共查询到20条相似文献，搜索用时 140 毫秒
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目前常用的水力学传统方法计算明槽水面线的方法中,尚未系统提出曲底明槽水面线的计算方法,本文根据明渠非恒定流的基本微分方程,导出计算明槽水面线的基本方程,并进行了试验验证,计算结果能很好的符合实测水面线. 相似文献
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在渠道设计中,通常按明渠均匀流计算渠道底坡.当渠道较短时,不能形成均匀流,则需按恒定渐变流理论计算渠道底坡,至今尚未发现探讨该类问题的文献.因此本文结合工程实例,分析了四种类型的水面线和渠道底坡间的关系,以及相应的底坡搜索区间,最后用性能稳健的二分法计算出了渠道底坡值. 相似文献
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计算明渠非恒定流的一个Lattice BGK模型 总被引：4，自引：1，他引：3
分析了Lattice Boltzmann(LB)方法的建模原理,通过比较LB的多尺度方程和明渠St.Venant方程,建立了计算一维明渠非恒定流的一个Lattice BGK模型。对几个典型应用实例进行了模拟分析,与Preissmann隐格式及特征线法作了比较,证明将该方法引入实际明渠非恒定流计算是可行的。 相似文献
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在有侧向流入(流出)的水平井流运动和连续性方程的基础上,建立了渗流与水平井流耦合数学模型,主要针对混合水头损失问题,进行了渗流与水平井流耦合数值计算,分析了常用的摩擦系数修正方法对计算结果的影响。数值模拟计算表明:层流或者光滑紊流流态时,不同的摩擦系数修正方法对结果影响较小;粗糙紊流流态时,不同的摩擦系数修正方法对结果影响较大。当水平井流是层流-光滑紊流流态时,使用了一种新的流态分界点识别方法对水平井流态进行判断,计算结果证实了方法的可靠性、合理性。 相似文献
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基于有限元方法中的虚位移原理,写出了不可压流Gao-Yong湍流方程组弱形式的微分方程表达式,利用有限元程序自动生成系统(FEPG)得到了全部有限元计算程序。对二维顶盖驱动方腔流进行了数值模拟,得到了方腔内的涡量分布和中心线上的速度变化曲线,并且成功地模拟出了高雷诺数时方腔内的双涡结构,计算结果与文献提供基准解符合良好。进一步证实了Gao-Yong湍流方程组能够准确模拟复杂湍流粘性场,并且为Gao-Yong湍流方程组的工程应用奠定了基础。 相似文献
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泥浆侵入二维数值模拟 总被引：3，自引：0，他引：3
石油钻井中由于井底压力略大于地层压力, 使得钻井泥浆侵入到原始地层中, 改变地层的电阻率, 影响了电阻率测井的准确性.以油水两相流的渗流方程、对流扩散方程和阿尔奇公式为理论模型, 采用有限差分方法对泥浆侵入过程进行二维数值离散, 针对麻黄山西探区储层实际情况输入模型中有关参数, 分别对侵入时间24 h和48 h, 解得给定侵入时刻储层的压力、含水饱和度、地层水矿化度和电阻率在垂向和径向的分布, 计算结果与实际情况相符, 可用其对实际电阻率测井值进行校正.通过一个低侵算例验证, 结果与理论分析相符合, 因此该方法可以用于垂向上非均匀储层的泥浆侵入计算. 相似文献
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半干旱区岩溶碳汇原位监测方法适宜性研究 总被引：1，自引：0，他引：1
选择正确的方法准确计算北方干旱半干旱岩溶区的岩溶碳汇量, 有助于提高我国岩溶碳汇效应估算精度和改进全球碳循环模型。利用水化学径流法和标准溶蚀试片法对山西马跑神泉域的岩溶碳汇量进行了计算, 结果表明, 标准溶蚀试片法计算出的流域碳汇量和碳汇强度为386.15 t/a和1.821 t/(km2·a), 水化学径流法的结果为2 084.08 t/a和9.83 t/(km2·a), 试片法计算结果仅为水化学径流法的1/5。试片溶蚀速率和土壤无机碳质量分数呈负相关关系, 进一步表明土壤无机碳质量分数高(是有机碳质量分数的2.85~5.06倍)是造成试片法计算结果偏小的主要原因:高含量的无机碳在半干旱气候条件下容易沉积, 从而使试片溶蚀速率偏小;流域边界清楚, 水化学和流量易于监测, 利用水化学径流法计算岩溶碳汇强度结果更为准确。因此, 在半干旱地区, 计算岩溶碳汇效应宜采用水化学径流法。 相似文献
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在三维非恒定渗流有限元计算中,不可避免地需计算自由面上的边界积分项。建议一种高精度数值积分的方法求取自由面边界积分项。其基本思路是,基于8节点空间等参单元,根据压力为零的边界条件确定自由面满足的曲面方程,将自由面边界积分转化为ξη平面上的二重积分;然后再计算自由面与三维等参单元的交点,将交点投影到局部坐标平面ξη上,并根据点与线的相对关系,确定投影点所围成的局部坐标积分区域;再将总积分区域划分成若干个三角形子区域,并利用变步长Simpson方法计算各三角形子区域上的二重积分,从而实现了高精度的自由面边界积分。该方法避免了单元中自由面为平面的假设,可提高计算精度,特别对于单元内自由面变化剧烈情况,更为显著。将该方法应用于砂槽模型和土坝的渗流分析中,计算结果与实际情况较为接近。 相似文献
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Meng Wang Jantiene E. M. Baartman Hongming Zhang Qinke Yang Shuqin Li Jiangtao Yang Cheng Cai Meili Wang Coen J. Ritsema Violette Geissen 《Earth Science Informatics》2018,11(4):579-590
The improvement of resolution of digital elevation models (DEMs) and the increasing application of the Revised Universal Soil Loss Equation (RUSLE) over large areas have created problems for the efficiency of calculating the LS factor for large data sets. The pretreatment for flat areas, flow accumulation, and slope-length calculation have traditionally been the most time-consuming steps. However, obtaining these features are generally usually considered as separate steps, and calculations still tend to be time-consuming. We developed an integrated method to improve the efficiency of calculating the LS factor. The calculation model contains algorithms for calculating flow direction, flow accumulation, slope length, and the LS factor. We used the Deterministic 8 method to develop flow-direction octrees (FDOTs), flat