径向导叶与流道式导叶性能分析与试验

以某一参数的阶段式多级泵的导叶为研究对象进行研究。通过数值模拟与试验验证相结合的研究方法,改传统的径向导叶为流道式导叶。以FLUENT为计算平台,基于Navier-Stokes方程和标准k-e湍流模型,采用SIMPLEC算法对比分析叶轮加原始径向导叶方案及叶轮加新设计的流道式导叶方案,数值模拟发现流道式导叶内部流场明显优于径向导叶内部流场。经过试验验证流道式导叶方案效率明显优于径向导叶方案,说明流道式导叶在水力性能方面比径向导叶更加出色。     

SCF型煤矿除尘通风机叶栅及后流道性能分析

为进一步提升除尘通风机的运行质量,针对煤矿企业常用的SCF型除尘通风机,对其叶栅部位和后流道流场运行情况进行仿真分析,以明确该SCF型除尘通风机在性能方面仍存在的不足;然后根据仿真分析数据,全方位地优化设计该SCF型除尘通风机各部件参数。结果显示,优化后的除尘通风机设备在理论上具有更高的性能优势,表明本次仿真分析方法具有潜在的应用价值。     

基于汽车液力变矩器数值仿真研究

研究汽车液力变矩器动力性能优化问题.液力变矩器作为自动变速器的液力传动元件可以实现汽车的自适应性无级变速稳定性控制等.传统的液力变矩器动力系统模型达不到自适应性能要求.为了解决上述问题,根据液力变矩器的实际工作状况,提出了一种新的液力变矩器汽车动力系统建模现代设计方法.可有机结合修正能头损失的束流理论,忽略掉非重要因素,以简化建模复杂程度.在假设的基础上建立流道的三维仿真模型,然后导入到划分计算网格中,进行仿真,结果表明,采用流场数值仿真技术,大大提高了模型的设计精度和设计效率,具有一定的实际应用价值.     

缩比试验模型设计与验证

为了预示导弹地下发射井中的噪声环境、检验某型多孔吸声材料的实际吸声效果,通过缩比模型试验进行了验证和仿真.按照缩比原则设计了缩小比例为1∶10的模型发动机,采用网格计算方法对缩比模型和原型发动机之间的温度场、速度场和压力场进行了定常仿真分析与比较.结果表明,缩比试验的结果与井下原型导弹的射流流场具有可比性,试验测量数据可以作为评价吸声材料的实际应用效果.对缩比模型的设计过程进行了研究.通过对模型发动机流场和原型发动机流场的仿真和比较,验证了缩比试验技术方案的合理性.     

重型燃气轮机IGV系统建模与故障仿真

重型燃气轮机是能源高效转换与清洁利用系统的核心动力装备。为确保重型燃气轮机的安全、稳定运行,以双连杆型进口导叶(IGV)系统为研究对象,进行分析建模与故障仿真研究。首先,对IGV系统进行机理分析,建立了液压驱动部分和机械传动部分的动力学模型。其次,基于模块化建模方法,在Simulink中搭建了非线性IGV系统仿真模型,并将IGV仿真模型输出与燃机电厂IGV历史运行数据进行对比。最后,对典型故障进行故障机理分析,分别建立了各类故障的动力学模型,并在Simulink中搭建了故障仿真模型。仿真结果表明,所建IGV系统模型能准确反映IGV角度跟随负荷的变化,与电厂实际运行数据一致;IGV系统故障模型与故障机理分析基本符合,具有较高的准确性。建模与故障仿真具有良好的研究前景,为燃气轮机IGV系统的动态分析和故障诊断提供了重要技术参考。     

某型强光爆震弹冲击波超压致伤半径仿真研究

研究某型强光爆震弹的冲击波超压致伤特性.为得到某型强光爆震弹对于人员致伤的安全半径,依据LS-DYNA结构非线性分析工具,结合爆炸冲击波超压的致伤效应理论,建立了相应的仿真模型并进行实验分析.先基于理论公式进行计算,对比理论计算数据和仿真数据,通过数值拟合,得出了仿真结果与理论计算结果的对比曲线,并结合实际分析了仿真数据的可靠性.结果表明,利用仿真数据可以计算出冲击波超压对人员致伤的安全半径,并具有一定的实践指导意义.     

空间晶体生长实验中流场的动态显示研究

矢量场可视化是科学计算可视化研究的重要方向.对于复杂环境条件下大数据量矢量场的可视化,传统的方法运算量大,实时性难以满足要求.以空间晶体生长实验中的流场数据可视化为应用背景,针对目前常用方法的不足,引入了一种全新的基于图像的流场可视化方法--IBFV方法,并对该方法的机理进行了深入地分析和研究,给出了一种基于OpenGL图形库的简单实现算法,最终应用于布里奇曼晶体生长实验中流场数据的实时动态显示.实践证明此方法独立于流场数据,具有良好的适用性和直观性,并具有极高的速度,在当前普通PC机上可以实现50fps的动态显示帧频,得到连续无抖动的流场动态图像仿真.     

