發(fā)布時(shí)間：2018-01-23 20:55

  本文關(guān)鍵詞： 超聲導(dǎo)波 桿類結(jié)構(gòu) 有限元仿真 二維傅立葉變換 頻散特性　出處：《北京工業(yè)大學(xué)》2014年碩士論文　論文類型：學(xué)位論文

【摘要】：平行鋼絲拉索、預(yù)應(yīng)力鋼絞線、鋼絲繩等被廣泛應(yīng)用在民用建筑和特種設(shè)備上，在其使用過程中因受服役條件與環(huán)境等因素影響，不可避免地會(huì)產(chǎn)生疲勞、銹蝕等現(xiàn)象，威脅整體結(jié)構(gòu)的正常使用和運(yùn)行安全。超聲導(dǎo)波技術(shù)具有實(shí)現(xiàn)上述結(jié)構(gòu)長(zhǎng)距離缺陷檢測(cè)的巨大潛力。建立并求解表征超聲導(dǎo)波傳播特性的頻散方程是將導(dǎo)波技術(shù)應(yīng)用于上述結(jié)構(gòu)缺陷檢測(cè)的理論基礎(chǔ)。由于平行鋼絲拉索、預(yù)應(yīng)力鋼絞線、鋼絲繩等幾何結(jié)構(gòu)復(fù)雜，加上鋼線內(nèi)部存在多樣的接觸類型，要得到頻散方程的解析解較為困難。理論分析中，通常將上述結(jié)構(gòu)等效為具有特殊截面的桿類結(jié)構(gòu)進(jìn)行研究，而忽略內(nèi)部鋼線的接觸。有限元仿真計(jì)算模型中既可以考慮桿類結(jié)構(gòu)的復(fù)雜幾何形狀，又可以考慮桿間的接觸，是分析超聲導(dǎo)波在上述結(jié)構(gòu)中頻散特性的有效手段，結(jié)合有效的信號(hào)處理方法，可以提取得到結(jié)構(gòu)的頻散曲線，為結(jié)構(gòu)的超聲導(dǎo)波檢測(cè)技術(shù)發(fā)展提供指導(dǎo)。 本文基于超聲導(dǎo)波傳播特性基本理論，采用有限元模擬中的瞬態(tài)動(dòng)力學(xué)分析方法，得出直桿結(jié)構(gòu)中的超聲導(dǎo)波信號(hào)，并分別采用短時(shí)傅立葉變換、二維傅立葉變換等分析方法，提取得到直桿中導(dǎo)波頻散曲線；在此基礎(chǔ)上，將有限元仿真方法與二維傅立葉變換方法相結(jié)合，對(duì)具有不同桿徑、螺旋角等參數(shù)的一階螺旋桿模型中的導(dǎo)波傳播特性進(jìn)行了研究；探索了鋼線間接觸條件對(duì)雙直桿、7芯鋼絞線中導(dǎo)波頻散特性的影響規(guī)律。具體工作包括： (1)基于ABAQUS有限元仿真平臺(tái)，建立直桿模型，模擬分析了超聲導(dǎo)波在直桿中的傳播特性，并分析了有限元網(wǎng)格劃分類型、網(wǎng)格尺寸及計(jì)算時(shí)間步長(zhǎng)對(duì)仿真結(jié)果計(jì)算精度的影響，，優(yōu)化了有限元仿真計(jì)算參數(shù)。 (2)分別采用短時(shí)傅立葉變換和二維傅立葉變換兩種分析方法，對(duì)有限元仿真計(jì)算所得直桿結(jié)構(gòu)中的導(dǎo)波仿真信號(hào)進(jìn)行處理，提取出1MHz以下頻率范圍內(nèi)直桿結(jié)構(gòu)的頻散曲線，并與理論頻散曲線進(jìn)行對(duì)比，分析出短時(shí)傅立葉變換、二維傅立葉變換兩種分析方法的有效性和計(jì)算精度。 (3)以一階螺旋桿為研究對(duì)象，引入螺旋坐標(biāo)系并推導(dǎo)了螺旋坐標(biāo)與笛卡爾坐標(biāo)的轉(zhuǎn)換關(guān)系，通過二維傅立葉變換方法對(duì)一階螺旋桿中導(dǎo)波傳播的加速度信號(hào)進(jìn)行處理，提取出頻率-波數(shù)分布曲線。研究了螺旋角和桿半徑兩個(gè)幾何參數(shù)對(duì)導(dǎo)波傳播的影響規(guī)律以及導(dǎo)波傳播中的頻率截止與模態(tài)分離等現(xiàn)象。 (4)采用二維傅立葉變換方法，探索性地研究了接觸條件下雙直桿結(jié)構(gòu)和7芯鋼絞線結(jié)構(gòu)的頻散特性。分析了接觸力變化時(shí)，在1MHz頻率范圍內(nèi)兩種結(jié)構(gòu)中頻散曲線的變化規(guī)律。
[Abstract]:Parallel steel wire cables, prestressed steel strands and wire ropes are widely used in civil buildings and special equipment. Due to the influence of service conditions and environment, fatigue will inevitably occur in the process of use. Corrosion, etc. Ultrasonic guided wave technology has great potential to realize long distance defect detection of the structure mentioned above. The dispersion equation of ultrasonic guided wave propagation characteristic is established and solved. Applied to the theoretical basis of structural defect detection, due to parallel wire cables. It is difficult to get the analytical solution of dispersion equation because of the complex geometric structure of prestressed steel strand and wire rope and the variety of contact types inside the steel wire. Usually, the above structure is equivalent to the rod structure with special section, but the contact of the internal steel wire is ignored. The complex geometry of the rod structure can be considered in the finite element simulation model. Considering the contact between rods, it is an effective means to analyze the dispersion characteristics of ultrasonic guided waves in the above structure. Combined with the effective signal processing