Investigation into the application of cross-correlation analysis on acoustic backscattered signals from suspended sediments to measure nearbed current profiles

In the present work, the potential of correlation methods applied to acoustic signals backscattered from suspended sediments, is examined with regard to the measurement of near-bed vertical profiles of the horizontal current velocity. The technique uses the cross-correlation of the backscattered signal between pairs of downward looking horizontally separated transducers, to measure the time taken for suspension structures to advect from one transducer to another. This approach requires a degree of spatial coherence in the suspension field, and advantage is taken of this coherence to measure the flow. To investigate the technique, backscattered data collected using an array of transducers has been examined. The array was deployed along stream in an estuarine environment, which was subject to strong rectilinear currents, and high levels of suspended sediment concentration. Using pairs of transducers with separations between 0.25–5.42 m, the structure of the suspension field has been assessed, the implication of these observations for measuring flow discussed, and nearbed measurements of current profiles obtained. The results show that in the estuarine environment investigated, if the transducer pair separation was of the order of a metre or less, and currents were sufficient to retain sediments in suspension, vertical profiles of the horizontal current could be measured. To assess the results conventional electromagnetic and impeller current meter measurements were collected at four heights above the bed. Comparison of the conventional reference measurements with the cross-correlation velocities show that the correlation method has the potential to provide reliable measurements of near-bed current profiles.     

基于场地效应的悬索桥随机地震响应分析

因大跨径悬索桥梁具有较大的跨越尺度,同时墩柱基础所处场地条件也存在差异,所以对其进行地震响应分析时需考虑局部场地效应。为了正确分析场地效应对大跨度桥梁的地震响应,以某悬索桥为研究背景,采用MIDAS/CIVIL有限元软件,建立该悬索桥的有限元模型,在考虑地震动的局部场地效应情况下列举9种不同的计算工况,对大跨度悬索桥进行时程分析,通过控制一个塔墩处场地类别,改变另一个塔墩处的场地类别来分析场地效应对桥梁跨中位移和弯矩的影响。研究结果显示:场地效应对悬索桥的跨中位移和弯矩存在一定影响,不同的场地条件对桥梁同一位置的破坏程度不同。     

应县木塔环境振动试验

对于复杂的塔状古建筑物,建立一个合适的简化的数学模型是不易实现的。与强迫振动试验相比,环境振动试验比较简单、方便,所确定出的小振幅水平下的木塔结构动力特性具有足够的精度。本文首先结合应县木塔结构环境振动测试实例对环境振动测试方法作了简要介绍,并采用随机信号数据频域分析方法对测试数据进行了分析,确定木塔结构的自振频率。同时,依据不同测点在固有频率处响应的比及零迟时互相关函数确定木塔结构的振型。最后,本文依据自功率谱和互功率谱采用半功率点法计算各振型的阻尼比。本文分析结果表明,在两水平方向上木塔的振动特性存在些微差异,第一振型阻尼比较第二振型阻尼比大。     

Non-linear buffeting response analysis of long-span suspension bridges with central buckle

The rigid central buckle employed in the Runyang Suspension Bridge (RSB) was the first time it was used in a suspension bridge in China. By using a spectral representation method and FFT technique combined with measured data,a 3D fluctuating wind field considering the tower wind effect is simulated. A novel FE model for buffeting analysis is then presented,in which a specific user-defined Matrix27 element in ANSYS is employed to simulate the aeroelastic forces and its stiffness or damping matrices are parameterized by wind velocity and vibration frequency. A nonlinear time history analysis is carried out to study the influence of the rigid central buckle on the wind-induced buffeting response of a long-span suspension bridge. The results can be used as a reference for wind resistance design of long-span suspension bridges with a rigid central buckle in the future.     

Effects of engineering geological condition on response of suspension bridges

The geological condition may vary largely from one support to another for a long span bridge. The effect of geological variability and spatial variation produced by propagation and coherence loss of seismic ground motion on the response of long span suspension bridges is investigated in this article. The case of Jiangyin Yangtse River Bridge, a suspension bridge with a main span of 1385 m, is studied in detail. Numerical results show that the geological difference at the supports has a significant effect on the seismic response of long span suspension bridges and, that it is unacceptable to neglect the difference. The effect of the propagation of seismic ground motion on the response of long span suspension bridges is far more important than that of the coherence loss. The response of bridges varies greatly with the horizontal apparent velocity in a very complex way, and there is a critical horizontal velocity for a given response quantity.     