脱硫塔优化设计的仿真与实验研究

研究发电厂降低SO2排放优化问题,为研究脱硫塔内不同给料方式的气固两相流流场对脱硫效率的影响,提出了采用多相流数值仿真的数学模型,并采用CFD软件对脱硫塔内流场进行了数值仿真.利用PIV技术测量实验数据,并将计算与实验测量的径向速度、轴向速度以及不同给料方式下SO2的排放量等数值进行了对比分析.经过仿真,结果表明,仿真结果与实验台测量值基本相符,并且在Z=150mm的密相区位置,双侧给料方式径向速度分布均匀,轴向速度呈现“环核流动”结构,利于物料与烟气充分混合,既能解决塔内物料堵塞,增强脱硫塔内循环,又可以提高脱硫效率,降低了SO2的排放量.     

航空发动机气路检测静电传感器仿真研究

针对航空发动机气路静电检测静电传感器的复杂工作环境,开展传感器的流场、电场、温度场耦合的多物理场建模与仿真研究。采用有限元分析软件建立静电传感器的数值模型并进行仿真分析,研究探针型静电传感器探极的直径、长度、布局位置对发动机尾气静电信号的影响,最后通过在尾气静电试验平台测试,对仿真分析的结论进行验证,从而为静电传感器的工程化应用提供理论支撑。     

面向演示验证的多模式多策略实验机制研究

以武器装备体系对抗演示验证为应用目标,在明确了演示验证仿真实验机制的研究内容基础上,针对演示验证提出了多模式运行机制和多策略管理机制的思想,并对演示仿真实验模式与验证(分析)仿真实验模式的关键属性进行了比较,重点分析了分布、并行和混合式等三种仿真技术框架下的多策略管理机制的运用.给出了混合仿真实验多策略管理机制要素组合空间坐标,比较并指出混合式仿真实验机制能较好地满足演示验证仿真实验的应用目标需求,是进一步研究的重点.     

European Community policy and the market

Abstract This paper starts with some reflections on the policy considerations and priorities which are shaping European Commission (EC) research programmes. Then it attempts to position the current projects which seek to capitalise on information and communications technologies for learning in relation to these priorities and the apparent realities of the marketplace. It concludes that while there are grounds to be optimistic about the contribution EC programmes can make to the efficiency and standard of education and training, they are still too technology driven.     

一种自适应子融合集成多分类器方法

融合集成方法已经广泛应用在模式识别领域,然而一些基分类器实时性能稳定性较差,导致多分类器融合性能差,针对上述问题本文提出了一种新的基于多分类器的子融合集成分类器系统。该方法考虑在度量层融合层次之上通过对各类基多分类器进行动态选择,票数最多的类别作为融合系统中对特征向量识别的类别,构成一种新的自适应子融合集成分类器方法。实验表明,该方法比传统的分类器以及分类融合方法识别准确率明显更高,具有更好的鲁棒性。     

Explanation and prediction: an architecture for default and abductive reasoning

Although there are many arguments that logic is an appropriate tool for artificial intelligence, there has been a perceived problem with the monotonicity of classical logic. This paper elaborates on the idea that reasoning should be viewed as theory formation where logic tells us the consequences of our assumptions. The two activities of predicting what is expected to be true and explaining observations are considered in a simple theory formation framework. Properties of each activity are discussed, along with a number of proposals as to what should be predicted or accepted as reasonable explanations. An architecture is proposed to combine explanation and prediction into one coherent framework. Algorithms used to implement the system as well as examples from a running implementation are given.     

Three Process Perspectives: Organizations, Teams, and People

This paper provides the author's personal views and perspectives on software process improvement. Starting with his first work on technology assessment in IBM over 20 years ago, Watts Humphrey describes the process improvement work he has been directly involved in. This includes the development of the early process assessment methods, the original design of the CMM, and the introduction of the Personal Software Process (PSP)^SM and Team Software Process (TSP){^SM}. In addition to describing the original motivation for this work, the author also reviews many of the problems he and his associates encountered and why they solved them the way they did. He also comments on the outstanding issues and likely directions for future work. Finally, this work has built on the experiences and contributions of many people. Mr. Humphrey only describes work that he was personally involved in and he names many of the key contributors. However, so many people have been involved in this work that a full list of the important participants would be impractical.     

