A 3D ERT study of solute transport in a large experimental tank

A high resolution, cross-borehole, 3D electrical resistivity tomography (ERT) study of solute transport was conducted in a large experimental tank. ERT voxels comprising the time sequence of electrical images were converted into a 3D array of ERT estimated fluid conductivity breakthrough curves and compared with direct measurements of fluid conductivity breakthrough made in wells. The 3D ERT images of solute transport behaviour were also compared with predictions based on a 3D finite-element, coupled flow and transport model, accounting for gravity induced flow caused by concentration differences.The tank (dimensions 185×245×186 cm) was filled with medium sand, with a gravel channel and a fine sand layer installed. This heterogeneous system was designed to complicate solute transport behaviour relative to a homogeneous sand tank, and to thus provide a challenging but insightful analysis of the ability of 3D ERT to resolve transport phenomena. Four ERT arrays and 20 piezometers were installed during filling. A NaCl tracer (conductivity 1.34 S/m) was injected and intensively monitored with 3D ERT and direct sampling of fluid chemistry in piezometers.We converted the bulk conductivity estimate for 250 voxels in the ERT imaged volume into ERT estimated voxel fluid conductivity by assuming that matrix conduction in the tank is negligible. In general, the ERT voxel response is in reasonable agreement with the shape of fluid conductivity breakthrough observed in six wells in which direct measurements of fluid conductivity were made. However, discrepancies occur, particularly at early times, which we attribute to differences between the scale of the image voxels and the fluid conductivity measurement, measurement errors mapped into the electrical inversion and artificial image roughness resulting from the inversion.ERT images revealed the 3D tracer distribution at 15 times after tracer injection. The general pattern and timing of solute breakthrough observed with ERT agreed with that predicted from the flow/transport modelling. However, the ERT images indicate a vertical component of tracer transport and preferential flow paths in the medium sand. We attribute this to transient vertical gradients established during tracer injection, and heterogeneity caused by sorting of the sand resulting from the filling procedure. In this study, ERT provided a unique dataset of 250 voxel breakthrough curves in 1.04 m³. The use of 3D ERT to generate an array of densely sampled estimated fluid conductivity breakthrough curves is a potentially powerful tool for quantifying solute transport processes.     

Spatio-temporal filtering using wavelets

 In this paper, a class of spatio-temporal processes with first-order autoregressive temporal structure and functional spatio-temporal interaction is introduced. The spatial second-order regularity is allowed to change over time and is characterized in terms of fractional Sobolev spaces. The associated filtering problem is considered, assuming that observations are defined by spatial linear functionals of the process of interest, being affected by additive noise. Conditions under which a stable solution to this problem is obtained are studied. A functional least-squares linear estimate fusion method is derived to calculate this solution A multiscale finite-dimensional approximation to the problem is obtained from the wavelet-based orthogonal expansions of the time cross-section spatial processes, which allows the numerical inversion of the linear operator involved.     

地层含水性研究的地球物理方法

论述了研究地层含水性的意义，指出了研究地层含水性的关键，提出了物性的基础，物探方法的选择是关键的技术路线。进而比较详细地介绍了地层含水性探测的各种电法的原理、仪器及方法的应用范围和条件，系统地阐述了针对西部水资源勘查应采用的技术方法，对地层含水性的电法勘探技术作了较为全面的评述；提出各方法综合运用、合理搭配的技术思路，可为西部水资源的勘查提供技术性指导。     

含天然气水合物沉积物的岩石物性模型与似海底反射层的AVA特征

研究含天然气水合物沉积物的岩石物性模型与似海底反射层的振幅随入射角变化(AVA)特征. 基于时间平均-Wood加权方程、三相介质波传播理论模型和弹性模量模型,计算并阐述含天然气水合物岩石弹性参数与水合物饱和度、含游离气岩石弹性参数与游离气饱和度的关系;给出不同模型AVA特征. 结果表明,不同天然气水合物饱和度、不同游离气饱和度的各种组合呈现形态相似但反射系数值不同的AVA特征.     

