,对硅酸钾（简称PS）加固前后的土样进行数值模拟。在考虑实际土样颗粒粒径和密度的前提下,拟合了生土PS加固前后的抗压和抗拉强度,并将拟合后的颗粒元模型应用于风蚀模拟。通过随机生成挟沙风颗粒,以一定的速度撞向土体,模拟挟沙风的吹蚀作用。挟沙风颗粒数与循环步数成正比例,因此,可以用挟沙风颗粒数来代表吹蚀时间的长短。挟沙风颗粒的速度则代表挟沙风风速。模拟结果表明,在20 m/s的挟沙风吹蚀作用下,风蚀程度随吹蚀时间的增加而增大,未加固土样的风蚀程度增幅度远大于加固土样;同样吹蚀时间条件下,加固土样的抗风蚀强度明显高于未加固土样。这些模拟结论与风洞试验结果的统计规律一致。本研究拟合的颗粒流模型可进一步应用于PS加固机制研究及耐风蚀、雨蚀、冻融等诸环境影响分析研究。 相似文献
3.
Assessing the risk of soil vulnerability to wind erosion through conditional simulation of soil water content in Sistan plain, Iran 总被引：1，自引：0，他引：1
Surface soil water content (SWC) is one of the key factors controlling wind erosion in Sistan plain, southeast of Iran. Knowledge of the spatial variability of surface SWC is then important to identify high-risk areas over the region. Sequential Gaussian simulation (SGSIM) is used to produce a series of equiprobable models of SWC spatial distribution across the study area. The simulated realizations are used to model the uncertainty attached to the surface SWC estimates through producing a probability map of not exceeding a specified critical threshold when soil becomes vulnerable to wind erosion. The results show that SGSIM is a suitable approach for modelling SWC uncertainty, generating realistic representations of the spatial distribution of SWC that honour the sample data and reproduce the sample semivariogram model. The uncertainty model obtained using SGSIM is compared with the model achieved through sequential indicator simulation (SISIM). According to accuracy plots, goodness statistics and probability interval width plots, SGSIM performs better for modelling local uncertainty than SISIM. Sequential simulation provided a probabilistic approach to assess the risk that SWC does not exceed a critical threshold that might cause soil vulnerability to wind erosion. The resulted risk map can be used in decision-making to delineate “vulnerable” areas where a treatment is needed. 相似文献
4.
岩体结构面粗糙度系数是快速估算结构面峰值抗剪强度的重要参数。但是结构面轮廓曲线复杂,单一统计参数无法量化表征粗糙度。为解决这一问题,收集了112条结构面轮廓曲线起伏角、起伏度、迹线长度3方面的8项统计参数,利用随机森林回归模型交叉验证的方法评估统计参数的重要性。结果表明：最大起伏度、起伏高度标准偏差、平均起伏角、起伏角标准差、平均相对起伏度及粗糙度剖面指数等6项统计参数重要性占比达到93.2%,且回归拟合系数趋于平稳,基于重要性评估结果建立最优超参数决策树数目(ntree)为400、参与节点分割的数目(mtry)为2的随机森林回归模型,模型预测结果拟合优度高达98.1%。与基于坡度均方根、结构函数及粗糙度剖面指数等传统线性回归结果对比,随机森林回归模型结果精度更高,误差更小,拟合优度提高6%以上,表明随机森林回归模型更适用于结构面粗糙度反演。 相似文献
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低坡度基岩弯曲河流在地质构造控制区域广泛存在（床面坡度小于5‰）,洪水对基岩弯曲河流的河床淤积与侵蚀具有较大影响,但以往研究对基岩弯曲河流的洪水动力结构认识不足。通过几何概化基岩弯曲河段,考虑Froude相似与边壁粗糙,建立基岩弯曲河道概化模型,分析洪水下的弯道水面线分布、时均流场与湍流结构特性。结果表明:在洪水流量下,弯顶上游出现最小水面横比降、凸岸水流分离、凹岸双环流发育、流速下潜且二次环流强度达到最大,在弯顶下游水面横比降达到最大并出现环流分裂;床面切应力分布于凸岸水流分离以及弯顶上游中心区域,横向动量输移集中于弯顶上游。试验结果为基岩弯曲河道中的床面侵蚀与沿程淤积提供了水动力方面的解释。 相似文献
6.