matrices (FMs) and first-in-first-out queues (FIFOQs) tracing the flow path. These data structures were much more time-efficient for calculating the slope length inside the flats, the flow accumulation, and the slope length linearly by traversing the FDOTs from their leaves to their roots, which can reduce the search scope and data swapping. We evaluated the accuracy and effectiveness of this integrated algorithm by calculating the LS factor for three areas of the Loess Plateau in China and SRTM DEM of China. The results indicated that this tool could substantially improve the efficiency of LS-factor calculations over large areas without reducing accuracy. 相似文献
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速流结构是公路泥石流防治体系中常用且有效的工程措施之一。文章基于底越式速流结构的受荷模式及边界条件,将汇流槽视为三次超静定梁,运用结构力学方法求解侧墙及嵌固桩的内力;将速流槽与嵌固桩引入Winkler模型,用弹性地基梁理论求解速流槽内力、位移及地基反力,由此提出底越式速流结构计算理论。以平川泥石流防治工程为例,进行内力计算。 相似文献
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A practical and efficient numerical scheme for the analysis of steady state unconfined seepage flows
The scaled boundary finite‐element method (SBFEM), a novel semi‐analytical technique, is applied to the analysis of the confined and unconfined seepage flow. This method combines the advantages of the finite‐element method and the boundary element method. In this method, only the boundary of the domain is discretized; no fundamental solution is required, and singularity problems can be modeled rigorously. Anisotropic and nonhomogeneous materials satisfying similarity are modeled without additional efforts. In this paper, SBFE equations and solution procedures for the analysis of seepage flow are outlined. The accuracy of the proposed method in modeling singularity problems is demonstrated by analyzing seepage flow under a concrete dam with a cutoff at heel. As only the boundary is discretized, the variable mesh technique is advisable for modeling unconfined seepage analyses. The accuracy, effectiveness, and efficiency of the method are demonstrated by modeling several unconfined seepage flow problems. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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Development of a discontinuous approach for modeling fluid flow in heterogeneous media using the numerical manifold method 
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下载免费PDF全文 In the numerical modeling of fluid flow in heterogeneous geological media, large material contrasts associated with complexly intersected material interfaces are challenging, not only related to mesh discretization but also for the accurate realization of the corresponding boundary constraints. To address these challenges, we developed a discontinuous approach for modeling fluid flow in heterogeneous media using the numerical manifold method (NMM) and the Lagrange multiplier method (LMM) for modeling boundary constraints. The advantages of NMM include meshing efficiency with fixed mathematical grids (covers), the convenience of increasing the approximation precision, and the high integration precision provided by simplex integration. In this discontinuous approach, the elements intersected by material interfaces are divided into different elements and linked together using the LMM. We derive and compare different forms of LMMs and arrive at a new LMM that is efficient in terms of not requiring additional Lagrange multiplier topology, yet stringently derived by physical principles, and accurate in numerical performance. To demonstrate the