悬浮隧道基于弹性边界的力学模型与移动荷载响应分析

悬浮隧道是一种创新型的水中交通结构,这种悬浮于水中的结构在考虑复杂边界条件下的力学建模及交通荷载引起的结构响应值得深入研究.本文将跨度范围内由多段锚索支撑的悬浮隧道视为弹性支撑梁,同时将两端的复杂边界条件考虑为具有不同约束刚度的竖向和转动弹性支撑,流体荷载由Morison方程考虑,建立了悬浮隧道在任意荷载作用下的动力学模型及考虑自振特性的特征方程.研究了跨内支撑刚度与边界约束参数多种组合条件下的频率、模态分布特征,得到了相应的敏感区间.同时,以某型号高铁列车为背景并将其考虑为一列移动集中力,研究了悬浮隧道结构关键位置的荷载响应与弹性支撑刚度之间的关系,结果表明跨内支撑刚度、边界约束刚度均对竖向位移存在显著影响,整体上约束刚度越大,相应的位移越小.     

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.     

分析两端扭转弹簧约束下简支输流管道的动力特性

研究了两端受扭转弹簧约束的简支输流管道的固有频率特性和静态失稳临界流速.根据梁模型横向弯曲振动模态函数,由端部支承和约束边界条件得到了其模态函数的一般表达式.根据动力方程的特征方程,具体分析了约束弹性刚度、流体压强、流速和管截面轴向力等参数对管道固有频率特性和静态失稳临界流速的影响.数值分析表明,约束弹性刚度的增大使管道的固有频率和失稳临界流速明显提高;流体流速、压强和管截面受到的轴向压力的增加使管道的固有频率和失稳临界流速降低.当管道的固有频率和失稳临界流速较低时,可以通过增加端部约束的方法来提高.     

多跨下承式拱桥面内全局动力学理论与自由振动研究

为弥补高维工程结构有限元分析对结构参数优化设计等的局限,本文基于欧拉伯努利梁理论与传递矩阵法,研究大跨度拱桥面内自由振动问题.首先,基于多跨拱桥的刚度分析,建立系统的全局动力学模型.其次,基于传递矩阵法建立系统的全局动力学理论,最后,以一座四跨下承式拱桥的平面力学模型,求解其面内自由振动时的固有频率与振型,并将所得结果与用同样参数建模的有限元分析结果对比,证明本文所建理论对求解该类问题的有效性与精确性.此外,通过整桥各跨矢跨比、吊杆截面面积、拱肋惯性矩等的多组参数组合分析了该系统面内自振频率的分布规律.结果表明：随着拱桥矢高增大,系统固有频率减小,因拱桥质量的快速增加,对整桥面内刚度影响显著;增大吊杆截面面积可在一定程度内增大拱桥的面内刚度,导致系统频率在一定范围内增大,且观察到Veering现象.     

变截面铁木辛柯梁振动特性快速计算方法

提出了一种快速计算变截面铁木辛柯梁横向振动特性的方法.基于铁木辛柯梁理论建立的变截面梁的横向振动方程,其梁的截面参数如有效剪切面积、密度、弯曲刚度、转动惯量等沿梁轴线连续或非连续变化；首先将变截面梁等效为多段均匀阶梯梁；然后基于相邻两段连接处的位移(位移、转角)和力(弯矩、剪力)连续条件,建立相邻两段模态函数间相互关系,并递推出首段段与末段模态函数相互关系,利用边界条件得到相应特征方程,使用Newton-Raphson方法计算其固有频率；最后针对梁常见边界条件,得到计算变截面铁木辛柯梁横向振动固有频率特征     

恒载效应对拱结构自振频率的影响分析

提出用样条有限点法分析拱的自振频率,采用3次B样条函数的线性组合作为位移振型函数,以曲杆变形理论为基础,根据Hamilton原理建立了考虑恒载效应影响时拱的振动频率方程.计算分析了恒载效应对拱结构自振频率的影响.结果表明恒载效应会使拱结构自振频率减小;影响大小与结构自身刚度有关;拱结构截面刚度一定时,拱矢跨比、径厚比越大,恒载效应对自振频率的影响越大.     

受轴向激励弹性支承梁的稳定性分析

对于广泛存在的弹性支撑梁,首次呈现支承弹簧刚度对轴向激励下梁横向振动稳定性的影响.应用Hamilton原理,建立了两端由线性弹簧支撑的受轴向激励梁的动力学控制方程.通过解析方法计算了受轴向压力梁的固有频率,得到了支撑弹簧刚度与系统固有频率和临界轴力的关系.Galerkin截断后,通过多尺度法和Runge-Kutta法,计算得到了梁参激振动稳态响应的半解析与数值解.讨论了激励幅值、支撑弹簧刚度、平均轴力对系统非线性响应幅值及软硬特性的影响.利用Routh-Hurwitz稳定性判据,求得系统的参激稳定边界,着重讨论了支撑弹簧刚度、阻尼系数的影响.研究发现,边界支撑弹簧的刚度可以显著改变受轴向激励梁的参激稳定边界.因此,研究结果将为广泛存在受到轴向激励结构的设计提供指导.     

开孔变截面微悬臂梁传感器的等效刚度和固有频率

研究新型开孔变截面微悬臂梁传感器的等效法向刚度及其对固有频率的影响.首先,考虑微梁纵截面孔洞结构引起的弯扭耦合效应,利用二次积分法获得在自由端集中载荷作用下悬臂梁的挠度,基于弹性材料的Hooke定律建立了微梁等效法向刚度分析的解析模型.然后,采用Rayleigh法获得了微梁的固有频率.最后,通过比对实验结果和有限元结果对解析模型进行了验证.研究表明:解析模型对于开孔变截面微梁刚度和频率的预测和标定具有较好的精度;微梁的等效刚度和固有频率与跨宽比负相关,却与内外宽度比正相关.有关结论可为新型变截面微纳机械传感器的设计提供理论依据和参考.     

弹性支撑浅拱的非线性动力行为分析

本文研究了两端转角均为转动弹簧支撑的铰支浅拱在外激励作用下的非线性动力学行为.基于弹性支撑浅拱的基本动力控制方程,采用多尺度法对内共振进行了摄动分析,并得到了极坐标形式的平均方程.弹性约束的刚度通过特征方程影响结构的自振频率和模态,且与平均方程的相关系数一一对应,文中还以最低两阶模态之间1:1内共振为对象进行了数值分析.结果显示系统存在模态交叉与转向两种内共振形式,另一方面结构参数处于某一范围之内时外激励激发的模态作用可导致出现准周期运动和混沌运动.     

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...     

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.