直曲增强型负泊松比超材料的力学性能与减振研究

负泊松比超材料结构作为一种新型智能材料与结构,精确计算超材料结构在大应变下的非线性力学性能对其在工程中的潜在应用具有重要意义.本文在弧形内凹负泊松比结构中加入直杆,设计了一类直杆增强型直曲耦合内凹超材料结构;利用能量法推导出了曲边内凹蜂窝结构的横/纵向等效泊松比与等效弹性模量的解析表达式,讨论结构各参数对结构等效泊松比与等效弹性模量的影响.考虑几何非线性大变形,建立了曲边内凹负泊松比结构的有限元模型,并与线性模拟结果对比,验证了解析表达式的正确性.结果表明,等效泊松比与等效弹性模量均随变形增大而变化,且变形越大差异越明显,大变形下须考虑几何非线性;利用谐响应分析计算结构的加速度级和加速度振级落差,凸显所设计超材料结构的减振性能;分析结构整体减振性能,发现其随层数增加逐渐增大;不随频率变化,在低频范围内对激励产生的响应能够起到抑制作用.因此,合理的设计超材料微结构对结构的低频振动具有很好的抑制作用,对负泊松比超材料减振结构设计具有一定的参考意义.     

梯度负泊松比蜂窝材料的冲击动力学性能分析

借助非线性有限元程序LS-DYNA,基于功能梯度材料的概念,改变蜂窝胞壁厚度,建立了具有密度梯度的内凹六边形负泊松比蜂窝材料模型.分析对比了均匀负泊松比蜂窝材料和梯度负泊松比蜂窝材料在不同面内冲击速度下的变形模式、动态响应和能量吸收特性.研究表明,梯度负泊松比蜂窝材料的动态响应和能量吸收能力受梯度、胞元内凹角度和冲击速度的影响.如果能适当选取各项参数,就可使材料在降低初始应力峰值的同时保持良好的能量吸收能力.因此,具有密度梯度的负泊松比蜂窝材料在结构防护方面具有良好的应用前景.     

压电超材料单元设计及在弹性梁减振中的应用

超材料是将不同性质的材料按照某种规律组合在一起形成的一种周期材料.由于其对弹性波的传递会产生带隙效应,因此在噪声控制、减振隔振等领域得到重视.本文设计了一种压电超材料,通过压电材料元胞的周期性排列,产生频率带隙,以获得减振效果.结构尺寸及厚度小,可以粘贴在主结构上.首先分析了设计的压电超材料色散特性;其次,利用压电超材料对悬臂梁结构进行了减振研究,分析了若干个元胞组成的压电超材料对梁振动能量的调控,并结合压电片上的电压曲线;最后,研究了分流电路中的电阻值和电感值对压电超材料梁减振特性的影响.提出此类压电超材料的进一步改进方向.     

复合负泊松比蜂窝超结构板低频减振特性研究

为实现低频宽带减振,将星型蜂窝与内凹六边形蜂窝组合,形成复合负泊松比蜂窝结构.利用多物理场软件COMSOL Multiphysics通过施加Floquet周期性边界条件获得了复合蜂窝元胞的色散曲线,并计算有限周期结构的传输特性,验证色散曲线中带隙的存在.设计并制备了复合蜂窝超结构板样件,通过试验分析其弹性波激励下的响应,验证有限元分析结果.以低频宽带为目标,利用遗传算法对结构参数进行优化,在1000~2000Hz打开了多条宽频带隙,可以为带隙设计提供有益指导.最后,将地铁实车测试获取的地板振动频谱作为激励,对超结构的减振性能进行了仿真测试,结果表明,复合蜂窝超结构板能够有效衰减列车地板1000~2000Hz的振动峰值.     

皮带秤称重传感器振动能吸收装置的研究与开发

为有效降低和消除振动,研发了皮带秤称重传感器振动能吸收装置.对油缸活塞的结构和液压油路控制增加液体流动的行程进行了设计,通过液体流动阻尼将振动能转换为热能,以此吸收振动能达到减振的目的.该装置采用了能量吸收器的振动能转换与吸收技术,具有运行同步、减振及时的优点.     

基于负刚度惯容型非线性能量汇的整星振动抑制

本文将负刚度元件集成到惯容型非线性能量汇中构成负刚度惯容型非线性能量汇,并将此装置应用到整星结构,讨论其减振效果.基于最大幅值减振百分比展示了负刚度惯容型非线性能量汇的减振性能,并通过对比讨论了负刚度元件对惯容型非线性能量汇减振性能的影响.最后讨论了负刚度惯容型非线性能量汇的参数影响及其优化.研究结果表明,作用于整星系统中的新型负刚度惯容型非线性能量汇具有很好的减振性能.     

