方位安装误差对调平性能的影响及对策

针对水平传感器存在较大方位安装误差角会导致调平时间延长的问题,该文简述了四点调平策略和动态水平传感器工作原理,建立了坐标矩阵、矩阵转换关系式,讨论了动态水平传感器的方位安装误差对调平系统的影响。试验结果表明,通过测试仪器使动态水平传感器的轴系与安装基座轴系平行的方法,可减小方位安装误差角,提高系统性能。     

浅论高校图书馆数字期刊采访

数字期刊已经成为高校图书馆馆藏资源不可或缺的一部分。本文对影响高校图书馆数字期刊采访的因素进行了分析,阐述了目前数字期刊数据库的基本框架,并提出了提高数字期刊采访质量的措施。     

行人交通研究综述

在界定行人交通范畴的基础上,提出了行人交通的研究体系,并分别介绍了其研究进展,包括行人交通流建模与仿真、行人交通事故分析与重建、行人交通应用研究。其中,重点论述了成本效益元胞模型、元胞自动机模型、磁力模型、社会力模型和排队网络模型的原理和适用条件;提炼了行人事故再现中的运动学动力学模型、行人交通伤和行人保护、不确性分析和自动优化、事故再现方法、计算机仿真再现技术五个关键问题的研究进展;阐述了国内外步行系统应用状况、Legion、PedGo、SimWalk、AnyLogic和VISSIM五种商业化行人交通仿真软件的基本功能和应用状况。最后探讨了行人交通研究目前的问题及未来的研究展卑。     

Cracking mechanism of secondary lining for a shallow and asymmetrically-loaded tunnel in loose deposits

Tunnels constructed in loose deposits with low strength and complex composition are usually subjected to asymmetrical stresses at the entrance and exit. The secondary tunnel lining is prone to excessive deformation, cracking, or even collapse, seriously affecting the safety of tunnel construction and operation. In this paper, a large shallow highway tunnel in loose deposits is used as an example to study the cracking mechanism of secondary lining. Triaxial consolidated-drained shear tests are carried out on large remolded specimens to obtain the mechanical parameters of the surrounding soil. Three-dimensional numerical modeling is conducted based on the field monitoring data to simulate the process of tunnel construction and to analyze the mechanical mechanism of cracking in the secondary lining. It is shown that even with the 30 m advance pipe roof at the tunnel entrance, the apparent difference in stiffness between the retaining wall and the surrounding soil results in an obvious stress concentration at the spring of the secondary lining near the end of the retaining wall, due to the effect of highly asymmetrical stresses. In addition, loose deposits are very sensitive to construction disturbances. Large horizontal deformation towards the lower topography occurs during tunnel construction. With increasing overburden depth, the stress concentration at the spring level and the horizontal deformation in the secondary lining increases, which are the main reasons for cracking in the secondary lining. These findings can be useful for tunnel design and construction in the similar type of loose deposits.     

模内层压模具动态温度控制系统的设计实现

介绍一种模内层压注塑模具的动态温度控制系统,系统基于CPLD、FPGA构建了可靠、独立和快速的测控平台,并通过优化的PID策略,实现了模温的精确测量与控制.模内层压注塑工艺采用动态温度控制,提高了产品品质和生产效率.     

Air flow behavior and gas dispersion in the recirculation ventilation system of a twin-tunnel construction

Forced ventilation and recirculation systems are usually used in the construction of long twin tunnels as they offer large amounts of fresh air economically. However, because of the confluence near the cross-aisle, the fluid behavior and gas concentration are very different than in traditional forced ventilation for a single tunnel. A three-dimensional numerical model was built to study the air flow behavior and hazardous gas dispersion near the cross-aisle of a twin-tunnel construction. Field measurements were also carried out to validate the numerical model. The results show that there is a “dead zone” ahead of the cross-aisle which has a much lower air velocity than in other parts of the twin tunnels and where hazardous gases are more concentrated and uniformly distributed. In the cross-aisle and confluence zone of the air flow-out tunnel, methane tends to gather at the top and hydrogen sulfide tends to gather at the bottom. Increasing the recirculation velocity does not eliminate the “dead zone” near the cross-aisle although it consumes a huge amount of energy. Increasing the air velocity of the duct is an effective method to improve the air quality, but it is also expensive, especially when the air duct is long. When a jet fan was placed ahead of the cross-aisle in this study, the “dead zone” was eliminated completely. With respect to the recirculation ventilation system of twin tunnels, local jet fans offer an effective and economical way to eliminate the “dead zone”.     

