The structure of separated flow past a circular cylinder in a rotating frame

Abstract

This paper examines the detailed E ^1/4-layer structure of separated flow past a circular cylinder in a low-Rossby-number rotating fluid as the Ekman number E tends to zero. This structure is based on an initial proposal by Page (1987) but with some modifications in response to further evidence, outlined both in this paper and elsewhere, on the behaviour of E ^1/4-layer flows in this context. Numerical calculations for flow in an E ^1/4 shear layer along the separated free streamline are described and the mass flux from this layer is then used to calculate the higher-order flow within the separation bubble. The flow structure is found to have two forms, depending on the value of the O(1) parameter λ, and these are compared with results from published “Navier-Stokes” type calculations for the flow at small but finite values of E.     

2012年4月11日苏门答腊Ms8.6地震前电离层TEC异常变化

基于IGS提供的GPS TEC资料和中国地壳运动观测网络提供的GPS数据解算的单站VTEC数据,采用统计分析处理方法,对2012年4月11日苏门答腊北部Ms8.6地震震前电离层TEC资料进行处理分析,结果表明:在震前5-6天以及地震当天,震中上空附近出现显著的电离层TEC异常扰动,异常形态有正有负,表现为先异常减小后异常增大最后变小,异常增大主要发生在下午至黄昏时段,即12:00-16:00 LT,持续时间约4小时.排除太阳活动和地磁扰动的影响后,4月5日出现的电离层TEC异常增大及呈现出共轭结构以及地震当天出现的异常扰动,可能与此次地震有关.     

井-地充电法圈定矿体边界异常特征研究

采用有限单元法对井-地充电法进行了数值模拟,通过对水平、倾斜等不同形态板状矿体在不同地电条件下井-地充电法异常的计算和讨论,研究了矿体的空间分布与电位梯度分布之间规律,并提出深宽比和深峰比的概念以讨论异常形态与地下地质体间的对应关系.计算结果表明:电位梯度峰值位置和矿体边界位置有一定的对应关系,利用电位梯度等值线形态及其峰值位置可有效获得矿体走向、倾向和边界等信息.     

Fluid pathways and high‐P metasomatism in a subducted continental slice (Mt. Emilius klippe,W. Alps)

The Mt. Emilius klippe (Western Alps, Italy) corresponds to a segment of the stretched Adriatic continental margin metamorphosed at granulite facies during Permian. This slice was subducted during the early Cenozoic Alpine subduction with the underlying eclogite facies remnants of the Tethyan seafloor (Zermatt‐Saas zone). Near the base of the Mt. Emilius massif, there is a shear zone with eclogite facies hydrofracture systems associated with deformation‐induced re‐equilibration of granulites during high‐P metamorphism. In the basal part of the massif, a pluri‐hectometre domain of sheared mafic boudins is hosted in the granulitic paragneiss. In these mafic boudins, there are garnetites, garnet veins and clinopyroxenites, as well as clinozoisite and calcite veins. These features record multiple events of fracture opening, brecciation, boudinage and parallelization of structures coevally with fluid–rock interaction, metasomatism and volume change. This integrated petrological, micro‐textural and geochemical investigation illustrates the multiplicity and the chemical variability of fluid sources during prograde to peak metamorphic evolution in the lawsonite–eclogite‐facies field (at ~2.15–2.4 GPa, 500–550 °C) during subduction of the Mt. Emilius slice. The calcite veins crosscutting the garnetites have relatively low δ¹⁸O_VSMOW values (～+6.5‰) near those for marble layers (and nearby calcsilicates) embedded within the metasomatized granulites (+8 to +10‰). It is proposed that infiltration of externally‐derived H₂O‐rich fluids derived from the plate interface flushed the marbles, promoting decarbonation followed by short‐distance transport and re‐precipitation along garnetite fractures. This study highlights the importance of inherited structural heterogeneities (such as mafic bodies or sills) in localizing deformation, draining fluids from the downgoing plate and creating long‐lasting mechanical instabilities during subduction zone deformation.     

