闭口单箱颤振的流场机理

应用粒子图像测试技术(PIV)测试了闭口单箱颤振过程中尾部风嘴附近的旋涡变化过程,采用相位平均的方法研究模型周期性振动与旋涡规律性演化之间的关系。当风速低于颤振临界风速时,模型尾部风嘴附近下侧的旋涡控制结构运动状态,结构振动幅度较小;当风速接近颤振临界风速时,尾部风嘴上侧的旋涡尺度明显增大并达到与下侧旋涡相匹配的程度时,结构振幅明显增加,尾部风嘴处上下侧旋涡的交替作用主导了结构的振动。结合计算流体动力学(CFD)的数值计算方法获得颤振时刻模型表面的压力场。通过对模型表面进行合理分区,并利用分块分析的思想研究了颤振过程中气流能量输入特点。分析结果表明振动中的模型通过迎风端风嘴从气流中吸收了大量的能量。在颤振临界风速下,一个完整的振动周期内气流输入到振动系统的能量不断增加,造成单箱的颤振多为结构稳定性的突然性丧失。

分体式衬砌台车在大断面二衬施工中的应用

对于地面及周边环境较为复杂的城市环境,通常采用暗挖法施工。随着城市地铁交通总量不断发展,埋深越来越大,北京地铁埋深已突破30m。该文结合工程实际情况,重点对分体式衬砌台车在单跨双线大断面二衬施工中的应用做了深入分析。该文通过对分体式二衬台车的施工流程、临时支撑拆除的风险控制、台车的安装、拆除及操作等方面的分析和研究,分析了分体式台车施工的几个优势。该文希望通过这些内容的分析与研究,能够为大断面二衬施工提供了新的思路和方法。

河段糙率分析及其应用

在洪水调查洪峰流量计算中,有两个问题难以解决,一是糙率选用,一是断面的应用。本文通过近几年一些试验资料从单断面糙率分析和某一河段糙率分析计算过程中,使我们在河段糙率上获得了一定的成果和规律。该成果和规律在比降-面积推流的应用上取得了较好的应用精度。

A fast block-matching algorithm based on variable shape search

Block-matching motion estimation plays an important role in video coding. The simple and efficient fast block-matching algorithm using Variable Shape Search (VSS) proposed in this paper is based on diamond search and hexagon search. The initial big diamond search is designed to fit the directional centre-biased characteristics of the real-world video se- quence, and the directional hexagon search is designed to identify a small region where the best motion vector is expected to locate. Finally, the small diamond search is used to select the best motion vector in the located small region. Experimental results showed that the proposed VSS algorithm can significantly reduce the computational complexity, and provide competitive computational speedup with similar distortion performance as compared with the popular Diamond-based Search (DS) algorithm in the MPEG-4 Simple Profile.

Sheet metal hardening curve determined by laminated sample and its adaptability to sheet forming processes

The hardening curve for sheet metal can be determined from the load-displacement curve of tensile specimen with rectangular cross-section. Therefore,uniaxial compression test on cylinder specimen made from laminated sample is put forward. Considering the influence of anisotropy on hardening properties and the stress state in popular forming process,plane strain compression test on cubic specimen made from laminated sample was advanced. Results show that the deformation range of hardening curves obtained from the presented methods is wide,which meets the need for the application in sheet metal forming processes. In view of the characteristics of methods presented in the paper and the stress strain state of various forming processes,the adaptability of the two methods presented in this paper is given.

不同形式的构架上避雷针性能对比分析

介绍了变电站构架上避雷针的常用形式(包括变断面单杆式钢管和角钢格构式),以某500kV变电站工程中构架上避雷针为例,通过在MIDAS结构分析软件中建立构架模型,对2种常用形式的构架上避雷针性能进行分析,得到各自的应力、变形和用钢量情况。计算结果表明,变断面单杆式钢管避雷针的杆件应力低于角钢格构式避雷针,变断面单杆式钢管避雷针的变形则高于角钢格构式避雷针;角钢格构式避雷针的用钢量约为变断面单杆式钢管式的74%,从结构性能、安全性和经济性角度综合考虑,角钢格构式避雷针优于变断面单杆式钢管避雷针。

Computer aided modeling and pore distribution of bionic porous bone structure

Artificial bone with porous structure is crucial for tissue scaffold and clinic implants.Scaffold provides structure support for cells and guides tissues regeneration for final tissue structure.A computational aided process of porous bone modeling was developed which described the design and fabrication of tissue scaffolds by considering intricate architecture,porosity and pore size.To simulate intricate bone structure,different constructive units were presented.In modeling process,bone contour was gotten from computed tomography(CT)images and was divided into two levels.Each level was represented by relatively reconstructive process.Pore size distribution was controlled by using mesh generation.The whole hexahedral mesh was reduced by unit structure,when a 3D mesh with various hexahedral elements was provided.The simulation results show that constructive structure of porous scaffold can meet the needs of clinic implants in accurate and controlled way.

北京地铁苏州街站车站暗挖施工技术探讨

探讨北京地铁苏州站车站暗挖逆筑法，双层双拱结构断面采用PBA法，单层双拱结构断面采用中洞法的施工技术和方法。

Experiment on Mode Ⅰ/Ⅱ Mixed Interfacial Fracture Characterization of Foam Core Sandwich Materials at Elevated Temperatures

Foam-cored sandwich materials have been widely used in the civil engineering due to their advantages such as lightweight,high strength,and excellent anti-corrosion ability. However,the interfacial bonding strength of foamcored sandwich materials is weakened at elevated temperatures. In practice,the effect of high temperature cannot be ignored,because the composites and foams are sensitive to the change of temperature in the environment. In this study,a series of single-leg bending beams were tested at different temperatures to evaluate the influences of high temperatures on Mode Ⅰ/Ⅱ mixed interfacial fracture of foam core sandwich materials. The temperature was from29 ℃ to 90 ℃,covered the glass transition temperature of composites and foam core,respectively. The Mode Ⅰ/Ⅱ mixed interfacial crack prorogation and its corresponding interfacial strain energy release rate were summarized.

中国四车道及以上超大断面公路隧道修建技术的发展

伴随经济的迅猛发展,对公路交通提出了更高的通行要求,新建、扩建的四车道及以上超大断面公路隧道频频出现,但却几乎没有学者对此方面的研究做出系统的归纳总结,诸多研究在类比引用时忽略工程案例更为细致的类别而存在些许不合理。基于此,通过广泛深入的调研,依据成因和特征将四车道及以上超大断面公路隧道分成3类:常规新建四车道公路隧道、原位扩建四车道公路隧道和分岔四车道及以上公路隧道;在此基础上,归纳总结分析了四车道及以上超大断面公路隧道断面形状、施工工法、施工力学和支护参数等的技术现状以及研究中存在的不足。在断面形状的研究上,实际工程采用的扁平率波动范围较大,并且大于目前理论研究得到的扁平率和国外大部分隧道采用的扁平率,更为合理的扁平率需要深入研究;在施工工法的研究上,有逐渐减少开挖分部,扩大施工空间,增强机械化施工的趋势,与之配套的自动化程度更高的施工机械急需研发;在施工力学的研究上,对围岩的荷载释放和渐进性破坏过程有了更加深入的认识,但是对深埋段围岩压力的计算方法仍没有统一的有说服力的计算理论;在支护参数的研究上,不同的工程呈现较大的差异,需对超大扁平隧道的支护参数进一步研究和优化,为完善相应的指南或规范奠定理论基础。最后对四车道及以上超大断面公路隧道的建造技术进行了展望,指出设计标准化、施工机械化、结构轻型化等是今后重点研究的内容。