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851.
852.
Modelling adsorptive solute transport in soils needs a number of parameters to describe its reaction kinetics and the values of these parameters are usually determined from batch and displacement experiments. Some experimental results reveal that when describing the adsorption as first-order kinetics, its associated reaction rates are not constants but vary with pore water velocity. Explanation of this varies but an independent verification of each explanation is difficult because simultaneously measuring the spatiotemporal distributions of dissolved and adsorbed solutes in soils is formidable. Pore-scale modelling could play an important role to address this gap and has received increased attention over the past few years. This paper investigated the transport of adsorptive solute in a simple porous medium using pore-scale modelling. Fluid flow through the void space of the medium was assumed to be laminar and in saturated condition, and solute transport consisted of advection and molecular diffusion; the sorption and desorption occurring at the fluid–solid interface were modelled as linear first-order kinetics. Based on the simulated spatiotemporal distribution of dissolved and adsorbed solutes at pore scale, volumetric-average reaction kinetics at macroscopic scale and its associated reactive parameters were measured. Both homogeneous adsorption where the reaction rates at microscopic scale are constant, and heterogeneous adsorption where the reaction rates vary from site to site, were investigated. The results indicate that, in contrast to previously thought, the macroscopic reaction rates directly measured from the pore-scale simulations do not change with pore velocity under both homogeneous and heterogeneous adsorptions. In particular, we found that for the homogeneous adsorption, the macroscopic adsorption remains first-order kinetic and can be described by constant reaction rates, regardless of flow rate; whilst for the heterogeneous adsorption, the macroscopic adsorption kinetics continues not to be affected by flow rate but is no longer first-order kinetics that can be described by constant reaction rates. We discuss how these findings could help explain some contrary literature reports over the dependence of reaction rates on pore water velocity. 相似文献
853.
854.
青藏高原东南缘地壳结构及云南鲁甸、景谷地震深部孕震环境 总被引:10,自引:5,他引:5
通过联合解释青藏高原东南缘地区Rayleigh波群速度频散和固定地震台站的远震接收函数,构建了青藏东南缘3维地壳剪切波速度模型。结果表明研究区地壳结构具有强烈的横向不均一性。该区地壳厚度变化强烈(30~65km),其总体趋势是东南浅、西北深。研究显示该区存在2个明显的壳内低速异常带,其中中地壳(15~20km)低速带主要分布在腾冲、川滇菱形块体内部;而25~40km深度范围的中、下地壳低速带主要出现在研究区的北部,而在四川盆地和研究区南部则普遍缺失。鲁甸地震所在地震带的上地壳表现为高速异常,中、下地壳范围内存在2个显著的壳内低速带。鲁甸地震主震及其多数余震分布在高速的上地壳之中。与之不同,景谷地震序列及其所在思茅-普洱地震带下方没有显著的壳内低速带的出现,但其上地壳则表现为S波低速异常,该上地壳低速异常可能与地壳强烈破碎及断层/微裂隙中的流体有关。 相似文献
855.
叠前逆时偏移是目前成像精度最高的地震偏移方法之一,其实现过程中的一个重要步骤是数值求解全波方程,所以快速有效求解全波方程的数值算法对逆时偏移至关重要. 四阶近似解析辛可分Runge-Kutta (NSPRK) 方法是近年发展的一种具有高效率、高精度的数值求解波动方程的保辛差分方法, 能在粗网格条件下有效压制数值频散, 从而提高计算效率, 节省计算机内存需求量. 本文利用四阶NSPRK方法构造的基本思想,发展了具有六阶空间精度的NSPRK方法,并对新的六阶NSPRK方法进行了详细的稳定性和数值频散分析,以及计算效率比较和波场模拟. 同时将该方法用于声波叠前逆时偏移中, 得到一种时间上保辛、空间具有六阶精度、低数值频散、可应用大步长进行波场延拓并能长时计算的叠前逆时偏移方法,对Sigsbee2B模型进行了偏移成像, 并和四阶NSPRK方法、传统的六阶差分方法、四阶Lax-Wendroff correction (LWC) 方法进行了对比. 数值结果表明, 基于六阶NSPRK方法的叠前逆时偏移能得到更好的成像结果, 是一种优于四阶NSPRK方法、传统的六阶差分方法、四阶LWC叠前逆时偏移的方法, 尤其是在粗网格情况下具有更明显的优越性. 相似文献
856.
对2001年昆仑山口西Ms81级地震产生的断层带,布设了沿断层和横跨断层的两条人工地震测线.通过对观测资料的定量分析和处理,求得了昆仑山断层带内部的细结构.分析工作包括从S波震相开始的振幅谱计算、速度频散计算、群速度测量,并用面波频散方法反演S波速度结构,用振幅谱比的方法估计断层带的Q值.野外试验结果表明,S波震相与围陷波组的时间差随炮点与台站之间距离增大而增加,在断层带外的测点上观测到与断层带相关的场地效应.最后得出昆仑山断层带宽度为250m、速度结构为断层内低速的分层结构和Q值为15(断层内)和30(围岩).虽然昆仑山口西地震的震级比美国加州Landers地震的震级(Ms76)大,且地震产生的破裂带长度长得多,但是这两个地震断层带的宽度却相差不大. 相似文献
857.
本文就石门超大型雄黄-雌黄矿床矿区化探方法的选择,异常下限的确定,远景区的圈定等作了阐述,并圈出了5个有找矿希望的远景区。 相似文献
858.
The flux-gradient model, often used to describe turbulent dispersion, implicitly defines an eddy diffusion coefficient K that is known to be related to the Eulerian probability density function (pdf) of the turbulent velocity field. In the strict limit of applicability of Fick's law, the relationship between K and the pdf is used to investigate the influence of non-Gaussianity on dispersion in homogeneous turbulence. A bi-Gaussian pdf is used as a closure model that allows for separate studies of skewness and kurtosis variations. The choice of model parameters can have a significant influence on K, especially when the pdf is bimodal. Both arbitrariness of the closure and bimodality are then reduced using the maximum entropy criterion for the selection of the free parameter of the closure scheme, together with the assumption that the model is valid only for those values of the parameters for which a unimodal pdf is possible. The variations of K are found to be sensitive to both skewness and kurtosis showing a more complex behaviour than that found in literature. 相似文献
859.
860.
Nonlinear Dispersion Effect on Wave Transformation 总被引:5,自引:2,他引:3
—A new nonlinear dispersion relation is given in this paper.which can overcome the limitationof the intermediate minimum value in the dispersion relation proposed by Kirby and Dalrymple(1986).and which has a better approximation to Hedges'empirical relation than the modified relations by Hedges(1987).Kirby and Dalrymple(1987)for shallow waters.The new dispersion relation is simple in form.thusit can be used easily in practice.Meanwhile,a general explicit approximation to the new dispersion rela-tion and other nonlinear dispersion relations is given.By use of the explicit approximation to the newdispersion relation along with the mild slope equation taking into account weakly nonlinear effect.amathematical model is obtained,and it is applied to laboratory data.The results show that the model de-veloped with the new dispersion relation predicts wave transformation over complicated topography quitewell. 相似文献