Unified fractional differential approach for transient interporosity flow in naturally fractured media     

《Advances in water resources》2014

A unified approach to modeling flows of slightly compressible fluids through naturally fractured media is presented. The unified fractional differential model is derived by combining the flow at micro scale for matrix blocks and macro scale for fractures, using the transient interporosity flow behavior at the interface between matrix blocks and fractures. The derived model is able to unify existing transient interporosity flow models formulated for different shapes of matrix blocks in any medium dimensions. The model is formulated in the form of a fractional order partial differential equation that involves Caputo derivative of order 1/2 with respect to time. Explicit solutions for the unified model are derived for different axisymmetrical spatial domains using Hankel or Hankel–Weber finite or infinite transforms. Comparisons between the predictions of the unified model and those obtained from existing transient interporosity flow models for matrix blocks in the form of slabs, spheres and cylinders are presented. It is shown that the unified fractional derivative model leads to solutions that are very close to those of transient interporosity flow models for fracture-dominant and transitional fracture-to-matrix dominant flow regimes. An analysis of the results of the unified model reveals that the pressure varies linearly with the logarithm of time for different flow regimes, with half slope for the transitional fracture-to-matrix dominant flow regime vs. the fracture and matrix dominant flow regimes. In addition, a new re-scaling that involves the characteristic length in the form of matrix block volume to surface area ratio is derived for the transient interporosity flow models for matrix blocks of different shapes. It is shown that the re-scaled transient interporosity flow models are governed by two dimensionless parameters Θ and Λ compared to only one dimensionless parameter Θ for the unified model. It is shown that the solutions of the transient interporosity flow models for different shapes of matrix blocks are almost identical for the re-scaled variables. Furthermore, the driving parameters for solution behavior are identified based on asymptotic approximations for different flow regimes. It is found that the matrix diffusion and the matrix area-to-volume ratio affect the solution behavior only for the transitional fracture-to-matrix dominant flow regime, that the capacitance ratio affects the solution behavior only for transitional and matrix dominant flow regimes and that the fracture diffusion is involved in all three flow regimes. Similar identification of the driving parameters is also presented in the re-scaled case.  相似文献   

Dynamic responses of two buildings connected by viscoelastic dampers under bidirectional earthquake excitations   总被引：1，自引：1，他引：0  

Z.D. Yang  Eddie S.S. Lam 《地震工程与工程振动(英文版)》2014,13(1):137-150

In this study,dynamic responses of two buildings connected by viscoelastic dampers under bidirectional excitations are extensively investigated.The two buildings are a 10-story building and a 16-story building,with the shorter building on the left.Viscoelastic dampers are installed at all fl oors of the shorter building.Equations of motion are formulated using a fractional derivative model to represent the viscoelastic dampers.Three cases are considered with mass eccentricities at 0,10% and-10% with respect to the dimensions of the buildings.The responses of the buildings are numerically predicted at different damper properties.The simulation results indicated that the maximum horizontal responses of the buildings without eccentricities are signifi cantly mitigated.However,torsional effects are adversely increased.For asymmetric buildings,the effectiveness of the connecting dampers is affected by building eccentricities.As a result,mass eccentricities must be taken into account in damper selection.When compared with vibrations induced by unidirectional excitations,bidirectional excitations can increase the responses of coupled asymmetric buildings.In addition,installing dampers only at the top fl oor of the shorter building may cause a sudden change in lateral stiffness of the taller building.Consequently,the story shear envelopes of the taller building are changed.  相似文献   

吉林西部盐碱地数字图像植被覆盖度的自动提取     

丁艳玲  赵凯  李晓峰  郑兴明 《地球信息科学学报》2013,(4):618-624

植被覆盖度是生态环境变化的重要指标,也是遥感反演的关键参数。盐碱地植被覆盖度的准确测量对研究地表植被蒸腾、土壤水分蒸发及土壤退化、盐碱化等具有重要意义。过绿指数(Excess Green index,ExG)对绿色植被比较敏感,能突显植被信息,去除土壤、阴影的干扰。通过对吉林西部盐碱地玉米、高粱、绿豆、杂草、土壤数字图像特征分析,利用改进过绿指数(Modified Excess Green index,MExG)算法计算植被和土壤的MExG值;并确定区分植被和土壤的MExG阈值为40,进而计算植被覆盖度。本文采用监督分类的最大似然法对比验证MExG自动提取结果,并对两种方法计算的玉米、高粱、绿豆和杂草的覆盖度,分别进行目视判读和t检验。研究表明,MExG自动提取方法具有客观性强,处理时间短,分类精度高等优点,是计算不同植被类型覆盖度的有效方法。  相似文献   

