分级进风旋流燃烧室内湍流燃烧的数值模拟

应用考虑湍流-化学反应相互作用的代数二阶矩-概率密度函数(PDF)湍流燃烧模型,对分级进风旋流燃烧室内两组工况下的甲烷湍流燃烧进行了数值模拟,得到的二氧化碳浓度和气体轴向脉动速度均方根值分布与实验数据相符合,得到的气体轴向和切向速度、轴向一切向脉动速度关联量、温度和氧气浓度分布与实验数据基本相符合.研究结果表明,选取适当的二次风率可以起到优化燃烧过程的作用.     

Verification and validation benchmarks

Verification and validation (V&V) are the primary means to assess the accuracy and reliability of computational simulations. V&V methods and procedures have fundamentally improved the credibility of simulations in several high-consequence fields, such as nuclear reactor safety, underground nuclear waste storage, and nuclear weapon safety. Although the terminology is not uniform across engineering disciplines, code verification deals with assessing the reliability of the software coding, and solution verification deals with assessing the numerical accuracy of the solution to a computational model. Validation addresses the physics modeling accuracy of a computational simulation by comparing the computational results with experimental data. Code verification benchmarks and validation benchmarks have been constructed for a number of years in every field of computational simulation. However, no comprehensive guidelines have been proposed for the construction and use of V&V benchmarks. For example, the field of nuclear reactor safety has not focused on code verification benchmarks, but it has placed great emphasis on developing validation benchmarks. Many of these validation benchmarks are closely related to the operations of actual reactors at near-safety-critical conditions, as opposed to being more fundamental-physics benchmarks. This paper presents recommendations for the effective design and use of code verification benchmarks based on manufactured solutions, classical analytical solutions, and highly accurate numerical solutions. In addition, this paper presents recommendations for the design and use of validation benchmarks, highlighting the careful design of building-block experiments, the estimation of experimental measurement uncertainty for both inputs and outputs to the code, validation metrics, and the role of model calibration in validation. It is argued that the understanding of predictive capability of a computational model is built on the level of achievement in V&V activities, how closely related the V&V benchmarks are to the actual application of interest, and the quantification of uncertainties related to the application of interest.     

Functional reliability analysis of Safety Grade Decay Heat Removal System of Indian 500 MWe PFBR

Passive systems are increasingly deployed in nuclear industry with an objective of increasing reliability and safety of operations with reduced cost. Methods for assessing the reliability of thermal-hydraulic passive systems, that is systems with moving working fluid, address the issues in natural buoyancy-driven flow that could result in a failure to meet the design safety limits under accident scenarios. This is referred as design functional reliability. This paper presents the results of functional reliability analysis carried out for the passive Safety Grade Decay Heat Removal System (SGDHRS) of Indian Prototype Fast Breeder Reactor (PFBR). The analysis is carried out based on the overall approach reported in the Reliability Methods for Passive System (RMPS, European Commission) project. Functional failure probability is calculated using Monte-Carlo method and also with method of moments.     

基于数学形态学的二维条码边缘检测算法

边缘模糊会导致二维条码识别率下降,提出了一种基于数学形态学边缘检测的二维条码识别算法,该算法最大的特点是用具有特定形态的结构元素去度量和提取图像中的对应形状以达到对图像分析和识别的目的,从而有效地降低边缘模糊对条码识别的影响。选取PDF417二维条码为应用对象,采用基于数学形态学对二维条码的识别算法选择合适的结构元素。实验结果表明与传统的几种边缘检测算法相比,基于数学形态学对二维条码的识别算法能够更有效地识别条码边界,显著地提高了条码的识别率。     

一种新的蜂窝网NLOS误差抑制算法

非视距传播(NLOS)误差是目前基于蜂窝网络的移动台定位系统提高定位精度必须解决的关键问题,该文提出一种基于概率密度估计和偏差Kalman滤波器的NLOS误差无偏估计算法。仿真结果表明,该算法在性能上优于现有同类算法,并且算法对环境先验知识的需求更少,具有更广泛的适用性。     

SAR多视图像的Stokes参数的统计分布

该文首先应用散射矩阵的Wishart 联合分布推导了高斯分布散射矩阵的Stokes参数分布,利用极化不变量思想得到了全部4个Stokes参数分布相当理想的理论结果,并与前人的结果进行了对比,体现了此分析算法的简洁性与统一性,他们可以具体描述Stokes参数的起伏性。在此基础上,求出了SAR多视情况下标准化Stokes参数分布的概率密度函数,从另一方面描述了SAR多视图像的随机状态特性,这些结果对于降低斑点噪声、地表分类与背景中的目标识别具有重要的指导意义。     

An improved mixing model providing joint statistics of scalar and scalar dissipation

For the calculation of nonpremixed turbulent flames with thin reaction zones the joint probability density function (PDF) of the mixture fraction and its dissipation rate plays an important role. The corresponding PDF transport equation involves a mixing model for the closure of the molecular mixing term. Here, the parameterized scalar profile (PSP) mixing model is extended to provide the required joint statistics. Model predictions are validated using direct numerical simulation (DNS) data of a passive scalar mixing in a statistically homogeneous turbulent flow. Comparisons between the DNS and the model predictions are provided, which involve different initial scalar-field lengthscales.     

汉语短文话题提取系统中SDTF*PDF算法的研究

互联网技术得到迅速发展以来,大量信息尤其是文本信息在网上传播。文中面向海量汉语短文话题提取系统中多信源、短文篇幅小的特点,结合词汇语义相似性度量,提出了一个词汇权重计算算法---SDTF PDF(ShortDocumentTermFrequency ProportionalDocumentFrequency),测试表明,基于该算法的汉语短文话题识别系统能够较准确地在海量中文文本信息中自动提取一段时间内(一天或一周,可以指定)的主要话题。     

二维码防伪技术在可变数据印刷中的应用

分析了二维码的防伪原理,提出了在可变数据印刷中应用二维码进行防伪的方案,在完成基于可变数据印刷的二维码的生成和识别实验的基础上,设计实验比较得出了不同二维码(PDF417码与QR码)的防伪特性的差异。理论分析及实验结果表明,利用二维码对可变数据印刷进行防伪的方案是可行的,并且不同二维码的防伪特性存在差异,在实际应用中可以根据具体的要求选用不同的二维码。     

Cost simulation in an item-based project involving construction engineering and management

Despite the extensive use of simulation in management, the continuous simulation model for cost estimation remains unexploited, especially for construction engineering and management. This study introduces streamlining Monte Carlo simulation procedures with evaluation of stochastic processes and input probability distribution selection via hypothesis testing, and specification of correlations between simulated variates. By using self-developed algorithms and a spreadsheet-add-on program, this investigation uses historical construction projects as case study data to create an early-stage cost distribution for budget allocation. While establishing the applicability of the proposed simulation procedures, this study demonstrates that the simulated cost results present superior simulation accuracy in addition to separating the principal work items and unit price component model. Generally, the precision and absolute error rates fall into acceptable ranges when the proposed systematic simulation procedures are adopted. The cost simulation approach offers a simplified decision tool for fairly assessing construction cost and uncertainties based on the experienced judgment of project managers.