Assessment of integration method for displacement determination using field accelerometer and geophone data

Abstract

A conventional French railway track was instrumented with accelerometers and geophones at three depths: sleeper (surface), interlayer (ITL, z=−0.93 m), and transition layer (TL, z=−1.20 m). A linear variable differential transformer (LVDT) was also used to monitor the displacement at the sleeper level. The recorded data allow the integration method (double for accelerometer and simple for geophone) for displacement determination to be assessed. Several questions need to be addressed prior to the selection of an adequate monitoring system: definition of signal filtering processes, influence on results of the different loading wavelengths, repeatability of measurements, train speed and axle load impact and their ranges of validity for each sensor. It was found that the main frequencies that caused more than 95% of the displacement of the monitored materials are in the low frequency range: <25 Hz for trains running up to 200 km/h. For an intercity train, the low frequencies are normally excited by long wavelengths, for instance, those corresponding to the 1/2 coach distance (λ=13.20 m), the bogies distance (λ=6.3 m), and the axle distance (λ=2.8 m). Comparison between the displacements deduced from the records of accelerometer and geophone and obtained from the records of LVDT shows quite consistent results; the mean displacement amplitudes obtained from accelerometers differ by only 20% from the LVDT records. The train speed does not have a strong effect on the obtained differences between sensors. The embedded sensors also gave consistent displacement results for each analysed depth. Moreover, the displacement amplitudes caused by different axle loads (locomotive or passenger coach) are distinguishable for all sensors at all depths. This validates the integration method used for the displacement determination.

目的

本文旨在研究不同波长载荷(包括车厢长度、构架长度以及轴距等)对位移确定的影响,利用积分方法确定位移的有效性和重复性的适用范围,以及研究列车速度和轴荷载对变形量的影响,为轨道基础位移监测提供重要的方法。

创新点

1. 评价和分析一种积分方法,该方法利用低通滤波法但不消除产生变形的主要频率;2. 通过对位移、速度和加速度传感器在时域和频域结果的比较,使重复性得到保证。

方法

利用线性可变差位移传感器、地震检波器以及加速度计获取轨道不同深度的位移、速度和加速度,然后利用巴特沃兹低通滤波器对3类数据进行滤波。通过对速度一阶积分、加速度二阶积分,获得由3 种传感器测试得到的位移并 验证其准确性。

结论

通过测试和分析发现,95%的位移幅值来自于 波长大于轴距(2.8m)的激励,对应的低频为25Hz(列车运行速度为200km/h)。通过线性可 变差位移传感器、地震检波器以及加速度计直接获得或间接积分获得的位移十分接近,验证了积分方法的有效性,且其具有较高的可重复性。