Simulation of fine particle formation by precipitation using computational fluid dynamics

The 4‐environment generalized micromixing (4‐EGM) model is applied to describe turbulent mixing and precipitation of barium sulfate in a tubular reactor. The model is implemented in the commercial computational fluid dynamics (CFD) software Fluent. The CFD code is first used to solve for the hydrodynamic fields (velocity, turbulence kinetic energy, turbulent energy dissipation). The species concentrations and moments of the crystal size distribution (CSD) are then computed using user‐defined transport equations. CFD simulations are performed for the tubular reactor used in an earlier experimental study of barium sulfate precipitation. The 4‐EGM CFD results are shown to compare favourably to CFD results found using the presumed beta PDF model. The latter has previously been shown to yield good agreement with experimental data for the mean crystal size at the outlet of the tubular reactor.     

基于PDF文档的网络学习资源建设

目前最流行的电子文档格式--PDF文档,集多媒体信息于一身,交互方式丰富,并且可在Web上发布和传递,具有独特优势.本文在分析PDF文档和Web数据库进行双向数据传递机理的基础上,对如何利用PDF文档结合ASP技术开发网络学习资源进行了探讨.     

飞机航路规划决策系统研究与开发

现代低空突防技术TF/TA2对飞机航路规划提出了新的要求,在研究战机任务规划、战术规划的基础上,设计了飞机航路规划决策系统,包括地形模拟、最优航路算法研究、航路决策、雷达辐射源库、火力威胁库的建立等。     

Auto-ignition during instationary jet evolution of dimethyl ether (DME) in a high-pressure atmosphere

The auto-ignition process during transient injection of gaseous dimethyl ether (DME) in a constant high-pressure atmosphere is studied experimentally by laser-optical methods and compared with numerical calculations. With different non-intrusive measurement techniques jet properties and auto-ignition are investigated at high temporal and spatial resolution. The open jet penetrates a constant pressure oxidative atmosphere of up to 4 MPa. During the transient evolution, the fuel jet entrains air at up to 720 K. The subsequent auto-ignition of the ignitable part of the jet occurs simultaneously over a wide spatial extension. The ignition delay times are not affected by variation of the nozzle exit velocity. Thus, the low-temperature oxidation is slow compared with the shorter time scales of mixing, so that chemical kinetics is dominating the process. The typical two-stage ignition is resolved optically with high-speed shadowgraphy at a sampling rate of 10 kHz. The 2D fields of jet velocity and transient mixture fraction are measured phase-coupled with Particle Image Velocimetry (PIV) and Tracer Laser Induced Fluorescence (LIF) during the time-frame of ignition. The instationary Probability Density Functions (PDF) of mixture fraction are described very well by Beta functions within the complete area of the open jet. Additional 1D flamelet simulations of the auto-ignition process are computed with a detailed reaction mechanism for DME [S. Fischer, F. Dryer, H. Curran, Int. J. Chem. Kinet. 32 (12) (2000) 713-740; H. Curran, S. Fischer, F. Dryer, Int. J. Chem. Kinet. 32 (12) (2000) 741-759]. Calculated ignition delay times are in very good agreement with the measured mean ignition delay times of 3 ms. Supplemental flamelet simulations address the influence of DME and air temperature, pressure and strain. Underneath a critical strain rate the air temperature is identified to be the most sensitive factor on ignition delay time.     

Relating thermal conductivity of soil skeleton with soil texture by the concept of“local thermal conductivity fluctuation”

The thermal conductivity of the soil skeletonλ;is an essential parameter from the point of view of the correct assessment of soil overall/effective conductivity.This work introduces the concept of“local thermal conductivity fluctuation”which characterizes the microscale variation of conductivity within the solid phase.It is proposed to link the“local fluctuation”of thermal conductivityλwith the soil texture-the information that is available at the scale of engineering applications.It was possible to relate the skeleton thermal conductivity with the grain size distribution of the soil.Finally,based on a large series of numerical simulations,the paper provides four triangle diagrams(at different organic matter contents:0%,2%,4%and 6%)relating the value ofλ;with volume fraction of individual soil separates.This result is extremely important from the practical point of view.One can quickly evaluateλ;value provided that information on the grain size distribution and organic matter content is available.     

