Stability analysis of shotcrete supported crown of NATM tunnels with discontinuity layout optimization

For tunnel constructed by New Austrian Tunnelling Method, the crown is the upper part of tunnel section, constructed during excavation process and supported by shotcrete. The stability of the crown has great influence on the safety of tunnel itself and the buildings above, which correlates, among others, with geometrical setup of tunnel and material properties of shotcrete and soil/rock. In this paper, aiming at analyzing the stability of shotcrete supported crown, a recently presented numerical method discontinuity layout optimization is adopted, which introduces a great amount of potential discontinuities cross over one another and provides a wide search space for efficient upper limit analysis. In the analysis, a well‐established hydration model of cementitious material is implemented for accounting the hydration of shotcrete. Then assumptions based on convergence‐confinement method are used for accounting the 3‐dimensional effect in 2‐dimensional analysis, finally providing time‐space–dependent assessments of stability of shotcrete supported crown.     

应用Hydrolight模式研究含油水体辐射传输特性的关键技术

辐射传输模式Hydrolight在国际水色遥感研究领域已被广泛用于解决水体光学的各种问题,也是进行石油类污染水体辐射传输特性研究的有效模型。结合Hydrolight模式的机理、应用现状及含油水体的特点,提出了将该模式应用于光学特性复杂的石油污染水体辐射传输特性研究时需要解决的关键技术,包括测定石油污染水体吸收系数和散射系数、建立石油污染吸收和散射特性随波长和深度变化的参数化模型、确定油物质的吸附后悬浮颗粒物体散射函数模型等方面。依据2018年8月和2016年8月分别在辽宁大连港和辽宁盘锦辽河油田等区域测定的含油水体数据,讨论了这些关键技术的解决方案。     

The IFFT-based SQM method against digital distortion in GNSS signals

Global navigation satellite systems (GNSS) signal deformations could threaten the position accuracy and integrity of GNSS, especially for safety critical applications. Digital distortion is an important kind of deformations caused by failures inside the baseband generation unit onboard the GNSS satellites. Multi-correlator technique, as a prevalent signal quality monitoring (SQM) method, was developed to reliably detect the signal anomaly and therefore protect airborne users from this integrity threat. However, the conventional multi-correlator technique is unable to estimate the degree of distortion quantitatively, while another SQM method, the chip domain observable, has a poor real-time capability so that it could not meet the stringent time to alarm requirements. To solve the above problem, we derived the spectrum form of the conventional Threat Model A first and proposed a IFFT-based SQM algorithm. This new method can perform SQM easily by analyzing the impulses after PSD division and IFFT: Detect the presence of digital distortion by judging whether there is an impulse after IFFT and estimate the degree of distortion by computing the offset of the impulse. The results show that the IFFT-based method can not only detect digital distortion real-timely but also estimate the digital distortion degree quantitatively.     

城市体系规模结构研究的新方法——位序累积规模模型

利用位序累积规模模型与位序-规模法则定量分析2000~2014年中国城市体系规模结构的省际差异及其变化特征。结论如下：使用位序-规模法则进行区域城市体系规模结构对比与演变分析时会存在较大的不确定性,而位序累积规模模型更能准确刻画区域城市体系规模结构的特征;中国各省区\begin{array}{c}\beta \end{array}值排名靠前的多属于自然地理条件优越、社会经济比较发达的地区,其变化大致表现出增幅东大西小、增长率南高北低的特征;位序累积规模模型能较准确地反映出自然与社会经济条件对区域城市体系规模结构的影响,但随着社会经济的发展,自然地理和基础设施条件对城市体系规模分布的影响不再显著。     

