Data assimilation methods for estimating a heterogeneous conductivity field by assimilating transient solute transport data via ensemble Kalman filter     

Juxiu Tong  Bill X. Hu  Jinzhong Yang 《水文研究》2013,27(26):3873-3884

An ensemble Kalman filter (EnKF) is developed to identify a hydraulic conductivity distribution in a heterogeneous medium by assimilating solute concentration measurements of solute transport in the field with a steady‐state flow. A synthetic case with the mixed Neumann/Dirichlet boundary conditions is designed to investigate the capacity of the data assimilation methods to identify a conductivity distribution. The developed method is demonstrated in 2‐D transient solute transport with two different initial instant solute injection areas. The influences of the observation error and model error on the updated results are considered in this study. The study results indicate that the EnKF method will significantly improve the estimation of the hydraulic conductivity field by assimilating solute concentration measurements. The larger area of the initial distribution and the more observed data obtained, the better the calculation results. When the standard deviation of the observation error varies from 1% to 30% of the solute concentration measurements, the simulated results by the data assimilation method do not change much, which indicates that assimilation results are not very sensitive to the standard deviation of the observation error in this study. When the inflation factor is more than 1.0 to enlarge the model error by increasing the forecast error covariance matrix, the updated results of the hydraulic conductivity by the data assimilation method are not good at all. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Formal definition and dating of the GSSP (Global Stratotype Section and Point) for the base of the Holocene using the Greenland NGRIP ice core,and selected auxiliary records     

Mike Walker  Sigfus Johnsen  Sune Olander Rasmussen  Trevor Popp  Jørgen‐Peder Steffensen  Phil Gibbard  Wim Hoek  John Lowe  John Andrews  Svante Björck  Les C. Cwynar  Konrad Hughen  Peter Kershaw  Bernd Kromer  Thomas Litt  David J. Lowe  Takeshi Nakagawa  Rewi Newnham  Jakob Schwander 《第四纪科学杂志》2009,24(1):3-17

The Greenland ice core from NorthGRIP (NGRIP) contains a proxy climate record across the Pleistocene–Holocene boundary of unprecedented clarity and resolution. Analysis of an array of physical and chemical parameters within the ice enables the base of the Holocene, as reflected in the first signs of climatic warming at the end of the Younger Dryas/Greenland Stadial 1 cold phase, to be located with a high degree of precision. This climatic event is most clearly reflected in an abrupt shift in deuterium excess values, accompanied by more gradual changes in δ¹⁸O, dust concentration, a range of chemical species, and annual layer thickness. A timescale based on multi‐parameter annual layer counting provides an age of 11 700 calendar yr b2 k (before AD 2000) for the base of the Holocene, with a maximum counting error of 99 yr. A proposal that an archived core from this unique sequence should constitute the Global Stratotype Section and Point (GSSP) for the base of the Holocene Series/Epoch (Quaternary System/Period) has been ratified by the International Union of Geological Sciences. Five auxiliary stratotypes for the Pleistocene–Holocene boundary have also been recognised. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Simultaneous operation of opposing reaction mechanisms: The influence of matrix heterogeneity on post-kinematic garnet crystallization in an inverted metamorphic sequence     

Freya R. George  Fred Gaidies 《Journal of Metamorphic Geology》2020,38(7):743-769

Metapelites from the inverted Barrovian sequence in the Sikkim Himalaya (northeast India) are shown to be largely continuous with respect to their bulk rock compositions, microstructures and pressure–temperature–time–deformation (P–T–t–D) histories. However, the upper garnet–lower staurolite zone demarcates a region of microstructurally anomalous post-kinematic garnet populations contained within strongly segregated matrices. The different microstructures within samples from this region cannot be attributed to differences in their thermobarometric histories or bulk compositions, but are instead interpreted to represent an otherwise unexposed level of the Daling Group that is now exposed along a post-metamorphic thrust splay. These heterogeneous samples contain several discrete garnet populations that progressively crystallized with increasing P–T. Garnet populations that experienced the most protracted growth now form complex polycrystals that exhibit crystallographically controlled and morphologically irregular interfaces adjacent to micaceous and quartzofeldspathic domains respectively. Electron backscatter diffraction indicates that these polycrystalline garnet structures contain numerous coalesced porphyroblasts that are structurally uncorrelated across their grain boundaries. However, a crystallographically preferred orientation at the polycrystal scale is interpreted to derive from epitaxial crystallization of early-formed garnet porphyroblasts on precursor mica. Later-nucleated porphyroblasts within polycrystals preferentially concentrated towards quartzofeldspathic domains, with the overall nucleation distribution likely controlled by a complex interplay between chemical heterogeneities, strain partitioning and epitaxial crystallization. The subsequent growth of these polycrystals was equally spatially heterogeneous; it was moderated by differences in the efficiency of grain boundary transfer between quartzofeldspathic and micaceous domains that precluded thin section-scale chemical equilibration. In contrast to samples from Sikkim containing more typical porphyroblastic populations in continuous and disseminated matrices, heterogeneous availability of garnet-forming components within this strongly layered matrix is shown to have resulted in grain-scale variations in growth rates and the spatial juxtapositioning of interface-controlled microstructures and locally equilibrated chemical compositions with those that were transport controlled.  相似文献   

