An extended stability criterion for density-driven flows in homogeneous porous media     

Jude L. Musuuza  Sabine Attinger  Florin A. Radu 《Advances in water resources》2009

Stability of density-driven flows is a challenging problem with current applications in major areas like energy exploration, water pollution, nuclear and oil industries. The mathematical model for such flows is a system of coupled non linear partial differential equations. To study the physical stability of the system, we consider steady-state flow and perturb the solution of the full system of equations (without Boussinesq approximation) and investigate how it evolves in time: if the solution does not grow indefinitely, the system is called stable. The perturbations are treated as being the result of sub-scale interactions between the velocity field and the solute mass. Making use of a two-scale expansion of the solution, we derived extended stability criteria that include the effects of density, viscosity and flow velocity in flow configurations aligned parallel as well as orthogonal to gravity forces. Numerical simulations with the numerical simulator d³f$d^{3}f$ are presented to test the theoretical stability criteria.  相似文献   

腾冲台强震前地电场线性极化特征     

张学民  卢军 《地震》2007,27(2):89-98

分析了位于云南西南部的腾冲地震台自1986年以来的大地电场记录资料, 分别针对4次远强震和中等地方震前的电场极化特征进行了分析。 结果表明, 在地震发生前3个月的时间内, 电场极化逐渐趋于线性, 而不象正常时段时数据分布比较分散。 地震越强, 其线性极化特征出现得越早。 电场异常的方向性与震中方位有一定关系, 但也与震源区的活动断裂走向有关。 综合分析了异常产生的机理, 认为异常可能来自震源, 而震源区构造是信号传播的最佳通道。 电场的震前线性极化异常具有非常典型的短临性, 对未来地震方位及时间预测具有一定的参考价值。  相似文献   

闪石族11—12种阳离子占位的X射线衍射估算   总被引：1，自引：0，他引：1  

张以谏  黄俊杰  刘万余  张建洪  王冠鑫 《岩石矿物学杂志》2000,19(1):55-68

本文扼要地介绍了用Ｘ射线衍射强度数据估算闪石族矿物各阳离子占位的方法。实测数据证实,这不权在理论上是可能的,而且在实验上也是可行的。无论是钙质闪石还是碱性闪石,估算精度多数达到９０％左右,可满足晶体化学研究之需。以估算的占位数按国际分类表判定的闪石种属与按成分分析的相比,两者的符合率达８０％～８５％,从而否定了前辈学者“闪石族不能用Ｘ射线粉末法研究”的断言,在这一问题上取得了突破性进展。  相似文献   

Baroclinic Instability in the Generalized Phillips’ Model Part II: Three-layer Model   总被引：2，自引：0，他引：2  

Li Yang 《大气科学进展》2000,17(3):413-432

The nonlinear stability of the three-layer generalized Phillips model, for which the velocity in each layer is constant and the top and bottom surfaces are either rigid or free, is studied by employing Arnol’d’s variational principle and a prior estimate method. The nonlinear stability criteria are established. For com-parison, the linear instability criteria are also obtained by using normal mode method, and the influences of the free parameter, β parameter and curvature in vertical profile of the horizontal velocity on the linear in-stability are discussed by use of the growth rate curves.The comparison between the nonlinear stability criterion and the linear one is made. It is shown that in some cases the two criteria are exactly the same in form, but in other cases, they are different. This phenom-enon, which reveals the nonlinear property of the linear instability features, is explained by the explosive resonant interaction (ERI). When there exists the ERI, i.e., the nonlinear mechanisms play a leading role in the dynamical system, the nonlinear stability criterion is different from the linear one; on the other hand, when there does not exist the ERI, the nonlinear stability criterion is the same as the linear one in form.  相似文献   