基于复小波噪声方差显著修正的SAR图像去噪

提出了一种基于复小波域统计建模与噪声方差估计显著性修正相结合的合成孔径雷达(Synthetic Aperture Radar,SAR)图像斑点噪声滤波方法。该方法首先通过对数变换将乘性噪声模型转化为加性噪声模型,然后对变换后的图像进行双树复小波变换(Dualtree Complex Wavelet Transform,DCWT),并对复数小波系数的统计分布进行建模。在此先验分布的基础上,通过运用贝叶斯估计方法从含噪系数中恢复原始系数,达到滤除噪声的目的。实验结果表明该方法在去除噪声的同时保留了图像的细节信息,取得了很好的降噪效果。     

How do children do mathematics with LOGO?

Abstract  This paper considers some results of a study designed to investigate the kinds of mathematical activity undertaken by children (aged between 8 and 11) as they learned to program in LOGO. A model of learning modes is proposed, which attempts to describe the ways in which children used and acquired understanding of the programming/mathematical concepts involved. The remainder of the paper is concerned with discussing the validity and limitations of the model, and its implications for further research and curriculum development.     

Editorial: Special issue on recent advances in hybrid control theory and applications

正The demands of a rapidly advancing technology for faster and more accurate controllers have always had a strong influence on the progress of automatic control theory.In recent years control problems have been arising with increasing frequency in widely different areas,which cannot be addressed using conventional control techniques.The principal reason for this is the fact that a highly competitive economy is forcing systems to operate in regimes where     

Information for Authors

正Aim The Journals of Zhejiang University-SCIENCE(A/B/C)areedited by the international board of distinguished Chinese andforeign scientists,and are aimed to present the latest devel-opments and achievements in scientific research in China andoverseas to the world’s scientific circles,especially to stimulateand promote academic exchange between Chinese and for-eign scientists everywhere.     

Enhancing a leaf radiative transfer model to estimate concentrations and in vivo specific absorption coefficients of total carotenoids and chlorophylls a and b from single-needle reflectance and transmittance

The relative concentrations of different pigments within a leaf have significant physiological and spectral consequences. Photosynthesis, light use efficiency, mass and energy exchange, and stress response are dependent on relationships among an ensemble of pigments. This ensemble also determines the visible characteristics of a leaf, which can be measured remotely and used to quantify leaf biochemistry and structure. But current remote sensing approaches are limited in their ability to resolve individual pigments. This paper focuses on the incorporation of three pigments—chlorophyll a, chlorophyll b, and total carotenoids—into the LIBERTY leaf radiative transfer model to better understand relationships between leaf biochemical, biophysical, and spectral properties.Pinus ponderosa and Pinus jeffreyi needles were collected from three sites in the California Sierra Nevada. Hemispheric single-leaf visible reflectance and transmittance and concentrations of chlorophylls a and b and total carotenoids of fresh needles were measured. These data were input to the enhanced LIBERTY model to estimate optical and biochemical properties of pine needles. The enhanced model successfully estimated reflectance (RMSE = 0.0255, BIAS = 0.00477, RMS%E = 16.7%), had variable success estimating transmittance (RMSE = 0.0442, BIAS = 0.0294, RMS%E = 181%), and generated very good estimates of carotenoid concentrations (RMSE = 2.48 µg/cm², BIAS = 0.143 µg/cm², RMS%E = 20.4%), good estimates of chlorophyll a concentrations (RMSE = 10.7 µg/cm², BIAS = − 0.992 µg/cm², RMS%E = 21.1%), and fair estimates of chlorophyll b concentrations (RMSE = 7.49 µg/cm², BIAS = − 2.12 µg/cm², RMS%E = 43.7%). Overall root mean squared errors of reflectance, transmittance, and pigment concentration estimates were lower for the three-pigment model than for the single-pigment model. The algorithm to estimate three in vivo specific absorption coefficients is robust, although estimated values are distorted by inconsistencies in model biophysics. The capacity to invert the model from single-leaf reflectance and transmittance was added to the model so it could be coupled with vegetation canopy models to estimate canopy biochemistry from remotely sensed data.     

Mr. Twinn’s bombes

This article discusses the history and design of the special versions of the bombe key-finding machines used by Britain’s Government Code & Cypher School (GC&CS) during World War II to attack the Enigma traffic of the Abwehr (the German military intelligence service). These special bombes were based on the design of their more numerous counterparts used against the traffic of the German armed services, but differed from them in important ways that highlight the adaptability of the British bombe design, and the power and flexibility of the diagonal board. Also discussed are the changes in the Abwehr indicating system that drove the development of these machines, the ingenious ways in which they were used, and some related developments involving the bombes used by the U.S. Navy’s cryptanalytic unit (OP-20-G).