Analysis of ground vibrations due to underground trains by 2.5D finite/infinite element approach

The 2.5D finite/infinite element approach is adopted to study wave propagation problems caused by underground moving trains. The irregularities of the near field, including the tunnel structure and parts of the soil, are modeled by the finite elements, and the wave propagation properties of the far field extending to infinity are modeled by the infinite elements. One particular feature of the 2.5D approach is that it enables the computation of the three-dimensional response of the half-space, taking into account the load-moving effect, using only a two-dimensional profile. Although the 2.5D finite/infinite element approach shows a great advantage in studying the wave propagation caused by moving trains, attention should be given to the calculation aspects, such as the rules for mesh establishment, in order to avoid producing inaccurate or erroneous results. In this paper, some essential points for consideration in analysis are highlighted, along with techniques to enhance the speed of the calculations. All these observations should prove useful in making the 2.5D finite/infinite element approach an effective one.

Simulation of near-fault bedrock strong ground-motion field by explicit finite element method

Based on presumed active fault and corresponding model, this paper predicted the near-fault ground motion filed of a scenario earthquake （Mw=6 3/4 ） in an active fault by the explicit finite element method in combination with the source time function with improved transmitting artificial boundary and with high-frequency vibration contained. The results indicate that the improved artificial boundary is stable in numerical computation and the predicted strong ground motion has a consistent characteristic with the observed motion.

Analysis on effect of surface fault to site ground motion using finite element method

Dynamic contact theory is applied to simulate the sliding of surface fault. Finite element method is used to analyze the effect of surface fault to site ground motions. Calculated results indicate that amplification effect is obvious in the area near surface fault, especially on the site that is in the downside fault. The results show that the effect of surface fault should be considered when important structure is constructed in the site with surface fault.

Apply of Explicit Finite Element in Seismic Ground Motion Computation

In this paper, we will use the explicit finite element to compute ground motion due to Tangshan earthquake. The explicit finite-element method uses one integration point and an hourglass control scheme. We implement the coarse-grain method in a structured finite-element mesh straightforwardly. At the same time, we also apply the coarse-grain method to a widely used, slightly unstructured finite-element mesh, where unstructured finite elements are only used in the vertical velocity transition zones. By the finite-element methods, we can compute the ground velocity with some distance to the seismogenic fault in Tangshan earthquake. Through the computation, we can find the main character of ground motion for the strike slip earthquake events and the high frequency vibration motion of ground motion.

Kinematic source model for simulation of near-fault ground motion field using explicit finite element method

This paper briefly reviews the characteristics and major processes of the explicit finite element method in modeling the near-fault ground motion field. The emphasis is on the finite element-related problems in the finite fault source modeling. A modified kinematic source model is presented, in which vibration with some high frequency components is introduced into the traditional slip time function to ensure that the source and ground motion include sufficient high frequency components. The model presented is verified through a simple modeling example. It is shown that the predicted near-fault ground motion field exhibits similar characteristics to those observed in strong motion records, such as the hanging wall effect, vertical effect, fling step effect and velocity pulse effect, etc.

Analysis of Different Rare Metals, Rare Earth Elements, and other Common Metals in Groundwater of South West Bank/Palestine by ICP/MS-Data and Health Aspects

Ground water samples are collected from south West Bank/Palestine and analyzed for different rare elements (Rb, Zr, U, P, Ti, V), rare earth elements (La, Ce, and Nd), and other common trace metals (Li, Na, Mg, Ca, Sr, Ba, K, Bi) that most of them usually have no maximum acceptable limits as either they are considered not to be toxic to human health or there is no sufficient data about their toxicity to human health. This study was conducted to determine the water quality of ground water which is used for drinking in the study area. Water samples from ten groundwater wells were obtained in three different dates of the year (November 2012, March 2013, and April 2013). Three water samples were obtained from each well for each sampling date;so a total of 90 water samples were collected from the ten wells. The results obtained from this study suggest a possible risk to the population of the study area given the high concentration of some metals that have no maximum allowed concentration, and the fact that for many people in the study area, ground water is a main source of their water supply.