Effect of vehicle weight on natural frequencies of bridges measured from traffic-induced vibration

Recently, ambient vibration test (AVT) is widely used to estimate dynamic characteristics of large civil structures. Dynamic characteristics can be affected by various environmental factors such as humidity, intensity of wind, and temperature. Besides these environmental conditions, the mass of vehicles may change the measured values when traffic-induced vibration is used as a source of AVT for bridges. The effect of vehicle mass on dynamic characteristics is investigated through traffic-induced vibration tests on three bridges; (1) three-span suspension bridge (128m +404m + 128m), (2) five-span continuous steel box girder bridge (59m + 3@95m + 59m), (3) simply supported plate girder bridge (46m). Acceleration histories of each measurement location under normal traffic are recorded for 30 minutes at field. These recorded histories are divided into individual vibrations and are combined into two groups according to the level of vibration ; one by heavy vehicles such as trucks and buses and the other by light vehicles such as passenger cars. Separate processing of the two groups of signals shows that, for the middle and long-span bridges, the difference can be hardly detected, but, for the short span bridges whose mass is relatively small, the measured natural frequencies can change up to 5.4%. Supported by: the Ministry of Construction and Transportation, Korea Highway Corporation and Hyundai E&C Co. Ltd. under Project No. R&D/970003-2.     

云南漾濞6.4级地震建筑结构震害特征调查分析

本文整理了云南大理州"5.21"6.4级地震震害调研与科考过程的部分成果。穿斗木架构结构和框架结构是云南大理州在低矮建筑和多高层建筑中广泛应用的两种结构形式。该研究基于震害调查结果,描述了地震过程中穿斗木架构结构和框架结构破坏的宏观现象,总结了两种典型结构的破坏形式,对震害成因进行了探讨。在此次震害调查过程中,科考人员还通过智能手机对结构基频进行了快速评估。在震后,研究人员对智能手机智能测振应用软件进行了更新,结合应用需求加入了测振地点和路线的地图信息,为震害调查与记录提供了便利。基于漾濞县震害科考与调研结果,为云南省穿斗木架构建筑及框架建筑的抗震方法与策略提出了建议,为震后建筑结构快速评价提供了新手段。     

基于OpenSees的强震下混凝土结构梁-梁碰撞行为数值实现

绝大多数针对极端作用下的结构连续倒塌分析,在分析过程中不能实时地根据构件的损伤状态对分析模型进行修改,也不能考虑连续倒塌过程中的各种碰撞问题。连续倒塌过程中发生的碰撞对结构响应预测有重大影响。本文依据钢筋混凝土框架结构发生梁-梁碰撞的机理,基于OpenSees平台建模,结合Matlab的混合编程计算碰撞力,通过添加碰撞时程力并对结构进行模型更新,合理地实现钢筋混凝土框架结构在强震作用下的连续倒塌过程中发生梁-梁碰撞的具体过程。将得到的结果和传统时程分析法的结果进行的对比表明,结合Matlab和OpenSees命令可以实时地计算碰撞力序列和对结构进行更新,梁-梁碰撞和构件的逐步失效使结构的水平位移和转角有一定的增大,竖向位移有一定减小。     

断层走向对刚构桥地震反应的影响

我国西部部分连续刚构桥临近地震断层建设,在抗震分析时通常会忽略断层走向与桥梁纵桥向夹角对其地震反应的影响。利用Midas Civil软件建立4座墩高不同的大跨度连续刚构桥模型,选取10组近断层强震记录进行时程分析,研究断层走向对刚构桥地震反应(位移和弯矩反应)的影响。结果显示：在水平双向近断层地震动输入下,桥梁主墩及主梁纵桥向地震反应在断层走向与纵桥向夹角为75°～135°范围内最大,而横桥向最大地震反应则发生在夹角为0°～30°或120°～180°范围;在三向近断层地震动输入下,与仅考虑水平双向地震动输入下的桥梁地震反应相比,竖向地震动对主梁竖向弯矩响应的影响较大,特别是主墩和主梁的交界处,增大比例可达2倍及以上。就文章选取的4座桥梁算例,不考虑断层走向和桥梁纵桥向的夹角则存在低估桥梁地震反应的可能,低估误差在15%～40%左右。     

海洋可控源电磁法发射源姿态影响研究

海洋电磁理论是建立在水平发射偶极的基础上.然而,由于海底洋流作用海洋可控源发射偶极可能产生水平摆动、倾斜和水平旋转,造成测量数据与理想状态的水平电偶极子的电磁响应有较大的偏差.为了研究发射源姿态变化对场的影响,本文提出利用欧拉旋转将发射偶极由源坐标系转换到地球坐标系,进而分析发射源姿态变化造成海洋电磁观测数据的误差分布...     