In this paper the effect of transient uplift/erosion on the relationship between surface heat flow and heat generation for
truncated exponential model of radiogenic heat source distribution and basal asthenospheric convection is investigated. Asthenospheric
convection is described by a parameterized model, in the form of a nonlinear heat flux boundary condition involving basal
temperature and mantle internal temperature. This boundary condition has been linearized and the analytical solution of the
problem is obtained by the eigenvalue-eigenfunction expansion method. The analytical solution is used to derive the nature
of surface heat flow and heat generation relationship. The results show that the linear relationship is maintained during
the uplift/erosion and the estimates of the slope of the linear relationship are different from the depth scale of the exponential
model and increase with the rate of uplift/erosion. The estimates of the reduced heat flow also increase with the rate of
uplift/erosion. These results would find applications in the interpretation of linear surface heat flow and heat generation
relationship which is observed in different tectonic environment. 相似文献
7.
An extended Greenwood‐Williamson modelbased normal interaction law for discrete element modelling of spherical particles with surface roughness 
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下载免费PDF全文 The current work aims to develop an improved random normal interaction law based on an extended Greenwood‐Williamson (GW) model for spherical particles with surface roughness in the discrete element modelling of particle systems. The extended GW model overcomes some theoretical defects of the classic GW model when incorporated into the discrete element framework. Based on 2 nondimensional forms in which only 2 surface roughness parameters are involved, an empirical formula of the improved interaction law is derived by the curve‐fitting technique. The resulting interaction law is incorporated into discrete element modelling to investigate the mechanical response of particle systems with different surface roughness. Numerical simulations are performed to model 1‐dimensional and 3‐dimensional compression tests to explore the macro and micro characteristics of granular particles with surface roughness. The results show that surface roughness makes the initial packing of a particle assembly looser and has a greater influence on looser packed samples as expected, but an assembly with moderate roughness may exhibit a higher strength. The limitations of the current development are also highlighted. 相似文献
8.
Wind tunnel experiments on the turbulent transmission over the near surface layer of different surfaces 总被引：1，自引：0，他引：1
To understand the generation and development mechanism of soil erosion, data of the wind profile from wind tunnel experiments were used, and the characteristics of the turbulent transmission with free stream velocity and the properties of the surfaces in arid and semi-arid regions were studied by the atmospheric aerodynamic method. The result showed that the turbulent momentum fluxes are proportional to the velocity and the roughness of the surfaces. In addition, they are closely related to the density of the roughness elements; the turbulent exchange coefficient over the near surface layer increases with height. 相似文献
9.
Bedrock surfaces exposed around Llyn Llydaw, North Wales demonstrate contrasting styles of erosion beneath a Late Devensian ice sheet and a Loch Lomond Stadial (LLS) valley glacier. Ice sheet erosion involved lee-side fracturing, surface fracture wear and abrasive wear, while LLS erosion was primarily by abrasive wear. Preservation of ice sheet erosional features indicates limited rates of erosion during the LLS. Analysis of the geometry and distribution of erosional markings suggests that the low erosional capacity of the LLS glacier was due to a low basal sliding velocity. This prevented the formation of lee-side cavities, reduced the debris flux over the bed and minimised particle-bed contact loads. Reconstructions of the mass balance and geometry of the LLS glacier indicate that most of its balance velocity could be achieved by internal deformation alone. A combination of low subglacial water pressures and an unusually rough substrate explain the low sliding velocities. High bed roughness is due to the absence of leeside cavities and a change in flow orientation between ice sheet and LLS times, which meant that the LLS glacier was in contact with roughness elements which were generated in cavities beneath the ice sheet. 相似文献
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为了研究采样尺寸、采样间距对结构面粗糙度评价结果的影响,本文以川藏线昌都至林芝段的色曲特大桥左岸高陡斜坡结构面为研究对象。使用无人机贴近摄影测量技术获取斜坡的三维空间坐标和表面纹理数据;室内实现斜坡的三维重建以及点云化处理;从点云模型上人为提取出37个结构面信息,使用MATLAB进行结构面规则网格化重建;基于Z2S法描述结构面粗糙度表征值在不同尺寸、不同间距下的变化规律。结果表明:结构面粗糙度的尺寸效应、间距效应明显,采样间距的增大使有效采样尺寸值减小。因此,在进行粗糙度研究时应选取较小的采样间距,采样尺寸应大于等于“真”有效采样尺寸值。此外,本文是无人机贴近摄影测量技术应用在结构面数据采集领域的一个案例,是进行结构面粗糙度特征研究的有益补充。 相似文献
12.
