Modelagem do comportamento dinâmico e análise de fadiga de pontes rodoviárias mistas (aço-concreto).

Considerando-se os diversos carregamentos que solicitam a estrutura de uma ponte rodoviária, ao longo de sua vida útil, alguns possuem um comportamento essencialmente dinâmico, ou seja, variam com o tempo, diferentemente do que é considerado na prática corrente de projeto desse tipo de obra de arte. Em geral, os projetistas desse tipo de estrutura têm tratado carregamentos como o de vento, tráfego de veículos e de pedestres como ações de natureza estática, ignorando seu perfil cíclico. Tal consideração, em diversas situações de projeto, tende a minorar os efeitos das ações dinâmicas sobre o sistema estrutural. Além disso, estruturas submetidas a solicitações cíclicas, sob uma carga inferior à caga máxima suportada pelo material, estão sujeitas ao fenômeno da fadiga. A consideração adequada de todos estes aspectos mostra-se fundamentalmente importante para correta avaliação dos níveis de esforços solicitantes do sistema estrutural e, bem como, para a identificação de fenômenos importantes como o da fadiga que pode vir a provocar, por exemplo, a ruptura de componentes estruturais sem aviso prévio ou motivo aparente. Para tal, nesta dissertação as técnicas para a contagem de ciclos de tensão e a aplicação das regras de dano acumulado foram analisadas através de curvas do tipo S-N, associadas a diversas normas de projeto. A ponte rodoviária mista (aço-concreto) investigada neste estudo é constituída por seis vigas de aço longitudinais com enrijecedores transversais, oito transversinas e por um tabuleiro de concreto armado. O modelo numérico-computacional, desenvolvido para a análise dinâmica da ponte, foi elaborado com base em técnicas usuais de discretização através do método dos elementos finitos. As mesas e almas das vigas, assim como os enrijecedores , foram modelados por elementos de casca e laje de concreto armado, por elementos sólidos. O carregamento dinâmico avaliado no presente estudo diz respeito ao tráfego de veículos, cuja representação se dá a partir de sistemas "massa-mola-amortecedor". Os comboios formados são adotados como sendo semi-infinitos, deslocando-se com velocidade constante sobre a ponte. As conclusões da presente investigação versam acerca da vida útil de serviço dos elementos estruturais de pontes mistas (aço-concreto).

Estudo do comportamento estrutural e análise de conforto humano de edifícios de concreto armado.

Atualmente, os projetos de edifícios altos necessitam cada vez mais de sistemas estruturais simples, que agilizem sua montagem, reduzindo os custos e promovendo maior flexibilidade de utilização para os espaços construídos. Com essa finalidade, estruturas com poucas vigas vêm sendo muito utilizadas. Entretanto, o sistema estrutural com poucas vigas pode ocasionar dois tipos de problemas, relacionados entre si, a saber: diminuição do sistema de contraventamento da edificação e vibrações excessivas. Portanto, é fundamental, nesses casos, a verificação da estabilidade global da estrutura, utilizando índices de sensibilidade além de outros parâmetros de projeto, como também, o desenvolvimento de um estudo minucioso acerca do conforto humano da edificação. Assim sendo, neste trabalho de pesquisa foram investigados quatro modelos estruturais de edifícios altos de concreto armado, com base no estudo da variação entre o número de pavimentos e a quantidade de vigas existentes em cada modelo, objetivando-se verificar quais os efeitos que tais variações podem vir a gerar sobre a estabilidade global e, bem como, sobre o conforto humano dos sistemas estruturais investigados. A modelagem numérica dos edifícios em estudo foi realizada através do emprego do programa ANSYS e, para tal, foram utilizadas técnicas básicas de discretização, por meio do método dos elementos finitos. As conclusões alcançadas ao longo da investigação versam acerca do estudo da resposta estrutural estática e dinâmica dos edifícios, no que diz respeito as variações dos valores dos parâmetros de instabilidade, dos valores dos deslocamentos e esforços, e, bem como, dos níveis de conforto humano de cada modelo estrutural analisado.