贵州省关岭县土地利用/土地覆被变化及土壤侵蚀效应研究   总被引：23，自引：4，他引：19  

万军  蔡运龙  张惠远  饶胜 《地理科学》2004,24(5):573-579

以贵州省关岭县为例,利用1987和1999年两个时段TM影象和相关资料,分析研究区12年间的土地利用/土地覆被变化及其土壤侵蚀风险。发现:(1)研究区土地利用动态变化较大,年均土地利用综合动态指数为1.36%;(2)旱地和草地互相转化比例高,草地开垦为旱地和旱地弃耕为草地的动态变化幅度远远超过旱地和草地最终面积变化的幅度;(3)山区土地利用的空间变化主要体现在垂直方向;(4)研究区裸土面积下降,一部分被植被覆盖,另一部分由于土壤流失殆尽,形成裸露基岩,故植被覆盖率和基岩出露率上升;(5)石漠化程度加剧,其中旱地石漠化发展速度最快;(6)土壤侵蚀形势严峻。  相似文献   

无限长源二维各向异性地层中CSAMT有限元模拟          下载免费PDF全文

熊治涛  唐新功 《地球物理学报》2017,60(5):1937-1945

可控源音频大地电磁测深法(CSAMT)基本上是基于电性各向同性理论的假设,而实际地层普遍表现为电性各向异性现象,因此研究各向异性地层条件下CSAMT方法的电磁响应具有重要的理论意义和应用价值.本文从有源Maxwell方程出发,推导出了二维各向异性地层条件下无限长线源频率域的电磁场响应,得到了一组平行于线源方向的电场分量E_x和磁场分量H_x的偏微分方程,并采用有限元法进行求解.模型的计算结果表明:不论是对均匀半空间还是一维层状介质中的各向异性二维体模型的计算,均能从结果中明显地看出各向同性背景场和各向异性异常体的存在;在计算中通过改变各向异性系数或各向异性旋转角,其结果在视电阻率和相位曲线上均存在显著区别.计算结果表明了在各向异性地层中,仍然采用各向同性的假设进行CSAMT资料的处理与解释,可能会带来比较严重的误差,这种情况下必须采用基于各向异性的地质模型对CSAMT资料进行处理和解释.研究结果对于提高CSAMT方法的勘探效果和应用水平具有重要的指导意义.  相似文献   

Linear geophysical inversion via the discrete cosine pseudo‐inverse: application to potential fields          下载免费PDF全文

J.L. Fernández‐Martínez  Z. Fernández‐Muñiz  J.L.G. Pallero  S. Bonvalot 《Geophysical Prospecting》2017,65(Z1):94-111

In this paper, we present a methodology to perform geophysical inversion of large‐scale linear systems via a covariance‐free orthogonal transformation: the discrete cosine transform. The methodology consists of compressing the matrix of the linear system as a digital image and using the interesting properties of orthogonal transformations to define an approximation of the Moore–Penrose pseudo‐inverse. This methodology is also highly scalable since the model reduction achieved by these techniques increases with the number of parameters of the linear system involved due to the high correlation needed for these parameters to accomplish very detailed forward predictions and allows for a very fast computation of the inverse problem solution. We show the application of this methodology to a simple synthetic two‐dimensional gravimetric problem for different dimensionalities and different levels of white Gaussian noise and to a synthetic linear system whose system matrix has been generated via geostatistical simulation to produce a random field with a given spatial correlation. The numerical results show that the discrete cosine transform pseudo‐inverse outperforms the classical least‐squares techniques, mainly in the presence of noise, since the solutions that are obtained are more stable and fit the observed data with the lowest root‐mean‐square error. Besides, we show that model reduction is a very effective way of parameter regularisation when the conditioning of the reduced discrete cosine transform matrix is taken into account. We finally show its application to the inversion of a real gravity profile in the Atacama Desert (north Chile) obtaining very successful results in this non‐linear inverse problem. The methodology presented here has a general character and can be applied to solve any linear and non‐linear inverse problems (through linearisation) arising in technology and, particularly, in geophysics, independently of the geophysical model discretisation and dimensionality. Nevertheless, the results shown in this paper are better in the case of ill‐conditioned inverse problems for which the matrix compression is more efficient. In that sense, a natural extension of this methodology would be its application to the set of normal equations.  相似文献   