Breach erosion of earthfill dams (BEED) model 总被引：1，自引：0，他引：1
A computer model has been developed for simulation of breach erosion of earthfill dams (BEED). The model incorporates the processes of surface erosion and slope sloughing to simulate breach enlargement. Depletion of reservoir water is approximated by a volume continuity equation while broad-crested weir hydraulics is utilized to describe flow over and through the breach. Due to the implicit form of these equations, an iterative solution is proposed with convergence achieved within only a few iterations. The BEED model is written in both FORTRAN 77 and BASIC computer languages. Testing of the model using historical data of the failures of Teton and Huaccoto dams showed that timing, shape, and magnitude of the predicted outflow hydrograph were adequately simulated by this model. The same is true for the dimensions of the terminal breach. A sensitivity analysis indicated that internal friction angle and the relation for surface erosion were the major factors affecting the model results. 相似文献
13.
WILLIAM D. McCAFFREY 《Sedimentology》2012,59(3):1101-1120
Large roughness features, caused by erosion of the sea floor, are commonly observed on the modern sea floor and beneath turbidite sandstone beds in outcrop. This paper aims to investigate the effect of such roughness elements on the turbulent velocity field and its consequences for the sediment carrying capacity of the flows. Experimental turbidity currents were run through a rectangular channel, with a single roughness element fixed to the bottom in some runs. The effect of this roughness element on the turbulent velocity field was determined by measuring vertical profiles of the vertical velocity component in the region downstream of the basal obstruction with the Ultrasonic Doppler Velocity Profiling technique. The experiments were set up to answer two research questions. (i) How does a single roughness element alter the distribution of vertical turbulence intensity? (ii) How does the altered profile evolve in the downstream direction? The results for runs over a plane substrate are similar to data presented previously and show a lower turbulence maximum near the channel floor, a turbulence minimum associated with the velocity maximum, and a turbulence maximum associated with the upper flow interface. In the runs in which the flows were perturbed by the single roughness element, the intensity of the lower turbulence maximum was increased between 41% to 81%. This excess turbulence dissipated upwards in the flow while it travelled further downstream, but was still observable at the most distal measurement location (at a distance ca 39 times the roughness height downstream of the element). All results point towards a similarity between the near bed turbulence structure of turbidity currents and free surface shear flows that has been proposed by previous authors, and this proposition is supported further by the apparent success of a shear velocity estimation method that is based on this similarity. Theory of turbulent dispersal of suspended sediment is used to discuss how the observed turbulent effects of a single large roughness element may impact on the suspended sediment distribution in real world turbidity currents. It is concluded that this impact may consist of a non‐equilibrium net‐upwards transport of suspended sediment, counteracting density stratification. Thus, erosive substrate topography created by frontal parts of natural turbidity flows may super‐elevate sediment concentrations in upper regions above equilibrium values in following flow stages, delay depletion of the flow via sedimentation and increase their run‐out distance. 相似文献
14.
J. M. T. Stam 《Mathematical Geology》1996,28(5):519-536
A two-dimensional analytical model is developed for the morphodynamics of aeolian dunes. The basis of the model is the sediment continuity equation, which is solved using a linearized sediment transport formula. The air flow over the topography is calculated with a steady-state boundary-layer model. This results in a series of analytical expressions for the shear stress, sediment transport, topography through time, and growth and migration of a sine-shaped dune. These expressions give quantitative relationships between bedform behavior (i.e., growth and migration) and factors such as wind velocity and surface roughness. In this way it can be seen that growth and migration rates increase for higher wind velocity, higher surface roughness and higher wave numbers (i.e., shorter wave lengths). 相似文献
15.
