关键词： 坑底隆起   监测方法   压差传感技术  

摘要： 针对基坑坑底隆起监测问题,提出了一种基于压差传感技术的坑底隆起监测方法。首先分析了压差传感技术原理,其次介绍了监测系统中的压差传感系统及相应的辅助系统,然后通过模型试验验证了监测系统的温度稳定性,最后将该监测系统应用于工程实践,并对监测结果进行了分析。所得主要结论如下:基于压差传感技术的坑底隆起监测系统通过测点处的液面变化来反映竖向位移。基坑坑底隆起值随着开挖深度的增加而增大;开挖深度较小时,坑底隆起随基坑开挖同时发生和结束;当基坑开挖深度不断增加,坑底隆起随基坑开挖同时发生,并在该层开挖结束后持续增大。开挖相同厚度的土层,深度越深,所引起的坑底隆起越大,坑底土体重新稳定所需要的时间也越长。

关键词： 流体力学   案例教学   引导式学习  

摘要： 流体力学难度大、内容多且原理性数学公式推导较多,因此学生学习效果普遍不佳。在课程教学过程中采取案例教学、根据学生个体基础不同层次要求以及提问-启发-引导式学习等一系列措施,打消学生课程学习初期顾虑,提升学生的学习兴趣。

关键词： 光合作用   流控振荡器   输沙能力   曝气充氧  

摘要： 从真实流体所具粘滞耗散特性出发,以数学解析法严谨地论证了淹没射流因沿程能量通量渐减,加以其动量通量沿程守恒,故其质量通量必然沿程递增,从而衍生出射流卷吸及附壁效应,于是,在专门设计的腔体中就会发生流控振荡现象.发生流控振荡的腔体的两个出口会交替地输出两股非共面动量通量射束并在其后形成顺流螺旋涡,在绕水平轴旋涡的流场中,重于水的沙粒将获得附加的悬浮功增量,而轻于水的气泡或藻菌团的上浮行动将受阻碍.前者会加大河流的挟沙能力,后者的影响将导致水藻所赖以滋长的光合能量锐减而枯萎,从而改善水质.

关键词： 低压环境   低压双流体细水雾   雾滴粒径分布   正庚烷油池火   灭火  

摘要： 基于民用飞机货舱低压变动环境下火灾特点,进一步探寻低压双流体细水雾灭火技术在低压环境的应用。采用马尔文粒径仪和低压燃烧测试舱等设备,对自行研发N2-水低压双流体细水雾系统进行测试;研究该系统的雾场特性和低压环境下的灭火特性机理。发现N2压力低于0.4 MPa便可得到雾场均匀、粒径较小;且方便可调双流体细水雾。低压舱内灭火实验结果表明,在低压下可有效地扑灭油池火,灭火时间呈现随环境压力降低而减小趋势。揭示火焰周围逆流扩散流动场和水雾对火焰与油面的冷却隔离作用,在抑灭油火中的重要作用。

关键词： Scanning Electron Microscope   Penetration depth   circulating fluidized bed boilers   Cofired   Alloy plating   Chromium nickel alloys   corrosive environment   CORROSION PRODUCTS   METAL ALLOY   vortex finder  

摘要： X-ray diffraction and scanning electron microscopy (SEM) were used on a corroded industrial-scale circulating fluidized bed (CFB) boiler vortex finder (VF) 253MA alloy plate material to identify the dominating corrosion products and to enable a qualified selection of candidate alloys for the long-term, full-scale exposure study. Alloys 253MA, 310S, 800H/HT, Alloy DS, and Alloy 600 were chosen, and the alloy plates were exposed to the CFB boiler combustion atmosphere having an average temperature of approximately 880 degrees C, consisting of a moist globally oxidizing gas, burning hydrocarbons, CO2, CO, SO2, HCl, NH3, N-2, alkali species, and erosive particles. The exposure times used in this study were 1750, 8000, 12000, and 16000 operating hours. After exposure, the alloy samples were cut, and cross-sections were dry-polished and analyzed with an SEM-backscatter electron detector (BSD) setup to quantify material loss and penetration depth of the corrosion attack. This work suggests two novel concepts: heavily affected depth (HAD) enabling quantitative evaluation of heavily degraded alloys and remaining serviceable metal thickness (RSMT) enabling the use of long-term corrosion data from one alloy to make rough service life estimations of other alloys exposed for significantly shorter periods. The findings of this work show that there is no simple correlation between the heavily affected depth of the alloy and the nickel, chromium, or iron content. Instead, there seem to be two successful alloy composition principles that work well for this application. Furthermore, the work shows that major improvements can be made in terms of both technical life-span and the cost-effectiveness of the VF application if the most appropriate alloy is selected. In this study, a replacement of the frequently used Alloy 253MA with Alloy 310S doubled the lifespan of full-scale VFs, reducing the average VF maintenance cost to half.

