核素随水-悬浮泥沙-底泥沙迁移模型

考虑了泥沙吸附和解吸、沉降和再悬浮对水相和泥沙相核素浓度的影响,根据质量守恒定律、吸附动力学方程和泥沙工程学建立了河流核素迁移的整体模型,进而得到分相模型.运用所得的模型对资江核电站排出的Sr在河流中迁移转化进行模拟,模拟结果表明所建模型基本上能反映Sr在水体中随水-悬浮泥沙-底泥沙的迁移规律.     

深海采矿船附近海底重金属迁移过程数值模拟

本文以水相和泥沙相核素的物理迁移为基础,分析深海采矿船附近海底重金属的迁移扩散、吸附解析和悬移沉降等作用,结合水力学、泥沙动力学等方程,建立了重金属迁移转化的整体模型和分相模型,并利用差分算法对模型进行求解,最后结合实验测定和实测资料给出的模型相关参数,运用MATLAB软件对重金属的迁移进行图像模拟,直观地反映重金属浓度的变化过程.     

马尔柯夫链在多介质环境归趋研究中的应用

以开放的环境系统为依托,阐述了马尔柯夫理论在多介质环境归趋研究中的科学性与合理性,并结合国家重点课题—黄河兰州段典型污染物迁移/转化特性及承纳水平研究,研究壬基酚聚氧乙烯醚(nonylphenol polyethoxylates—NPEOs)在黄河兰州段的环境归趋.研究结果表明,利用马尔柯夫模型可以确定污染物在环境介质间的迁移时间、环境介质内的滞留时间、任意时刻污染物在不同环境介质内的含量、给定时间内不同迁移转化过程的迁移量和降解量、环境系统达到稳定的时间、污染物在环境系统内的稳定分布、以及污染物的环境容量或排放标准.     

矿区土壤中含水率及重金属迁移转化的数值模拟

本文基于由连续性方程和达西定律所推出的土壤中水分运动基本方程,以一维垂向水分方程为研究对象,构造稳定收敛的有限差分格式,运用MATLAB数学工具,对地面饱水情况下土壤水分运动的一维垂向方程进行了数值模拟,得到了土壤中水分的迁移规律;同时,综合考虑对流扩散作用以及土壤对重金属的吸附解吸作用,利用非饱和土壤中重金属离子迁移转化模型,对锌离子在矿区土壤中的迁移转化进行了数值模拟,展示了锌离子在矿区土壤中的浓度分布规律．     

“蛋圆”、“果圆”、“8”形线

高考数学中创新的能力立意,已经成为每年高考命题的“热亮”与“亮点”．这类问题要求考生具有即时性学习、阅读、理解、迁移的能力,能运用所学的新知识（如新概念、新定义、新运算、新定理等）来解决新问题,对培养学生的创新思想和能力大有裨益．这类问题求解的基本策略是：对新知识进行信息提取、转换、迁移,使之与已有知识相联系,从而转化为常规问题和常规运算而获解．本文仅就圆锥曲线的创新能力立意问题（圆锥曲线弧合成的曲线）例析如下．     

矿尘影响下生态系统脆弱性级联传播模型分析

为了解决矿尘连续排放并迁移对地表生态系统造成的脆弱性问题,提出了基于函数地理Petri网的脆弱性级联传播模型。综合考虑污染物迁移方向和生态环境在地理空间上的关联关系,直观地构造了基于级联传播的污染Petri网。在此基础上,定义了基于VCPM的脆弱度和阈值的概念,利用两者的关系进行脆弱性级联传播分析,从而明确级联传播的三种状态。最后,以神府煤田矿尘迁移作为污染物连续排放的污染源,通过模型方法的模拟仿真分析,对生态环境系统在级联传播下的脆弱性进行了深入探讨。已有的研究方法和结果不仅在生态环境脆弱性研究领域做出了新的贡献,而且为环境的修复和重建提供了参考价值。     

谨防熟题的负迁移

在认知过程中,利用好迁移具有很重要的意义．正向的迁移能由旧知识生成新的知识,而负迁移则不利于正确地生成新知识,对提高思维能力和解题能力有害．学习中应该尽量促进正迁移而避免负迁移．     

动态粗集的一种新结构

Z.Pawlak粗集理论是一种研究和处理静态知识的静态粗集理论.提出研究和处理动态知识的动态粗集理论,给出动态粗集的数学表示,定义知识库上的元素迁移系数、D-粗集、D-近似集等概念,研究D-粗集的迁移特性,给出D-粗集退化定理、D-粗集转化定理、迁移平衡定理等,并进行实例分析和意义解析.D-粗集是Pawlak粗集的一般形式,而Pawlak粗集可以看作D-粗集的一种特例.     

