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将追踪自由表面的流体体积(VOF)法应用于曲线坐标系下水流控制方程的求解中,计入流线弯曲对水流紊动特性的影响,建立了垂向二维强紊动水流的曲率修正的紊流模型,并对溢流坝反弧段的紊流特性进行了数值模拟。数值计算时,采用有限体积法离散水流的控制方程;物理变量,如:压力P、紊动参量κ、ε、γt等,采用交错方式排列(交错网格布置),用SIMPLEC算法求解离散方程。计算结果表明,得到的溢流坝反弧段的自由表面位置、速度场、压力场、剪应力分布和紊动能分布与实验结果吻合良好。 相似文献
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灌区分水口多为直角, 附近普遍存在冲刷、淤积及结构破坏现象。天然河流分、汇流多为锐角, 为探索非直角分水口区域明渠水流紊动特性, 以30°分水角明渠为研究对象, 采用声学多普勒点式流速仪测量各断面上的三维瞬时流速, 分析典型断面上的时均流速、环流强度、紊动强度、紊动能和床面剪切应力分布规律。试验结果显示: 分水口处水流横向流速沿渠宽方向变化较大, 易形成环流, 导致局部冲淤现象明显; 靠近口门侧水流紊动强度变化剧烈且分布无规律, 最大值出现在口门上唇断面; 分水口处下层水体紊动能明显大于上层水体, 紊动能较大值多集中在口门附近; 口门断面下唇附近床面剪切应力较大, 易出现冲刷侵蚀, 破坏渠道稳定; 与直角分水口相比, 分水角为30°时, 泥沙颗粒不易进入侧渠道, 水流对渠底及边壁侵蚀速率较低。研究结果可为灌区渠系设计及运行提供参考。 相似文献
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提出σ坐标系垂向分层的优化方法,较好地解决了传统σ坐标变换用于底孔泄流数值模拟时存在网格边界变化的问题;采用一维水流模型为立面二维模型提供自由水面边界,即"动刚盖法"确定自由表面;根据坝前趋孔水流的流动特性和水下纵坡稳定性受力分析,分别导出σ坐标系下床面泥沙边界条件和底孔泄流初期河床滑塌的判别式。在此基础上建立底孔泄流条件下立面二维水流泥沙数学模型,并将之应用于有刚性护坦条件下冲刷漏斗形成的数值模拟。模拟结果表明,漏斗冲刷平段长度、漏斗纵坡等数值试验结果与水槽试验基本一致,验证了模型的合理性和可靠性。 相似文献
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针对天然河流交汇区域复杂的地形条件及水流运动特性,采用水气两相流三维数值模型,对长江与嘉陵江交汇区水流运动进行深入研究,分析了交汇区域分离区、剪切层、流速场及螺旋度的变化特性。研究结果表明:长江与嘉陵江交汇的水流分离区形状受地形影响明显,随着水位的增加向右岸移动,剪切层整体呈一个扭曲的曲面;干支流原有的环流在交汇之后重新汇合,左岸未出现明显的环流,右岸逆时针的环流有减弱趋势,交汇区域纵向流速呈现高速与低速带分布特征。此外,长江和嘉陵江在交汇口下游螺旋度呈现左侧为负、右侧为正的对称分布,水流结构表现出逐渐形成双螺旋流的趋势,其中左侧的螺旋流逆时针运动,右侧的螺旋流顺时针运动。 相似文献
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受地形、地质等条件影响,明渠收缩过渡段在输水工程中十分常见,过渡段长度过短,会导致水面波动,水体紊动加剧。为研究明渠不同长度过渡段内纵向时均流速及紊动强度的分布规律,通过室内模型试验,利用二维电磁流速仪ACM2-RS测量了渠道内沿程中垂线不同深度处瞬时流速。试验结果表明:收缩段内,纵向时均流速沿程增加,紊动强度沿程降低,遵循涡旋的拉伸机制和线性扭曲理论;受二次流影响,最大流速位于水面以下,且最大流速的位置随二次流作用的增强而降低;不同长度过渡段对下游纵向流速分布和紊动强度影响不同,过渡段越短,下游水流紊动越强,但非渠底附近紊动强度沿垂向先减后增的规律不变。 相似文献
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采用σ坐标变换拟合复杂边界、VOF方法追踪自由水面变化和SIMPLE算法求解控制方程等建立垂向二维非恒定水流及悬浮物分布数学模型。该模型适用于变量在横向上分布基本均匀的水流流动特性及悬浮物扩散迁移过程的模拟,与刚盖假定或静水压强假定等条件下建立的垂向二维数学模型相比更符合实际情况。分别对概化水库水流结构的沿程变化、明渠均匀流及带有槽沟的明渠非均匀流及悬浮物浓度分布进行了模拟,计算结果与实测值符合良好。模型的应用可为河道或水库的洪水调度、水污染控制、取水工程优化等提供参考。 相似文献
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为进一步深化对明渠总流控制方程的认识,探究总流能量损失的构成与分布特点,通过理论分析,在黏性流体力学理论的框架下构建了描述明渠恒定紊流总体特性的总流积分模型与总流微分模型的控制方程,其模型参数能直接通过流动统计特征量在过流断面上的分布来获取,由此实现明渠流的流场特性描述与总流描述的统一,并得到了总流能量损失的显示表达式。同时指出,总流能量损失由黏性耗散与维持紊动两部分构成,在矩形明渠恒定均匀流紊流的分类能量损失构成中,壁面上以黏性耗散部分为主,维持紊动部分的能量损失密度随着离开壁面距离的增加而快速增加,且随着雷诺数的增大,其增加速度也越快。 相似文献
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为进一步深化对明渠总流控制方程的认识,探究总流能量损失的构成与分布特点,通过理论分析,在黏性流体力学理论的框架下构建了描述明渠恒定紊流总体特性的总流积分模型与总流微分模型的控制方程,其模型参数能直接通过流动统计特征量在过流断面上的分布来获取,由此实现明渠流的流场特性描述与总流描述的统一,并得到了总流能量损失的显示表达式。同时指出,总流能量损失由黏性耗散与维持紊动两部分构成,在矩形明渠恒定均匀流紊流的分类能量损失构成中,壁面上以黏性耗散部分为主,维持紊动部分的能量损失密度随着离开壁面距离的增加而快速增加,且随着雷诺数的增大,其增加速度也越快。 相似文献