accuracy and efficiency of the NMM with the developed LMM for boundary constraints, we simulate a number of verification and demonstration examples, involving a Dirichlet boundary condition and dense and intersected material interfaces. Last, we applied the developed model for modeling fluid flow in heterogeneous media with several material zones containing a fault and an opening. We show that the developed discontinuous approach is very suitable for modeling fluid flow in strongly heterogeneous media with good accuracy for large material contrasts, complex Dirichlet boundary conditions, or complexly intersected material interfaces. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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Well modeling plays an important role in numerical reservoir simulation. The main difficulty in well modeling is the difference in scale between the wellbore radius and well gridblock dimension used in the simulation. The Peaceman equation is widely used in reservoir simulation to match gridblock pressure to the local solution of the diffusivity equation describing the flow near the well. However, this approach was developed under the assumption of radial flow. At the same time, the well inflow equation can be solved within the Green’s function (GF) formalism which allows the solution to be obtained without the assumption of radial flow. The GF solution can be presented as a series over the eigenvalues of the Laplace differential operator. However, this series converges conditionally and its direct summation is time-consuming. In Posvyanskii et al. (2008), a method for fast summation of such a series was proposed and successfully applied for analyzing the pressure build up curves. In this paper, we adopt the same technique for calculating the well indices for horizontal, slanted and partially penetrated wells. Additionally, the role of different boundary conditions is considered. The semi-analytical expressions for well indices are obtained and compared to the solution of the Peaceman equation. It is shown that in some cases, the difference between these solutions can be significant. The use of the obtained expression in numerical flow simulation allows well inflow to be modeled with high accuracy even on a coarse grid. 相似文献
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A new artificial boundary approach for transient seepage problems in unbounded domain is presented. The artificial boundary condition at the truncated boundary is derived from the analytical solutions for transient seepage problems in one dimension, including solutions, respectively, for flow in one‐dimensional infinite space and for radial flow in an infinite layer, and then it is tentatively applied for some two dimensional problems in addition to the one‐dimensional problems mentioned above. The boundary conditions derived relate the time‐dependent boundary flux with the time derivative of the hydraulic head at the truncated boundary, which makes the implementation much easier compared with the infinite element method. The accuracy and efficiency of the artificial boundary are validated by several numerical examples, which shows that the proposed boundary can give very good results for one‐dimensional transient seepage problems, as expected, whereas reasonable results can be also obtained for two‐dimensional problems, such as two‐dimensional axisymmetric flow and flow in an infinite plane. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献