桅杆结构竖向杆件损伤位置识别的时域方法

桅杆结构在工程上应用广泛,但破坏事故时有发生,竖向杆件是其损伤发生的主要部位之一。由于桅杆结构具有强非线性,已经发展得比较完善的基于频域的损伤识别方法不适用于桅杆结构,对其进行损伤诊断成为一大难题。本文利用桅杆结构长细比大、柔性强的特点,探讨了竖向杆件刚度变化与节点水平位移响应的关系,并提出了基于水平位移时程响应的竖向杆件损伤位置识别的指标,说明了竖向杆件损伤的时域识别步骤,通过几个数值算例证明该指标能对损伤的竖向杆件位置准确地进行识别,最后,分析了信号测量噪声对识别指标的影响。     

Dispersion calculation method based on S-transform and coordinate rotation for Love channel waves with two components

Dispersion analysis is an important part of in-seam seismic data processing, and the calculation accuracy of the dispersion curve directly influences pickup errors of channel wave travel time. To extract an accurate channel wave dispersion curve from in-seam seismic two-component signals, we proposed a time–frequency analysis method based on single-trace signal processing; in addition, we formulated a dispersion calculation equation, based on S-transform, with a freely adjusted filter window width. To unify the azimuth of seismic wave propagation received by a two-component geophone, the original in-seam seismic data undergoes coordinate rotation. The rotation angle can be calculated based on P-wave characteristics, with high energy in the wave propagation direction and weak energy in the vertical direction. With this angle acquisition, a two-component signal can be converted to horizontal and vertical directions. Because Love channel waves have a particle vibration track perpendicular to the wave propagation direction, the signal in the horizontal and vertical directions is mainly Love channel waves. More accurate dispersion characters of Love channel waves can be extracted after the coordinate rotation of two-component signals.     

Sea-floor-mounted rotating side-scan sonar for making time-lapse sonographs

A rotating side-scan sonar system was designed to make time-lapse sonographs of a circular area of the sea floor. To construct the system, the transducers of a commercial side-scan system (frequency 105 kHz; pulse length 0.1 ms; horizontal beam width 1°; vertical beam width 20°; beam depressed 10° with respect to horizontal) were mounted 2 m above the sea floor on a vertical shaft that had a rotation speed of 0.5 rpm.The radially collected sonar images are recorded linearly on a standard side-scan recorder. To convert the linear record to a radial record, the original moving record is photographed through a slit by a rotating camera, exposing a circular image on film.Records that are collected with this system offer several advantages over records that are collected with towed systems. Bottom features are presented in nearly true plan geometry, and transducer yaw, pitch, and roll are eliminated. Most importantly, repeated observations can be made from a single point, and bedform movements of <50 cm can be measured. In quiet seas the maximum useful range of the system varies from 30 m (for mapping ripples) to 200 m (for mapping 10-m wavelength sand waves) to 450 m or more (for mapping gravel patches).     

Performance of “G-Pisa” ring laser gyro at the Virgo site

The ring laser gyroscope ??G-Pisa?? has been taking data inside the Virgo interferometer central area with the aim of performing high sensitivity measurements of rotations in the vertical as well as in the horizontal orientation. We discuss the main characteristics of the instrument, describing its mechanical design and presenting the measured sensitivity limit. By applying a simple effective model for the laser gyroscope, we show that the stability of the sensor above 10?s of integration time is mainly limited by backscattering effects. The horizontal rotation rate signal is also compared with the signals recorded by the Virgo environmental monitoring system and by a biaxial mechanical tiltmeter rigidly fixed on top of the gyrolaser mounting frame.     

基于能量合成法的塔式结构刚度识别研究

在Rayleigh能量法和Southwell＇s频率合成法的基础上,将结构的振动基频表示为由各变形元和惯性元组成的子系统频率的合成,其中变形元为结构的弯曲变形和剪切变形,惯性元为结构的分布质量和塔顶附加质量。通过选取满足边界条件的挠度函数,建立了底部固定、顶端带有附加质量的塔式结构基频与刚度的关系,因此可通过测量结构的振动基频识别出塔式结构的抗弯刚度和抗剪刚度。以某钢塔为计算实例,采用该算法推导出了结构振动基频与弹性模量的关系,只要知道截面的几何尺寸和材料性质,便可快速识别出各截面的刚度。有限元空间建模计算结果证明了本文提出的算法具有较高精度。该方法适合底部固定的塔式结构,可为复杂空间塔式结构使用状态的监测与评估提供参考。     

Hanger replacement influence on seismic response of suspension bridges: Implementation to the Bosphorus Bridge subjected to multi-support excitation

