泵送混凝土开裂原因及防治

本文详细论述了引起泵送混凝土开裂的设计上配筋率及配筋方式,材性上的胶结材、集料、外加剂及混凝土配合比,施工中的浇注、养护、管理等原因,针对泵送混凝土开裂的沉降收缩、塑性收缩、干燥收缩及温度收缩提出根据结构形式进行防裂配筋设计,组成材料及配合比,施工中的布料、振捣、养护温湿度、收光及严禁二次加水等技术及管理要求以及一旦发现早期裂纹的补救办法等可行的防治措施,确保泵送混凝土不产生有害裂缝.     

整合统计的结构损伤动力诊断三步法

结构损伤诊断是结构健康监测的核心内容之一。在部分前人工作的基础上，针对土木工程结构损伤识别的妻求(单元级诊断)及实际工程中存在的测试噪声干扰问题，结合统计方法发展了一套由损伤识别、损伤定位的单元筛选和搜索、单元损伤反演组成的三阶段结构损伤诊断流程。利用钢筋混凝土三跨连续梁的有限元模型，在存在较大测试误差(模态随机噪声)的条件下，对单／多损伤工况进行了险证诊断，结果表明该流程强健有效，具有良好工程应用前景。     

A spectral‐element method for modelling cavitation in transient fluid–structure interaction

In an underwater‐shock environment, cavitation (boiling) occurs as a result of reflection of the shock wave from the free surface and/or wetted structure causing the pressure in the water to fall below its vapour pressure. If the explosion is sufficiently distant from the structure, the motion of the fluid surrounding the structure may be assumed small, which allows linearization of the governing fluid equations. In 1984, Felippa and DeRuntz developed the cavitating acoustic finite‐element (CAFE) method for modelling this phenomenon. While their approach is robust, it is too expensive for realistic 3D simulations. In the work reported here, the efficiency and flexibility of the CAFE approach has been substantially improved by: (i) separating the total field into equilibrium, incident, and scattered components, (ii) replacing the bilinear CAFE basis functions with high‐order Legendre‐polynomial basis functions, which produces a cavitating acoustic spectral element (CASE) formulation, (iii) employing a simple, non‐conformal coupling method for the structure and fluid finite‐element models, and (iv) introducing structure–fluid time‐step subcycling. Field separation provides flexibility, as it admits non‐acoustic incident fields that propagate without numerical dispersion. The use of CASE affords a significant reduction in the number of fluid degrees of freedom required to reach a given level of accuracy. The combined use of subcycling and non‐conformal coupling affords order‐of‐magnitude savings in computational effort. These benefits are illustrated with 1D and 3D canonical underwatershock problems. Copyright © 2004 John Wiley & Sons, Ltd.     

对一次高频保护跳闸事故的分析

在一次系统故障过程中。输电线路的两套高频保护装置CSL-101B型和LFP-901B型动作行为不一致。本文就此展开分析，以达到正确理解两种保护动作行为的目的。并对加强高频保护的现场管理提出意见。     

Visibility threshold in sharpness for people with different regional backgrounds

Abstract— The influence of regional background on the visibility of sharpness differences has been investigated by blurring various still images to different extents. The assessment of sharpness has been performed both in China by Chinese people and in the Netherlands by European people. The results showed that both Chinese characters and Roman text were clearly more critical image material for judging sharpness than natural images. Independent on whether the image contained Chinese characters or Roman text, the visibility threshold for a difference in sharpness was the same for both the Chinese and European people. When related to a diagonal step response, the threshold on average equaled an angular resolution of 5 arcsec.     

步进电机细分驱动技术的软件实施

步进电机是采用脉冲信号作为驱动信号源的电动机,在微量进给及准确定位等数控领域有着广泛的应用。为使步进电机能更好地满足控制要求,需要采用细分驱动技术。本文论述的是利用软件编程、通过设定循环控制字来分配驱动脉冲信号源,并利用升／降速技术来提高步进电机的控制精度。     

阶梯形修理复合材料层合板拉伸性能研究

为获得不同参数对阶梯形修理结构拉伸力学性能的影响,本文开展了试验研究.针对铺层数目为8层的复合材料层合板,分别研究了阶梯数目为2个、4个和8个的无附加层的情况.另外针对4个阶梯的情况,研究了附加层数目的影响.作为对比,对相同修理区大小情况下的斜切形挖补修理结构也进行了测试.结果显示,对阶梯形修理结构,拉伸强度随阶梯数目的增加而增加,当阶梯数目由2个增加到8个时,修理接头的强度恢复率由36%增加到67%.通过引入附加层能够有效的提高修理结构的强度,但随着附加层的引入以及附加层数目的增加,修理结构强度的分散性变大.阶梯形修理和斜切形挖补修理的对比显示,相同修理面积的情况下,由于斜切形挖补修理能够提供更加均匀的胶膜应力分布,斜切形挖补的修理效率要高于阶梯形修理,相比4个阶梯的阶梯形修理,斜切形挖补修理强度能够提高25%.最后,根据修理接头表面各点的应力/应变分布规律,获得了拉伸载荷作用下修理接头的失效机理和失效过程.     

步进电机在CT5235车床数控改造中的应用研究

为了满足加工水轮机中具有回转曲面的过流面需要 ,采用步进机作为控制车床的刀架与滑枕的进给驱动和单片机作为运动控制器来改造现有的CT5 2 3 5立车 ,实现简易数控化。     

阶梯往复变温和高纯氮气对气体渗氮的影响

针对气体渗氮工艺存在的周期长和脆性大两个问题进行了初步的探讨。依据气体渗氮的动力学,采用阶梯往复式变温、扩散期通高纯氮气以及预氧化等方法对传统气体渗氮工艺进行了改进。结果表明：在渗氮质量高于传统方法的基础上,气体渗氮的周期大约缩短４０％。     

一种随机并行算法-aloPex算法的改进

alopex算法是一种新的启发式与随机优化相结合的算法。通过对alopex算法的研究和大量的试验,对alopex算法的优化策略做了一定的改进,以提高该算法的收敛性和收敛速度。实验证明,这种改进是可行的,而且是有效的。