各种求解对流—弥散方程数值方法的比较

文中对一维对流—弥散问题,用有限元素法,有限差分法,带有上风因子的有限差分法,对时间导数取高价差分,指数差分格式,以及几种不同形式的采用运动座标系求解方法进行了计算比较,计算结果表明,釆用不投影或少投影的在运动坐标系中求解对流—弥散方程的方法最为有效,无论以对流为主还是以弥散为主的问题,都能得到较好的结果,且所得的解不出现振动。     

黏土贯穿裂隙污染物迁移的实验和数值模拟研究

为研究裂隙黏土中的溶质运移,研制一套适用于裂隙黏土中溶质运移的实验装置,通过测定实验装置内示踪剂溶液的电导率来监测溶质的运移规律。实验结果发现模型底部监测孔处的渗出液浓度在短时间内就趋于稳定达到最大,表明黏土中裂隙的存在会使溶质顺着裂隙快速穿过黏土层,形成优先流现象,从而对黏土层下部的水体造成污染。采用数值方法对室内试验进行模拟分析,讨论了提高水头和改变岩土体两种方法来进行预测,结果显示黏土层上部水头变化对黏土中的溶质浓度影响不大,且不同土体中如均出现贯穿型裂隙,那么污染物进入含水层的时间基本一致,防渗失效,这时改变防渗材料没有意义。     

斜生栅藻对乙酰甲胺磷的急慢性毒性响应

为了解有机磷农药乙酰甲胺磷污染对本土水生敏感性物种斜生栅藻（ Scenedesmus obliquus）的毒性效应,在实验室条件下采用静态毒性试验,研究了乙酰甲胺磷对斜生栅藻96 h急性毒性效应,并在急性试验基础上进行慢性试验,分析了斜生栅藻连续染毒14 d的叶绿素质量浓度、可溶性蛋白质量分数以及丙二醛（ MDA）质量摩尔浓度的变化．结果表明：乙酰甲胺磷的96 h EC50为482.9 mg/L,属低毒农药,但在1 mg/L低质量浓度下可促进藻细胞生长;乙酰甲胺磷对栅藻光合作用无明显影响,但可通过干扰藻细胞代谢活动和引起膜脂过氧化反应,对斜生栅藻产生毒性作用;可溶蛋白和MDA可作为有效的生物标志物对农药引起的毒性做出评价．研究结果可为本土水生敏感性物种的保护和农药安全使用标准的制定提供理论依据．     

GCr15轴承钢连铸冷却速率下凝固原位观察

GCr15轴承钢在连铸凝固过程中的组织生长与溶质偏析是碳化物液析的重要诱因,成为产品质量提升的关键.为此,针对国内某钢厂240 mm×240 mm GCr15轴承钢的连铸过程,选取方坯表面下方40、80和120 mm位置处的坯样为研究对象,首先建立二维凝固传热模型,结合红外测温试验,求解它们在糊状区的平均冷却速率,然后...     

解溶质运移问题的特征有限分析法

针对解溶质运移模型会出现数值误差的问题,结合特征线法求解对流问题和有限分析法能求单元解析解的优点,推导得到了求解对流扩散方程的特征有限分析格式。算例表明,该格式有较高的计算精度,是对有限分析格式的拓展。     

原地爆破浸出开采中的溶质运移特性

研究了某铀矿原地爆破浸出开采中的溶质运移特性,针对溶质在矿堆中的输运与分布受到对流、分子扩散、机械弥散、吸附和化学反应等多种因素的影响,基于质量守恒定律推导出了原地爆破浸出过程溶质运移的基本方程.采用解析-优化法确定了溶质运移的水动力弥散系数和阻滞系数等有关参数,结合解析-优化参数得出溶液浓度值与试验测试值拟合曲线吻合,并通过现场工业浸出试验验证了数学模型的有效性.     

A NEW NUMERICAL METHOD FOR GROUNDWATER FIOW AND SOLUTE TRANSPORT USING VELOCITY FIELD

A new numerical method for groundwater flow analysis was introduced to estimate simultaneously velocity vectors and water pressure head. The method could be employed to handle the vertical flow under variably saturated conditions and for horizontal flow as well. The method allows for better estimation of velocities at the element nodes which can be used as direct input to transport models. The advection-dispersion process was treated by the Eulerian-Lagrangian approach with particle tracking technique using the velocities at FEM nodes. The method was verified with the classical one dimensional model and applied to simulate contaminant transport process through a slurry wall as a barrier to prevent leachate pollution from a sanitary landfill.     

SIMULATION OF SOLUTE TRANSPORT IN A PARALLEL SINGLE FRACTURE WITH LBM/MMP MIXED METHOD

This article deals with the solute transport in a single fracture with the combination of the Lattice Boltzmann Method （LBM） and Modified Moment Propagation （MMP） method, and this mixed method is proved to have several advantages over the LBM and Moment Propagation （MP） mixed method which leads to negative concentrations under some conditions in computation. The disadvantage of LBM/MP has been overcome to a certain extent. Also, this work presents an LBM solution of modeling single fractures with uniformly or randomly distributed grains, which can provide a new path of applying the LBM in solute transport simulation in fractures.     

纳米晶合金体系的热稳定性计算

为研究纳米晶合金体系的热稳定性,采用第一性原理和热力学计算相结合的方法建立了多尺度耦合模型,可同时考虑在添加元素、溶质浓度、晶粒尺寸和温度等变量共同作用下纳米晶合金体系的热力学性质.研究获得了金属化合物和固溶体合金中纳米晶组织失稳的临界条件和热稳定性调控参量.针对纳米晶金属化合物体系,预测了热失稳临界晶粒尺寸及其影响机制.针对纳米晶固溶体合金偏聚体系,揭示了初始晶粒尺寸和溶质浓度对合金热稳定性的双重调控机制.实验结果证实了模型的合理性,制备获得了具有高热稳定性的系列纳米晶合金材料.

     

A one-dimensional transport model for multi-component solute in saturated soil

A modified multi-component solute diffusion equation described with diffusion flux was derived in detail based on the classical Maxwell-Stefan diffusion theory. The friction between the solute species and the soil skeleton wall, which is proportional to the relative velocity between the solute species and the soil skeleton, is introduced. The chemical potential gradient is considered the driving force. A one-dimensional model for transport of multi-component solute in saturated soil was developed based on the modified diffusion equation and the modified competitive Langmuir adsorption equation. Numerical calculation of a case of two heavy metal ion species, which was chosen as an example, was carried out using the finite element software COMSOL Multiphysics. A comparative analysis was performed between the multi-component solute transport model developed in this study and the convection-diffusion transport model of single-component solute based on Fick's law. Simulation results show that the transport behavior of each species in a multi-component solute system is different from that in a single-component system, and the friction characteristics considered in the developed model contribute to obstructing the movement of each solute component. At the same time, the influence of modified competitive Langmuir adsorption on solute transport was investigated. These research results can provide strong theoretical support for the design of antifouling barriers in landfills and the maintenance of operation stability.