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。     

CTD海上剖面测量性能综合评定方法研究

随着国产温盐深剖面仪（Conductivity-Temperature-Depth profiler,CTD） 测量性能的不断提高,其使用范围和规模也逐步扩大,需要规范CTD 海上剖面测量性能评定方法。在威海附近海域开展基于锚泊式平台CTD 海上比对试验,通过改变同架比对CTD 数量、引入相关系数和平均差数据处理方法研究海上比对试验效果,提出以精准度和灵敏度为目标层的CTD 海上剖面测量性能评价指标体系,实现了对被测CTD 海上剖面测量性能相对全面的评价,准确量化了被测CTD 在实际海洋环境中的剖面测量性能,为国产CTD 海上剖面测量性能的优化提供依据。     

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。     

Identification of modal parameters of a 600-m-high skyscraper from field vibration tests

Accurate prediction of the dynamic responses of a high-rise building subjected to dynamic loads such as earthquake and wind excitations requires the information of its structural dynamic properties such as modal parameters including natural frequencies and damping ratios. This paper presents the identification results of the modal parameters based on field vibration tests on a 600-m high skyscraper. A set of tests, including ambient vibration test (AVT) and free vibration test (FVT), were conducted on the skyscraper to identify its modal parameters. Firstly, this paper presents and discusses the modal parameters of the skyscraper assessed by several identification methods applied to the AVT measurements. These methods include the wavelet transform (WT) method, the stochastic subspace identification (SSI) method, and the random decrement technique (RDT). Secondly, an active mass damper (AMD) system with total mass 1000 tons equipped into the skyscraper was used to excite the building for estimation of the modal parameters by FVT. Thirdly, this paper presents observations on the structural dynamic behavior of the skyscraper with the operation of the AMD system during a typhoon event. The field measurement results show that the AMD system functioned efficiently for suppression of the wind-induced vibrations of the skyscraper during the typhoon. This paper aims to further understand the structural dynamic properties of super-tall buildings and provide useful information for structural design and vibration control of future skyscrapers.     

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.     

Experimental simulation of degrading structures through active control

In experimental studies of structural behaviour, it is often desirable, even necessary, to perform tests on a test structure from its undamaged state, through its damaged states, and finally to failure. The fact that experiments of this type are not often done primarily because of its prohibitive cost. In this paper, a testing procedure is proposed in which a test structure is allowed to undergo its degradation in real time yet it is not physically damaged, thus allowing it to be reused. The underlying concept is that of active structural control. Considerable research and development of active structural control in civil engineering has taken place relative to responsive control of structures against damaging environmental loads. While the use of active control systems to simulate damage in an experimental setting as proposed in this paper appears to be new, much of the existing knowledge base in active structural control is directly applicable. © 1998 John Wiley & Sons, Ltd.