基于二维傅立叶变换的杆类结构导波频散特性有限元分析

发布时间：2018-01-23 20:55

本文关键词： 超声导波杆类结构有限元仿真二维傅立叶变换频散特性　出处：《北京工业大学》2014年硕士论文　论文类型：学位论文

【摘要】：平行钢丝拉索、预应力钢绞线、钢丝绳等被广泛应用在民用建筑和特种设备上，在其使用过程中因受服役条件与环境等因素影响，不可避免地会产生疲劳、锈蚀等现象，威胁整体结构的正常使用和运行安全。超声导波技术具有实现上述结构长距离缺陷检测的巨大潜力。建立并求解表征超声导波传播特性的频散方程是将导波技术应用于上述结构缺陷检测的理论基础。由于平行钢丝拉索、预应力钢绞线、钢丝绳等几何结构复杂，加上钢线内部存在多样的接触类型，要得到频散方程的解析解较为困难。理论分析中，通常将上述结构等效为具有特殊截面的杆类结构进行研究，而忽略内部钢线的接触。有限元仿真计算模型中既可以考虑杆类结构的复杂几何形状，又可以考虑杆间的接触，是分析超声导波在上述结构中频散特性的有效手段，结合有效的信号处理方法，可以提取得到结构的频散曲线，为结构的超声导波检测技术发展提供指导。本文基于超声导波传播特性基本理论，采用有限元模拟中的瞬态动力学分析方法，得出直杆结构中的超声导波信号，并分别采用短时傅立叶变换、二维傅立叶变换等分析方法，提取得到直杆中导波频散曲线；在此基础上，将有限元仿真方法与二维傅立叶变换方法相结合，对具有不同杆径、螺旋角等参数的一阶螺旋杆模型中的导波传播特性进行了研究；探索了钢线间接触条件对双直杆、7芯钢绞线中导波频散特性的影响规律。具体工作包括： (1)基于ABAQUS有限元仿真平台，建立直杆模型，模拟分析了超声导波在直杆中的传播特性，并分析了有限元网格划分类型、网格尺寸及计算时间步长对仿真结果计算精度的影响，，优化了有限元仿真计算参数。 (2)分别采用短时傅立叶变换和二维傅立叶变换两种分析方法，对有限元仿真计算所得直杆结构中的导波仿真信号进行处理，提取出1MHz以下频率范围内直杆结构的频散曲线，并与理论频散曲线进行对比，分析出短时傅立叶变换、二维傅立叶变换两种分析方法的有效性和计算精度。 (3)以一阶螺旋杆为研究对象，引入螺旋坐标系并推导了螺旋坐标与笛卡尔坐标的转换关系，通过二维傅立叶变换方法对一阶螺旋杆中导波传播的加速度信号进行处理，提取出频率-波数分布曲线。研究了螺旋角和杆半径两个几何参数对导波传播的影响规律以及导波传播中的频率截止与模态分离等现象。 (4)采用二维傅立叶变换方法，探索性地研究了接触条件下双直杆结构和7芯钢绞线结构的频散特性。分析了接触力变化时，在1MHz频率范围内两种结构中频散曲线的变化规律。
[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.
【学位授予单位】：北京工业大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TB553

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