Measurements of dynamic properties of a medium span suspension bridge by using the wavelet transforms

The aim of this paper is to show the capabilities of the real-time kinematic (RTK) global positioning network system (GPS) to measure the low-frequency vibration of a medium span suspension bridge. In particular, this paper presents the results of studies conducted on the identification of modal parameters including natural frequencies, damping coefficients and mode shapes of a suspension bridge using ambient excitation loads. A real-time kinematic (RTK) global positioning system (GPS) was designed and installed on the Nottingham Wilford Bridge to provide long-term and real-time measurement of bridge deck movement. An approach to estimate modal parameters, from only output data in the time domain using the wavelet transform, is presented. Displacements responses of the bridge are used in the wavelet transform to identify its dynamic characteristics. The modal properties were extracted using a two-step methodology. In the first step, the random decrement method was used to transform random signals in free vibration responses. Secondly, a wavelets-based technique was used to extract natural frequencies and to determine the mode shapes of the structure. This method was compared with the well-established techniques eigensystem realisation algorithm showing a difference of 1% in the estimated first natural frequency.The efficiency of RTK–GPS was demonstrated in the full-scale measurement. In particular, the results showed that the RTK–GPS data can be used for extracting modal properties from in-service-loads induced low-frequency vibration (<5 Hz) by processing the signal with the wavelets transform.     

一种用于散货码头的GPS精度提升算法

GPS是广泛应用于散货码头的自动化和远程监控中的一种设备.但由于噪声的存在,GPS接收器并不能提供高精度的定位.主要阐述了一种基于卡尔曼滤波器快速去除噪声的方法,并提高GPS系统的定位精度.通过实验法,卡尔曼滤波器的关键参数首先被确定,然后通过卡尔曼滤波器的自动递归运算,快速获取正确的GPS定位数据.最后,还通过了一组对比实验,验证了这种算法的有效性.     

Talkha steel highway bridge monitoring and movement identification using RTK-GPS technique

Monitoring the bridge deformation is the vital task in bridge maintenance and management. Talkha highway steel bridge is one of the two oldest steel bridges in Mansoura city. Nowadays, the Real Time Kinematic-Global Positioning System (RTK-GPS) is capable of providing fast and accurate measurements of bridge oscillations. Also, the movement and damage severity can be identified using the dynamic bridge characteristics obtained from GPS. The aim of the present work is to demonstrate the use of RTK-GPS (1 Hz) to provide data for use in the assessment of existing structures. The moving average filter is used to de-noising the GPS observations. Finite Impulse Response (FIR) with moving average are used to extract the dynamic response and frequency domain of the bridge and Neural Network Auto-Regressive (NNAR) model is used to identify the bridge movement. The results indicate that: (1) the moving average filter is simple and suitable to smooth high noises and errors of GPS observation signals; (2) the multi-filter of short-period can reveal the dynamic displacement of bridge deck movement; (3) the low-frequency movements of the bridge could not be completed and the observation time should be increased to complete it and (4) the movement output of the NNAR is highly conformed with the observation filter.     

High-Precision Simulation of Onboard Signal Receivers in Global Navigation Systems

Aircrafts and spacecrafts that make use of global navigation satellite systems (GNSS) carry onboard signal receivers. The development of software for modeling the operation of such receivers is considered in this article. The plausible simulation of receiver operation is resolved into subsidiary problems. The formation of the satellites’ ephemeris data is important here. The proposed design approach is to develop an information system capable of monitoring the constellation of navigation satellites on the basis of the corresponding data files provided by different centers of GNSS analysis. The proposed approach is shown to be more effective than the available alternatives.     

Noise characteristics of high-frequency,short-duration GPS records from analysis of identical,collocated instruments

High-rate (>1 Hz) GPS, currently used for measurement of dynamic processes and as a universal time and frequency standard, is usually assumed to be affected by site-specific errors and only limited studies of the error properties of high-frequency (10 Hz), short-duration (<100 s) GPS records exist. Preliminary studies, provided evidence of instrument-specific errors, which were investigated on the basis of systematic experiments with various types of stationary, collocated, identical GPS units. This analysis revealed differences between couples of receiver/antenna units, while spectral analyses revealed low-frequency colored noise, statistically significant below 0.2 Hz and, gradually decaying with increasing duration of observations, so that above 2.5 Hz measurements are contaminated only by white noise.     