大地电磁资料精细处理和二维反演解释技术研究(五)——利用阻抗张量成像识别大地线性构造   总被引：9，自引：6，他引：3       下载免费PDF全文

陈小斌  郭春玲 《地球物理学报》2017,60(2):766-777

大地线性构造往往与块体或物性的边界、断裂的几何延伸相关联,是地学研究的重要目标构造.在大地电磁法中,传统的方法是通过反演得到的电性结构的差异来解译线性构造,是一种间接分析方法.由于线性构造发育处走向和倾向明显,二维性较其他地方一般会更强,故而在阻抗张量成像分析中,相应的二维有效因子就会比较大,最佳主轴统计分布会更加明显.据此,本文利用大地电磁阻抗张量成像(包括最佳主轴统计成像、构造维性成像)来探测识别大地线性构造.本文首先通过三维理论模型的研究结果来验证这一技术在线性结构探测中的有效性,然后将其应用于郯庐断裂带南段实测剖面的具体分析中,展示了这一技术在线性构造探测中的实用性及其数据处理与分析过程.本文研究表明,大地电磁阻抗张量成像技术可独立于反演为地质解释尤其是线性构造的解释提供诸多参考信息.  相似文献   

瓜什则盆地的地应力场分析与模拟     

海洋 《华南地震》2019,39(3):101-108

基于水压致裂法地应力测试的原理,系统性研究分析了瓜什则盆地区域内的地应力场特征,这为成宁铁路控制性工程甘青特长隧道的选线设计提供了重要的参考依据。首先,根据区域内钻孔的地应力测试结果,采用有限元方法进行了区域地应力场的三维数值模拟,确定了该区域内的水平应力大于垂直应力的基本特征;其次,根据多个水平构造应力场的水平切片,分析了水平构造应力场随深度的变化,说明了该区域内水平构造应力场具有由东北向西南挤压的应力变化特征;然后,根据区域岩体抗拉强度分布,发现该区域内存在一个低抗拉强度带,它的地层结构相对较复杂,且其工程地质特征主要表现为地层破碎带或断层;最后,采用最小二乘法拟合了CK方案隧道横截面最大切向应力与最大水平主应力的线性回归模型,并预测了该方案隧道地层的岩爆发育程度。  相似文献   

Modeling and mapping aboveground biomass of the restored mangroves using ALOS-2 PALSAR-2 in East Kalimantan,Indonesia     

《International Journal of Applied Earth Observation and Geoinformation》2020

Accurate estimation of forest aboveground biomass (AGB) using remote sensing is a requisite for monitoring, reporting and verification (MRV) system of the United Nations Programme on Reducing Emissions from Deforestation and Forest Degradation. However, attaining high accuracy remains a great challenge in the diverse tropical forests. Among available technologies, l-band Synthetic Aperture Radar (SAR) estimates AGB with reasonably high accuracy in the terrestrial tropical forests. Nevertheless, the accuracy is relatively low in the mangrove forests. In this context, the study was carried out to model and map AGB using backscatter coefficients of Advanced Land Observing Satellite-2 (ALOS-2) Phased Array l-band SAR-2 (PALSAR-2) in part of the restored mangrove forest at Mahakam Delta, Indonesia. PALSAR-2 data was acquired with image scene observation during the peak low tide on 30 July 2018 from Japan Aerospace Exploration Agency. The forest parameters namely tree height and diameter at breast height were measured from 71 field plots in September-October 2018. The parameters were used in mangrove allometry to calculate the field AGB. Finally, HV polarized backscatter coefficients of PALSAR-2 were used to model AGB using linear regression. The model demonstrated a comparatively high performance using three distinct methods viz. independent validation (R² of 0.89 and RMSE of 23.16 tons ha⁻¹), random k-fold cross validation (R² of 0.89 and RMSE of 24.59 tons ha⁻¹) and leave location out cross validation (LLO CV) (R² of 0.88 and RMSE of 24.05 tons ha⁻¹). The high accuracy of the LLO CV indicates no spatial overfitting in the model. Thus, the model based on LLO CV was used to map AGB in the study area. This is the first study that successfully obtains high accuracy in modeling AGB in the mangrove forest. Therefore, it offers a significant contribution to the MRV mechanism for monitoring mangrove forests in the tropics and sub-tropics.  相似文献