铁路瓦斯隧道分类分级标准探讨

瓦斯隧道分类分级对施工、运营安全有着极为重要的影响。首先,分析和对比现行瓦斯隧道规程、规范、指南以及煤矿系统相关规范对瓦斯隧道(矿井)的分类分级和设防标准;然后,总结瓦斯隧道分类分级中存在的问题,提出根据规划、建设、运营阶段掌握的资料深度及工作重点采用三阶段分类分级法,并给出各阶段的分类分级标准;最后,以运营隧道瓦斯环境等级分级为基础,构建瓦斯隧道设防标准,根据设防标准可建立瓦斯设防结构体系,为瓦斯隧道建设和运营安全提供保障。     

上承式钢筋混凝土拱桥构造研究

为研究上承式钢筋混凝土拱桥构造对结构受力的影响,利用有限元方法分析某无砟轨道上承式钢筋混凝土拱桥拱肋厚度及腹拱跨度对结构受力的影响。通过计算分析得出采用增加拱肋厚度、减小腹拱跨度的方式,能有效改善局部受力,降低腹拱墩范围的应力水平使结构受力更为合理的结论。     

转向架用SMA490BW钢焊接接头超高周疲劳性能的影响因素

对转向架用SMA490BW钢焊接试样,采用冲击电流为1.5A、冲击时间分别为5,10,15或20min的超声冲击、低温热处理、机械打磨(磨平焊缝余高、打磨焊趾)的处理方法,通过残余应力测试和超声疲劳试验,对比分析应力集中、晶粒细化、残余应力等因素单独作用时对焊接接头超高周疲劳性能的影响程度,并借助扫描电镜观察疲劳断口,分析焊接接头超声冲击前后的裂纹萌生位置变化及失效模式。结果表明:经超声冲击或机械打磨后,焊接试样的疲劳寿命均得到不同程度的提高;磨平焊缝余高对提高焊接接头疲劳寿命最为显著,较原始焊接试样其疲劳寿命可提高约86.4倍;改善应力集中、细化表层晶粒、引入残余压应力对延长焊接接头寿命的贡献比分别约为59%,28%和13%;焊态及冲击态试样的疲劳裂纹大多萌生于焊趾表面,部分冲击态试样的裂纹转而从表面的机械加工的缺陷处萌生,少数从材料内部缺陷处萌生并扩展至断裂失效。     

高速动车组角焊缝应力集中的识别方法

针对高速动车组焊接构架角焊缝处应力集中无法采用名义应力法识别的问题,基于结构应力法,将角焊缝焊趾处的非线性应力分解为满足外载荷平衡的结构应力和自平衡的缺口应力,然后根据力的平衡方程得到各节点力及其力矩与线力及其线力矩间的对应关系,进而推导出结构应力的计算公式,并给出角焊缝应力集中识别流程;基于所给出的算法和识别流程,采用C/C++以及ANSYS软件提供的APDL语言开发出焊接结构应力识别专用软件WSS,对某高速动车组焊接构架上诸多角焊缝应力集中进行识别,验证了基于结构应力的角焊缝应力集中识别方法不仅能给出应力集中的具体位置,还能给出具体的应力峰值及其对应的疲劳寿命,可用于优化高速动车组焊接构架的抗疲劳设计。     

浅埋暗挖小净距隧道应力集中现象分析

研究目的:小净距隧道暗挖施工中,由于邻近导洞之间土柱应力集中,影响其安全状态和邻近后行隧道的施工,并影响到先行隧道的安全,严重的还可能造成周边建筑物、地中管线等设施的破坏。因此,对浅埋暗挖小净距隧道应力集中现象进行分析,对保证施工安全十分重要。研究结论:本文结合宣武门车站小净距群洞暗挖施工,通过实测数据分析应力集中现象,量化了群洞施工时中间土柱的应力应变效应,分析了土柱沉降规律、土压力变化特征,监测结果显示:(1)相邻导洞中土柱体中间部位沉降值最大,达到-14.8 mm,是其他区域的1.1～2倍,土柱体的沉降与土压力的关系和理论分析吻合,表明该部位产生明显的应力集中;(2)后行隧道对先行隧道产生微小的拉力作用。同时,按照开挖面与监测点的距离,对土柱沉降规律和土压力变化规律进行阶段划分,为采取措施降低应力集中现象提供依据。     

