风沙二相流动的三流体模型

本文来用连续介质观点研究风沙运动，这一工作的关键在于如何正确地模化颗粒相的应力．通过对气－团二相流研究中常用的双流体模型的分析，我们发现此模型在研究风沙运动时有相当的缺陷，即使是研究最简单的风沙流──定常二维充分发展的流场也是如此．基于此，我们提出了将向上、向下运动的颗粒用两种拟流体来表征的三流体模型．相对于双流体模型，三流体模型较好地反映了流场的内部结构及边界状况对流动的影响，而且固相应力的主要部分也可用应变量显式表示．对近似求解相当有利．最后，本文给出了三流体模型的风沙流运动方程组并讨论了相应的边界条件的提法．     

水平环空井筒内流体携砂影响因素研究

基于流体动力学和液固两相流流动理论,建立了砂粒在环空液体中运移的流动模型.在忽略固相颗粒在液相中微观运动状况的基础上,通过数值模拟的方法,研究岩屑在不同流动参数下的运移规律,揭示砂粒在流体流动中的运动规律.研究结果表明,流体粘度和入口流量两个参数对固液两相流动中岩屑的运移影响较大.入口流量和流体粘度增加,流体对岩屑的携带作用增强,且携带的颗粒直径也变大.     

自驱动Janus微球的分数Brownian运动研究

Janus微球是形状规则但表面构成不同的特殊颗粒.在PIV实验平台上,以Pt-SiO2型Janus颗粒(Φ=1μm,Φ=2μm)为研究对象,获取了通过非对称催化分解H2O2产生自驱动情况下颗粒的不规则运动轨迹,通过统计得出不同观测时间下Janus颗粒在不同浓度H2O2溶液(0%,2.5%,5%,10%和15%)中的Hurst指数,实验清晰地表明了颗粒轨迹所具有的无规则运动与定向运动的叠加以及反常扩散特征.随后将这一复杂运动分解为随机的Brownian(布朗)运动、自驱动及随机转动的共同作用,并得出了不同因素所主导的特征时间尺度,合理地解释了所观察到的现象.     

基于格子boltzmann方法固井环空介观微间隙气体窜槽研究

固井环空微间隙气体窜槽现象直接影响固井质量与油田生产,准确地描述固井环空微间隙气体窜槽的流动规律是有效控制气体窜槽的核心与"瓶颈"问题.从微观粒子运动角度出发,基于格子Boltzmann方法建立了固井环空微间隙气体粒子流动模型.选取大庆油田某区块计算模拟不同环空压差下微间隙内气体粒子流动速度分布规律,计算结果揭示了固井气窜气体粒子在微环间隙内流动的本质,为后续固井气窜问题的研究开辟新的思路.     

存在中间产品退出的混合型生产系统效率测度与分解研究

混合型生产系统是系统内部同时存在串联子系统和并联子系统的复杂生产系统.以存在中间产品退出的混合型生产系统为研究对象,针对其效率测度与分解问题在总系统效率函数表达、中间产品退出比例确定和子系统效率分解三方面的表征,构建了一种基于DEA理论框架的效率测度与分解模型.在求解该模型的过程中,借鉴交叉效率思想解决复杂模型非线性求解问题,并提出一种中立的第二目标规划优化效率分解中最优解不唯一问题.最后通过一个算例验证该模型的可行性和有效性.     

液固两相圆柱绕流尾迹内颗粒扩散分布的离散涡数值研究

基于离散涡方法求得的非定常水流场和颗粒的Lagrange运动方程,数值模拟了稀疏液固两相圆柱绕流尾迹内颗粒的扩散分布．获得了流动的涡谱与3种不同St数颗粒（St=0.25,1.0,40）在流场中的分布．通过引入扩散函数来定量表示颗粒在流场中的纵向扩散强度,并计算得到了不同St数颗粒的扩散函数随时间的变化．数值结果揭示出了液固两相圆柱绕流尾迹中的颗粒扩散分布与颗粒的St数和尾涡结构密切相关:1) 中小St数(St=0.25～4.0)颗粒在运动过程中不能进入涡核区,而在旋涡结构的外沿聚集,且颗粒的St数愈大,其越远离涡核区域;2） 在圆柱绕流尾迹区域内,中小St数(St=0.25～4.0)颗粒的纵向扩散强度随其St数的增大而减小．     