侧风对直升机沙盲特性的影响

直升机旋翼与地面复杂干扰流场诱导沙床沙粒运动,形成沙盲现象,然而侧风改变旋翼与地面干扰流场,改变沙云形态和沙盲现象。因此,将侧风作用项嵌入基于黏性涡粒子的旋翼/地面气动干扰模型,体现侧风对旋翼与地面干扰流场的作用,并基于离散单元法的沙粒动力学模型,增加侧风引起的气动力,体现侧风对沙粒运动的作用。研究侧风对直升机前飞沙盲特性的影响,并分析侧风速度、风向对直升机沙盲特性的影响规律。结果表明:侧风对直升机沙盲沙云形态影响显著,且左侧风显著增强沙尘浓度,而迎风状态减小沙尘浓度;随着侧风速度的增加,左侧风状态下的沙尘浓度先增加后减小。

Non-Split PML Boundary Condition for Finite Element Time-Domain Modeling of Ground Penetrating Radar

As a highly efficient absorbing boundary condition, Perfectly Matched Layer (PML) has been widely used in Finite Difference Time Domain (FDTD) simulation of Ground Penetrating Radar (GPR) based on the first order electromagnetic wave equation. However, the PML boundary condition is difficult to apply in GPR Finite Element Time Domain (FETD) simulation based on the second order electromagnetic wave equation. This paper developed a non-split perfectly matched layer (NPML) boundary condition for GPR FETD simulation based on the second order electromagnetic wave equation. Taking two-dimensional TM wave equation as an example, the second order frequency domain equation of GPR was derived according to the definition of complex extending coordinate transformation. Then it transformed into time domain by means of auxiliary differential equation method, and its FETD equation is derived based on Galerkin method. On this basis, a GPR FETD forward program based on NPML boundary condition is developed. The merits of NPML boundary condition are certified by compared with wave field snapshots, signal and reflection errors of homogeneous medium model with split and non-split PML boundary conditions. The comparison demonstrated that the NPML algorithm can reduce memory occupation and improve calculation efficiency. Furthermore, numerical simulation of a complex model verifies the good absorption effects of the NPML boundary condition in complex structures.

医保省级统筹关键要素与运行机制模型构建研究

目的:研究医保省级统筹的关键要素与运行机制,为推动医保省级统筹提供借鉴参考。方法:以贵州省为例,通过访谈,收集以“医保省级统筹”为主题的相关文本资料,运用扎根理论提取并分析关键要素。结果:通过逐级编码,提取医保省级统筹相关概念71个,归纳为17个初始范畴、8个主范畴、5个核心范畴,据此构建医保省级统筹的运行机制模型。结论:聚焦问题靶向,关注目标导向,优化决策,细化执行,强化监管,保障医保省级统筹稳健开展。

跨地裂缝三孔斜交箱涵结构受力性能和变形规律研究

以西安站改扩建项目为工程背景,完成足尺三孔斜交箱涵结构受力性能数值模拟研究,分析荷载与地裂缝协同作用下结构的受力过程与可能破坏形态,开展缩尺比例为1∶15的三孔斜交箱涵缩尺模型静载试验,与有限元结果进行对比分析,明确变形缝斜交和板墙开洞等复杂条件下箱涵结构的裂缝发展、位移变形和应力分布规律,验证了数值分析的可行性,并提出设计建议。结果表明:足尺数值模型与缩尺试验模型的应力路径和裂缝分布吻合较好;最不利工况下,箱涵顶板混凝土开裂部位较多,纵向挠度变形较小;斜交变形缝处,钝角较锐角处更易产生应力集中现象,各部位易出现应力集中的顺序依次为跨中、钝角、锐角和板墙隅角;采用平行于变形缝的斜向布筋方式可降低因钢筋截断而产生的应力集中,优化传力路径;建议在顶板洞口横向位置处增设暗梁,洞角布置斜向钢筋,降低洞口周围的局部集中应力。

“政府信任”的概念框架再建构——基于733位农民访谈资料的扎根理论研究

通过对733位农村居民抽样田野访谈资料的扎根理论研究,可以提炼出中国农民政府信任的基本要素,即政府的权威、动机、能力、品德、绩效、可及性和回应性。它们构成政府信任概念的基本框架与维度。按照“输入—转换—输出—反馈”的政府过程逻辑,政府的动机属于输入环节的特质,能力和品德属于转换环节的特质,绩效属于输出性特质,可及性和回应性可看作反馈环节的互动性特质,而政府的权威则是其核心特质。在那些信任政府的农民中提及次数最多的是政府的绩效,而不信任政府的农民提及最多的却是政府的可及性。