泥石流排导结构对于减轻泥石流对周围建筑物的损毁起到了显著作用,但目前大多数排导结构难以抵御泥石流的强烈侵蚀磨损和周围环境恶劣时伴随产生的腐蚀磨损。首先,通过分析泥石流排导结构侵蚀和腐蚀磨损机理,应用相关磨损量计算公式,提出了考虑侵蚀和腐蚀的泥石流排导结构耦合磨损计算公式。然后,以此为基础,针对磨损过程的动态性和随机性,建立了泥石流排导结构耦合磨损随机过程模型,推导了任意时刻磨损量的分布函数,实现了评估泥石流排导结构的动态可靠性和概率失效时间。最后,通过具体算例分析验证了模型的实用性,可为今后泥石流排导结构的磨损定量评估提供理论参考。 相似文献
16.
库岸泥石流危险性评价, 受具有随机性、非线性与未确知性特点的诸多因素的影响与控制, 是一个极其复杂的难题。以金沙江下游乌东德库区为例, 据其特有的地质环境条件, 选取爆发历史、地质条件、地形条件、诱发因素共4类10种泥石流影响因子, 并建立分级标准将库岸泥石流危险性分为4个等级:极度危险、高度危险、中度危险、轻度危险。应用集对分析理论分析利用区间数表示的泥石流影响因子, 建立了基于联系期望概念的库岸泥石流危险性评价新模型, 可统一分析泥石流危险性评价指标的区间形式及演化态势。实例分析结果表明, 该方法评判结果可靠, 且能简化区间数关系的分析过程。 相似文献
17.
A. J. Desbarats 《Mathematical Geology》1994,26(1):1-21
Steady-state radial flow in three-dimensional heterogeneous media is investigated using a geostatistical approach. The goal of the study is to develop a model of the relationship between corescale hydraulic conductivities measured at the wellbore and the conductivity of the surrounding drainage region as measured by a larger scale flow experiment such as a pump test. Conductivity at the point or core-scale is modeled as a stationary and multivariate lognormal spatial random function. Conductivity of the drainage region is obtained by a weighted nonlinear spatial average over the point-scale values within. This empirical spatial averaging process is shown to yield excellent approximations of true effective drainage region conductivities calculated using a numerical flow model. The geostatistical model for point-scale conductivity and the spatial averaging process are used to determine the first and second order ensemble moments of drainage region conductivity. In particular, an expression is derived for the conditional expectation of drainage region conductivity given point-scale values measured at the wellbore. The results are illustrated in a case study of a well from a sandstone oil reservoir where both core and transient-test conductivity data from the same interval are available for comparison. 相似文献
18.
A fully coupled transient two‐dimensional model was employed to study fundamentals of flood‐induced surface erosion in a particle bed. The interaction of the liquid and solid phases is the key mechanism related to surface erosion. The solid phase was idealized at a particle scale by using the discrete element method. The fluid phase was modeled at a mesoscale level and solved using the lattice Boltzmann method. The fluid forces applied on the particles were calculated on the basis of the momentum the fluid exchanges with the particle. The proposed approach was used to model both single particles and particle beds subjected to Couette flow conditions. The behavior of both the single particle and the particle bed depended on particle diameter and surface shear fluid velocity. The conducted simulations show that the fluid flow profile penetrates the bed for a small distance. This penetration initiates sheet‐flow and surface erosion as the fluid interacts with particles. The effect of suppressing particle rotation on the fluid‐induced forces on the particle was also examined. Suppressing particle spinning may lead to underestimated erosion rate. Results of fluid and particle velocities were compared against experimental results and appeared to agree with the observed trends.Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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利用野外模拟降雨试验,研究不同植被类型的侵蚀产沙、径流、地表糙度和入渗规律以及相关关系。结果表明,植被对水沙调控作用大小依次为:植物根系,整个坡面植被,坡面下部植被和坡面上部植被。林草地具有蓄水减沙的水土保持措施功效,该机制通过植物根系对水沙的调控作用实现;草地具有直接拦沙的水土保持功效,该机制通过地表植被对水沙的调控作用体现。累计产沙量随累计径流量呈幂函数递增趋势,具有很好的相关性;坡面径流产沙过程分为发育期、活跃期和稳定期3个阶段。植被覆盖度越大,地表糙度变化越小。 相似文献