Spectral analysis of nonlocal regularization in two‐dimensional finite element models     

Xilin Lu  Jean‐Pierre Bardet  Maosong Huang 《国际地质力学数值与分析法杂志》2012,36(2):219-235

Strain‐softening in geomaterials often leads to ill‐posed boundary‐valued problems (BVP), which cannot be solved with finite element methods without introducing some kind of regularization such as nonlocal plasticity. Hereafter we propose to apply spectral analysis for testing the performance of nonlocal plasticity in regularizing ill‐posed BVP and producing mesh‐independent solutions when local plasticity usually fails. The spectral analysis consists of examining the eigenvalues and eigenvectors of the global tangential stiffness matrix of the incremental equilibrium equations. Based on spectral analysis, we propose a criterion for passing or failing the test of constitutive regularization in the context of BVP. If the eigenvalues of the tangential operator are all positive then the regularization succeeds, otherwise it fails and may not prevent artificial mesh‐dependent solutions from appearing. The approach is illustrated in the particular case of a biaxial compression with strain‐softening plasticity. In this particular case, local softening plasticity is found to produce negative eigenvalues in the tangential stiffness matrix, which indicates ill‐posed BVP. In contrast, nonlocal softening plasticity always produces positive eigenvalues, which regularizes ill‐posed BVP. The dominant eigenvectors, which generate localized deformation patterns, have a bandwidth independent of mesh size, provided that the mesh is fine enough to capture localization. These mesh‐independent eigenmodes explain why nonlocal plasticity produces numerical solutions that are mesh‐independent. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

古尔班通古特沙漠及周边区域冬季大气边界层高度对地表积雪的响应     

张梦肖  王豫  买买提艾力·买买提依明  刘永强  高佳程  肖婉秋  温聪  宋美琪  艾力亚尔·艾海提  王卫平  孟湘尧 《冰川冻土》2022,44(5):1558-1569

古尔班通古特沙漠是中国唯一冬季存在长期积雪的沙漠,在此特殊地理环境下,沙漠及周边区域冬季雪深和边界层高度的时空变化特征和相互关系尚未明确。本文利用1980—2019年SMMR（Scanning Multichannel Microwave Radiometer）、SSM/I（Special Sensor Microwave/Imager）、SSMI/S（Special Sensor Microwave Imager/Sounder）被动微波遥感雪深数据、古尔班通古特沙漠腹地雪深观测数据和ERA5再分析资料（the Fifth Generation ECMWF Reanalysis）边界层高度数据,分析了沙漠及周边区域冬季雪深和边界层高度的时空变化特征与相互关系。结果表明：古尔班通古特沙漠及周边区域冬季雪深年均值为8.45 cm,整体呈现东北部和南部积雪较深,其他区域积雪较浅并呈现出由沙漠中心区域向四周逐渐减少的特点,雪深在古尔班通古特沙漠及其东北、南边的邻近区域呈升高趋势,剩余地区呈下降趋势。古尔班通古特沙漠及周边区域冬季边界层高度年均值为105.54 m,呈现东南部和西北部高,中心沙漠区域、东北部、西南部较低的特点,边界层高度在沙漠及周边区域升高而其他区域降低。古尔班通古特沙漠的冬季雪深和大气边界层高度时空变化整体呈负相关,其中93.17%以上的沙漠区域呈负相关,平均相关系数为-0.32,最大相关系数绝对值为-0.58,空间相关系数为-0.42（P<0.05）。  相似文献   

基于单、双重渗透介质降雨边界处理的改进     

窦智  刘一民  周志芳  庄超  卫云波 《岩土力学》2022,43(3):789-798

在降雨入渗模拟中,现有研究无法准确实现复杂降雨条件下降雨边界在流量与压力两类边界之间的双向动态转换。基于饱和?非饱和渗流理论,将降雨补给流量与实际入渗流量的差值作为两类边界动态转换的判别条件,改进了单重渗透介质降雨边界动态转换控制方程,并进一步提出了双重渗透介质降雨边界处理方法及控制方程,在此基础上进行了数值试验及工程实例验证。结果表明：改进的降雨边界动态转换控制方程克服了传统降雨边界只能实现流量到压力边界单向转换的局限性,可准确实现流量边界与压力边界的双向动态实时转换;案例边坡的降雨入渗模拟结果说明了改进后降雨边界的正确性和工程适用性。  相似文献   