Multi-environment PDF modeling for non-catalytic partial oxidation process under MILD oxy-combustion condition

The multi-environment probability density function approach has been applied to numerically investigate the Moderate or Intense Low-Oxygen (MILD) oxy-combustion processes encountered in the non-catalytic partial oxidation (POX) gasifier. The multi-environment PDF approach has the form of a conventional Eulerian scheme and retains the desirable property of a particle-based method. Micro-mixing is represented via the IEM model, and the detailed chemistry is based on GRI 3.0 mechanism without NOx chemistry. In terms of the mean temperature, the present multi-environment PDF approach yields the overall agreement with the measurements in the highly fuel-rich MILD oxy-combustion situation with the strong flue gas recirculation even if there exist the certain discrepancies in the upstream region. Special emphasis is given to the effects of the fuel/oxygen injection velocity and O₂/CH₄ ratio on the characteristics of the strongly recirculated MILD oxy-combustion processes. Depending on injection velocity or O₂/CH₄ ratio, the present MEPDF approach well reproduces the qualitative flame transition characteristics from MILD combustion to conventional combustion. The higher fuel/oxygen injection velocity leads to the much longer jet penetration and the much higher SDR level which makes the ignition to occur at further downstream region. The relatively lower O₂/CH₄ ratios maintain the basic characteristics of the MILD combustion while the highest O₂/CH₄ ratio locally creates the oxy-flame like structure rather than the non-visible flame field. Based on numerical results, the detailed discussions are made for flame stabilization, auto-ignition process and precise flame structure in terms of recirculation rate, distribution of turbulent Damköhler number, scalar dissipation rate, mean temperature and mole fraction of CH₂O and OH.     

TF法则嵌入机制的动态局域加权网络模型

分析目前加权局域世界演化模型已取得的研究成果,在其基础上进行综合改进与完善,提出一种TF法则嵌入机制的动态局域加权网络模型(TF-DLW),该模型在演化过程中融入了TF法则和BBV权值动态演化机制。平均场理论和计算机模拟仿真均验证了该模型强度分布具有幂率特性。同时,计算机仿真中强度分布、边权分布以及度分布均出现了幂率肥尾现象,三角形结构的嵌入使得模型能更平稳地调节聚类系数的大小。实验表明,TF-DLW演化模型继承了许多复杂模型具有的幂率分布特性,而且可以快速平稳地调控簇系数的范围大小。     

Web文本中维吾尔语领域术语的自动发现

针对维吾尔语领域术语获取难度大,人工扩充领域术语工作量大、效率低等特点,利用词汇共现原理,以维吾尔语连接词和互信息(MI)为工具,快速扩充原始维吾尔语领域术语;建立了以维吾尔语领域术语为特征模板,利用条件随机场(CRF)模型实现Web文本中维吾尔语领域术语的自动发现方法,并在此基础上实现长维吾尔语领域术语的自动发现。实验表明,对短维吾尔语领域术语的自动发现准确率为 97.59%,召回率为 93.38%,对长维吾尔语领域术语的自动发现正确率达到55.72%。     

无线传感器网络中基于区域通信覆盖的节点定位投放算法

针对无线传感器网络中传感器节点投放分布对投放区域有效通信信号覆盖的影响,该文提出了一种基于通信覆盖的分布式投放概率覆盖(DDCP)算法。在保证投放精度的前提下,该算法根据传感器节点在投放区域中位置的不确定性以及信号衰减特性,建立信号覆盖模型,并通过概率优化获取传感器节点的最佳投放位置和投放数目。这样改善了区域通信覆盖,同时提高了投放效率和节省网络资源。通过仿真比较了在不同定位投放方法下的各相关性数据,验证了该算法实现高效投放的优越性和正确性。     

RS码技术在PDF417码纠错码编译码中的应用研究

在引入RS码编译码原理的基础上,通过对二维条码PDF417码和四一七国家条码规范的分析和研究,将RS码技术应用到PDF417码纠错码的编码、译码算法过程中,完成了PDF417纠错的实现,同时给出了在GF（929）域中计算3的幂值的方法,解决了中间结果过大导致数据溢出的问题。为PDF417码的纠错码提供了一个完整的解决方案。