GNSS定位接收器的校准

目前,全球导航卫星系统(Global navigation satellite system,GNSS)接收器不仅是精密测量的主要工具,而且还用于大地测量、地球物理和许多其他工业应用中。确保GNSS测量精度、通用性和寿命的唯一方法是对其接收机进行校准。本文讨论了影响单台GNSS接收机标定精度的参数,并根据以往的经验研究,建立了一个大地基准点作为校准的参考。此外,还讨论了这种校准对国际单位(Systeme international unit,SI unit)的可追溯性。通过三年多的长期测量,验证了基准点的稳定性。最后,对单台样本GNSS接收机进行了标定,并推导了不确定度计算公式。     

基于遗传神经网络的机器人腕力传感器动态建模与补偿方法

介绍用于MotomamV3X机器人上的新型多维腕力传感器,比较遗传算法与人工神经网络的特点,将遗传算法的交叉和变异操作进行改进,提出一种融合改进遗传算法(Genetic algorithm, GA)的函数连接型人工神经网络(Functional link artificial neural network, FLANN),并将其用于所介绍的新型机器人腕力传感器动态建模与动态性能补偿中。介绍动态建模与动态补偿原理及改进遗传神经网络算法,给出该传感器的动态模型和动态补偿模型。该方法利用腕力传感器的动态标定数据,采用改进遗传神经网络搜索和优化模型参数,保留了遗传算法的全局搜索能力和FLANN结构简单,鲁棒性好,且具备自学习能力的特点,克服了FLANN容易陷入局部极小的缺陷,具有快的网络训练速度及高的动态建模精度。理论分析和试验结果都证实了所提出的动态建模与动态补偿方法的有效性。     

基于单片机的GPS接收机的设计

卫星导航系统GPS技术,目前己被用在各行各业中。GPS系统的部分用户主要是各种型号的GPS接收机。文章以单片机为核心,通过GPS接收模块,接收GPS卫星信号,然后将数据发送到单片机的串口,单片机执行串口中断,提取所需要的数据,最后将数据通过1602液晶显示出来。文中主要阐述了硬件设计和软件。     

Sensitivity and analysis GPS signals based bridge damage using GPS observations and wavelet transform

This paper uses GPS monitoring system on the Yonghe Bridge. After a year from re-construction of this bridge, cracks were pronounced 48.2 m far from the beginning of the abutment. To analyze the movements of bridge tower, the current operational safety, the cause of bridge cracks and sensitivity of GPS signals, and its movements were observed under different stress factors such as wind speed, temperature change and traffic loads. The observed lateral, longitudinal of bridge’s towers were studied. Two analytical methods namely; DWT and FT were used for the analysis of observation data. The analysis of test results indicates that: (1) The STFT is a significant step forward from the traditional FFT in terms of structural response analysis. (2) The sensitivity of GPS signals does not depend on the position of GPS antenna; and (3) the cracks of bridge deck bring out the frequency of the bridge tower movement transient characteristics.     

Global dynamic modeling of electro-hydraulic 3-UPS/S parallel stabilized platform by bond graph

Dynamic modeling of a parallel manipulator(PM) is an important issue. A complete PM system is actually composed of multiple physical domains. As PMs are widely used in various fields, the importance of modeling the global dynamic model of the PM system becomes increasingly prominent. Currently there lacks further research in global dynamic modeling. A unified modeling approach for the multi-energy domains PM system is proposed based on bond graph and a global dynamic model of the 3-UPS/S parallel stabilized platform involving mechanical and electrical-hydraulic elements is built. Firstly, the screw bond graph theory is improved based on the screw theory, the modular joint model is modeled and the normalized dynamic model of the mechanism is established. Secondly, combined with the electro-hydraulic servo system model built by traditional bond graph, the global dynamic model of the system is obtained, and then the motion, force and power of any element can be obtained directly. Lastly, the experiments and simulations of the driving forces, pressure and flow are performed, and the results show that, the theoretical calculation results of the driving forces are in accord with the experimental ones, and the pressure and flow of the first limb and the third limb are symmetry with each other. The results are reasonable and verify the correctness and effectiveness of the model and the method. The proposed dynamic modeling method provides a reference for modeling of other multi-energy domains system which contains complex PM.     

Real-time averaging of position data from multiple GPS receivers

Making GPS more accurate and/or reliable by combining it with other sensors and applying sophisticated data processing techniques has been attempted many times. Our approach to enhancing the performance of GPS is much simpler than most. We combine multiple (up to eight) consumer-grade GPS receivers into a system that averages their data in real time, requiring no other sensors, augmentation technologies, or powerful processors. The results show significant improvement in both accuracy and reliability of the data over that of a single receiver, and the distribution of error more closely resembles the normal distribution (as compared to a single receiver). Our multi-GPS system shows potential to be an inexpensive way to achieve better GPS performance with only “off-the-shelf” equipment.     

空气阻尼悬置非线性动态特性建模与仿真

由于空气阻尼悬置为汽车动力总成等系统的隔振元件,其性能与成本介于橡胶悬置与液阻悬置之间,以一典型空气悬置为研究对象,建立了动力学特性仿真分析的集总参数非线性模型。对其动特性进行了数值仿真,并与实验值进行了对比分析,结果证明了所建立模型的正确性。对影响空气悬置动特性的各因素进行了趋势研究,揭示了节流孔直径、节流孔长度、初始体积、激励振幅与绝热指数等因素对空气悬置特征参数的影响规律,其中减小节流孔直径可显著提高空气悬置阻尼。此研究的建模与仿真方法有助于空气悬置产品的设计与开发。     

