离散过程

Spectral element methods for partial differencial equation is introduced in this study from viewpoint of the collocation approximation of Chebyshev polynomial. Wave Equation and its space discretization are deduced. Two time integral methods, central difference method and implicit Newmark method, are introduced, and their stability and applicability are also discussed in some details. The significance of absorbing boundary conditions in spectral element methods for Aeroacoustics is explained, and Clayton-Engquist-Majda absorbing boundary conditions is emphasized and introduced, then the discrete scheme of this boundary conditions is deduced and applied to spectral element methods for wave equation.

本文从Chebyshev多项式逼近理论出发，详细介绍了谱元方法求解偏微分方程的过程；推导了流体中的声波动方程并在空间上对其进行了谱元离散；详细讨论了两种时间积分方法──中心差分法和Newmark方法，分析了它们的稳定性条件，并从理论上对比了两种方法的优缺点和适用范围；将吸收边界条件推广应用于谱元方法求解气动声学问题中，重点介绍了Clayton-Engquist-Majda吸收边界条件的原理和公式，推导了该吸收边界条件的变分形式，并将其引入波动方程的离散形式中。

The book is divided into 14 chapters, including Introduction, continuous control system theory, process and discrete sampling, Z transform, sampled-data systems, discrete approximation of continuous system the equivalent, based on mathematical transform the classical design method, based on state space pole placement design methodology, multi-variable system of quadratic optimal control, quantitative effects, the choice of sampling period, the digital control system modeling, digital control system for a variety of design methods, variables quadratic optimal control systems, sampling cycle of selection, non-linear control of the problem, as well as digital control system, a typical application - Disk drive servo control design.

全书共分14章，内容包括概论、连续控制系统理论、采样过程和离散化、Z变换、采样数据系统、连续系统的近似离散等效、基于数学变换的经典设计方法、基于状态空间的极点配置设计方法、多变量系统的二次型最优控制、量化效应、采样周期的选择、数字控制系统的建模问题、数字控制系统的各种设计方法、变量系统的二次型最优控制、采样周期的选择、非线性控制的有关问题，以及数字控制系统的一个典型应用——磁盘驱动器的伺服控制设计等。

The application of the lattice Boltzmann method in unsteady open channel flows was studied in detail in the paper. An existing lattice BGK model was mended; For the problem of negative local equilibrium and evolutionary distribution, we proposed a lattice Boltzmann model based on cell-population equilibrium, which is a direct non-negative approximation to the continuous Maxwell distribution. The model reduces the transport and collision, two basic evolution steps in the LB model, to transport of the non-equilibrium distribution.

本文系统的研究了格子Boltzmann 方法在明渠非恒定流中的应用问题，改进了一个现有的LB 模型，数值实验表明此改进是有效的；在平衡态分布函数及分布函数的非负性问题上，作者提出了一个基于单元均衡的格子Boltzmann 模型，通过直接对Maxwell 分布函数的离散化实现对速度分布函数的非负离散，这种方法将传统模型演化过程中的碰撞和输运两个步骤直接表现为粒子的输运。

"Sampling",In signal processing, sampling is the reduction of a continuous signal to a discrete signal.

"，"在信号处理领域中，取样是将信号从连续时间域上的模拟信号转换到离散时间域上的离散信号的过程。

The discrete element method and the finite element method have their own advantages and weaknesses. Basically, the DEM was developed for predicting the failure problems accompanying with the transition from continuum to non-continuum media. However, it is not accurate to calculate the problem of continuum media. The FEM may forecast the failure area of the material reasonably, while it is hard to calculate the failure process in brittle media. Therefore it becomes a good choice to combine the two methods to construct a hybrid model.

离散元法和有限元法等数值计算方法各有其优势，同时也都存在不足之处：离散元法适于处理由连续介质向非连续介质转化的破坏问题，但对于连续体计算结果精度不高；有限元法适于预测材料破坏的区域，但难以直接用于计算脆性材料破坏过程，因此将两种方法结合可以形成一种较好的混合模型。

Firstly expound the structure of the OFDM system, then analysis the working principle of OFDM communication and research into the key technologies in OFDM system: string conversion, sub-carrier modulation and demodulation, inverse Discrete Fourier Transformation, Discrete Fourier Transformation, cyclic prefix Insert, etc.

