地理信息标准化实现机制之一:一致性测试

一致性测试作为一种标准化检测手段和评价方法,目前已应用于信息技术、工业自动化系统与集成等多种领域,但在国内地理信息领域,一致性测试尚处于待开展状态,本文对地理信息一致性测试机制中所涉及的主要概念、对象、过程、方法进行了综述,旨在促进国内地理信息领域一致性测试机制的建立和发展。     

基于三维激光扫描的堆积体滑坡变形机理及阈值模型试验研究

为分析白龙江流域舟曲段江顶崖滑坡的变形演化机理及其阈值,设计降雨条件下的大型堆积体滑坡物理模型试验,采用FARO FocusS 350三维激光扫描仪进行滑坡数据采集、处理,获取滑坡在不同降雨工况的点云模型数据,对比分析不同降雨工况下滑坡宏观及局部特征点的变化情况。研究表明：滑坡模型表面出现持续、快速、变化鲜明的整体变形特征,伴随出现滑坡模型中、前部横向、纵向的张拉裂缝,表明在非饱和渗流影响下,堆积体滑坡模型的基质吸力降低、孔隙水压力以及滑坡体重力荷载增加,导致滑坡模型临近失稳;根据滑坡模型宏观变形情况,其变形演化过程可划分为：初始变形阶段、等速变形阶段和加速变形阶段,3个不同变形阶段坡体宏观变形各自有其特点。通过对试验阶段的变形特征分析,设立了滑坡变形速率阈值,分别为0.01 m/h、0.02 m/h、0.2 m/h。基于三维激光扫描技术坡体监测,结合坡体变形宏观和局部分析的优势,在保证高精度监测、采集、处理的同时,得到坡体的整体变形和位移。     

Dynamic testing and system identification of a multi-span highway bridge

A simple and effective procedure for conducting the free vibration test on highway bridges is presented. The impulsive force in each direction is generated by a loaded truck that either stops suddenly or falls down from a rigid block. The feasibility of the procedure is demonstrated in identification of the dynamic properties, i.e. the vibration frequencies, mode shapes, and damping ratios, of a three-span box-girder concrete bridge using the Ibrahim Time-Domain (ITD) technique. Up to 14 modes have been identified for the present case. For the purpose of verification, ambient vibration tests were also carried out, with the data processed by the random decrement (Randomdec) technique to yield the free vibration response, followed by the ITD technique. The dynamic properties identified from the two types of test correlate very well with each other, indicating the validity of each procedure described herein. Although many more modes can be identified from the free vibration test because of the higher quality of data produced, the easiness and general applicability of the ambient vibration test can still be appreciated. A comparison of the experimental results with those by the finite element method indicated a lesser degree of correlation, implying that the finite element model adopted in design requires further refinement, say, through a more realistic evaluation of the boundary conditions, geometric and material properties of the bridge. Copyright © 1999 John Wiley & Sons Ltd.     

Real-time on-line test for MDOF systems

This paper presents a test system for conducting on-line tests in a real time and a series of real-time on-line tests conducted to verify the effectiveness of the system. The proposed system is characterized by (1) use of a Digital Signal Processor (DSP) now readily available, (2) adoption of the C language to ensure easy programming, and (3) separation of response analysis and displacement signal generation to apply the system for tests with complex structures. To create displacement signals successively without being interrupted by the computation of equations of motion, extrapolation and interpolation procedures using present and past target displacements are developed. Base-isolated building models were chosen for the real-time on-line test. The effectiveness of the extrapolation and interpolation procedures was demonstrated through a series of real-time on-line tests applied to the models treated as SDOF structures. A five-storey base-isolated building model (treated as a six DOF structure) was tested for various ground motions, and it was verified that the system is able to simulate earthquake responses involving large displacements and large velocities. The number of DOFs that can be handled in the proposed system was investigated, and it was found that the system is capable of performing the test with reasonable accuracy for up to 10 DOF structures with a range of response frequency not greater than 3·0 Hz, or 12 DOF structures with a range of response frequency not greater than 2·0 Hz. Copyright © 1999 John Wiley & Sons, Ltd.     