基于BDND的脊波域井下视频图像改进中值滤波算法

井下视频图像总体上色调偏暗,目标信息对比度不高,且由于井下存在大量粉尘,导致图像中存在高密度的随机噪声,增加了图像判读与分析的困难。为此,首先对井下视频图像进行多尺度脊波分解,对分解得到的低频系数和高频系数分别进行系数重构,得到井下视频图像的背景图像和细节图像;其次,根据背景图像灰度直方图的分布特征,采用高斯分布函数进行规定化处理;然后,在分析中值滤波（Median filtering,MF）特征的基础上,采用边界判别噪声检测方法（Boundary discrimination noise detection,BDND）对其进行改进,提出了一种基于BDND的改进中值滤波算法并用于处理细节图像,该算法根据细节图像局部区域灰度值的分布特征,设定2个自适应阈值t₁和t₂,将经过2次噪声检测后处于［t₁,t₂］区间内的灰度值对应的像素点标记为非噪声点,对其余像素点分别进行中值滤波;最后,对于直方图规定化处理后的背景图像和滤波后的细节图像进行叠加。采用C++语言对所提算法进行编程试验,结果表明,该算法对于不同模糊程度的井下视频图像均有较好的滤波效果,其性能相对于中值滤波、加权中值滤波、开关中值滤波等同类算法而言有了一定程度的提升。     

试论传统藏式餐饮器皿与食品特色

文章以藏式餐饮器皿与食品为研究对象,从传统器皿的分类与图案特色、各类器物的制作工艺以及藏族独特食品的特点等方面,初步分析了器皿与食品在藏族餐饮文化体系中所具有的重要性。     

The effect of external water pressure on the liner behavior of large cross-section tunnels

Recent extreme weather with heavy rainfall has brought new challenges to the operation of a karst tunnel as a large amount of groundwater flowing toward the tunnel in a short time exceeded the drainage capacity and caused high external water pressure. By evacuating the air in the inner space of the tunnel structure, an apparatus was developed to simulate the external water pressure on the tunnel structure. It was also employed to study the behavior of a highway tunnel structure with a large cross section considering cavities behind the liner. The results showed that the bending moment of the liner increased with the external water pressure, which helps to decrease the nonuniform distribution of the thrust force, and the maximum bending moment and eccentricity were generally located at the knees or side walls. Lower external water pressure contributed to reducing the eccentricity of the liner while higher external water pressure does not further reduce the eccentricity. Under external water pressure, fractures appeared first at the knee, then at the invert and finally at the vault. The air tightness tests under external water pressure also showed that the cavity decreased the bearing capacity of the liner and significantly aggravated the fractures in the liner nearby. The results help to estimate the bearing capacity of the liner under external water pressure, and the method of simulating external water pressure can also be used to study tunnels with different cross section geometries.     

城市高密度居住区停车方案决策——地下单层库双层机械无避让式停车探讨

随着城市居民汽车拥有量的不断攀升,建普通地下一层车库直接停车的方式,已经不能满足其居民停车的基本需求。因此,开始出现建负二层、负三层地下车库,近年各种机械式立体停车也均是应对策略之一。本文就今大中城市高密度住区常采用的两种地下停车——地下单层库双层机械式停车与地下双层库直停式停车方式进行比较分析,认为对于新建居住区,更经济和适用的方式是建造一定层高的地下一层车库,内置双层机械无避让式停车,是目前乃至今后一段时间一般大中城市高密度居住区可采取的较合理的方式。但愿本文能为未来一段时间内,城市居住区的规划与设计在停车方案的决策上提供一定的参考。