固相颗粒在钻井液振动筛筛面上的抛掷运动规律研究

通过δ函数和单位阶跃函数表示平面惯性椭圆振动筛筛面上固相颗粒的受力，建立了微分方程形式的颗粒在筛面上的抛掷运动数学模型。对其解进行分析，给出了颗粒的抛掷周期和抛掷距离对于振动筛或岩屑参数的依赖关系以及这些关系的数值计算分析方法。     

二维气固两相混合层中固粒对流场影响的研究

采用双向耦合模型对含有固粒的二维气固两相混合层流场进行了研究。流场采用拟谱方法直接数值模拟,固粒采用颗粒-轨道模型,在考虑流场对固粒作用的同时,考虑固粒对流场的反作用。结果发现固粒的浓度和Stokes数对流场影响明显。固粒的作用使涡量扩散加快,并阻碍流场的变化,减弱了流场中拟序结构的强度,缩短涡的生存期;固粒在流场中的分布规律与单相耦合所得结果相似。     

粉尘气体中激波绕射的数值研究*

本文针对稀相气固两相体系,选取双流体耦合模型,综合运用算子分裂技术和高精度高分辨率数值方法,研究了激波在粉尘气体中沿90°拐角的绕射特性,揭示了固相颗粒及其物性改变对激波绕射特征和波后流场结构的影响.     

固液两相流中的K－ε双方程湍流模式

建立了固液两相流中更一般的Ｋ－ε双方程湍流模式．模化了固相和液相的连续方程、动量方程及Ｋ方程和ε方程．该湍流模型考虑了固液两相间速度的滑移，颗粒间的作用及相间作用．使用本文所建立的湍流模型，数值预测了一管湍流中的沙水混合流动，其预测结果与实验结果比较一致．     

Detailed computational and experimental fluid dynamics of fluidized beds

To describe the hydrodynamic phenomena prevailing in large industrial scale fluidized beds continuum models are required. The flow in these systems depends strongly on particle–particle interaction and gas–particle interaction. For this reason, proper closure relations for these two interactions are vital for reliable predictions on the basis of continuum models. Gas–particle interaction can be studied with the use of the lattice Boltzmann model (LBM), while the particle–particle interaction can suitably be studied with a discrete particle model. In this work it is shown that the discrete particle model, utilizing a LBM based drag model, has the capability to generate insight and eventually closure relations in processes such as mixing, segregation and homogeneous fluidization.     

Bubbling,riddling, blowout and critical curves

This paper provides a survey of some recent results and examples concerning the use of the method of critical curves in the study of chaos synchronization in discrete dynamical systems with an invariant one-dimensional submanifold. Some examples of two-dimensional discrete dynamical systems, which exhibit synchronization of chaoti1c trajectories with the related phenomena of bubbling, on–off intermittency, blowout and riddles basins, are examined by the usual local analysis in terms of transverse Lyapunov exponents, whereas segments of critical curves are used to obtain the boundary of a two-dimensional compact trapping region containing the one-dimensional Milnor chaotic attractor on which synchronized dynamics occur. Thanks to the folding action of critical curves, the existence of such a compact region may strongly influence the effects of bubbling and blowout bifurcations, as it acts like a ‘trapping vessel’ inside which bubbling and blowout phenomena are bounded by the global dynamical forces of the dynamical system.     

Optimal discrete long-term operation of nuclear-hydrothermal power systems

We discuss in this paper an algorithm for solving the optimal long-term operating problem of a hydrothermal-nuclear power system by application of the minimum norm optimization technique. The algorithm proposed here has the ability to deal with large-scale power systems and with equality and/or inequality constraints on the variables. A discrete model for the xenon and iodine concentrations is used, as well as a discrete model for hydro reservoirs. The optimization is done on a monthly time basis. For simplicity of the problem formulation, the transmission line losses are considered as a part of the load.This work supported by the Natural Sciences and Engineering Research Council of Canada, Grant No. A4146.     

A model for determining machine requirements in a multistage manufacturing system with discretely distributed demand

A model is presented for resolving the problem of determining the optimum number of machines, and their discrete operating rates, required to meet discretely distributed production demands with a minimum total expected cost. The model is developed for a serial, multistage manufacturing system with both straight-time and overtime operating periods.     

Power processes and their application to reliability

We introduce the stochastic process we call a power process and show that under certain conditions it is stochastically monotone. We use it to model a deteriorative system where operating times and repair times are general discrete random variables, and illustrate our results with numerical examples.     