关键词： 行星流体动力学   解法器   并行计算   众核加速   GMRES   性能优化  

摘要： 数值模拟是行星流体动力学研究的主要工具.本文介绍CPU-MIC异构众核平台的行星流体动力学数值模拟,计算并模拟地球外核的磁流体运动.本文在已有工作的基础上^([1-3]),添加了CPU-MIC异构众核环境的数值模拟支持.首先描述了CPU-MIC异构众核环境的上的数值模拟流程,然后给出了MIC上的分布式并行GMRES(m)众核解法器的实现算法.其次,实现了解法器的计算核心稀疏矩阵向量乘(SpMV)在MIC上的分布式并行算法,该SpMV实现了计算-通信重叠、数据传输-计算重叠.再次,为加速行星流体动力学方程收敛,给出了MIC上以SpMV为基本操作的分布式并行多项式预条件子.最后,提出了一些MIC众核平台的优化措施,如多线程、流存储和数据传输优化等.天河2号数值模拟表明相比CPU版的数值模拟,CPU-MIC异构众核环境下数值模拟在单MIC卡和64块MIC卡分别取得了6.93和6.0倍的加速比.

关键词： Circulating fluidized bed ash   Blast-furnace slag   Compressive strength   Frost resistance   Carbonation   Sulfuric acid resistance  

摘要： The aim of this study is to investigate the compressive strength and durability of zero-cement mortar fabricated using 100% by-products by incorporating circulating fluidized bed ash (CFB), blast-furnace slag (BFS), and recycled aggregates. CFB can potentially react as an alkali activator with BFS. The compressive strength of zero-cement mortar with an optimal mix proportion of CFB:BFS = 75:25 can reach approximately 28 MPa after 91 days of curing, which is mainly dependent on the curing temperature, water to-binder ratio, and aggregate type, but not the curing environment. Moreover, for the sake of application to building construction, the strength can be enhanced to 40 MPa after 28 days and 50 MPa after 91 days by maintaining a 40% water-to-binder ratio and incorporating BFS with a fineness of 600 m(2)/kg, 2.5% calcium sulfate (CS), and 6% Ca(OH)(2). CFB-based zero-cement mortar shows a tendency to improve the chloride diffusion suppression, frost resistance, and carbonation resistance when the water-to-binder ratio is reduced. Furthermore, the investigated zero-cement mortar presents excellent sulfuric acid resistance compared with the cement-based mortar. Although the use of zero-cement mortar is currently limited, the manufactured product is considered to have a potential application as an environmental load reduction material. (C) 2017 Elsevier Ltd. All rights reserved.

关键词： 微流体系统   飞秒激光   微通道   选择性腐蚀比  

摘要： 传统的半导体工艺制作微流体系统中微通道,只能对材料进行表面加工。飞秒激光具有极高的峰值功率和超短的脉冲持续时间,能够对材料直接进行三维加工,为高效率、高质量的微通道加工提供了可能。通过研究飞秒激光加工参数,包括激光脉冲能量、扫描速度和偏振态对玻璃微通道的选择性腐蚀比影响规律,发现当激光脉冲能量在2~10μJ变化时,微通道宽度变大,2μJ时微通道长宽选择性腐蚀比L/D高于其它脉冲能量参数,但随着腐蚀时间的延长,宽度变化越来越小,最后趋于稳定;当激光扫描速度在0.20~0.45mm/s之间变化时,随着腐蚀时间的延长微通道长宽选择性腐蚀比L/D逐渐增大,但当速度增加到0.35mm/s左右时选择性腐蚀比L/D增到最大,此后呈现下降趋势,同样随着腐蚀时间的延长,腐蚀通道的宽度变化越来越小,逐渐趋于平稳;当偏振态从线偏振到圆偏振变化时,线偏振时的微通道长宽选择性腐蚀比L/D更大。实验结果表明:获得较大微通道长宽选择性腐蚀比L/D的最优加工参数为激光脉冲能量2μJ,激光扫描速度0.35mm/s,线偏振。

关键词： 无排气加注   微重力   液氮   数值模拟   压力变化曲线  

摘要： 针对加注系统受注贮箱,采用CFD方法就液氮贮箱无排气加注过程开展数值仿真,对比了不同重力水平下的无排气加注性能,分析了加注口结构、壁面初始温度、加注流体温度和加注流量等因素对微重力无排气加注性能的影响规律。所构建的二维轴对称模型将流体区与固壁区一起作为求解区域并划分网格,并通过植入用户自定义程序(UDF)计算加注口液体闪蒸过程及气液之间的热质交换。经过实验数据验证,该模型能够合理展示箱内温度场分布和相分布情况,并获得贮箱压力等参数变化信息。数值计算结果表明:(1)加注条件相同时,微重力工况较常重力工况体现出更好的无排气加注性能。(2)微重力条件下,无排气加注性能几乎不受加注口结构的影响,壁面初始温度和加注流体温度越高,贮箱压力越高,加注流量仅对加注时间有显著影响。

关键词： 幂律流体   圆柱射流   粒度   索特平均直径(SMD)  

摘要： 基于自行搭建的射流系统和定容燃烧弹系统,采用三维相位多普勒技术,实现对幂律流体圆柱射流在封闭空间内不同工况下破碎液滴粒度场分布规律的测量.结果表明,对于同一种幂律流体,在相同的喷射压力、环境压力和喷嘴结构参数下,索特平均直径(SMD)随射流轴向位置的增大而减小;在同一轴向位置,SMD基本沿径向两侧呈对称分布,越远离中心SMD越大,射流速度越大,这种对称分布现象越明显;控制其他参数相同,SMD随着射流速度的增大而逐渐变小;随着环境压力的增大,SMD逐渐减小;喷嘴其他参数相同,SMD随着喷嘴直径的减小而逐渐减小;对于不同的幂律流体,黏度越大,SMD越大.试验结果与不稳定性理论分析所给出的幂律流体射流破碎规律是一致的.