震前电磁波异常的两种短临形态特征探讨

根据连云港地震局监测的几起地震前电磁波短临异常,结合1996年11月9日长江口6.1级地震等震例,进行对比分析。对异常产生的两种形态特征原因进行探讨,希望能揭示一些震前电磁波异常的规律及与地震短临三要素的内在联系。     

Effect of fracture pressure depletion regimes on the dual-porosity shape factor for flow of compressible fluids in fractured porous media

A precise value of the matrix-fracture transfer shape factor is essential for modeling fluid flow in fractured porous media by a dual-porosity approach. The slightly compressible fluid shape factor has been widely investigated in the literature. In a recent study, we have developed a transfer function for flow of a compressible fluid using a constant fracture pressure boundary condition [Ranjbar E, Hassanzadeh H, Matrix-fracture transfer shape factor for modeling flow of a compressible fluid in dual-porosity media. Adv Water Res 2011;34(5):627-39. doi:10.1016/j.advwatres.2011.02.012]. However, for a compressible fluid, the consequence of a pressure depletion boundary condition on the shape factor has not been investigated in the previous studies. The main purpose of this paper is, therefore, to investigate the effect of the fracture pressure depletion regime on the shape factor for single-phase flow of a compressible fluid. In the current study, a model for evaluation of the shape factor is derived using solutions of a nonlinear diffusivity equation subject to different pressure depletion regimes. A combination of the heat integral method, the method of moments and Duhamel’s theorem is used to solve this nonlinear equation. The developed solution is validated by fine-grid numerical simulations. The presented model can recover the shape factor of slightly compressible fluids reported in the literature. This study demonstrates that in the case of a single-phase flow of compressible fluid, the shape factor is a function of the imposed boundary condition in the fracture and its variability with time. It is shown that such dependence can be described by an exponentially declining fracture pressure with different decline exponents. These findings improve our understanding of fluid flow in fractured porous media.     

A fractal model for the starting pressure gradient for Bingham fluids in porous media embedded with randomly distributed fractal-like tree networks

An analytical expression is derived for the starting pressure gradient for Bingham fluids in porous media embedded with randomly distributed fractal-like tree networks based on fractal theory and technique. The proposed model relates the flow rate and the starting pressure gradient to the structural parameters of porous media and microstructural parameters of fractal-like tree networks, the yield stress and fractal dimensions of porous media and maximum mother diameter of randomly distributed fractal-like tree networks. The results show that the starting pressure gradient decreases with the increase of porosity of matrix material, fractal dimension for mother diameters, diameter ratio and permeability, and the starting pressure gradient increases with the increase of the length ratio and the yield stress. The model predictions from the present model for the starting pressure gradient are in good agreement with the available expression.     

山西定襄七岩泉水氡异常变化分析

采用定性和定量相结合的方法,对定襄泉2008年出现的异常进行现场调查,收集观测环境基础资料,排查可能的干扰因素,定量分析干扰因素对观测值的影响程度。对趋势异常变化的可信度进行分析,并结合研究成果和以往震例,分析认为定襄泉水氡高值异常变化是可信的,应密切跟踪此异常的发展变化。     

2009年7月9日云南姚安6.0级地震预测回顾

基于2009年7月9日姚安6.0级地震发生之前形变观测前兆异常,给出该地震三要素,总结其前兆异常特点,反思运用单台前兆观测资料预报地震过程中存在的问题,为今后的地震预测积累经验.     

ANALYSIS ON EFFECT OF SOUTH ASIA HIGH ON MID-SUMMER EXTREME DROUGHT AND FLOOD IN SICHUAN-CHONGQING REGION

NCEP/NCAR data are utilized to analyze an extreme flood year （1998） and an extreme dry year （2006） in the Sichuan-Chongqing region （SCR） and the results are as follows. The positive divergence of South Asia High （SAH） is stronger in the flood year; the position of the ridge line of SAH is southward compared with the annual average; Western Pacific Subtropical High （WPSH） extends westward and its ridge line is southward. In the drought year, the positive divergence of SAH is weaker, its ridge line is northward, and the position of WPSH is also northward. As shown in the dynamics, in drought （flood） years, negative （positive） vorticity advection in the upper atmosphere can cause the atmosphere to ascend （descend）, and anomalous circulation of SAH displays divergence （convergence）, and anomalous circulation of the lower atmosphere shows convergence （divergence）. Thermal structure of the atmosphere shows that there is warm （cold） temperature advection in the lower atmosphere, and the vertical distribution of diabetic heating causes SAH＇s local circulation to display convergence （divergence） and affects vertical motion of the lower atmosphere circulation eventually. To some extent, the two extreme years in the SCR is closely related to the vertical motion of atmosphere circulation and the variation of such vertical motion is caused by differences of interactions between SAH and lower atmosphere circulations.