Seismic events with non-shear component: I. Shallow earthquakes with a possible tensile source component

The concept of seismicity of fast tensile fracturing is introduced and supported by the results of shear and of combined shear and tensile displacements along a loaded stress concentrator. The seismicity of tensile fracturing is demonstrated by means of acoustic (elastic) signals obtained during tensile fracturing in physical models under load; the basic physical relations between the parameters characterizing the loaded medium, load conditions, shear and tensile displacements, and release of acoustic energy are presented. For determining the tensile-source component in earthquakes a procedure based on the construction of radiation patterns is suggested and submitted for discussion. The criteria for selecting earthquakes with possible shear-tensile source mechanisms are listed and discussed. The existence of such a combined seismic source is sought in two shallow earthquakes which occurred in southern Iran in March 1977. In general, the paper should be regarded as a proposal to utilize the radiation characteristics of a seismic source—with all their insufficiencies—as a quick and simple tool for seeking combined shear and tensile mechanisms of seismic energy release.     

Laboratory simulation of ‘the wick effect’ in salt weathering of rock

‘The wick effect’ is the upward migration of saline solutions into rocks and their subsequent crystallization. Lower Carboniferous sandstone blocks of rectangular shape have been subjected to this process in the laboratory using a range of salt types, a range of salt concentrations, and various mixtures of salts. Some treatments produced severe disintegration, notably sodium carbonate and a mixture of sodium carbonate with magnesium sulphate, whereas other salts (including sodium chloride and gypsum) were much less effective. The debris produced by this experimental salt weathering included appreciable quantities of silt-sized material, which were analysed with a laser granulometer. Such material could provide a source for desert loess.     

三向地震模拟振动台静力平衡系统的设计与分析

我国自行研制的三向六自由度大型地震模拟振动台采用蓄能器液压马达系统作为其重力平衡装置。用修正的滞弹性模型近似描述蓄能器液压马达系统是合理的，按照静态准则和动态准则设计该系统，确保系统能满足设计要求。本文并对蓄能器流动民达压力控制系统、启动特性和平衡特性进行了分析。     

提取多参数无量纲地震前兆信息的均方差方法的物理基础

本文研究了提取多参数无量纲地震前兆信息的均方差方法的物理基础。该方法的物理基础是地震孕育过程中当破裂应力达到５０％以上时，岩石弹性、变形性、电性、磁性和热性等性质都会发生显著变化，结果导致岩体物理参数绝对值及其变化速率和测量误差的改变。利用均方差方法来计算这些变化，一方面消除了前兆参数的季节性干扰，另一方面突出了前兆信息。     

Random simulation and GPS decorrelation

 (i) A random simulation approach is proposed, which is at the centre of a numerical comparison of the performances of different GPS decorrelation methods. The most significant advantage of the approach is that it does not depend on nor favour any particular satellite–receiver geometry and weighting system. (ii) An inverse integer Cholesky decorrelation method is proposed, which will be shown to out-perform the integer Gaussian decorrelation and the Lenstra, Lenstra and Lovász (LLL) algorithm, and thus indicates that the integer Gaussian decorrelation is not the best decorrelation technique and that further improvement is possible. (iii) The performance study of the LLL algorithm is the first of its kind and the results have shown that the algorithm can indeed be used for decorrelation, but that it performs worse than the integer Gaussian decorrelation and the inverse integer Cholesky decorrelation. (iv) Simulations have also shown that no decorrelation techniques available to date can guarantee a smaller condition number, especially in the case of high dimension, although reducing the condition number is the goal of decorrelation. Received: 26 April 2000 / Accepted: 5 March 2001     

不同覆盖条件对土壤水热分布影响的计算机模拟Ⅱ——有限元分析及应用

在本研究的第一部分已建立了数学模型的基础上,本文进行了有限元分析。应用Galerkin法进行了空间域的离散,应用差分法及Douglas-Dapont预报校正法完成了时间域的离散及非线性处理。然后用Fortran-77编写了计算机程序,实现了不同覆盖层下非匀质土壤水热分布的定量分析,并进行了田间实验验证。计算与验证结果表明:塑膜膜侧种植校膜中心种植在地温稍高含水量稍低的情况下,可节约用膜7%;透水率很低的纸张在改进耐久性的基础上可能在一定条件下作为塑膜的代用品。