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.     

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.     

镍氢电池在放电过程中的电极极化

利用暂态技术－电流阶跃法对镍氢电池的正负极在放电过程中的电化学极化、浓差极化及欧姆极化进行了研究。镍氢电池放电电压的衰减主要是由正极衰减引起的,浓差极化又是正极衰减的主要原因。负极的电化学极化和浓差极化随放电深度的增加而变化,但电化学极化增加的幅度较小。     

正电子湮没研究Al、Nb共掺CaCu3Ti4O12陶瓷高介电常数机理

关于CaCu₃Ti₄O₁₂陶瓷的高介电常数机理,目前广泛接受的是非本征的内阻挡层电容模型。该模型认为在多晶中元素变价、缺陷和非化学计量比等导致的半导化晶粒被绝缘晶界层,即内阻挡层所包围。其中内阻挡层的厚度对材料的介电性能影响较大,而扫描电子显微镜（SEM）测试表明样品晶界呈稀烂的果酱状,SEM难以测量晶界区域绝缘内阻挡层厚度。本文采用正电子湮没技术表征其厚度,通过对CaCu₃Ti₄O₁₂陶瓷共掺不同浓度的Al、Nb（CaCu₃Ti_4-xAl_0.5xNb_0.5xO₁₂,x=0.2%、0.5%、5.0%）改变其晶粒和晶界的微观结构,研究CaCu₃Ti₄O₁₂陶瓷高介电常数机理。正电子湮没结果显示,掺杂样品符合多普勒展宽谱S参数的变化趋势与平均寿命的变化趋势一致。x=0.5%掺杂样品的介电常数最高,其平均寿命、S参数和湮没长寿命成分均最小,阻挡层最薄。实验结果验证了描述CaCu₃Ti₄O₁₂陶瓷高介电常数机理的内阻挡层电容模型的预测。     

核动力堆热功率跟踪系统的多步模型算法控制仿真研究

动力堆控制系统是一带不确定参数及干扰的复杂非线性系统,采用常规的古典控制很难保证其势功率精确跟踪负荷的变化。本工作利用系统开环脉冲响应序列建立了一非参数模型,并应用多步模型算法控制原理提出了一种动力堆热功率跟踪数字控制方法。该方法跟踪调节性能好、鲁棒性强、能消除不可测干扰。通过仿真检验和调试证明了该方法的正确性和有效性,并实现了热功率-负荷的高精度匹配。     

基于G4芯片的微型热敏打印机的实现

基于G4的微型热敏打印机的设计与实现方案,全速打印速度约为25行汉字/秒.本系统由G4芯片(基于ARM7TDMI),LTPZ245B热敏打印头,打印头过热保护电路,打印头加热电路,打印头温测电路,步进电机驱动电路,缺纸检测电路以及控制软件等组成,本文介绍了热敏打印原理并给出本方案的硬件设计电路以及软件设计流程.     

负电容压电阻尼振动系统控制器参数研究

实验中发现负电容电路参数对负电容压电阻尼振动系统的振动幅值的衰减影响很大,推导了负电容压电阻尼振动系统的振动幅值随负电容电路参数的变化关系,并进行了仿真和实验研究,理论仿真和实验结果表明:负电容值越接近于压电片的固有电容,压电阻尼控制系统的衰减性能越好,串联电阻越小,压电阻尼控制系统的衰减性能越好.     

电容式电磁流量计信号处理新方法研究

电容式电磁流量计采用电容耦合的方式检测流量信号,其信号微弱、易受干扰、信噪比低,使得流量信号检出难度较大。对此,本文在信号处理中引入了互相关检测技术,设计了一种适合矩形波励磁下的电磁流量计信号特点的旋转电容滤波方式,采用的滤波器具有很高的信噪比,并且实现简单。在此基础上研制了一套原理样机,实验结果表明,该方法是有效的。     

添加致孔剂制备树脂基活性炭及电容性能研究

以碱性条件下合成的热固性酚醛树脂(PF)为原料,聚乙烯醇缩丁醛(PVB)和聚乙烯二醇(PEG)为致孔剂,采用聚合物共混炭化活化法制备双电层电容器用活性炭材料.通过热重(TG)分析探讨了PF,PF与PVB、PEG的共混物在炭化过程中的热解行为.考察了活化温度和活化时间对所得活性炭的收率、BET比表面积、孔径分布和比电容的影响,并进一步探讨了以这种活性炭材料作电极的双电层电容器的电容性能.结果表明,随着活化温度的升高,活化温度对活性炭收率的影响更为显著,所得活性炭的收率下降.聚合物PEG较PVB更适合作为成孔剂来控制活性炭的中孔孔径分布.酚醛树脂基活性炭电极比电容在850℃活化1 h为79.2F/g,而聚乙烯二醇/酚醛、聚乙烯醇缩丁醛/酚醛混合树脂基活性炭电极比电容则分别高达130.5和145.6F/g.