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作为河、湖以及滨海湿地生态系统中必不可少的组成部分,水生植被具有重要的生态服务价值,且许多生态服务价值是通过改变水体动力条件实现的。含植被水流研究不仅可用于科学阐明水生植被的生态环境效应,还能指导河湖生态系统修复及污染治理的工程实践。本文考虑单向明渠流与波浪2种水动力环境,对国内外有关水生植被对水流结构以及泥沙运动影响研究的主要成果进行梳理。单向明渠流条件下,植被对水动力的影响研究主要集中于植被对水流阻力的影响以及冠层内水体的紊动结构与紊动尺度特征;波浪条件下,植被对波高与波浪流速的减弱作用以及冠层内水体的时均与紊动结构特征是研究重点。受水动力条件控制,植被影响下的泥沙运动特征也受到广泛关注,且研究焦点为单向明渠流条件下水生植被对泥沙起动与输移的影响以及波浪条件下植被对床底泥沙再悬浮的影响。 相似文献
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The rotation behavior of rigid elliptical inclusions adherent to the viscous matrix in simple shear flow is investigated using a 2-D finite element numerical model. Several simulations were performed using different ratios (S) between shear zone width and inclusion's least principal axis. A computational strategy was devised to calculate pressure and viscous forces exerted on the inclusion and deduce its angular velocity. For large S values, results agree remarkably well with theoretical predictions, while for small S values results deviate significantly from theory but are in agreement with previous analogue experiments. The numerical model provided detailed and coherent information about the physical parameters involved in the process (e.g., pressure, strain rate and vorticity distributions within the model). 相似文献
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This paper presents the results of a set of numerical models focussing on structural controls on hydrothermal mineralization.We first give an overview of natural phenomena of structurally-controlled ore formation and the background theory and mechanisms for such controls. We then provide the results of a group of simple 2D numerical models validated through comparison with Cu-vein structure observed near the Shilu Copper deposit(Yangchun,Guangdong Province, China) and finally a case study of 3D numerical modelling applied to the Hodgkinson Province in North Queensland(Australia).Two modelling approaches,discrete deformation modelling and continuum coupled deformation and fluid flow modelling,are involved.The 2D model-derived patterns are remarkably consistent with the Cu-vein structure from the Shilu Copper deposit,and show that both modelling approaches can realistically simulate the mechanical behaviours of shear and dilatant fractures.The continuum coupled deformation and fluid flow model indicates that pattern of the Cuveins near the Shilu deposit is the result of shear strain localization,development of dilation and fluid focussing into the dilatant fracture segments.The 3D case-study models(with deformation and fluid flow coupling) on the Hodgkinson Province generated a number of potential gold mineralization targets. 相似文献
13.