利用修正离散纵标法解决一类特殊迁移方程的特征值问题

利用修正的离散纵标法讨论平板几何各向异性散射的一类特殊的迁移方程特征值的求解问题,给出了这类迁移方程的具体形式及转化方法.最后通过Matlab编程算出近似值.     

公路运输有毒物泄漏造成水体污染的数学模型及求解方法研究

公路运送有毒物发生交通事故导致有毒物泄漏引发水体污染会造成严重影响.首先分析了污染事故的特点,危害.然后根据水力学及污染物的迁移转化规律,建立了有毒物泄漏水体后的弥散数学模型,即将控制水流的圣维南方程和描述有毒物迁移的对流弥散方程进行耦合.运用低数值耗散的半离散中心迎风格式求解方程,其结果可以预测污染河段长度和延续时间.最后通过实例进行了模拟计算.     

A fast non-iterative numerical algorithm to predict unsteady partial cavitation on hydrofoils

A new algorithm to predict partial sheet cavity behavior on hydrofoils is proposed. The proposed algorithm models the unsteady partial cavitation using Boundary Element Method (BEM). In the proposed method the spatial iterative scheme is removed by means of a new approach determining the instantaneous cavity length. This iterative scheme is required in conventional algorithms to obtain the cavity length at each time step. Performance of the new algorithm for various unsteady cavitating flows with different reduced frequencies, cavitation numbers, hydrofoil geometries and inflow conditions are investigated. Comparison between the obtained results using the proposed method and those of conventional ones indicates that the present algorithm works well with sufficient accuracy. Moreover, it is shown that the proposed method is computationally more efficient than the conventional one for unsteady sheet cavitation analysis on hydrofoils.     

On a Synthetic Jet Flow

Velocity vector field of a synthetic jet has been investigated experimentally. The synthetic jet is generated by an electrodynamical system designed for control of a free shear layer. To catch unsteady periodical structures the phase average method is applied to time series of instantaneous velocities. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

The topology of the sectional streamlines

The unsteady, three-dimensional full Navier-Stokes equations are solved using a Beam-Warming implicit algorithm in this paper. Computations of the flow over a 76° sweep delta wing at 36.5° angle of attack is presented. The sectional streamlines are depicted and the evolution of the instantaneous crossflow topology of the leading-edge vortex is analyzed. It is found that, along the axis, the topology of the primary vortex alters several times starting from stable focus near the apex to unstable focus, and lasts back to stable focus near wake edge; The stable limit cycle and unstable limit cycle are shown in this evolution. These various altering topologies stem from the stretching and compression of the vortex core.     

A time-delay model for the effect of toxicant in a single species growth with stage-structure

In this paper, we investigate a single-species growth model with stage-structure consisting of immature and mature stages for the effects of toxicants with constant maturation time-delay. We study the dynamics of our model in three cases: an instantaneous emission of toxicant, a constant emission of toxicant, and a periodic emission of toxicant into the environment. We present results on positivity and boundedness of all solutions under appropriate conditions. The model equations are analyzed mathematically with regard to the nature of equilibria and their stabilities using the theory of nonlinear differential equations and computer simulations. It is shown that under suitable conditions, there exists a globally asymptotically stable positive equilibrium. It is concluded from the analysis that as the concentration of toxicant in the environment increases, equilibrium densities of both immature and mature populations decrease. It is also noted that the effects of toxicants are more on the equilibrium level of immature population in comparison to the mature population.     

