Proof of the equivalence of Tanizawa–Berkvens’ and Cointe–van Daalen's formulations for the time derivative of the velocity potential for non-linear potential flow solvers

Dealing with freely-floating bodies in the framework of non-linear potential flow theory may require solving Laplace's equation for the time derivative of the velocity potential. At present, there are two competing formulations for the body boundary condition. The first one was derived by Cointe [1] in 2D. It was later extended to 3D by van Daalen [2]. The second formulation was derived by Tanizawa [3] in 2D. It was extended to 3D by Berkvens [4]. In this paper, a proof is given that the Cointe–van Daalen's and the Tanizawa–Berkvens’ formulations are equivalent. It leads to a simplified version of Cointe–van Daalen's formulation. The formulation is validated against the analytical solution for a moving sphere in an unbounded water domain.     

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

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.     

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

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.     

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

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.     

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

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.     

广东阳江盆地遥感数据地温反演及地热异常靶区圈定

地热能是一种安全、清洁、稳定的可再生能源,广东阳江地区的地热资源开发潜力巨大,但研究程度较低。热红外遥感技术能够高效地圈定地热异常区并对隐伏断裂进行预测,笔者等选取研究区landsat8遥感数据,通过分析地表温度、地热异常点及人类活动的关系,利用大气校正方法对该区潜在的地热异常进行了预测。在排除人为热影响下得到高温地热异常区9处,排除湖泊水域以及海拔的影响下得到低温地热异常区4处。在此基础上,利用地表温度与归一化植被指数计算研究区的温度植被干旱指数值（TVDI）,预测可能存在的隐伏断裂23 处。最后结合岩性、断裂构造有效地圈定了5处地热靶区,主要分布在研究区西南区域和新洲镇附近。研究结果有助于预测阳江地区具有开发前景的地热异常区、识别圈定具有勘探意义的靶区以及预测隐伏断裂,对该区后续地热资源的进一步研究具有重要的意义。     

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

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）。     

基于单、双重渗透介质降雨边界处理的改进

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。     

基于边界位移法的地下结构推覆试验可行性研究

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。     

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

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。