砂土液化流动变形的简化方法 总被引：1，自引：0，他引：1
已有的液化砂土流动特性试验结果表明,砂土在液化流动状态下是剪切稀化非牛顿流体,可以用幂函数表示其剪应力-剪应变率的关系,从而建立了砂土液化流动的本构方程。基于FLAC3D程序的二次开发平台,将液化流动本构方程开发到FLAC3D中,建立了液化流动变形的简化分析方法。通过倾斜场地的液化流动变形分析,发现倾斜场地的液化变形曲线可以用正弦函数曲线描述,这与Towhata的理论分析成果一致,验证了本方法的合理性。分析了液化层坡度、稠度系数、流动指数以及弹性参数等变量对液化变形的影响。计算结果表明,液化变形随液化层坡度的增大而逐渐增大,液化砂土的稠度系数和流动指数对液化流动变形有重要的影响,而弹性参数对变形基本无影响,因此,在实际工程分析中,需要对流动模型参数进行深入研究。 相似文献
14.
本构模型是描述泥石流流变特性的关键,也是决定其动力过程数值模拟准确性的核心问题之一。泥石流流体属多相混合物,现有的研究已证实其存在剪切增稠或剪切变稀的现象,传统基于Bingham及Cross线性本构关系的数值模型难以准确描述泥石流流变特性。文中探讨了Bingham模型在低剪应变率下的数值发散问题,在光滑粒子流体动力学（SPH）方法框架上建立了整合Herschel-Bulkley-Papanastasiou(HBP）本构关系的稀性泥石流动力过程三维数值模型。相比传统基于浅水波假设的二维数值模型,所述方法从三维尺度建立SPH形式下的泥石流浆体纳维?斯托克斯方程并进行数值求解,可获取泥石流速度场时空分布及堆积形态,同时采用HBP本构关系描述泥石流流变特性,能在确保数值收敛的前提下反映泥石流流体在塑性屈服过渡段及大变形状态下应力?应变的非线性变化。为验证提出方法的合理性,结合小型模型槽实验观测进行了对比,结果表明数值模拟与实测结果基本吻合。 相似文献
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Excess pore pressure and grain crushing of sands by means of undrained and naturally drained ring-shear tests 总被引：5，自引：0，他引：5
An investigation of excess pore-pressure generation of a weathered granitic sand, taken from the source area of a typical landslide caused as a result of liquefaction, and a fine silica sand was conducted, in which grain crushing within the shear zone of ring-shear test specimens was examined as the key phenomenon of rapid long-runout motion of landslides. In order to investigate and explain the low average apparent-friction angle, mobilized in a liquidized landslide, speed-controlled ring-shear tests were conducted under undrained conditions on weathered granitic-sand specimens, formed under a wide range of initial void ratios. It was revealed that very small steady-state shear resistances were obtained irrespective of the initial void ratios, which can explain the low average apparent-friction angle. In addition, two series of ring-shear tests on weathered-granitic and fine-silica sands were conducted under naturally drained conditions by keeping the upper drain valve of the shear box open during the tests. The first series of tests was performed under differing total normal stresses, but at the same shear speed, and the second series was conducted at differing shear speeds, but under the same total normal stress. In order to investigate and analyze excess pore-pressure generation and dissipation within the shear zone that is associated with grain crushing, permeability analyses were conducted by passing water through the sample box of the ring-shear test apparatus before and after shearing. In addition, grain-size distribution analyses of samples taken from the shear zone after shearing were carried out. For the weathered granitic-sand samples, a significant change in bulk permeability and large amount of grain crushing were observed. In these tests on the above soil, a considerable reduction of shear resistance, which increased proportionally to the total normal stress and shear speed, were obtained. It was observed that due to grain crushing, finer grains that lowered the permeability of the soil in the shear zone, were formed. It is likely that the decrease in permeability facilitated the generation of high excess pore pressures by reducing the pore-pressure dissipation rate from the shear zone; thus, flow behaviour was exhibited even under naturally drained conditions. 相似文献
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A. Ghazvinian V. Sarfarazi W. Schubert M. Blumel 《Rock Mechanics and Rock Engineering》2012,45(5):677-693
Particle flow code 2D (PFC2D) was adopted to simulate the shear behavior of rocklike material samples containing planar non-persistent joints. Direct shear loading was conducted to investigate the effect of joint separation on the failure behavior of rock bridges. Initially calibration of PFC was undertaken with respect to the data obtained from experimental laboratory tests to ensure the conformity of the simulated numerical models response. Furthermore, validation of the simulated models were cross checked with the results of direct shear tests performed on non-persistent jointed physical models. Through numerical direct shear tests, the failure process was visually observed, and the failure patterns were found reasonably similar to the experimentally observed trends. The discrete element simulations demonstrated that the macro-scale shear zone resulted from the progressive failure of the tension-induced micro-cracks. The failure pattern was mostly influenced by joint separation, while the shear strength was linked to the failure pattern and failure mechanism. Furthermore, it was observed that the failure zone is relatively narrow and has a symmetrical pattern when rock bridges occupy a low percentage of the total shear surface. This may be due to the high stress interactions between the subsequent joints separated by a rock bridge. In contrast, when rock bridges are occupying sufficient area prohibiting the stress interactions to occur then the rupture of surface is more complex and turns into a shear zone. This zone was observed to be relatively thick with an unsymmetrical pattern. The shear strength of rock bridges is reduced by increasing the joint length as a result of increasing both the stress concentration at tip of the joints and the stress interaction between the joints. 相似文献
17.