Acidity of Aerosols during Winter Heavy Haze Events in Beijing and Gucheng,China

We investigated the acidity and concentrations of water-soluble ions in PM_2.5 aerosol samples collected from an urban site in Beijing and a rural site in Gucheng, Hebei Province from November 2016 to January 2017 to gain an insight into the formation of secondary inorganic species. The average SO₄^2–, NO₃^–, and NH₄⁺ concentrations were 8.3, 12.5, and 14.1 μg m^–3, respectively, at the urban site and 14.0, 14.2, and 24.2 μg m^–3, respectively, at the rural site. The nitrogen and sulfur oxidation ratios in urban Beijing were correlated with relative humidity (with correlation coefficient r = 0.79 and 0.67, respectively) and the aerosol loadings. Based on a parameterization model, we found that the rate constant of the heterogeneous reactions for SO₂ on polluted days was about 10 times higher than that on clear days, suggesting that the heterogeneous reactions in the aerosol water played an essential role in haze events. The ISORROPIA II model was used to predict the aerosol pH, which had a mean (range) of 5.0 (4.9–5.2) and 5.3 (4.6–6.3) at the urban and rural site, respectively. Under the conditions with this predicted pH value, oxidation by dissolved NO₂ and the hydrolysis of N₂O₅ may be the major heterogeneous reactions forming SO₄^2– and NO₃^– in haze. We also analyzed the sensitivity of the aerosol pH to changes in the concentrations of SO₄^2–, NO₃^–, and NH₄⁺ under haze conditions. The aerosol pH was more sensitive to the SO₄^2– and NH₄⁺ concentrations with opposing trends, than to the NO₃^– concentrations. The sensitivity of the pH was relatively weak overall, which was attributed to the buffering effect of NH₃ partitioning.     

Acidity of Aerosols during Winter Heavy Haze Events in Beijing and Gucheng,China

We investigated the acidity and concentrations of water-soluble ions in PM_(2.5) aerosol samples collected from an urban site in Beijing and a rural site in Gucheng, Hebei Province from November 2016 to January 2017 to gain an insight into the formation of secondary inorganic species. The average SO_4~(2–), NO_3~–, and NH_4~+ concentrations were 8.3,12.5, and 14.1 μg m~(–3), respectively, at the urban site and 14.0, 14.2, and 24.2 μg m~(–3), respectively, at the rural site.The nitrogen and sulfur oxidation ratios in urban Beijing were correlated with relative humidity(with correlation coefficient r = 0.79 and 0.67, respectively) and the aerosol loadings. Based on a parameterization model, we found that the rate constant of the heterogeneous reactions for SO_2 on polluted days was about 10 times higher than that on clear days, suggesting that the heterogeneous reactions in the aerosol water played an essential role in haze events.The ISORROPIA II model was used to predict the aerosol pH, which had a mean(range) of 5.0(4.9–5.2) and 5.3(4.6–6.3) at the urban and rural site, respectively. Under the conditions with this predicted pH value, oxidation by dissolved NO_2 and the hydrolysis of N_2O_5 may be the major heterogeneous reactions forming SO_4~(2–) and NO_3~– in haze.We also analyzed the sensitivity of the aerosol p H to changes in the concentrations of SO_4~(2–), NO_3~–, and NH_4~+ under haze conditions. The aerosol p H was more sensitive to the SO_4~(2–) and NH_4~+ concentrations with opposing trends, than to the NO_3~– concentrations. The sensitivity of the p H was relatively weak overall, which was attributed to the buffering effect of NH_3 partitioning.     

基于数理统计方法的闪电气候研究

基于广东省1999—2015年闪电定位系统数据,利用数理统计方法得出广东省闪电气候年际变化特征、季节变化特征、月变化特征,利用最小二乘法得到闪电密度气候变化趋势系数和年、季节的气候倾向率。利用Matlab来对广东省1999—2013年的雷暴日进行分析,得出其年际周期变化规律,最后采用EOF方法,借助Arc GIS平台得出广东省闪电密度空间向量场分布图。结果表明:由1999—2015年,广东全省的地闪密度总体趋势是逐渐增加,闪电日数最多的月份集中在6—8月(夏季);雷暴日存在变化具有周期性、规律性,分别有13～16 a,7～11 a、2～6 a 3种不同尺度的周期;闪电密度空间分布特征主要有一致型、局部型、纬向型和经向型4种类型。     

