基于细观混凝土模型的时间逆转损伤成像方法研究

发布时间：2018-04-24 18:59

本文选题：混凝土结构 + 细观模型　；参考：《江苏大学》2017年硕士论文

【摘要】：本文提出了一种针对混凝土结构损伤检测的时间逆转损伤成像方法。本文以检测混凝土结构中与骨料尺寸相近的微小损伤为目的,为了改进先前研究中将混凝土结构视为均质材料而造成的研究实用性不足的缺点,引入细观混凝土随机骨料模型。该模型将混凝土结构视为由水泥浆基底、骨料及黏粘层组成的三相复合材料,基于Monte Carlo随机样本原理并结合Matlab软件建立。在数值模拟分析中,将建立的细观模型导入有限元分析软件进行超声波场模拟。采用自适应性强的时间逆转模型(Time Reversed Model-TRM)进行损伤定位,并提出了一种基于小波变换的峰值时刻波场成像方法。最终搭建实验平台并浇筑真实混凝土试件进行验证。实验结果表明时间逆转模型对于复杂混凝土结构的损伤定位具有强的适用性,基于小波变换的峰值时刻成像法能够消除噪声干扰提高成像精度。本文提出的基于细观混凝土模型的时间逆转损伤成像方法的主要研究内容有:1)依据真实混凝土试件的骨料级配曲线并结合骨料投放理论生成混凝土细观几何模型,基于Comsol with Matlab软件的交互性,将建立的二维模型导入Comsol Multiphysics软件进行损伤及传感器的设置和网格划分以完善仿真模型。2)修正时间逆转损伤成像模型(TRM),以用于混凝土结构主动损伤检测研究。TRM分为正向检测和逆时成像两个部分:正向检测过程通过单点激励多点接收模式得到包含损伤散射回波信号的一系列结构响应信号,从数值角度进行时间反演并作为逆时过程的输入信号;逆时成像过程选用等效弹性参数模型,几何尺寸与随机骨料模型相同,时反信号在相应几何位置同时加载形成时反波场,时反波场在损伤位置会发生干涉叠加从而导致能量峰值的出现,通过确定干涉峰值时刻,并获取该时刻对应原始波场以及小波变换能量场完成成像。与原始数据波场图相比,小波变换处理成像结果消除了杂波干扰,成像结果更加清晰。进一步对等效弹性参数模型中等效弹性参数的取值进行讨论,并且在骨料尺寸范围内调整损伤大小以验证成像精度,结果显示成像结果匹配度高,对于非均质混凝土结构的损伤检测已很好满足工程实际需求。3)搭建实验平台,浇筑混凝土试块并预设通孔损伤,通过激励超声信号并接收结构响应信号获取损伤散射回波,将损伤信号时反处理并在等效弹性参数模型中加载获取时反波场数据并进行小波变换处理,基于小波变换数据进行峰值时刻波场成像,完成实验验证。
[Abstract]:This paper presents a time reversal damage imaging method for damage detection of concrete structures. In order to detect the small damage in concrete structure which is close to aggregate size, in order to improve the deficiency of research practicability caused by using concrete structure as homogenous material in previous studies, this paper introduces a meso-concrete random aggregate model. In this model, the concrete structure is regarded as a three-phase composite composed of cement slurry substrate, aggregate and viscous layer. It is based on Monte Carlo random sample principle and combined with Matlab software. In the numerical simulation, the established mesoscopic model is introduced into the finite element analysis software to simulate the ultrasonic field. The time Reversed Model-TRM (time Reversed Model-TRM) is used to locate the damage, and a peak time wave field imaging method based on wavelet transform is proposed. Finally, the experimental platform is built and the real concrete specimen is built for verification. The experimental results show that the time reversal model is applicable to the damage location of complex concrete structures, and the peak moment imaging method based on wavelet transform can eliminate the noise interference and improve the imaging accuracy. In this paper, the main research contents of time reversal damage imaging method based on meso-concrete model are: (1) according to the aggregate gradation curve of real concrete specimen and combining with aggregate dropping theory, the concrete meso geometric model is generated. Based on the interactivity of Comsol with Matlab software, The two-dimensional model is imported into the Comsol Multiphysics software for damage and sensor setting and meshing to perfect the simulation model. 2) the modified time reversal damage imaging model is used to study the active damage detection of concrete structures. Forward detection and inverse time imaging are two parts: the forward detection process obtains a series of structural response signals including the damage scattering echo signal by single point excitation multi-point receiving mode. Time inversion is carried out from a numerical point of view and used as the input signal of the inverse time process, the equivalent elastic parameter model is used in the inverse imaging process, and the geometric dimension is the same as that of the random aggregate model, and the time inverse signal is loaded at the corresponding geometric position at the same time to form the inverse wave field. The interference superposition of the time inverse wave field in the damage position leads to the appearance of the peak energy. By determining the interference peak time and obtaining the time corresponding to the original wave field and the wavelet transform energy field, the imaging is completed. Compared with the original data, the wavelet transform can eliminate the clutter, and the imaging result is clearer. Furthermore, the value of equivalent elastic parameters in the model of equivalent elastic parameters is discussed, and the damage size is adjusted within the size range of aggregate to verify the imaging accuracy. The results show that the imaging results have a high matching degree. For the damage detection of heterogeneous concrete structure, it has met the actual engineering demand. 3) build the experimental platform, put the concrete test block and preset the through hole damage, and obtain the damage scattering echo by exciting the ultrasonic signal and receiving the structural response signal. The damage signal is processed in time and the acquired inverse wave field data are loaded in the equivalent elastic parameter model and processed by wavelet transform. The peak time wave field is imaged based on the wavelet transform data and the experimental verification is completed.
【学位授予单位】：江苏大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU37;TU317

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