基于MSC Adams的3-UPS并联机床动态特性仿真

以3-UPS并联机床为研究对象,应用虚拟样机技术建立机构参数化仿真模型,给出并联机床虚拟样机联合仿真设计方案. 通过对样机模型动力学分析,确定影响整机动态性能的关键部件,采用MSC Adams完成这些部件的弹性体建模. 通过动态仿真分析给出弹性并联机构的动态响应、固有频率等动态特性参数,为并联机床整机的优化设计奠定基础.     

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.     

飞行器空气舵系统的高效刚度分配优化方法研究

空气舵系统是飞行器典型操纵部件,其伺服作动器、连杆、摇臂、舵轴和舵面等子结构对空气舵系统的整体刚度有着不同程度的贡献,合理分配各子结构的刚度,可使空气舵系统的整体刚度得到进一步优化.本文提出了一种基于多体系统传递矩阵法和遗传算法相结合的空气舵系统高效刚度分配优化方法.首先,基于多体系统传递矩阵法建立了以结构尺寸和材料属性为参数的高效结构动力学计算模型,仿真结果表明,基于该计算模型所预测的空气舵第一阶俯仰模态固有频率与商业软件计算结果的误差仅为1.06%.其次,基于本文建立的高效结构动力学计算模型对各子结构刚度对空气舵系统动力学特性的贡献进行了灵敏度分析,给出了各部件对系统固有频率贡献的规律.最后,采取将遗传算法和多体系统传递矩阵法相结合的思路,以所建立的空气舵高效结构动力学模型为适应度函数,各子部件尺寸作为待优化变量,空气舵系统整体质量为约束条件,对空气舵系统各个子结构的刚度分配进行了优化.优化结果表明,在保持空气舵系统整体重量不变的条件下,可将空气舵系统第一阶俯仰模态固有频率提高约15.8%.     

弹性支撑梁在移动荷载作用下的响应分析

考虑弹性支撑刚度对弹性支撑梁固有频率及模态的影响,比较前二阶频率受弹性支撑刚度影响的规律及大小.选取二阶模态,利用模态叠加原理,研究弹性支撑梁在移动荷载和移动车辆作用下的动力响应.研究中,一阶模态考虑为简支梁一阶模态与弹性支撑梁的刚体平动相叠加,二阶模态考虑为简支梁二阶模态与弹性支撑梁的刚体转动相叠加.研究结果表明:考...     

弹性支撑下风电机组传动系统结构动力分析

考虑水平轴风力发电机组齿轮箱弹性支撑的柔性连接特性,基于集中质量思想和拉格朗日方法,建立风力发电机传动系统多体动力学模型,研究了齿轮箱弹性支撑对传动系统结构动力学特性的影响.利用动力学模型和模态分析方法,得到了由弹性支撑耦合到系统后的模态频率,并获取了在该模态激励下的模态动能分布.采用变参数方法进行传动系统模态对齿轮箱弹性支撑刚度变化的敏感性分析,利用模态叠加法进行齿轮箱体的动响应分析.数值求解结果和分析表明,考虑齿轮箱弹性支撑的传动系统某阶固有频率即为弹性支撑下齿轮箱体振动主模态;弹性支撑线刚度对传动系统低频率固有模态存在一定影响;齿轮箱体振动分析时应考虑1阶和2阶的低频模态较为合理.本研究工作对传动链系统方案可靠性设计和抑制传动链振动的加阻控制提供了一定理论基础.     

基于子结构的风力发电高塔系统的动力特性分析

采用子结构模态综合(Component Mode Synthesis,CMS)法和频响综合(Frequency response function-Based Substructure,FBS)法分析大型高耸装配结构风力发电高塔系统动力特性.通过子结构模态或频率响应函数(Frequency Response Function,FRF)信息综合成整体的模态或FRF信息,在保证整体分析精度的条件下提高计算效率,同时解决风电塔系统模态和FRF信息不易获得的问题.建立风电塔系统各个子结构的有限元模型和整体模型,分别使用MSC Nastran和LMS Virtual.Lab对各个子结构进行模态综合和频响综合分析,并将综合的结果与整体建模计算的结果进行对比,验证采用子结构CMS法和FBS法分析风力发电高塔系统的可行性和正确性.     

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.     

石墨烯树脂复合材料板1∶3内共振非线性动力学分析

石墨烯是一种新型的碳纳米材料,将石墨烯添加到不同基体中可达到增强基体力学性能,并优化结构的效果.本文主要研究了在悬臂边界条件下石墨烯复合材料板的非线性动力学行为,通过Halpin-Tsai模型计算了复合材料板的等效杨氏模量,运用一阶剪切板理论和Hamilton原理得到复合材料板的非线性动力学方程.通过模态缩聚,得到复合材料板横向位移的运动控制方程.应用Rayleigh-Ritz法计算出复合材料板的固有频率,发现第二阶与第四阶固有频率间存在1:3的关系.利用多尺度法研究了复合材料板在1:3内共振情况下的非线性振动响应,通过数值模拟分析了外激励对板结构非线性振动响应的影响.结果表明:横向外激励对复合材料板的非线性动力学行为影响较大,对实际工程具有一定的指导意义.     

大范围运动矩形板动力刚化分析

针对大范围运动下弹性矩形板，采用有限元技术和Lagrange方程建立了系统刚柔耦合一次近似动力学方程组．不同于传统动力学建模方法，本文采用两个弧长变量和一个笛卡尔坐标变量来描述板的变形，利用有限元方法离散，在动力学方程中得到了动力刚度项．数值仿真表明，在大范围运动下，传统的动力学模型不能正确的预示系统动力学行为；而本文动力学模型能够较好的预测系统的动力学行为，且比采用假设模态离散板变形的方法更为精确．     

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.