基于边界位移法的地下结构推覆试验可行性研究     

徐琨鹏  景立平  程新俊  梁海安  宾佳 《岩土力学》2022,43(1):127-138

地震过程中地下结构变形主要受周边土体变形控制。基于该思想,现已提出一种在土?结构有限元模型侧边施加土体变形的地下结构抗震简化分析方法——边界位移法,但缺乏相关试验研究。为探索土体侧边施加推覆位移的试验方法可行性,以自行研制的岩土综合试验模型箱为试验平台,以1:10缩尺的大开车站区间隧道为研究对象,开展了大型土?地下结构系统推覆试验。通过应变、位移和应力的分析,揭示了试验过程中地下结构及周边土体的反应特性。结果表明：由于土体材料的强非线性特征,土体侧边施加的倒三角形变形在传递过程中会产生衰减,地下结构受到剪切变形和挤压变形的耦合作用;中柱与底板交接处是整体结构中的抗震薄弱位置;水平基床系数与土层位移水平及结构侧壁的破坏阶段相关;结构整体刚度大于等代土体,两者的侧向变形比值小于1。随着推覆水平增加比值逐渐增大,通过变形特征能够量化土?结构相互作用,有效填补了土?结构相互作用系数试验研究的空白。试验方法与结论,对地下结构抗震分析及推覆试验可行性研究具有重要指导意义。  相似文献   

有机污染物在含土工膜复合隔离墙和含水层系统的运移半解析模型     

郑紫荆  朱云海  王巧  谢海建  陈赟 《岩土力学》2022,(2):453-465

为评估土工膜与土-膨润土组成的复合隔离墙对有机污染物的防污性能,建立了污染物在源区域发生降解扩散时透过复合隔离墙的一维瞬态扩散模型。通过拉普拉斯变换和Talbot数值反演获得了模型解。第3类入流边界条件下,考虑源区的扩散和降解时,第1类隔离墙(土工膜/土-膨润土)和第2类隔离墙(土-膨润土/土工膜/土-膨润土)100 a的击穿浓度分别较源浓度恒定时减少了59%和53%。由于假设土工膜渗透系数高于10^–12 m/s,污染物在复合隔离墙中的对流作用不能忽略,因此,采用第2类复合隔离墙使土-膨润土能更好地发挥主导隔离作用。将土工膜的渗透系数从10^–10 m/s减少到10^–16 m/s,第1类复合隔离墙的击穿时间从26 a增加到188 a,第2类复合隔离墙的击穿时间从32 a增加到81 a。利用抽水井调整墙体内外为负水头差及提高源区的污染物降解能力,可使隔离墙的防污性能得到较大提升。  相似文献   

塔里木盆地一次“东灌”沙尘暴大气边界层特征     

阿不力米提江.阿布力克木  李娜  赵克明  孙鸣婧  闵月 《沙漠与绿洲气象(新疆气象)》2019,13(5):55-61

利用探空、NCEP/NCAR 1°×1°再分析资料、地面气象站观测资料,对新疆塔里木盆地2014年10月28—29日的沙尘暴天气过程前、中、后大气稳定度、混合层厚度、风、温、湿廓线等边界层特征量进行分析。结果表明:此次天气过程为欧洲脊东移,推动西西伯利亚低槽快速进入北疆地区,随后东移翻越东天山进入南疆,造成"东灌"沙尘暴天气;沙尘暴造成边界层特征量表现为K指数减小,沙氏指数增大,理查逊数减小,混合层厚度降低等特征;风向由偏西风转为偏东风,风速则在静风转为30 m/s的偏东急流;温度为沙尘暴之前为贴地逆温,之后大气混合比较均匀,相对湿度为先增加后减小,沙尘暴天气是一个降温增湿的过程,边界层风、温、湿廓线都打破了原有分布规律;沙尘暴过程是大气不稳定层结变为稳定层结的过程。  相似文献   

江苏沿海近地层风阵性及台风对其影响          下载免费PDF全文

陈燕  张宁 《应用气象学报》2019,30(2):177-190

为了研究风阵性特征,尤其是在受台风影响时湍流特征对安全开发利用风能资源的影响,利用江苏沿海5座测风塔2009年6月—2012年11月的梯度风观测数据,分析了近地层风阵性基本特征,并筛选了7个对江苏产生较大影响的台风,包括罕见的正面登陆台风达维（1210）,分析台风影响下风阵性特征。研究发现:江苏沿海地区低层的风脉动性比高层强,10 m高度的年平均阵风系数和湍流强度分别为1.50和0.20;海陆分布明显影响风阵性,离岸风的湍流强度明显大于向岸风;当风速等级小于6级时,风阵性随风速增大而一致性减小,之后则稳定少变;在台风中心附近,受风速、风向快速多变的影响,湍流强度和阵风系数均远大于台风外围和没有台风影响的情况,湍流强度和阵风系数在30~50 m高度之间增加,在6~7级风时出现风阵性的局部峰值区。  相似文献