弹性箔片轴承-盘式永磁电机转子系统轴向冲击响应

轴向磁通永磁(Axial Flux Permanent Magnet,AFPM)电机在给转子输出周向电磁转矩的同时,还作为一种“磁轴承”,与弹性箔片轴承(Gas Foil Bearings,GFBs)并联工作.当GFBs支承的单定子单转子AFPM电机转速发生突变时(如加、减速),叶轮或者透平会产生一个瞬时轴向力.为揭示此轴向冲击对转子系统振动的影响机理,针对采用2个径向GFBs和1个轴向GFB支承的单定子单转子AFPM电机,建立了系统的刚性转子动力学方程,计入了永磁体的轴向吸力、径向回复力以及轴向GFB的推力对转子振动的影响.计算显示：轴向冲击对横向振动的影响非常小,箔片结构刚度的非线性效应会对转子振荡幅值和时间均产生影响,永磁体的负刚度绝对值越大,轴向振幅越大.在设计时,要注意永磁轴承刚度、箔片结构刚度和结构阻尼的合理匹配,以保证转子在轴向冲击下的轴向振荡时间和振幅均不超过允许值.     

声学超材料和声子晶体专刊征稿启事

作为动力学与控制学科新兴的研究范畴,声学超材料和声子晶体为研究“人为操控弹性介质及结构中振动和波的传播”掀开了崭新的篇章。声学超材料和声子晶体是多种材料或结构周期性排布而成的、具有自然材料所不具备超常波动特性的人工结构或复合材料。声学超材料和声子晶体的优异特性,如吸声隔声、隔振与减振、负折射、超分辨率成像、滤波、隐身、非互易传输、波动主动调控、拓扑波动等,为装备的振动噪声控制、故障诊断、信号处理、     

冲击减振器与非线性能量阱耦合系统的振动抑制研究

建立了冲击减振器与非线性能量阱耦合系统的新型吸振模型,数值模拟的结果验证了该吸振装置的高效性.分析了其参数对主结构振幅、能量耗散以及振动频率的影响,即使系统的初始输入能量变化范围较大,耦合装置也能取得很好的吸振效果.进一步的研究结果表明适当的间隙和较高的碰撞恢复系数既可以增加系统的碰撞运动次数,又能使系统在每次碰撞过程中耗散更多的能量,且该系统中的强非线性刚度有利于吸振.     

基于自相关和经验模态分解的转子碰摩故障分析

针对转子故障振动信号具有周期性的特点,提出一种用于分离转子故障振动信号的新方法,该方法首先应用自相关处理对振动信号进行降噪处理,然后采用经验模态分解(EMD)对振动信号进行分解,得出各个本征模态函数(IMF),并对IMF进行频谱分析,从频谱图上可以清晰地观察出转子的故障特征频率.试验结果表明,振动信号经自相关处理后起到了很好的降噪效果,碰摩所产生的冲击信号上下不对称;EMD分解方法能有效地突出故障特征频率成分,该方法可广泛用于旋转机械振动信号时频分析领域.     

Only connect: teaching, technology and telesis

Abstract This paper describes an approach to the design of interactive multimedia materials being developed in a European Community project. The developmental process is seen as a dialogue between technologists and teachers. This dialogue is often problematic because of the differences in training, experience and culture between them. Conditions needed for fruitful dialogue are described and the generic model for learning design used in the project is explained.     

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。     

Avoiding semantic and temporal gaps in developing software intensive systems

Development of software intensive systems (systems) in practice involves a series of self-contained phases for the lifecycle of a system. Semantic and temporal gaps, which occur among phases and among developer disciplines within and across phases, hinder the ongoing development of a system because of the interdependencies among phases and among disciplines. Such gaps are magnified among systems that are developed at different times by different development teams, which may limit reuse of artifacts of systems development and interoperability among the systems. This article discusses such gaps and a systems development process for avoiding them.     

Designing economic np control charts: A programmed simulation approach

This paper presents control charts models and the necessary simulation software for the location of economic values of the control parameters. The simulation program is written in FORTRAN, requires only 10K of main storage, and can run on most mini and micro computers. Two models are presented - one describes the process when it is operating at full capacity and the other when the process is operating under capacity. The models allow the product quality to deteriorate to a further level before an existing out-of-control state is detected, and they can also be used in situations where no prior knowledge exists of the out-of-control causes and the resulting proportion defectives.     

The development of robot art

Going through a few examples of robot artists who are recognized worldwide, we try to analyze the deepest meaning of what is called “robot art” and the related art field definition. We also try to highlight its well-marked borders, such as kinetic sculptures, kinetic art, cyber art, and cyberpunk. A brief excursion into the importance of the context, the message, and its semiotics is also provided, case by case, together with a few hints on the history of this discipline in the light of an artistic perspective. Therefore, the aim of this article is to try to summarize the main characteristics that might classify robot art as a unique and innovative discipline, and to track down some of the principles by which a robotic artifact can or cannot be considered an art piece in terms of social, cultural, and strictly artistic interest. This work was presented in part at the 13th International Symposium on Artificial Life and Robotics, Oita, Japan, January 31–February 2, 2008     

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.