压电智能挠性悬臂板主动振动控制试验研究

航天器上太阳帆板这种悬臂外伸薄板结构的挠性附件，存在有扰动条件下引起的振动，可采用压电智能结构对悬臂板进行主动振动控制。文章对设计的挠性悬臂板系统进行系统辨识，得到板系统的前三阶模态频率及阻尼比，并采用PD控制和PPF控制算法对板的前三阶模态(包括弯曲模态和扭转模态)进行主动振动控制。试验结果表明，采用压电智能结构可以抑制挠性悬臂板的振动．效果明显。     

压电复合梁高阶有限元模型与主动振动控制研究

大型柔性空间结构的振动控制问题引起了广泛的关注.压电材料以其低质量、宽频带和适应性强等特点,非常适合于柔性空间结构的振动控制.本文针对上下表面粘贴有分布式压电传感器和作动器的智能层梁结构,提出了一种考虑压电材料对结构质量、刚度影响的高阶有限元模型.考虑到空间结构可能承受较大的热载荷,在模型中计及了压电材料的热电耦合效应.采用常增益负反馈控制方法、常增益速度负反馈控制方法、Lyapunov反馈控制方法和线性二次型调节器方法(LQR)设计主动控制器,实现了智能层梁结构脉冲激励下的振动主动控制.仿真结果表明,LQR方法更能有效的实现结构振动控制,并且具有更低的作动器峰值电压,但不能消除热载荷引起的结构静变形.     

挠性航天器姿态机动的变结构主动振动抑制

针对挠性航天器大角度姿态机动的振动抑制问题, 提出了一种双回路鲁棒主动振动控制方法. 首先, 对各低阶振动模态设计正位置反馈补偿器, 增加挠性模态的阻尼, 使其振动能够快速衰减; 然后, 基于变结构输出反馈控制理论, 给出控制器的设计方法. 最后, 将该方法应用于挠性航天器姿态机动控制, 仿真结果表明, 所提出的方法是可行而有效的.     

压电智能结构的主动控制及压电执行器布局优化

本文对压电梁、板结构振动主动控制进行了研究,分别建立了压电悬臂梁的耦合动力学方程以及Kirchhoff假设下矩形压电薄板的耦合动力学方程,通过采用独立模态空间控制法,实现了对压电智能结构前两阶模态的主动振动控制.为提高主动控制的抑振效果,通过仿真实例分析了压电执行器在梁上的不同布局对于主动控制抑振效果的影响,得到了压电执行器粘附于悬臂梁上的最佳布局.最后实验验证了压电悬臂梁在自由振动以及模态共振下压电执行器对于悬臂梁响应控制的可行性和有效性.     

挠性智能梁的振动控制

研究采用共位配置的压电敏感器和致动器的挠性是臂梁的振动控制问题,建立了智能梁的模型,设计了一种线性反馈控制律,并应用无空维空间的ＬａＳａｌｌｅ不变原理和线性半群理论证明了当敏感器和控制器的分布使得系统能镇条件成立时,所设计的控制抑制了梁的振动。     

柔性智能结构的振动主动控制仿真和实验研究

基于模态坐标表示的含压电片结构横向振动系统方程,采用独立模态法直接针对系统的高阶模型设计控制律,利用劳斯判据证明由所设计的控制器引起的控制溢出可被有效抑制,极大地降低了由于模型降阶引起的误差。同时,对压电柔性悬臂梁的高阶振动模态进行主动控制仿真模拟和实验研究,结果表明施加主动控制后柔性悬臂梁的模态阻尼显著提高,受控悬臂梁的振动得到了快速抑制。仿真计算和实验结果取得了良好的一致性。研究结果表明,利用压电陶瓷作为驱动元件,采用独立模态控制法实现柔性结构的振动抑制是一种高效的振动主动控制方法,在航天航空等领域中     

三轴稳定挠性卫星姿态机动时变滑模变结构和主动振动控制

针对带有控制受限的挠性卫星的姿态机动和振动控制问题, 给出了一类仅利用输出信息的变结构控制和 基于智能材料的主动振动控制技术相结合的复合控制方法. 首先给出变结构姿态控制器的设计来完成卫星姿态机动, 并给出一种切换机制以实现挠性卫星快速姿态机动; 其次, 采用分布式压电元件作为作动器, 设计了应变速率反馈补偿器以增加挠性结构的阻尼, 使其振动能够很快衰减. 最后, 将本文提出的方法应用于三轴稳定挠性卫星的姿态机动控制, 仿真结果表明: 在推力器的控制受限条件下, 完成姿态机动的同时, 有效地抑制挠性附件的振动.     

挠性结构中智能材料配置和振动控制的一体化最优设计

针对挠性结构振动控制中智能材料的特性，综合考虑压电敏感器／致动器的位置、尺寸、质量及其对挠性结构刚度特性的影响和控制律，建立系统状态空间模型，提出一种新的优化配置的性能指标和最优设计方法。运用李雅普诺夫稳定性定理证明了闭环系统的全局渐近稳定性，性能指标的最小值可取为相应矩阵的迹而不依赖于系统的初始状态。采用遗传算法寻优，仿真表明该设计方法能够快速的抑制系统的振动。     

阵列式压电模态传感器的实验研究

通过一组阵列式压电薄膜,设计未知边界条件下振动梁的模态传感器。在梁表面均匀布置一组具有相同形状的矩形聚偏氟乙烯(PVDF)薄膜,通过测量PVDF输出与激励力之间的频率响应函数,利用伪逆方法设计这组PVDF的加权系数,从而实现对结构模态坐标的测量。实验研究表明:该方法设计的模态传感器具有良好的滤波效果,非目标阶模态坐标峰值与目标阶相比,下降了12 dB以上,并且不需要预先知道结构的边界条件或者模态信息。进一步讨论了当振动梁的边界条件发生微小扰动时所设计模态传感器的鲁棒性。     

挠性航天器鲁棒后步滑模姿态跟踪及主动振动控制

针对挠性航天器姿态跟踪及振动抑制问题,提出一种双回路鲁棒控制方法.首先,采用滑模控制与后步法设,计了姿态跟踪控制器,基于Lyapunov方法分析系统的渐近稳定性,并从实际应用角度考虑了反作用飞轮的动态特性;其次,为抑制挠性结构的振动,采用压电智能材料作为敏感器和作动器,设计了应变速率反馈补偿器.仿真结果表明,所提方法在保证完成姿态跟踪任务的同时,能有效抑制挠性附件的振动.     

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.