GPS多天线变形监测系统的数据采集与控制

针对大型GPS变形监测项目成本高的问题，研究了GPS多天线技术，实现了一机对多点的监测。基于PCI04硬件平台，在VisualC＋＋6．0下开发了GPS多天线系统的数据采集与控制软件，实现了多天线微波开关的控制、与GPS接收机的通信以及GPS信息的RINEX标准格式转化。实验表明，该技术对GPS信噪比和测量精度几乎没有影响，而且大大降低了变形监测系统的成本，具有重要的经济价值和社会价值。     

接收机位置误差对GNSS定时的影响分析

不准确的接收机位置信息将会影响用户的定时结果。从理论推导和试验两方面研究了接收机位置误差对定时结果的影响。首先理论上通过对伪距观测方程求一阶微分推导得出定时接收机位置误差对定时的最大影响量;为排除卫星位置误差的影响,利用IGS提供的卫星精确位置,通过引入不同量级的接收机位置误差开展试验,对理论分析结果进行了验证;再通过接收机坐标置偏试验分析不同方向置偏不同量级的位置误差下GPS/GLONASS接收机的观测数据,分析了实际运行环境中的位置误差对接收机定时结果的影响。试验结果表明接收机的纬度、经度分量误差均会对定时结果的准确度和稳定度产生影响,纬度误差每增大1″,对GPS和GLONASS定时准确度的影响分别小于5、15 ns,对稳定度的影响分别小于10和15 ns;经度误差每增大1″,对GPS和GLONASS准确度的影响均小于1 ns,对稳定度的影响均小于10 ns;高程坐标分量误差每增加1 m,会出现约3 ns的定时偏差,对定时稳定度的影响则最大约0.3 ns/m。在实际应用中,用户可参考本文的结论根据所需定时精度的需求,考虑定时接收机输入坐标的精确度。     

一类迟滞非线性振动系统建模新方法

用理论和试验相结合的手段研究一类迟滞非线性振动系统的动力建模, 提出一种新的建模方法, 用此方法建立非线性模型用来描述这类系统的动态特性。该模型用非线性刚度和非线性阻尼机理构造, 刚度和阻尼机理由理论和试验推出, 模型中的参数由试验数据辨识。用所建模型重构恢复力——位移迟滞环, 结果表明, 该模型能很好描述这类非线性振动系统的特性, 模型中各参数的重要性得到展示, 提出的建模方法实用且有效。     

装配式钢桁架桥振动模态分析与试验研究

桥梁结构的动力学特性是其结构分析与优化设计的基础,以某型装配式钢桁架桥为研究对象,利用有限元软件ANSYS建立了该桥的三维空间有限元分析模型,并采用分块兰索斯法对其进行了模态分析,得到了桥梁的10阶固有频率和振型,而后基于环境激励的工作模态试验方法开展试验研究,通过试验数据的对比,验证了该分析方法的可靠性,为该型钢桁架桥的动力特性分析提供了直接的数据支持。     

应变片用于斯特林发动机活塞位移的动态测量

结合自由活塞斯特林发动机的结构特点,提出了采用应变片响应板弹簧变形来动态测量活塞位移的方法。根据应变片的电阻应变效应与应变仪的电桥原理,建立了一套应变片测量位移的动态标定试验系统,将动态标定数据与静态标定数据进行了比较分析。试验结果表明,应变片测量位移的方法存在一定的正反向、动静态差异,应变片的粘贴位置也会直接影响测量准确性。基于应变片传感器体积小,与板弹簧结合粘贴无需占用专门的空间,通过标定校准和合理的安装位置,仍然是一种较好的位移测量传感器。     

基于遗传神经网络的加速度传感器动态建模方法

提出了利用遗传神经网络实现加速度传感器动态建模的新方法，介绍动态建模原理以及算法，给出用遗传神经网络建立的加速度传感器动态数学模型。该方法利用加速度传感器的动态标定数据，采用遗传神经网络搜索和优化动态模型参数。这样，既保留遗传算法的全局搜索能力，克服神经网络容易陷入局部极小的缺陷，又具有神经网络局部搜索能力强的特点。结果表明：以上提出的动态建模方法具有建模精度高、鲁棒性好等优点。     

Remote calibration system for frequency based on in-place benchmark

According to the deficiencies of remote calibration mode based on material object reference, a new model of a remote calibration system for frequency based on in-place benchmark is introduced, which is made of a calibration subsystem on the spot and a remote management subsystem. The key technology of some key problems for the remote calibration system is particularly discussed, including the time and frequency benchmark receiving module based on global positioning system (GPS), frequency comparison based on a phase method, frequency division based on dual high-frequency phase locked loop (PLL), and remote calibration based on the web. The results show that the system possesses some characteristics, such as high precision, good versatility, and no limitation of time and place.     

基于USB总线的GPS数据采集系统设计

通用串行总线(USB)是一种高传输速率的串行接口总线，由于它具有即插即用、易于扩展和高速传输的特点，非常适合作为现代智能仪器的通信接口。现在被广泛应用于计算机的各种外设、数字设备和工业领域当中。对USB技术应用于GPS数据采集系统的可行性进行了分析，并重点介绍了硬件设计、设备固件设计、设备驱动程序设计及应用程序设计等方法。