UNSTEADY STATE DISPERSION OF AIR POLLUTANTS UNDER THE EFFECTS OF DELAYED AND NONDELAYED REMOVAL MECHANISMS

Abstract In this paper, we present a two‐dimensional time‐dependent mathematical model for studying the unsteady state dispersion of air pollutants emitted from an elevated line source in the atmosphere under the simultaneous effects of delayed (slow) and nondelayed (instantaneous) removal mechanisms. The wind speed and coefficient of diffusion are taken as functions of the vertical height above the ground. The deposition of pollutants on the absorptive ground and leakage into the atmosphere at the inversion layer are also included in the model by applying appropriate boundary conditions. The model is solved numerically by the fractional step method. The Lagrangian approach is used to solve the advection part, whereas the Eulerian finite difference scheme is applied to solve the part with the diffusion and removal processes. The solutions are analyzed to observe the effects of coexisting delayed and nondelayed removal mechanisms on overall dispersion. Comparison of delayed and nondelayed removal processes of equal capacity shows that the latter (nondelayed) process is more effective than the former (delayed removal) in the removal of pollutants from the atmosphere.     

Dynamics of coal dust flame acceleration: A feedback control model for unsteady flow

Several modeling concepts borrowed from control theory are employed to develop an algebraic and ordinary differential equations model for the dynamics of unsteady coal dust flame acceleration in a constant area duct closed at one end, e.g., in a coal mine tunnel. We are particularly concerned with modeling the feedback mechanisms which cause a coal dust flame to accelerate, leading to detonation. Previous experimental studies have been conducted on both coal dust flame propagation and on individual coal particle combustion. Based on the results, a physical model is proposed in which coal dust flame acceleration is entirely controlled, in a feedback fashion, by volatiles emission and their reaction. A control system model is developed that employs five well-stirred reactor subsystems with three feedback interaction mechanisms. The model consists of a leading shock wave, followed by a variable length volatiles emission region ahead of the flame, a fixed length burning region immediately behind the flame front, and a variable length exhaust region extending back to the closed end of the duct. The feedback mechanisms incorporated into the model include heat transfer and pressurization from the burning region to the volatiles emission region, and pressurization from the volatiles emission region to the turbulent mixing region behind the shock wave. Each well-stirred reactor is described by a system of algebraic and ordinary differential equations for the rate of change of conditions inside the reactor. Numerical simulation results reveal that, despite far-reaching simplifications (ordinary instead of partial differential equations, ideal gases insteady of two-phase flow, separation of volatiles emission and combustion, neglection of char burning), the model exhibits the fundamental dynamic properties of the flame propagation process. The model agrees with qualitative photographic experimental results and is applicable to both the case where the flame accelerates to detonation and to the case where the combustion process dies out.     

Localization of acoustic sources in subsonic jets

The sound in the acoustic far–field of a round jet is generated by a multitude of unsteady flow structures with different length and time scales. Most likely, different components of the noise spectrum are created by different structures in the jet which emit sound in different directions. Based on Lighthill's acoustic analogy, we present a method for relating flow structures of the jet with far–field noise spectra and their associated directivity patterns. The method allows to determine what kind of noise (with respect to frequency and emission direction) is generated at a given streamwise location. We illustrate the method with numerical results for a round isothermal jet. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

On some unsteady flows of a non-Newtonian fluid

Some properties of unsteady unidirectional flows of a fluid of second grade are considered for flows impulsively started from rest by the motion of a boundary or two boundaries or by sudden application of a pressure gradient. Flows considered are: unsteady flow over a plane wall, unsteady Couette flow, flow between two parallel plates suddenly set in motion with the same speed, flow due to one rigid boundary moved suddenly and one being free, unsteady Poiseuille flow and unsteady generalized Couette flow. The results obtained are compared with those of the exact solutions of the Navier–Stokes equations. It is found that the stress at time zero on the stationary boundary for the flows generated by impulsive motion of a boundary or two boundaries is finite for a fluid of second grade and infinite for a Newtonian fluid. Furthermore, it is shown that for unsteady Poiseuille flow the stress at time zero on the boundary is zero for a Newtonian fluid, but it is not zero for a fluid of second grade.     

绕振动机翼非定常气动力迟滞特性的模拟研究

利用数值模拟方法开展了机翼在不同条件下,由于俯仰振动引起的非定常气动力迟滞特性的模拟计算研究.根据有限体积方法对非定常欧拉方程进行数值求解,以确定相应问题的流场及气动力特性;同时,分别以具有NACA-0012翼型的矩形机翼和带有65°后掠角的三角翼为例,研究了机翼绕不同转轴或以不同频率振动的非定常气动力迟滞特性.