基于PIV观测土体动态变形时程的可行性探讨

Discussion on the feasibility of monitoring soil dynamic deformation time history based on PIV

图像变形量测技术在分析土体变形矢量场和等势云图方面已获得广泛应用,但在获取土体动态变形时程方面目前尚未见探讨。为探明图像变形测量在土体动态变形时程观测中的可行性与基本要求,结合土体图像与变形模拟方法,利用PIV量测技术,分别对不同动荷载频率、图像采集帧率、应变计算窗口、应变大小等情况的图像测量结果作出分析,并提出动态窗口应变分析算法计算动态应变。研究表明:在实现位移时程与加速度时程观测时,正弦波的图像采集帧率应≥6倍输入波频率,Northridge波、LomaGilroy波、Tangshan波的图像采集帧率需分别≥20Hz、≥10Hz和≥6Hz;大比例应变计算窗口可有效缩小应变场的离散性,但会导致非均恒分布应变的计算结果偏离真值;提出的动态窗口应变分析算法可兼顾计算结果的平滑度与精准度,更有利于动态应变分析。

Image deformation measurement technology has been widely used in analyzing soil deformation vector field and equipotential cloud map,but it has not been discussed in obtaining soil dynamic deformation time history.In order to explore the applicability and basic requirements of image measurement technology in the observation of soil dynamic deformation time history,combined with soil image and deformation simulation method,PIV technology is used to analyze the image measurement results of different dynamic load frequency,image acquisition frequency,strain calculation window and strain amplitude,and a variable window strain analysis algorithm is proposed to calculate the dynamic strain.The research shows that the image acquisition frequency of sinusoidal load must be at least 6 times the load frequency,and the image acquisition frequencies of Northridge accelerogram record,Lomagilroy accelerogram record and Tangshan accelerogram record shall be≥20 Hz,≥10 Hz and≥6 Hz respectively,when realizing the observation of displacement time series and acceleration time series;a large strain calculation window can effectively reduce the discreteness of the strain field,but it will lead to the calculation results of non-constant distribution strain deviate from the true value;the proposed variable window strain analysis algorithm can give consideration to the smoothness and accuracy of the calculation results,which is more conducive to dynamic strain analysis.