Quality optimisation for laser machining under transient conditions

Quality improvements in laser machining have been achieved by a newly developed model-based optimisation strategy. The specific aims of such efforts are to assure machining quality right up to boundaries or pre-machined sections, which are inherent in intricate part geometry. Such boundaries frustrate heat-transfer and result in bulk heating of the workpiece. This in turn leads to a degradation of the machining quality. In order to achieve such optimisation, transient heat-transfer is modeled. Close inspection of the laser–workpiece interaction zone reveals that the machining front exhibits dynamic behaviour, and such mobility plays a significant role in temperature determination. Non-linear parameter adaption profiles are generated via the optimisation strategy in order to stabilise the machining front temperatures. Currently, trial-and-error based experimentation is needed in order to improve machining quality in such regions. Thus model-based optimisation has the added benefit of reducing this step whilst leading to an optimal solution. Experimental results are presented and it is demonstrated that such process manipulation can lead to significant quality improvements.     

新型FRP筋在混凝土结构中的应用及研究

钢筋锈蚀是影响混凝土结构耐久性的首要因素,而纤维增强聚合物筋（FRP筋）是一种具有高强、轻质、耐腐蚀、耐疲劳等特点的新型复合材料,用其代替钢筋是解决钢筋锈蚀问题的新途径之一。本文对新型FRP筋的基本性能及特点进行分析,并介绍了国内外有关FRP筋的最新研究进展。     

多台冷水机组的优化配置与节能运行研究

本文针对公共建筑中的空调能耗,尤其是冷水机组能耗过大的问题,建立了多台冷水机组配置模型及优化目标.以某办公建筑为例,分析了不同运行策略下多台冷水机组运行时的能耗,同时对不同策略和配置情况下的运行情况进行了经济性比较.分析可知,当选用多台机组时,平均分配负荷的运行策略比较节能,节能效果视组合方式的不同而不同,其中容量相同的组合方式采用该运行策略优势最为明显.     

某转换高层建筑抗震超限设计与施工控制

全面介绍了某转换高层建筑的抗震设计与施工控制措施。根据该结构的超限情况,在设计中有针对性地采取了比现行规范更严格的抗震措施,关键构件采用抗震性能化方法设计;对转换层进行精细的有限元分析,以考察构件的空间整体效应;并对框支节点进行了三维空间精细设计,同时制定严格的施工控制措施。实践表明,本工程采取的超限设计对策和施工控制措施,可有效解决框支转换结构中的钢筋密集、施工质量难以保证等技术难题,确保该结构达到预期的抗震性能目标。     

建筑节能软件发展现状

从暖通空调系统设计与分析、建模方法、建筑与暖通空调系统的整合、模拟方法的选择等方面阐述总结了国外建筑节能软件,分析了国内常用的中国建筑科学研究院开发的PBECA、清华斯维尔THS-BECS与天正建筑节能软件TBEC的特点以及现状,并指出国内建筑节能软件相对于国外建筑节能软件在发展中遇到的问题。     

再生粗骨料混凝土力学性能试验研究

以某10年龄期的既有建筑物废弃混凝土作为再生粗骨料原料,配制了坍落度达140 mm的C40泵送混凝土。以再生粗骨料取代率、粉煤灰取代率为主要研究参量,对配制的混凝土试块的立方体抗压、棱柱体抗压、劈裂抗拉和弹性模量等力学性能指标进行了系统的试验研究。结果表明,再生混凝土的抗压、劈裂抗拉破坏形态与普通混凝土基本一致。在满足坍落度一定的前提下,立方体抗压强度、棱柱体抗压强度和弹性模量随着再生骨料取代率的增加而降低,而随着粉煤灰取代率的增加而有所提升;劈裂抗拉强度离散性较大,无明显规律;各力学指标间关系受再生粗骨料和粉煤灰取代率的影响也不明显。研究结果可为再生粗骨料的应用提供参考。     

Moving-window extended Kalman filter for structural damage detection with unknown process and measurement noises