新疆阜康地区森林资源与环境的空间分析

研究了新疆阜康地区森林植被资源与环境的特征和其30年来的变化，利用Arcinfo强大的空间分析功能，对资源、DEM模型、景观指数、环境价值和新疆降水量的地统计学规律进行较全面的分析。本文分为五个部分： 1、新疆阜康地区森林资源与环境空间数据库的建立森林资源与环境空间数据库的建立是它们空问分析的基础。利用多期的遥感图象和该区的地形图，建立森林分类图形和属性库（包括森林和环境自变量集）一体化的GIS空间数据库。为了提高TM遥感图象的分类精度，利用ERDAS图象处理软件，对它进行包括主成分、降噪、去条带和自然色彩变换等增强处理，采用监督分类和人工判读相结合的方法进行分类，采用R2V、ERDAS、Arcview、Arcinfo等软件的集成，使得小班面层与某些线层的无缝联接。成功地形成一套适于西部GIS的森林资源与环境空间数据库的技术路径。此外，对新疆阜康北部地区森林资源动态进行初步分析。 2、新疆阜康地区数字高程模型(DEM)及其粗差检测分析为了提高生态建模的精度，模拟和提取该区的地面特征至关重要。在已建立的森林资源与环境空间数据库的支持下，利用Arcinfo和ERDAS，建立了新疆阜康地区的1：5万数字高程模型(DEM)。通过提取地形的海拔、坡度、坡向特征因子，分析森林植被的垂直分布。通过对DEM的粗差检测分析，分析阜康地区的数字高程模型精度。 3、新疆阜康地区景观格局变化分析在1977年、1987年、1999年森林资源与环境空间数据库的支持下，利用景观分析软件编制三个时段的新疆阜康地区植被景观类型图，并分析了近30年来新疆阜康地区景观动态与景观格局变化。结果表明：①在此期间整个研究区的斑块数减少，斑块平均面积扩大，景观中面积在不同景观要素类型之间的分配更加不均衡，景观面积向少数几种类型聚集。说明了在这期间阜康地区的景观类型有向单一化方向发展的趋势;②农耕地分布呈破碎化的趋势，斑块平均面积变小，斑块间离散程度也更高：这些变化说明人为的经济活动在阜康地区的加剧，③天然林面积减少较多，水域的面积却呈现上升的趋势，冰川及永久积雪的面积呈下降趋势， 4、新疆阜康地区森林生态效益的初步分析从广义森林生态效益定义出发，针对12种森林生态效益因变量不完全独立、且各自的自变量集不完全相同，引入具有多对多特征且整体上相容的似乎不相关广义线性模型。通过构造12种森林生态效益的“有效面积系数”和“市场逼近系数”，在森林资源与环境空间数据库的支持下，对新疆阜康地区两期的森林生态效益进行科学的计量。结果表明：新疆阜康地区的森林生态效益货币量1987年是90673.8万元，1999年是84134.4万元，总体上呈下降趋势。 5、利用新疆气象站资料研究年降雨量的空间分布规律利用ArcGIS地统计学模块，在2000年新疆气候信息空间数据库和新疆DEM模型的支持下，做出了新疆地区的年降水量空间分布图。根据新疆气候资料建立趋势而分析模型、模拟了新疆降水量空间分布的趋势值。采用3种算法（距离权重法、普通Kriging法、协同Kriging方法）计算并比较分析了研究区多年的平均降水量的时空变化。利用模拟产生的精度最优的栅格降水空间数据库，建立的多年平均降水资源信息系统，可快速计算研究区内任一地域单元中降水的总量及其空间变化，可以生成高精度的气候要素空间分布图。

Prediction of tread block forces for a free-rolling tyre in contact with a rough road

This paper describes a new approach to model the forces on a tread block for a free-rolling tyre in contact with a rough road. A theoretical analysis based on realistic tread mechanical properties and road roughness is presented, indicating partial contact between a tread block and a rough road. Hence an asperity-scale indentation model is developed using a semi-empirical formulation, taking into account both the rubber viscoelasticity and the tread block geometry. The model aims to capture the essential details of the contact at the simplest level, to make it suitable as part of a time-domain dynamic analysis of the coupled tyre-road system. The indentation model is found to have a good correlation with the finite element (FE) predictions and is validated against experimental results using a rolling contact rig. When coupled to a deformed tyre belt profile, the indentation model predicts normal and tangential force histories inside the tyre contact patch that show good agreement with FE predictions. © 2012 Elsevier B.V..