用于颗粒土微观力学行为试验的微型三轴试验仪

颗粒土的微观力学行为（如土颗粒的运动与破碎等）决定着其宏观应力-应变行为,如应变局部化、应力硬化等。为研究颗粒土的微观力学行为,开发了一台微型三轴试验装置。它的轴向加载系统由伺服控制的步进转动马达与涡轮传动的减速器组成,围压由GDS压力控制器提供,压力室采用高透光率,高强度的轻质材料制成。借助于X射线显微CT及图像处理分析技术,该装置能实现对干砂土微尺寸试样（直径为8 mm,高度为16 mm）在三轴剪切条件下微观特性的无损检测。采用该三轴试验装置对粒径为0.60～1.18 mm 的LBS（Leighton Buzzard sand）试样在1.5 MPa的围压下进行了试验。结果显示,试验装置测得应力-应变曲线合理,显微CT 图像特征清晰,能够用于颗粒土体微观土力学行为的试验研究。     

吉东南新太古代晚期片麻岩类的时代、成因及其对早期地壳形成演化的制约

吉林省东南部通化地区广泛出露早前寒武纪花岗质片麻岩类,其岩石组成、形成时代和成因对深化认识华北克拉通东北缘早期地壳形成演化历史具有重要意义。本文系统的岩石学、锆石U-Pb年代学、元素和Lu-Hf同位素地球化学等研究结果表明,这些花岗质片麻岩类按照SiO₂质量分数总体可划分为高硅和低硅两组：前者主要由二长花岗质片麻岩、奥长花岗质片麻岩及英云闪长质片麻岩组成,其原岩形成于2 549~2 557 Ma;而后者由石英二长闪长质片麻岩及花岗闪长岩质片麻岩组成,其原岩形成于2 534~2 552 Ma;并且两组岩石都含有约2 600 Ma的捕获锆石,共同遭受了约2 500 Ma变质作用的影响。地球化学分析结果显示,低硅岩组具有较高的MgO、CaO、Na₂O质量分数,属于高钾—中钾钙碱性系列,并且富集LREE、亏损HREE和HFSE;与之相比,高硅岩组则具有较低的MgO和CaO质量分数,显示更强烈的轻、重稀土元素分馏以及Nb、Ta、P、Ti等亏损的特征;但两者均具有较弱的正或负Eu异常。结合区域最新研究成果,认为研究区低硅和高硅两组岩石应具有相同的源区,其形成可能与大洋板片俯冲、岩浆底侵引起的地壳部分熔融作用有关。此外,两组岩石具有相似的ε_Hf（t）值（2.72~7.95）和模式年龄（2.86~2.55 Ga）,暗示区域主要存在新太古代晚期地壳生长事件;结合区域内变质火山岩的研究进展,认为吉林省东南部通化地区花岗质片麻岩类可能形成于活动大陆边缘的构造背景。     

Two Improvements on Numerical Simulation of 2-DOF Vortex-Induced Vibration with Low Mass Ratio

Till now, there have been lots of researches on numerical simulation of vortex-induced vibration. Acceptable results have been obtained for fixed cylinders with low Reynolds number. However, for responses of 2-DOF vortex-induced vibration with low mass ratio, the accuracy is not satisfactory, especially for the maximum amplitudes. In Jauvtis and Williamson''s work, the maximum amplitude of the cylinder with low mass ratio m*=2.6 can reach as large as 1.5D to be called as the “super-upper branch”, but from current literatures, few simulation results can achieve such value, even fail to capture the upper branch. Besides, it is found that the amplitude decays too fast in the lower branch with the RANS-based turbulence model. The reason is likely to be the defects of the turbulence model itself in the prediction of unsteady separated flows as well as the unreasonable setting of the numerical simulation parameters. Aiming at above issues, a modified turbulence model is proposed in this paper, and the effect of the acceleration of flow field on the response of vortex-induced vibration is studied based on OpenFOAM. By analyzing the responses of amplitude, phase and trajectory, frequency and vortex mode, it is proved that the vortex-induced vibration can be predicted accurately with the modified turbulence model under appropriate flow field acceleration.