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  本文選題：混凝土結(jié)構(gòu) + 細觀模型��； 參考：《江蘇大學》2017年碩士論文

【摘要】：本文提出了一種針對混凝土結(jié)構(gòu)損傷檢測的時間逆轉(zhuǎn)損傷成像方法。本文以檢測混凝土結(jié)構(gòu)中與骨料尺寸相近的微小損傷為目的,為了改進先前研究中將混凝土結(jié)構(gòu)視為均質(zhì)材料而造成的研究實用性不足的缺點,引入細觀混凝土隨機骨料模型。該模型將混凝土結(jié)構(gòu)視為由水泥漿基底、骨料及黏粘層組成的三相復合材料,基于Monte Carlo隨機樣本原理并結(jié)合Matlab軟件建立。在數(shù)值模擬分析中,將建立的細觀模型導入有限元分析軟件進行超聲波場模擬。采用自適應(yīng)性強的時間逆轉(zhuǎn)模型(Time Reversed Model-TRM)進行損傷定位,并提出了一種基于小波變換的峰值時刻波場成像方法。最終搭建實驗平臺并澆筑真實混凝土試件進行驗證。實驗結(jié)果表明時間逆轉(zhuǎn)模型對于復雜混凝土結(jié)構(gòu)的損傷定位具有強的適用性,基于小波變換的峰值時刻成像法能夠消除噪聲干擾提高成像精度。本文提出的基于細觀混凝土模型的時間逆轉(zhuǎn)損傷成像方法的主要研究內(nèi)容有:1)依據(jù)真實混凝土試件的骨料級配曲線并結(jié)合骨料投放理論生成混凝土細觀幾何模型,基于Comsol with Matlab軟件的交互性,將建立的二維模型導入Comsol Multiphysics軟件進行損傷及傳感器的設(shè)置和網(wǎng)格劃分以完善仿真模型。2)修正時間逆轉(zhuǎn)損傷成像模型(TRM),以用于混凝土結(jié)構(gòu)主動損傷檢測研究。TRM分為正向檢測和逆時成像兩個部分:正向檢測過程通過單點激勵多點接收模式得到包含損傷散射回波信號的一系列結(jié)構(gòu)響應(yīng)信號,從數(shù)值角度進行時間反演并作為逆時過程的輸入信號;逆時成像過程選用等效彈性參數(shù)模型,幾何尺寸與隨機骨料模型相同,時反信號在相應(yīng)幾何位置同時加載形成時反波場,時反波場在損傷位置會發(fā)生干涉疊加從而導致能量峰值的出現(xiàn),通過確定干涉峰值時刻,并獲取該時刻對應(yīng)原始波場以及小波變換能量場完成成像。與原始數(shù)據(jù)波場圖相比,小波變換處理成像結(jié)果消除了雜波干擾,成像結(jié)果更加清晰。進一步對等效彈性參數(shù)模型中等效彈性參數(shù)的取值進行討論,并且在骨料尺寸范圍內(nèi)調(diào)整損傷大小以驗證成像精度,結(jié)果顯示成像結(jié)果匹配度高,對于非均質(zhì)混凝土結(jié)構(gòu)的損傷檢測已很好滿足工程實際需求。3)搭建實驗平臺,澆筑混凝土試塊并預設(shè)通孔損傷,通過激勵超聲信號并接收結(jié)構(gòu)響應(yīng)信號獲取損傷散射回波,將損傷信號時反處理并在等效彈性參數(shù)模型中加載獲取時反波場數(shù)據(jù)并進行小波變換處理,基于小波變換數(shù)據(jù)進行峰值時刻波場成像,完成實驗驗證。
[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.
【學位授予單位】：江蘇大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TU37;TU317

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