Disturbed state model for sand–geosynthetic interfaces and application to pull-out tests

Successful numerical simulation of geosynthetic-reinforced earth structures depends on selecting proper constitutive models for soils, geosynthetics and soil–geosynthetic interfaces. Many constitutive models are available for modelling soils and geosynthetics. However, constitutive models for soil–geosynthetic interfaces which can capture most of the important characteristics of interface response are not readily available. In this paper, an elasto-plastic constitutive model based on the disturbed state concept (DSC) for geosynthetic–soil interfaces has been presented. The proposed model is capable of capturing most of the important characteristics of interface response, such as dilation, hardening and softening. The behaviour of interfaces under the direct shear test has been predicted by the model. The present model has been implemented in the finite element procedure in association with the thin-layer element. Five pull-out tests with two different geogrids have been simulated numerically using FEM. For the calibration of the constitutive models used in FEM, the standard laboratory tests used are: (1) triaxial tests for the sand, (2) direct shear tests for the interfaces and (3) axial tension tests for the geogrids. The results of the finite element simulations of pull-out tests agree well with the test data. The proposed model can be used for the stress-deformation study of geosynthetic-reinforced embankments through numerical simulation. Copyright © 1999 John Wiley & Sons, Ltd.     

气象中使用统计检验的几个问题

针对目前在气象和气候要素变化分析中,对相关系数和合成分析使用统计检验存在的若干问题进行评论。认为对相关系数等统计检验,不应该称为“信度检验”,其检验水平也不应该称为“95％置信度”,而应该称为“显性检验”,“显性水平为5％”。     

CINRAD/CB脉冲多普勒天气雷达数字中频接收机

介绍CINRAD/CB脉冲多普勒天气雷达数字中频接收机的主要功能和技术性能.CINRAD/CB雷达接收机的主要特点是高灵敏、采用了数字中频采样、带AGC的大动态接收范围、低相噪频率综合器、在线测试、系统在线定标和整机性能的测量等技术,采用了高稳定频率源和全相干技术体制.简述了CINRAD/CB雷达接收机的组成和工作原理,给出接收系统的组成框图,对该系统接收机的灵敏度、噪声系数、动态范围等性能指标进行了分析.     

2013年长江中下游夏季高温干旱演变过程及环流异常成因简析

利用改进的CIn指数,结合NCEP/NCAR再分析资料,逐候分析2013年夏季长江中下游地区高温干旱演变过程和高温异常成因。结果表明：改进后的CIn指数能够准确识别此次干旱过程,整体持续时间近一个月。旱情从7月第4候湖南南部开始,8月第3候干旱程度最强,特旱中心位于湖南省中东部,浙江省为高温中心,8月第4候旱情得到缓解。在干旱成因上,极涡位置异常偏西,影响长江中下游地区冷空气偏弱,南亚高压东伸与西太平洋副热带高压西伸明显;鄂霍次克海至菲律宾一带呈较强的EAP遥相关型,其中长江中下游地区位势高度的正异常加强了西太平洋副热带高压的中心强度并使其位置偏西;乌拉尔山地区的阻塞高压与西太平洋副热带高压相对峙,有利于西太平洋副热带高压长期稳定地控制在长江中下游地区;同时欧亚大陆与西太平洋海陆温差增大,东亚夏季风偏强,西太平洋副热带高压异常偏北,长江中下游地区下沉气流强盛,在西太平洋副热带高压和南亚高压共同作用下,造成持续的高温干旱过程。     

大功率激电测深法寻找焦家式深部金矿床的应用研究

大功率的激电测深法在寻找焦家式深部金矿中取得了大量的资料,由多次去除极化单元场的原理对导出大功率激电测深资料进行消除浅部强激电干扰异常,从而突出了深部矿床的激电异常,并利用处理后的激电测深曲线,定量求取了深部金矿蚀变矿化带的顶界面埋深。认为当供电极距达到一定值时,极化电场仍然会反映到地表,因此该方法可以寻找焦家式破碎带蚀变岩型的深部金矿床。     

RAMS模式在山谷城市模拟性能的检验

 利用2005年冬季兰州边界层试验的观测数据,分别从边界层结构、近地面温度和风速、地表通量等几个方面检验了RAMS在山谷城市的模拟性能。RAMS模式能很好地捕捉边界层结构特征,模拟的白天混合层高度和夜间稳定边界层高度和观测值非常一致。模式能较好地模拟近地面温度和地表通量的日变化特征。对模拟偏差进行统计分析,结果显示RAMS对近地面温度和风速的模拟结果是可以接受的:近地面温度的平均偏差为-1.73 ℃,RMSE为2.16 ℃,风速的平均偏差为0.35 m·s-1,RMSE和RMSVE分别为1.61 m·s-1和3.15 m·s-1。研究表明,RAMS适合作为研究兰州山谷城市大气边界层的工具。