轴向运动功能梯度粘弹性梁横向振动的稳定性分析

基于Euler梁理论研究了轴向运动功能梯度粘弹性梁横向振动的稳定性问题.基于问题的数学模型和控制方程,利用微分求积法求得了轴向匀速运动功能梯度粘弹性梁亚临界区域内横向振动的复频率,分析其随着轴向运动速度、材料梯度指数等参数的变化情况,探讨上述参数对超临界区域失稳形式的影响.然后应用多尺度法结合边界条件分析了轴向速度带有周期扰动成分的变速运动功能梯度粘弹性梁的失稳问题,重点讨论了当速度扰动频率为固有频率二倍或者为两固有频率之和/差时所发生的次谐波共振及组合共振所导致的失稳.数值算例表明,随着梯度指数的增大,匀速运动功能梯度粘弹性梁的临界发散速度、耦合速度以及变速运动功能梯度粘弹性梁的稳定区域减小,且粘弹性系数的影响逐渐变弱,同等条件下,轴向运动功能梯度粘弹性固支梁比简支梁更为稳定.     

轴向运动复合材料薄壁梁的横向振动分析

研究可轴向运动复合材料薄壁梁的动力学特性.基于VAM（变分渐进法）复合材料薄壁梁理论,采用Euler Bernoulli梁模型并根据Hamilton原理来建立复合材料薄壁梁的动力学方程.应用假设模态法对薄壁梁进行自由振动分析,通过比较研究验证了该建模方法的正确性,并分析了几何参数和物理参数对薄壁梁固有频率的影响.推导了轴向运动复合材料薄壁梁的横向振动方程,借助四阶Runge-Kutta法进行数值计算,研究了不同纤维铺层方式和不同匀速度大小对可轴向运动复合材料薄壁梁横向振动末端位移响应的影响.     

运动车辆梁模型的横向振动频率及模态

将运动车辆的车身模型化为Eder-Bernoulli梁,车轮模型化为梁两端边界处的弹性不等的弹簧,形成半车模型.通过复模态分析法研究平滑路面上移动车体的横向振动特性,给出车体横向振动的频率方程以及模态的表达式,通过数值方法求解系统固有频率以及模态函数.并通过数值算例研究车辆运行速度、车体刚度、轮胎弹性系数对车体横向振动...     

用微分求积法分析轴向移动粘弹性梁的非平面非线性振动

用微分求积法分析了轴向移动粘弹性梁非平面非线性振动的动力学行为.轴向移动粘弹性梁非平面非线性振动的数学模型是一非常复杂的非线性偏微分方程组.首先用微分求积法对其控制方程组进行空间离散,得到非线性常微分方程组,然后求解常微分方程组得到数值结果.在数值结果的基础上结合非线性动力学理论,利用分叉图、时间历程图、相图对其非线性动力学特性进行了分析.     

热环境中超临界黏弹性输流管道自由振动分析

基于Euler-Bernoulli梁模型,本文研究了热环境中输流管道在超临界范围内流固耦合自由振动特性.考虑温度增量以及初始轴向拉力作用,在两端简支边界条件下,利用广义Hamilton原理建立输流管道横向振动偏微分-积分控制方程.通过解析方法得到输流管道非平凡静平衡位形及临界流速精确表达式,与微分求积单元法(DQEM)数值结果吻合较好.基于复模态法,结合伽辽金(Galerkin)法离散系统偏微分-积分控制方程,得到热环境下超临界输流管道的模态函数和固有频率.结果表明,温度增量越大,临界流速越小,此时的管道越容易屈曲,但相同流速下超临界管道固有频率越大;初始拉力越大,临界流速越大,相同流速下超临界固有频率越小.该研究可以为热环境中超临界状态下的管道系统振动设计提供理论指导.     

用微分求积法分析轴向加速粘弹性梁的非线性动力学行为

用微分求积数值方法求解了轴向加速粘弹性梁的横向振动控制方程,其方程是一复杂的非线性偏微分方程.并在数值结果的基础上利用分叉图分析了轴向定常加速度以及轴向加速度变化幅值对轴向加速粘弹性梁的非线性动力学行为的影响.     

轴向运动粘弹性夹层梁的横向振动

研究了小扰度下轴向匀速运动粘弹性夹层梁的振动模态和固有频率.基于Kelvin粘弹性本构方程,建立了轴向运动粘弹性夹层梁横向振动控制方程.分别采用Galerkin截断和复模态分析方法,研究两端简支的粘弹性夹层梁的固有频率和模态函数,讨论了轴向运动速度、夹心层与约束层厚度比、初始轴力等参数对夹层梁固有频率、临界速度及稳定性的影响.     

基于无网格法考虑热效应及剪切效应FGM梁的动力学建模与仿真

将无网格点插值法和无网格径向基点插值法用于温度场中旋转柔性功能梯度材料梁的动力学分析.在考虑剪切效应的基础上,在梁本构关系中计及热应变,采用4种离散方法描述梁的变形场,运用第二类Lagrange方程,推导出大范围运动功能梯度材料梁的一次近似刚柔耦合动力学方程,研究不同温度变化下梁的动力学响应.通过动力学仿真得出以下结论：温度场对沿横向对称分布的功能梯度材料梁的横向变形影响较小,对纵向变形的影响较大,且在计算温度荷载作用下的梁末端变形时不应忽略轴向变形影响.     

两端带有弹簧支撑的轴向运动梁振动分析

研究外部激励下,两端带有弹簧支撑的轴向运动梁的横向振动.运用广义哈密顿原理,推导得到运动梁的控制方程.通过数值方法研究系统的固有频率和模态,解析分析得到轴向运动梁的临界速度表达式并考虑弹簧刚度对临界速度的影响.发现临界速度随弹簧刚度增大而收敛于某一值.运用Galerkin截断法数值研究两端带有弹簧支撑的轴向运动梁的稳态幅频响应曲线,并通过计算力传递率来研究系统的隔振效果.发现力传递率在高频外激励下存在多个峰值.     

轴向运动薄板非线性振动及其稳定性研究

应用增量谐波平衡法(IHB法)研究轴向运动薄板横向非线性振动特性及其稳定性.通过Hamilton原理推导出了非惯性参考系下四边简支轴向运动薄板的横向振动微分方程,然后利用Galerkin方法离散运动方程.对离散后的非线性方程组应用IHB法进行非线性振动分析,研究了在固有频率之比ω20/ω10接近于3:1情况下,外激励频率ω在ω10附近的具有内部共振的基谐波响应.最后用多元Floquet理论分析了系统周期解的稳定性,其中采用Hsu方法来计算转移矩阵.通过对具体例子的数值计算,分别得到了自由振动和不同外激励下的频幅相应曲线,通过对比运动梁模型和运动薄板模型的计算结果,分析了各种模型的适用范围.     

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.