On mathematical models and numerical simulation of the fluidization of polydisperse suspensions

The well-known Masliyah–Lockett–Bassoon (MLB) model for sedimentation of small particles is extended to fluidization of polydisperse suspensions. For N particle species that differ in size and density, this model leads to a first-order system of N conservation laws, which in general is of mixed (in the case N = 2, hyperbolic–elliptic) type. By a simple algebraic steady-state analysis, we derive necessary compatibility conditions on the size and density parameters that admit the formation of stationary fluidized beds. We then proceed to determine the composition of polydisperse fluidized beds of given compatible species by varying the fluidization velocity and the initial composition of the suspensions, and prove that, within the framework of the MLB model combined with the Richardson–Zaki formula, the constructed bidisperse beds always cause the equations to be hyperbolic. This means that these states are always predicted to be stable. The transient behaviour of the MLB model applied to fluidization is illustrated by three numerical examples, in which the system of conservation laws is solved for N = 2, N = 3 and N = 5, respectively. These examples illustrate the effects of bed expansion and layer inversion caused by successively increasing the applied fluidization velocity and show that the predicted fluidized states are indeed attained.     

On the fluidization of Petri nets and marking homothecy

The analysis of Discrete Event Dynamic Systems suffers from the well known state explosion problem. A classical technique to overcome it is to relax the behavior by partially removing the integrality constraints and thus to deal with hybrid or continuous systems. In the Petri nets framework, continuous net systems (technically hybrid systems) are the result of removing the integrality constraint in the firing of transitions. This relaxation may highly reduce the complexity of analysis techniques but may not preserve important properties of the original system. This paper deals with the basic operation of fluidization. More precisely, it aims at establishing conditions that a discrete system must satisfy so that a given property is preserved by the continuous relaxation. These conditions will be mainly based on the marking homothetic behavior of the system. The focus will be on logical properties as boundedness, B-fairness, deadlock-freeness, liveness and reversibility. Furthermore, testing homothetic monotonicity of some properties in the discrete systems is also studied, as well as techniques to improve the quality of the fluid relaxation by removing spurious solutions.     

Dynamic modeling of the power market and analysis of its complex behavior based on a nonlinear complementarity function

In order to accurately simulate the dynamic decision-making behaviors of market participants, a new dynamic model of power markets that considers the constraints of realistic power networks is proposed in this paper. This model is represented by discrete difference equations embedded within the optimization problem of market clearing. Compared with existing dynamic models, the remarkable characteristic of the proposed model is twofold: it accurately reflects the process of market clearing by the Independent System Operator (ISO) while considering the inherent physical characteristics of power networks, i.e., the complex network constraints; and it describes the market condition that the generation and demand sides bid simultaneously. Using a nonlinear complementary function, the complex discrete difference dynamic model is transformed into a set of familiar discrete difference algebraic equations. Then, the complex dynamic behaviors of power markets are quantitatively analyzed. Corresponding to different operating conditions of power network, such as congestion or non-congestion, the Nash equilibrium of power markets and its stability are calculated, and the periodic and even chaotic dynamic behaviors are exhibited when the market parameters are beyond the stability region of the Nash equilibrium.     

DYNAMICS OF SPATIAL EXPLOITATION: A METAPOPULATION APPROACH

ABSTRACT. In this paper we present a bioeconomic model of a harvesting industry operating over a heterogeneous environment comprised of discrete biological populations interconnected by dispersal processes. The model generalizes the Gordon [1954]/Smith [1968] model of open-access rent dissipation by accounting for intertemporal and spatial “Ricardian” patterns of exploitation. This model yields a simple, but insightful, framework from which one can investigate factors that contribute to the evolution of resource exploitation patterns over space and time. For example, we find that exploitation patterns are driven by biological and fleet dispersal and biological and economic heterogeneity. We conclude that one cannot really understand the biological processes operating in an exploited system without knowing as much about the harvesting system as about the biological system.     

A new forecasting method for time continuous model of dynamic system

Usually a linear differential equation is used to represent continuous dynamic systems, but a linear difference equation is used to represent discrete dynamic systems. AGO is one of the most important characteristics of grey theory, and its main purpose is to reduce the randomness of data. A linear differential equation, instead of a linear difference equation, is used to replace the grey differential equation to analyze discrete systems in this paper. Approximating a k-order derivative by operating after spline curve fitting of 1-AGO data, a model is directly established by means of the least square method. ARIMA models are used to analyze the leading indicator in advance, and the Fourier series with suitably chosen values of parameters is used in the fitting of leading indicator. This model is called the GDM(2, 2, 1) model.