基于分数阶导数的非定常蠕变本构模型研究     

何志磊  朱珍德  朱明礼  李志敬 《岩土力学》2016,37(3):737-744

针对锦屏二级水电站深埋长大隧洞围岩在开挖过程中呈现明显的流变劣化特征,基于分数阶微积分理论,用Abel黏壶替换西原模型中的牛顿黏壶,推导出基于分数阶导数的蠕变本构方程,同时考虑岩石在蠕变过程中,尤其是所受应力超过其长期强度时,蠕变参数是非定常的特征,把蠕变参数的非定常性引入本构方程中,建立了基于分数阶导数的非定常蠕变本构模型。结合锦屏二级水电站引水隧洞主要围岩之一的大理岩的室内剪切蠕变试验的结果,对模型中的参数进行反演,结果表明,基于分数阶导数的非定常蠕变本构模型能够在蠕变初期和拐点处与试验结果很好地吻合,并且可以克服西原模型不能反映蠕变第3阶段的不足。通过对模型中参数的敏感性进行分析,得出分数阶阶数、非定常参数对岩石蠕变的影响规律。研究结果表明,提出的基于分数阶导数的非定常蠕变模型能够很好地反映大理岩的蠕变全过程。  相似文献   

WorldView-2近红外光谱波段反演马尾松植被信息的比较研究   总被引：1，自引：0，他引：1  

胡秀娟  徐涵秋  黄绍霖  张灿  唐菲 《地球信息科学学报》2016,18(4):537-543

WorldView-2卫星自2009年发射至今,已为用户提供了大量高性能的影像产品。与众多高分辨率卫星影像不同,WorldView-2有2个近红外波段,即近红外1(Near-infrared1,NIR1)和近红外2(Near-infrared2,NIR2),但目前这2个波段在应用上的区别并不清楚。因此,本文以福建省长汀县河田地区的马尾松林为例,采用NIR1和NIR2这2个近红外波段分别构建了3种植被指数(NDVI、ARVI和NDMVI),以探索二者在植被信息反演方面的差异。结果表明,NIR1构建的植被指数在马尾松林提取精度上高于NIR2,并具有更丰富的植被信息量。经统计可知,NIR1所构建的植被指数信息量比NIR2分别大8.0%(NDVI)、12.3%(ARVI)和7.3%(NDMVI);在反演植被覆盖度方面,NIR1也比NIR2具有更高的精度,其模拟的植被覆盖度与实际植被覆盖度的拟合度更高,误差更小。NIR1和NIR2所表现出的差异是因为马尾松在这2个近红外波段的光谱反射不同,其反射在NIR1的波长范围内达到最强,而在NIR2的波长范围内则出现了小幅下降。  相似文献   

动态高压下陨石矿物的冲击熔融和分离结晶及其地球化学意义          下载免费PDF全文

谢先德  陈鸣 《地学前缘》2009,16(1):134

应用近代微束矿物学分析测试技术,对在中国陨落的随州、寺巷口和岩庄等三块球粒陨石中矿物的冲击熔融和分离结晶作用进行了较系统的研究。查明存在有硅酸盐单矿物熔体、硅酸盐矿物混合熔体和全岩熔体三种组成不同的冲击熔体。研究结果显示:(1)三种熔融相与未熔相之间在主成分和微量元素组成上没有明显差别,说明它们是原地熔融的产物,但在较大的冲击熔块中,也发现冲击熔融作用引发了一部分元素,如亲铁元素、硒元素和轻重稀土元素的分异现象;(2)查明Al2O3、Cr2O3、Na2O和CaO等优先进入从冲击熔体结晶的辉石常压相或辉石的高压相——镁铁榴石(属地幔过渡带矿物)中;(3)Al元素能进入阿基莫石(即辉石的钛铁矿结构相,属下地幔矿物)中,以固熔体形式稳定下来。ELNES的测定查明,其氧化铁组分中Fe3+/∑Fe的比值高达0.67(3);(4)陨石全岩熔体中硅酸盐相与金属-硫化物相之间为完全不混熔,后者以孤立的共结体团块产于硅酸盐熔体之中,除Zn、Na、Cr、Co和Cu在硫化物相中和Na在金属相中有明显富集外,其他元素的浓度则无明显变化;(5)在寺巷口陨石熔脉的金属-硫化物共结团块内发现了FeNi金属-硫化铁-磁铁矿组合,进一步证实了S和O等轻元素可以加入到以Fe-Ni金属为主要组成的地核成分中去;(6)在岩庄陨石的FeNi金属-硫化铁共结体团块的硫化铁内发现了Na、Mn和Fe的磷酸盐矿物小球体,说明P和Na、Mn等元素也能成为地核的组成元素。以上研究在行星演化、地幔矿物学和地球化学,以及陨石学研究上均有着重要的科学意义。  相似文献   

Permian High Ba-Sr Granitoids: Geochemistry, Age and Tectonic Implications of Erlangshan Pluton, Urad Zhongqi, Inner Mongolia   总被引：1，自引：0，他引：1  

LUO Hongling  WU Tairan  ZHAO Lei  HE Yuankai  JIN Xu 《《地质学报》英文版》2009,83(3):603-614