亚硒酸钠对小鼠脾细胞DNA合成的影响

本文通过1次和多次给小鼠不同剂量的亚硒酸钠,以~3H-TdR掺入脾细胞DNA为指标,同时进行全血硒浓度测定,观察了补硒对小鼠体内细胞DNA合成的影响以及与血硒浓度的关系。结果表明:①亚硒酸钠对脾细胞DNA合成呈双相作用,低剂量促进其合成,高剂量则产生毒性抑制作用,毒性作用短暂、可逆,与1次大剂量有关。②多次给硒,最终血硒浓度与毒性作用之间不呈正相关。③补硒的单次剂量和方式影响稳态血硒浓度水平。     

高填方涵洞地基及路堤受力、变形机理试验研究

由高填方涵洞工程目前的设计施工以及运营现状提出存在的问题,依托汾离高速公路进行了精心的试验工程,研究分析了高填方涵洞工程中的拱顶填土、两侧边坡、涵洞结构和地基的相互受力变形机理及破坏形式,提出了相应的设计施工新措施。     

Dynamic anti-plane interaction between an impermeable crack and a circular cavity in an infinite piezoelectric medium

Wave propagation in an infinite elastic piezoelectric medium with a circular cavity and an impermeable crack subjected to steady-state anti-plane shearing was studied based on Green＇s function and the crack-division technique. Theoretical solutions were derived for the whole elastic displacement and electric potential field in the interaction between the circular cavity and the impermeable crack. Expressions were obtained on the dynamic stress concentration factor （DSCF） at the cavity＇s edge, the dynamic stress intensity factor （DSIF） and the dynamic electric displacement intensity factor （DEDIF） at the crack tip. Numerical solutions were performed and plotted with different incident wave numbers, parameters of piezoelectric materials and geometries of the structure. Finally, some of the calculation results were compared with the case of dynamic anti-plane interaction of a permeable crack and a circular cavity in an infinite piezoelectric medium. This paper can provide a valuable reference for the design of piezoelectric actuators and sensors widely used in marine structures.     

出海闸复合基础的力学特性研究

通过对出海闸的整体有限元数值计算(计入复合基础的底板、桩与土的共同作用),计算其结构的位移场及应力场.结论是复合基础底板与单一基础底板的内力、位移在大小、分布、控制工况及危险点上完全不同.由于桩基对底板的作用,基础底板出现应力集中为该复合基础的明显特征.     

Remotely-sensed chlorophyll a observations of the northern Red Sea indicate seasonal variability and influence of coastal reefs

The biological dynamics of the open northern Red Sea (21.5°–27.5° N, 33.5°–40° E) have not been studied extensively, due in part to both the inaccessibility of this desert region and political considerations. Remotely-sensed chlorophyll a data therefore provide a framework to investigate the primary patterns of biological activity in this oceanic basin. Monthly chlorophyll a data from the 8-year Sea-viewing Wide Field-of-View sensor (SeaWiFS) mission, and data from the Moderate Resolution Imaging Spectroradiometer (MODIS), were analyzed with the Goddard Earth Sciences Data and Information Services Center (GES DISC) online data analysis system “Giovanni”. The data indicate that despite the normal low chlorophyll a concentrations (0.1–0.2 mg m^− 3) in these oligotrophic waters, there is a characteristic seasonal bloom in March–April in the northernmost open Red Sea (24° to 27.5° N) concurrent with minimum sea surface temperature. The location of the highest chlorophyll concentrations is consistent with a linear box model [Eshel, G., and Naik, N.H., 1997. Climatological coastal jet collision, intermediate water formation, and the general circulation of the Red Sea. J. Phys. Oceanogr. 27(7), 1233–1257.] of Red Sea circulation. Two years in the data set exhibited a different seasonal cycle consisting of a relatively weak northern spring bloom and elevated chlorophyll concentrations to the south (21.5° to 24° N).The data also indicate that large coral reef complexes may be sources of either nutrients or chlorophyll-rich detritus and sediment, enhancing chlorophyll a concentration in waters adjacent to the reefs.