The effects of hanger replacement from inclined to vertical configuration on seismic response of long-span suspension bridges are investigated considering multi-support earthquake excitation. The Bosphorus Bridge is investigated due to its recent comprehensive rehabilitation, mainly involving hanger replacement. The finite-fault stochastic simulation method (FINSIM) is utilized for multi-point earthquake time-history generation. The developed finite element (FE) model both for the inclined and vertical hanger arrangement are verified through the structural health monitoring (SHM) data. Based on the comparative analysis, the tension force of vertical hangers is found to be lower than that of inclined hangers, whereas the tension force of the main and back-stay cables remains the same. The compressive axial force of the deck decreases relatively in the case of the vertical hanger arrangement, whereas the cross-sectional forces at the tower base section increase. The approach viaducts are not affected by the vertical hanger arrangement. According to the demand/capacity ratios for damage estimation under the max. earthquake (2475 years return period), structural damage on the tower base section may be expected for both hanger arrangements, while these sections perform well under design scenario earthquake. The expansion joint of the bridge with inclined hangers is also estimated to be damaged; however, this displacement is lower in the case of the vertical hanger arrangement due to the viscous dampers. The findings also reveal that a change in hanger form of a suspension bridge can necessitate other structural retrofit, such as using viscous dampers to limit longitudinal displacements of the deck and retrofitting the bridge towers.     

采用双向调谐质量阻尼器的大跨度桥梁风振控制仿真分析

传统的调谐质量阻尼器（TMD）设计均仅针对结构某一阶模态单独设置,当用于密频结构减振时会导致附加质量过多。为减小TMD的附加质量,结合大跨度斜拉桥结构的密频与风致耦合振动特点,提出了一种新型的双向共享质量与电涡流阻尼式TMD。具体实现方式是：水平、竖向TMD的刚度构件分别采用悬臂梁与压簧,将水平向TMD整体置于压簧上面,从而构成竖向TMD的质量;导体板固定不动,使安装在TMD质量块的永磁体阵列随质量块竖向或水平方向运动,从而分别产生竖向与水平向的电磁涡流阻尼。研究结果表明：（1）电涡流阻尼可以很好地实现双向TMD装置的共享阻尼,且电涡流阻尼的大小可以很方便地调节;（2）采用双向TMD进行斜拉桥的风致振动控制减振效果良好,可行性强。     

Simulations of non‐stationary frequency content and its importance to seismic assessment of structures

To verify the importance of the non‐stationary frequency characteristic of seismic ground motion, a joint time–frequency analysis technique of time signals, called chirplet‐based signal approximation, is developed to extract the non‐stationary frequency information from the recorded data. The chirplet‐based signal approximation is clear in concept, similar to Fourier Transform in mathematical expressions but with different base functions. Case studies show that the chirplet‐based signal approximation can represent the joint time–frequency variation of seismic ground motion quite well. Both the random models of uniform modulating process and evolutionary process are employed to generate artificial seismic waves. The joint time–frequency modulating function in the random model of evolutionary process is determined by chirplet‐based signal approximation. Finally, non‐linear response analysis of a SODF system and a frame structure is performed based on the generated artificial seismic waves. The results show that the non‐stationary frequency characteristic of seismic ground motion can significantly change the non‐linear response characteristics of structures, particularly when a structure goes into collapse phase under seismic action. It is concluded that non‐stationary frequency characteristic of seismic ground motion should be considered for the assessment of seismic capacity of structures. Copyright © 2002 John Wiley & Sons, Ltd.     

微动测试技术在古建筑拱桥结构检测中的应用

在古桥梁建筑结构保护中,无损高精度检测一直是一个重要的研究课题。为识别古桥梁拱桥的结构损伤问题,以上海青浦迎祥桥为研究对象,采用全站仪对桥梁结构的变形进行观测及分析,评价桥梁的变形及受力状态;采用微动测试技术,获取结构的损伤动力特性参数,包括固有频率及振动模态。通过分析现有桥梁的模态分布,观测振动模态的突变位置确定结构损伤位置,比较结构的变形特性,对结构的损伤程度进行评价。     

混凝土框架模型结构参数的识别

框架结构是常见的建筑结构形式,也是结构损伤诊断的主要研究对象之一。本文以钢筋混凝土框架结构模型的振动测试数据为基础,采用灵敏度分析方法,对结构的物理参数进行识别。有限元分析中,考虑框架结构的节点转动,采用静凝聚方法得到结构刚度矩阵。参数识别结果表明,对于不同的固有频率和振型的测试信息组合所识别的物理参数有所不同。根据已知的概率分布,利用MonteCarlo方法,将模态参数的不确定性传递给物理参数,得到了物理参数的不确定性。