Response covariance-based sensor placement for structural damage detection

One important function of a structural health monitoring system is to detect structural damage in a structure. However, this is a very challenging task since the measurement is often incomplete in a civil structure due to a limited number of sensors. This paper presents a response covariance-based sensor placement method for structural damage detection with two objective functions for optimisation. The relationship between the covariance of acceleration responses and the covariance of unit impulse responses of a structure subjected to multiple white noise excitations is first derived. The response covariance-based damage detection method is then presented. Two objective functions based on the response covariance sensitivity and the response independence are, respectively, formulated and finally integrated into a single objective function for optimal sensor placement. Numerical studies are conducted to investigate the feasibility and effectiveness of the proposed method via a three-dimensional frame structure. Numerical results show that the proposed method with the backward sequential sensor placement algorithm is effective for damage detection.     

Using retrospective sampling to estimate models of relationship status in large longitudinal social networks

Estimation of longitudinal models of relationship status between all pairs of individuals (dyads) in social networks is challenging due to the complex inter-dependencies among observations and lengthy computation times. To reduce the computational burden of model estimation, a method is developed that subsamples the “always-null” dyads in which no relationships develop throughout the period of observation. The informative sampling process is accounted for by weighting the likelihood contributions of the observations by the inverses of the sampling probabilities. This weighted-likelihood estimation method is implemented using Bayesian computation and evaluated in terms of its bias, efficiency, and speed of computation under various settings. Comparisons are also made to a full information likelihood-based procedure that is only feasible to compute when limited follow-up observations are available. Calculations are performed on two real social networks of very different sizes. The easily computed weighted-likelihood procedure closely approximates the corresponding estimates for the full network, even when using low sub-sampling fractions. The fast computation times make the weighted-likelihood approach practical and able to be applied to networks of any size.     

Mesh independence of galerkin approach by preconditioning

Preconditioning the discrete Galerkin system for a bounded elliptic linear problem, by the Choleski factors of the Gramian, we obtain a mesh independent condition number. Moreover, the rate of convergence of the multigrid method is also mesh independent. Our example give a justification to the oscillatory movement of the discrete solution of a well known problem.     

职业教育视野下的当代建筑理论教学

以当代建筑历史与理论教学的转型为背景,以英国建筑联盟学院1～5年级历史与理论课程的分析为线索,展开对建筑理论学习在职业教育中所承担角色这一问题的思考,并提出与知识学习不同的新的观念—思维方式的训练和独立视野的形成。     

浅谈非独立法人的实验室——与组织之间资源共享

越来越多的企业组织内部检测实验室申请CNAS认证,而检测实验室与其所属组织存在很多的软件硬件资源的共用,实验室如何做到既与组织有效共享资源又能确保公正独立.该文对此进行了科学分析,依据<检测和校准实验室能力认可准则>的相关影响要素进行识别,并且提出了客观抖学的处理方法,对非独立法人的实验室管理有着实用的指导意义.     

叠加Y环单元频率选择表面的设计

对Y环单元进行改造得到了叠加Y环单元图形,以延迟频率选择表面(FSS)的高次谐振,实现无干扰的单通带滤波器.运用谱域法分析得到的叠加Y环单元,并与Y环单元进行对比,分别讨论其角度稳定性、极化稳定性、-3 dB带宽和高次谐振点.分析表明:当中心频点同为17.6 GHz时,叠加Y环单元具有更窄的带宽,而高次谐波向后延迟6....     

基于Timoshenko梁理论的回传射线矩阵法在传感器优化布置中的应用研究

由于结构存在阻尼现象,弹性波在传播过程中信号强度必然会随传播距离而衰减.据此提出弹性波极限传播距离与传感器极限布置间距概念,考虑到在高频率处剪切变形引起的转动惯量对结构动力特性的影响比较大,基于Timoshenko梁理论,结合经典回传射线矩阵法,提出使用局部散射矩阵确定结构损伤检测中的传感器布置极限间距,并将其应用到传感器优化算法中.针对指定检测系统,以桥梁结构Benchmark模型为例,验证算法的有效性.     

油气开采企业开展深层煤炭地下气化业务的前景分析

我国主要含油气盆地深层煤炭资源蕴藏量丰富,但长期以来未能得到有效开发利用。煤炭地下气化技术（UCG）属于煤炭资源清洁高效开发和利用的范畴,符合国家“能源革命”的相关要求,国内外的发展经验已经初步证实,UCG在技术、经济和市场方面均是可行的。分析结果认为,油气企业在推动深层UCG发展的进程中具有很大的优势,具体表现在以下方面：①国家政策层面大力支持UCG工业化;②油气开采企业具有一定的资源优势;③油气开采企业具有明显的工程技术优势;④油气开采企业具有类似的生产控制经验;⑤油气开采企业具有市场保障优势和天然气替代效益驱动;⑥油气开采企业具有利用深层UCG建设地下储气库的综合优势。综合宏观的国际形势及UCG业务发展所面临的困难,提出了对我国深层UCG可持续发展的建议：可以由油气开采企业牵头,煤炭开采企业和燃气发电企业参与,集中各家优势力量,实现互利共赢。结论认为,发展深层UCG业务可以将原来无法开发利用的深层煤炭资源转化为现实的、长期的清洁能源供应,这将有力推动中国“能源独立”的进程。     

超材料吸波器的极化特性研究进展

超材料由于具有吸波特性而引起了人们的极大兴趣.简要介绍了超材料产生吸波的原理,并着重阐述了吸波超材料在微波段、光波段以及太赫兹波段的极化特性和相应超材料吸波器结构的模拟及实验研究进展.这种超材料的吸波特性在军事和民用上具有潜在的应用价值.