并行计算模型参数动态分析软件包设计

并行计算模型的发展引入越来越多的模型参数。对并行计算模型参数动态采集分析软件包DEMPAT的整体框架进行研究,实现基于硬件性能计数器的存储层次参数采集模块。实验表明,该模块能够准确快速地获取存储层次参数且具有较好的可移植性。

黄土高原典型草原区草地土壤种子库的动态分析

采用野外调查取样和室内试验相结合的方法,研究了黄土高原典型草原区草地土壤种子库的物种组成、密度、时空格局和物种多样性等特征。结果表明,(1)土壤种子库中共统计到37个物种,隶属于16科,其中禾本科、菊科、唇形科、豆科和毛茛科的植物占优势。(2)从返青期到枯黄期,种子库中豆科、禾本科、堇菜科所占比例呈下降趋势,唇形科和菊科所占比例明显提高,种子库的密度也显著提高。(3)种子库中种子数量在垂直分布上呈现出由表层土壤向深层逐层减少的变化规律;在水平分布上的变化规律为:封禁>放牧;阴坡>阳坡;下坡>中坡>上坡。(4)封禁地土壤种子库中的Margalef丰富度和Shannon—Wienner指数都高于放牧地,Pielou均匀性指数低于放牧地。从返青期到枯黄期,封禁地和放牧地土壤种子库的Margalef丰富度、Shannon—Wienner指数、Pielou均匀性指数都呈下降趋势。

GAS-PHASE SYNTHESIS OF DERIVATIVE OF C-60-C60S+

Gas phase ion-molecular reactions of C-60 with the ion system of CS2 have been studied in the ion source of mass spectrometer. It was found for the first time that the sulfuric derivative of C-60-C60S+ was the main ions in the ion source, they did not react with C-60 to form adduct ions due to their highly saturated structures. According to the dynamic analysis, the product ion came from the reaction of C-60 with the fragment ion S+. The adduct ion may have the structure of epsulfide that is advantageous in energy.

Winter counter-wind currents off the southeastern China coast: A review

This review covers the discovery and studies of the year-round northeastward currents off the southeastern China coast, paying special attention to its upwind characteristic in winter, mainly focusing on work by Chinese oceanographers. This current system is a prominent and unique phenomenon in the shelf circulation of the world ocean. The general features of the current system are summarized. The evidence for the existence and the variation of the three parts of the currents-the South China Sea Warm Current, the Taiwan Strait Warm Current and the Taiwan Warm Current-are separately elucidated. The formation mechanisms of the current as a whole are explained using dynamic analysis and numerical simulation results. Some suggestions for further studies are also made.

有限元结构动力分析的广义特征值的神经计算

广义特征值问题是结构动力分析计算的关键之一.应用Reyle igh极小值原理,将神经网络的能量函数的极小点对应于广义特征值问题的最小特征值所对应的特征向量,在神经网络朝着能量函数极小点运动的同时得到了最小特征值所对应的特征向量的精确解答.从特征值的变分特性出发,给出了基于罚函数法的其他特征值的神经网络求解方案,从而在理论上给出了广义特征值问题的所有特征值的神经网络求解方法.仿真计算表明,该方法正确、有效可行.

可重构单体机器人动力学分析与控制

给出了可重构机器人在移动过程中的动力学模型,并提出了相应两种控制方法,即构形调整法和状态调整法。通过仿真试验得到,构形调整法能够在不影响状态的情况下,同时满足机器人运动稳定性和越障性的要求,增强了机器人运动的鲁棒性。

一种6自由度柔索并联机器人的动力学研究

采用串联约束 /并联驱动的原理 ,通过加入约束机构 ,设计一种新型柔索驱动并联机器人。然而由于约束机构的引入 ,机器人的动力学分析变得更为复杂。在对机器人进行运动学分析的基础上 ,利用牛顿 欧拉法建立机器人动力学方程。仿真结果证明了该方法的有效性