Abstract: Erlangshan Pluton from Urad Zhongqi, central Inner Mongolia, is located in the middle segment of the northern margin of the North China Plate. The rocks consist mainly of diorites with gneissic structure. Petrochemical characteristics reveal that the diorites belong to metaluminous, high-potassium calc-alkaline series, with chemical signatures of I-type granites. They are characterized by low SiO2 contents (56.63%–58.53%) and A/CNK (0.90–0.96), high Al2O3 contents (17.30%–17.96%) and Na2O/K2O ratios (1.20–1.70), enrichment in large ion lithophile elements (LILE, e.g., Ba=556–915 ppm, Sr=463–595 ppm), and relative depletion in high field strength elements (HFSE, e.g., Nb, Ta, Ti) in primitive mantle-normalized spidergram, and right-declined rare earth element patterns with slightly negative Eu anomalies (d?Eu=0.72–0.90). They have Sr/Y ratios (20–25) evidently less than Kebu Pluton (49–75) to its east. Sensitive high resolution ion micro-probe U-Pb zircon dating of the diorites has yielded an intrusive age of 270±8?Ma. This leads us to conclude that Erlangshan diorites were formed by mixing between the middle or lower crustal-derived magma and minor mantle-derived mafic magma, followed by fractional crystallization, which was trigged by crustal extension and fault activity in post-collisional setting.  相似文献   

Quality evaluation model for map labeling   总被引：2，自引：0，他引：2  

FANHong ZHANGZuxun DUDaosheng 《地球空间信息科学学报》2005,8(1):72-78

This paper discusses and sums up the basic criterions of guaranteeing the labeling quality and abstracts the four basic factors including the conflict for a label with a label, overlay for label with the features, position‘s priority and the association for a label with its feature. By establishing the scoring system, a formalized four-factors quality evaluation model is constructed. Last, this paper introduces the experimental result of the quality evaluation model applied to the automatic map labeling system-MapLabel.  相似文献   

西藏驱龙斑岩铜矿床岩浆演化过程中的Cu同位素分馏     

聂龙敏  李振清  房小捷 《矿床地质》2012,31(4):718-726

随着同位素测试技术的发展,高温下重同位素分馏逐渐运用到地球化学领域.为了探索岩浆演化过程中是否会发生Cu同位素分馏,文章对西藏驱龙斑岩铜矿床同来源、不同演化阶段的两套岩浆岩(闪长岩包体和花岗闪长岩)进行了Cu同位素测试.测试结果显示,闪长岩包体的δ65Cu值集中在+0.08‰-+0.35‰之间,平均值为+0.25‰,花岗闪长岩的δ65Cu值为+0.42‰～+0.87‰,平均值为+0.60‰.△65Cu花岗闪长岩-闪长岩包体≈+0.4‰,并且δ65Cu值与样品w(SiO)变化存在一定的正相关性.结合地质学及同位素方面考虑,花岗闪长岩和闪长岩包体的Cu同位素组成差异可能是岩浆演化过程中发生了Cu同位素分馏所致.在驱龙矿区中新世岩浆演化过程中,随着岩浆去气作用,63Cu随HS-、Cl-等挥发分优先进入气相,导致残留岩浆熔体相对富集65Cu.此外,两者的Cu同位素组成差异也可能与岩浆演化过程中斜长石、角闪石、黑云母等矿物的不断结晶分离有关,矿物结晶分离时,基性矿物富集63Cu,而残余熔体则富集65Cu.  相似文献   

火成碳酸岩的实验岩石学研究及对地球深部碳循环的意义   总被引：3，自引：0，他引：3  

宋文磊  许成  刘琼  王林均  吴敏  曾亮 《地质论评》2012,58(4):726-744

火成碳酸岩是地表出露较少的幔源岩石之一。实验岩石学研究表明碳酸盐化的橄榄岩和循环的地壳物质(如碳酸盐化榴辉岩或泥质岩)的低程度(<1%)部分熔融均可以产生碳酸岩质的熔体,其中碳酸盐化泥质岩具有最低的熔融温度且更加富碱质、CO2和不相容元素;富CO2的霞石质等硅酸盐岩浆也可以通过不混溶或分离结晶作用产生碳酸岩,用于解释碳酸岩在空间中常与碱性硅酸岩的共生关系。由于碳酸岩熔体具有极低的粘度和高的活性,形成后在上升过程中会将二辉橄榄岩转变为异剥橄榄岩,是引起地幔交代作用和地幔地球化学不均一性的重要介质之一。实验表明在俯冲作用过程中,大多数的碳酸盐在位于岛弧之下的含水熔融并不分解而是被带入到深部地幔并且稳定存在,含碳地幔的熔融又会形成碳酸岩质的熔体,这说明俯冲循环物质可能对碳酸岩的成因也起着重要的作用。然而,对于碳酸岩的初始熔体成分、岩浆演化、地幔交代作用、成矿特征以及碳从地球深部返回到地表的途径和过程等都存在着很大的争议。我国火成碳酸岩出露相对较多,分布广泛,因此,加强我国碳酸岩以及伴生硅酸岩的成因研究,同时开展与碳酸岩相关的实验岩石学工作,不仅可以检验现有的成因理论,而且有助于提高我国对火成碳酸岩的研究水平;由于其特殊的成因背景,还可为许多存在很大争议的重大地质事件提供新的科学依据。  相似文献