该文首先阐述了OFDM系统的结构，分析了OFDM通信系统的工作原理，研究了OFDM系统实现过程中串并转换、子载波调制解调、离散逆傅里叶变换、离散傅里叶变换、循环前缀插入等关键技术。

The combinatorial and delimitative algorithm of engineering structure design with different discrete set and its software system is introduced in this paper.

引 言 离散变量优化设计是指在优化设计过程中，设计变量的取值不是在某一范围内连续变化而是只能取某些符合一定条件的离散值。

In this paper, a Robust Discrete Optimization model of elevator group control system is presented for dealing with the uncertainty in elevator traffic flow and computational complexity in scheduling. Based on RDO theory, we propose a new elevator group scheduling Algorithm. Comparison is carried between the RDO algorithm and other scheduling algorithms under the virtual simulation platform of elevator group scheduling.

针对电梯群控调度过程中交通流的不确定性和优化求解复杂性问题，本文通过建立电梯群控调度系统的鲁棒离散优化模型，实现了一种基于鲁棒离散优化理论的新的电梯群控优化调度算法。

This paper introduces the food refrigerated theory and the basis of the current industry refrigerated developments in the situation; And then in the long cylindrical-shaped food heat conduction process and the mathematical model using the method of differential thermal conduction equations for discrete, Programming come through long cylindrical-shaped food cooling process numerical solution; After further analysis of numerical solution of the test results; Finally, the impact of the cooling process food all relevant factors, such as moisture content, wind speed and temperature of the cooling medium for in-depth research, while comparing the different shapes of food to food cooling process.

本文首先介绍了有关食品冷冻冷藏的基础理论和目前冷冻冷藏行业的发展的发展概况；然后研究了长圆柱状食品热传导过程的数学模型并利用差分的方法对热传导方程进行离散，通过编程得出长圆柱状食品冷却过程的数值解；之后再分析解对数值解的结果进行验证；最后对影响食品冷却过程的各相关因素，如含水率、风速和冷却介质温度等进行了深入的研究，同时又对比了不同形状的食品对食品冷却过程的影响。

Recent years as development of the computer and software, it becomes reality using numeric simulation to research grouting in clay. Using the software of PFC2D, the grouting in clay is lucubrated and such achievements are reached: Grouting technologies in existence grouting material and serosity are studied and rational methods are put forward in choosing grouting technology and serosity.(2) Base on numeric simulation biax test a method is explored to simulate clay with PFC2D.(3) A method is explored to simulate grouting using PFC2D.(4) The relation between serosity pressure and diffuseness of grouting in clay with different initial stress is studied.(5) The stress transformation of clay is studied during grouting.(6) The stress distribution is studied under different serosity pressure.(7) The normal stresss and shear stresss at any section are studied.

近年来随着计算技术的发展，使得采用数值模拟的方式研究均质土体中的注浆成为可能，本文则利用离散元程序PFC2D对均质土体中注浆进行了研究，主要做了以下几方面的工作：(1)研究了现有注浆加固技术、注浆材料以及浆液的性质，阐述了合理选择注浆方式以及浆液的方法；(2)采用数值双轴实验，探索了应用离散元模型模拟土体的方法：(3)探索了采用颗粒流程序进行注浆数值模拟的方法途径；(4)研究了在粘土中注浆不同侧向土压力条件下浆液扩散范围与注浆压力规律；(5)研究了注浆过程中不同阶段土体中压应力的变化；(6)研究了不同注浆压力对土体应力分稚的影响：(7)研究了注浆过程中土体中任一截面处正应力与剪应力的对比关系。

In the United States, chronic alcoholism and hepatitis C are the most common ones.

在美国，慢性酒精中毒，肝炎是最常见的。

If you have any questions, you can contact me anytime.

如果有任何问题，你可以随时联系我。