带式输送机停机动态过程的计算机仿真

研究了带式输送机停机过程的动态设计 ,通过分析提出了输送机停机过程的力学模型为两种 :第 1模型与启动过程的力学模型相同 ,第 2模型为具有固定端的振动模型·分析了制动力的传动机理 ;在综合各种停机方式的基础上给出了停机过程的分类 ,提出了控制速度停机、自由停机和制动停机的计算方式及其计算方法 ;开发了带式输送机动态分析软件BCD .2 0的停机计算部分 ;应用软件对停机过程进行仿真研究 ,对停机过程进行了分析 ;给出了停机过程的动态设计方法和拉紧装置行程的计算式 ;得出了不同的停机方式结束后输送带的张力分布是不同的结果·所提出的方法可用于大型带式输送机停机过程的合理设计 ,避免事故的发生

液压反铲挖掘机工作装置有限元动态分析

针对挖掘机工作装置的结构特点 ,建立了其系统 3维有限元模型 ,通过分析得出了系统的固有频率和振型 ,以及结构动态响应各时刻的变形和应力分布规律。比较了工作装置在开挖难度较小和较大 2种情况下 ,挖掘阻力对系统动力响应的影响

机器人手臂弹性动力学分析的高效算法

本文提出一种用于机器人手臂弹性动力学分析的新方法,该方法采用了动力学方程缩减技术,使计算时间大为减少。在此基础上针对关节型机器人结构特点,提出了考虑手臂关节之间的弹性连接的数学模型,使计算精度得到提高,最后给出了一个实例。

层状反倾向结构岩质边坡变形机理及稳定性研究

Toppling is a major failure model in anti-dip layered rock slopes. Because of the limited by testing means and experimental apparatus, present research on the deformation mechanism and stability analysis are mainly focus on the 2-Dimensional deformation, and the research really based on 3-Dimension is still limited. Therefore, based on the present research station, the article rely on the important hydroelectric project of typical anti-dip layered rock slopes -- The left bank slope of Long-tan hydropower-station in Guang Xi, China, and focused on the influencing factors, deformation mechanism and stability analysis of anti-dip layered rock slopes, three problems as follows are researched in this paper. (1) Deformation influencing factor analysis on ant-dip layered rock slopes Three influencing factors are included: geological factor, engineering factor and environmental factor. It is concluded that the toppling deformation of anti-dip layered rock slopes are more sensitive to geological and engineering factors, but less sensitive to environmental factor. In addition, the sensitivity of various factors to the rock toppling deformation is also arranged sequentially as follows: construction, gravitation, rainfall (underground water) and rock structure intensity, etc. (2) 3D deformation study on the anti-dip layered toppling rock slopes Used 3D Distinct Element Method (3DEC) analyzed the 3D deformation characteristic of anti-dip layered rock slops. It can be seen that the toppling characteristics are obvious when the inter-angle between slope direction and layer striking direction is under 20o, when the inter-angle is over 20o and equal or less than 40o，the toppling deformation characteristics decrease sharply with increase of inter-angle, when the inter-angle is over 40o , the slope deformation is not controlled by joints but influenced by other failure mode. Therefore, in order to quantify the toppling characteristics, a differential value of displacement vector angle between layered rock slope and block rock slope is proposed as a key index to distinguish failure model for anti-dip layered rock slopes, and it was applied to study the toppling of the rock slopes at Guangxi Long-tan hydropower station, China. The results indicated that the index was effective and instructive for analyzing the anti-dip layered rock slopes. (3) Stability analysis methods Because of the imperfection of some present slope analysis methods, based on slope failure mode and those three influencing factors, “slope stability entropy” method is defined in this paper, which makes good use of the sensitivity of relational matrix to influencing factors on slope stability and the qualification characteristics for information entropy to the irregularity of slope deformation. By this method, not only the randomness of geologic body on the base of dynamic analysis of slope failure mode is fully concerned, but also it makes the analysis time-saving and simple. Finally, the research findings were used to the engineering example successfully, and rational conclusion has been obtained.