Numerical evaluation of three non‐coaxial kinematic models using the distinct element method for elliptical granular materials 
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下载免费PDF全文 This paper presents a numerical evaluation of three non‐coaxial kinematic models by performing Distinct Element Method (DEM) simple shear tests on specimens composed of elliptical particles with different aspect ratios of 1.4 and 1.7. The models evaluated are the double‐shearing model, the double‐sliding free‐rotating model and the double slip and rotation rate model (DSR2 model). Two modes of monotonic and cyclic simple shear tests were simulated to evaluate the role played by the inherent anisotropy of the specimens. The main findings are supported by all the DEM simple shear tests, irrespective of particle shape, specimen density or shear mode. The evaluation demonstrates that the assumption in the double‐shearing model is inconsistent with the DEM results and that the energy dissipation requirements in the double‐sliding free‐rotating model appear to be too restrictive to describe the kinematic flow of elliptical particle systems. In contrast, the predictions made by the DSR2 model agree reasonably well with the DEM data, which demonstrates that the DSR2 model can effectively predict the non‐coaxial kinematic behavior of elliptical particle systems. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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海底泥流是海底斜坡发生失稳滑动后,经复杂的水土交换作用演变成的稀式海底滑坡体,表现出土体和流体的双重特征,而现有的测试方法难以获得低剪切应变率下连续变化的强度值,不能很好地揭示其综合强度特性。利用新型全流动贯入仪和RST流变仪,对模拟海底泥流在不同剪切应变率下的流变和强度特性进行了多组试验研究,并基于试验结果分析了不排水剪切强度、屈服应力和表观黏度与含水率的相关性。基于剪切稀化理论,提出分阶段拟合模式来描述海底泥流从低剪切应变率到中高剪切应变率的流变关系;通过多种常规流变模式拟合结果的对比分析,显示出新流变模式的适用性和优势。考虑强度软化的影响,建立了全剪切应变率范围内海底泥流的不排水剪切强度模型,为海底泥流运动过程的数值模拟和灾害评价提供科学依据。 相似文献
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Effects of pore water pressure dissipation on rate dependency of shear strength in localised failure of soils 下载免费PDF全文
下载免费PDF全文 The paper presents analytical solutions for the evolution of excess pore pressures in the vicinity of a shear band in a rate‐dependent, strain‐softening permeable soil, with the aim to explore, both qualitatively and quantitatively, the potential variation of failure shear stress in the shear band. The solutions encompass both dissipation of a pre‐existing pore pressure regime within the main soil domain, and the effects of generation of additional pore pressure within the shear band itself. The simplified analytical solutions were checked by numerical inversion of exact solutions in Laplace transform space, confirming their high accuracy. The solutions show that it is possible for the failure shear stress to rise initially because of short‐term dissipation of the pre‐existing excess pore pressure at a faster rate than generation of new excess pore pressure within the shear band. This apparent strain hardening in a strain‐softening soil can be misleading in that it can temporarily slow down the sliding mass and create a false sense of stabilization of the slope. It can also result in additional temporary shear resistance for sliding foundations or pipelines on the seabed. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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This paper presents a numerical model for simulating free surface flow in porous media with spatially varying porosity. The governing equations are based on the mixture theory. The resistance forces between solid and fluid is assumed to be nonlinear. A multiphase SPH approach is presented to solve the governing equations. In the multiphase SPH, water is modeled as a weakly compressible fluid, and solid phase is discretized by fixed solid particles carrying information of porosity. The model is validated by several numerical examples including seepage through specimen, fast flow through rockfill dam and wave interaction with porous structure. Good agreements between numerical results and experimental data are obtained in terms of flow rate and evolution of free surface. Parameter study shows that (1) the nonlinear resistance law provides more accurate results; (2) particle size and porosity have significant influence on the porous flow. 相似文献