The extended Kalman filter (EKF), as a popular tool for optimally estimating system state from noisy measurement, has been used successfully in various areas over the past several decades. However, classical EKF has several limitations when applied to structural system identification; thus, researchers have proposed a number of variations for this method. The current study focuses on using EKF for real-time system identification and damage detection in civil structures. An improved EKF approach, called moving-window EKF (MWEKF), is proposed in this paper after a discussion on the problems associated with the application of classical EKF in time-variant systems. The proposed approach uses the moving-window technique to estimate several statistical properties. MWEKF is more robust and adaptive in structural damage detection compared with classical EKF because of the following reasons: (1) it is insensitive to the selection of the initial state vector; (2) it exhibits more accurate system parameter identification; and (3) it is immune to the inaccurate assumption of noise levels because measurement and process noise levels are estimated in this approach. The salient features of MWEKF are illustrated through numerical simulations of time-variant structural systems and an experiment on a three-story steel shear building model. Results demonstrate that MWEKF is a robust and effective tool for system identification and damage detection in civil structures.     

正常使用极限状态下受弯构件跨高比计算方法的研究

在本课题组短期刚度研究和混凝土新规范基础上,介绍了受弯构件在满足承载力极限状态情况下,不需进行挠度验算的跨高比取值的计算方法,并给出了常用荷载和跨度条件下,不需挠度计算的跨高比表格,可供设计人员在进行初步设计时参考。     

Critical review of flow boiling heat transfer of CO2–lubricant mixtures

This paper presents a comprehensive review on the flow boiling heat transfer of CO₂–lubricant mixtures. Some of the immiscible lubricants in CO₂ include alkyl naphthalene/alkylbenzne (AN/AB) and polyalphaolefin (PAO), while polyalkylene glycol (PAG) is partially miscible, and polyol ester (POE) is completely miscible. The effect of oil concentration, vapour quality, heat and mass fluxes and saturation temperature is addressed. One database has been created by collecting the experimental data from the open literature on the flow boiling heat transfer of CO₂–lubricant mixtures, along with empirical correlations. A simple simulation model has been developed in EES software package to compare the empirical correlations with the CO₂–lubricant mixtures experimental database. Most empirical correlations fail to predict the flow boiling heat transfer coefficient in good agreement with the experimental data. Hence, further research is needed to develop appropriate correlations for the flow boiling heat transfer of CO₂–lubricant mixtures.     

Solvothermal synthesis of Pd10–Ni45–Co45/rGO composites as novel electrocatalysts for enhancement of the performance of DBFC

In this research, three Pd decorated Ni and Co catalyst nanoparticle were synthesized on reduced graphene oxide (rGO) supports are synthesized through a facile solvothermal procedure. Borohydride oxidation reaction (BOR) activity and performance of prepared electrocatalysts respect to NaBH₄ oxidation is evaluated by various electrochemical techniques in the three-electrode and the fuel cell configuration. Among the prepared catalysts, Pd₁₀–Ni₄₅–Co₄₅/rGO exhibits the highest BOR activity. The cyclic voltammograms showed that the measured current at 0.5 V for the electrode of Pd₁₀–Ni₄₅–Co₄₅/rGO is as much as 108 mA cm⁻² higher than Pd₁₀–Ni₉₀/rGO and 185 mA cm⁻² higher than Pd₁₀Co₉₀/rGO. X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectra were employed to study the morphology and crystal structure of the prepared catalyst. The results of DBFC test show that the Pd₁₀–Ni₄₅–Co₄₅/rGO nanoparticles as anodic catalyst, enhanced power density to 50.4 mW cm⁻² which is 10.5% and 45.2% higher than power density of DBFCs with Pd₁₀–Ni₉₀/rGO (45.6 mW cm⁻²) and Pd₁₀Co₉₀/rGO (34.7 mW cm⁻²) anode catalysts, respectively. These results indicate that the competency of operating procedure for assembling nickel alloys electrodes can improve the activity of the prepared catalysts for BOR considerably.