红色旅游区文化元素旅游体验质量:基于网络文本数据

红色旅游区文化元素的挖掘和识别是提升游客旅游体验质量的关键。文章综合运用网络文本分析、扎根理论以及IPA分析等方法,以西柏坡红色旅游区为例,构建红色旅游区文化元素的概念模型,分析和评价大数据下红色旅游区文化元素的旅游体验质量。研究结果表明:游客对西柏坡红色旅游区的整体感知主要集中在历史回顾、红色之旅、旅游吸引物和红色精神上,且情感整体呈现积极状态;从旅游体验内容来看,风土人情、历史印记、文化体验三个层面既是游客旅游体验内容的来源,同时也构成游客对西柏坡红色旅游区文化元素的感知时间序列;就旅游体验质量而言,游客对西柏坡红色旅游区的相关评价整体呈上升趋势,自然景观和人文精神给游客带来较高质量的旅游体验,但生活氛围、建筑风貌、红色故事挖掘等方面还存在诸多问题亟待改善。

河西走廊东部西北气流型沙尘暴的大气物理特征

利用2006-2022年河西走廊东部常规高空地面观测资料、民勤探空站8时和20时间隔50 m高空加密观测资料,分析冬季和春季西北气流型沙尘暴气象要素时间、垂直结构变化及大气层结特征。结果表明:(1)研究区西北气流型沙尘暴出现在地气温度和温差最大、相对湿度最小、地面气压和风速陡增时,春季,沙尘暴发生时,风速大、地表干且近地层热力对流最强。(2)垂直结构特征是早干晚湿、风速随高度递增,风向先顺转后逆转,低层暖高层冷;春季低层气温较高,垂直温度梯度增幅大,温度露点差大,冷暖空气强度强且交汇高度较低(1 km附近),层结不稳定,易发生沙尘暴。(3)春季8时和冬季20时位温随不稳定层结高度变化梯度较大,即沙尘暴春季出现早于冬季。春季20时和冬季8时不稳定高度厚而低,因而春季下午到夜间和冬季中午沙尘暴较强。(4)500 hPa冷平流中心强度(≥-34℃)和西北急流(≥26 m/s)越强,对应700 hPa河西风速>20 m/s及低层暖区范围越大,沙尘暴强度越强,持续时间越长。

军民资源深度融合:要素体系、主体结构与影响因素

军民资源深度融合是从供给侧角度提升军民融合程度、实现军民需求与供给动态平衡的内在要求。通过对当前我国军民资源共享内容进行编码提取,提炼出由要素实体性、联结性、渗透性和准备性构成的通则框架体系,进一步基于要素交互链接特征、资源共享敛散程度、多元主体复杂程度等归纳出3种异质主体协作结构,分析不同结构的影响因素并梳理影响军民资源深度融合的主要因素,进而使用决策实验室分析法剖析各因素属性及相互作用,依属性组合分为关键—驱动、支持—驱动、支持—导向、关键—导向四类,并提出各类因素在主体协作结构调整中的应对策略。最后,分别从军民公共服务平台运营、各地军民资源共享模式和政策供给体系3个方面提出对策建议。