method, the dispersion curve of the structure can be extracted. It provides guidance for the development of ultrasonic guided wave detection technology. Based on the basic theory of ultrasonic guided wave propagation characteristics, the transient dynamic analysis method in finite element simulation is used to obtain the ultrasonic guided wave signal in the straight bar structure, and the short time Fourier transform is used respectively. Two dimensional Fourier transform and other analytical methods were used to extract the dispersion curve of guided wave in the straight rod. On this basis, combining the finite element simulation method with the two-dimensional Fourier transform method, the propagation characteristics of guided wave in the first-order helical rod model with different rod diameter and helical angle are studied. The influence of the contact conditions between steel wires on the dispersion characteristics of guided waves in the steel strands with double straight rods and 7 cores is explored. The specific work includes: 1) based on the ABAQUS finite element simulation platform, the straight bar model is established, and the propagation characteristics of ultrasonic guided waves in the bar are simulated and analyzed, and the type of finite element mesh generation is analyzed. The effect of mesh size and calculation time step on the accuracy of the simulation results is discussed. The finite element simulation parameters are optimized. 2) two kinds of analysis methods, short time Fourier transform and two dimensional Fourier transform, are used to deal with the simulated signal of guided wave in the straight bar structure by finite element simulation. The dispersion curve of the straight bar structure in the frequency range below 1MHz is extracted, and compared with the theoretical dispersion curve, the short-time Fourier transform is analyzed. The validity and accuracy of two-dimensional Fourier transform analysis methods. Taking the first order helical bar as the research object, the helical coordinate system is introduced and the transformation relationship between the helical coordinate and the Cartesian coordinate is deduced. The acceleration signal of guided wave propagation in the first order helical rod is processed by two-dimensional Fourier transform method. The distribution curve of frequency-wave number was extracted, and the influence of helix angle and rod radius on guided wave propagation was studied, and the phenomena of frequency cutoff and modal separation in guided wave propagation were studied. In this paper, the dispersion characteristics of double straight bar structure and 7 core steel strand structure under contact condition are studied by using two dimensional Fourier transform method, and the variation of contact force is analyzed. The variation of intermediate dispersion curves of two structures in the frequency range of 1 MHz.
【學(xué)位授予單位】：北京工業(yè)大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2014
【分類號(hào)】：TB553

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