山丘区地表基质空间异质性特征及其对植被生态影响

地表基质是地球表层孕育和支撑森林、草原、水、湿地等各类自然资源的基础物质,受地球关键带空间结构、元素特征等因素的影响,山丘区地表基质呈现明显的空间异质性特征,并显著影响着所属植被的空间分布和生态演化。研究地表基质空间异质性特征及其对植被生态的影响机理,对于进一步认识地球关键带结构及地表作用规律,支撑国土空间生态环境修复具有重要意义。以宁波山丘区地表基质为研究对象,采取剖面研究和样品测试的方法,从地表基质空间结构和元素特征角度,对花岗岩、流纹岩和玄武岩3类典型地表基质空间异质性进行了分析。研究发现,花岗岩类具有土质粗、透水性强等特点,流纹岩类具有土质较粗、浅表透气好等特点,玄武岩类具有土质细、通气性差等特点。此外,花岗岩类主量和微量元素较缺乏,流纹岩类富含Mo和Zn,玄武岩类富含Fe、Mg、Co、Cu、Zn等元素,且玄武岩CIA值明显高于花岗岩和流纹岩。结果表明,山丘区地表基质空间异质性主要受基岩的结构和元素组成影响,并对植被生长产生明显的生态效应。地表基质的空间结构主要影响水分的分布与运移,元素特征影响着养分的分布状况,由此引起的水分和养分的空间分布和丰度差异直接影响着植被生长。

土壤特性对圆环型直流接地极暂态温升的影响

温升是影响直流接地极安全运行的重要因素,为研究土壤特性对圆环型直流接地极暂态温升的影响,建立了水平圆环型直流接地极的有限元模型,对比分析了不同土壤特性下水平双圆环直流接地极的温升变化规律。仿真结果表明:土壤导热系数、比热容和土壤电阻率是重要影响因素;在水平双层土壤中,接地极的最高温升与土壤电阻率成正比,上层土壤电阻率的影响较下层土壤电阻率更为明显,而下层土壤电阻率对内环与外环的最高温升差值影响较大;上层土壤超过一定厚度后,上层土壤厚度的变化对极环最高温升的影响较小。研究成果可为特高压直流接地极选址及设计提供参考。

配电网单相接地故障的电场检测装置研制

为了提升电场检测精度,研制配电网单相接地故障的电场检测装置。利用低通调理电路采集传感单元在电场中产生的感应电压,实时计算出线路附近的电场强度。使用COMSOL软件对输电线路单相接地故障情况进行有限元仿真,观察空间电场的变化情况。搭建工频均匀电场试验平台,对PCB传感单元进行电场强度测量校正,验证COMSOL电场强度仿真值。利用验证后的仿真值对平行半圆板电场测量传感单元进行校正,建立输电线路模型,对输电线路发生单相接地故障前后的电场强度进行测量。实验结果表明,当线路A相发生接地故障时,其周围电场强度迅速减小,而B、C两相周围电场强度增大,与仿真结果一致,电场检测精度较高。

弹性滑板支座不同摩擦系数对楼层反应谱的影响

采用课题组建立的楼层反应谱Benchmark模型,研究弹性滑板支座不同摩擦系数对楼层反应谱的影响.使用ETABS软件建立隔震结构有限元模型,在底层柱底和基础之间布置弹性滑板支座,为了使楼层反应谱具有实用性和代表性,输入FEMA P695中推荐的22条远场地震动,分别对4个摩擦系数的基础隔震结构进行非线性时程分析,研究弹性滑板支座摩擦系数对楼层反应谱的影响,且与铅芯橡胶支座隔震结构楼层反应谱进行比较.结果表明:摩擦系数影响楼层反应谱的谱值,但不改变楼层反应谱峰值出现的周期,不影响楼层反应谱的频谱特征;在周期0~6 s内,文中4种摩擦系数的弹性滑板支座结构的楼层反应谱谱值均小于铅芯橡胶支座的谱值,说明该结构弹性滑板支座的隔震性能优于铅芯橡胶支座.

长江漫滩区超深地连墙成槽土体变形研究

现阶段工程设计中往往忽略成槽引起的土体变形,但当工程对环境变形较为敏感时,该部分土体变形值得受到进一步关注。文章针对长江漫滩区超深地下连续墙成槽引起的土体变形问题,依托南京江北新区地下空间一期工程,建立了超深地连墙成槽有限元模型,计算了成槽引起的地表沉降及土体侧移,分析了土体变形发展规律及槽壁加固、超载等因素的影响。结果表明,超深地连墙成槽引起的地表沉降和加固范围内的土体侧移主要发生在成槽前期,深层抓槽对浅层土体影响程度有限。地表沉降主要由超载引起,而水平位移受超载影响程度较小,影响深度约13 m。当超载为50 kPa时,槽壁加固可使最大地表沉降降低37.3%,可使加固范围内的最大土体侧移降低61.3%。