论文标题:基于MATLAB的超声波声场模拟及可视化研究
Investigation on Simulation and Visibility of Ultrasonic Field Based on MATLAB
论文作者
论文导师 林莉,论文学位 硕士,论文专业 材料无损检测与评价
论文单位 大连理工大学,点击次数 162,论文页数 73页File Size5915K
2008-05-30论文网 http://www.lw23.com/lunwen_301824297/
Ultrasonic Sound Field;; M-language of Matlab;; Simulation;;Visualization
随着超声检测技术的不断发展,超声检测过程的模拟成为研究热点。超声波声场关系到缺陷的定位定量以及检测精度和灵敏度,了解声场结构及分布特征对于提高检测可靠性、准确性以及提高检测效率至关重要,所以超声波声场模拟在整个超声检测技术的模拟中具有重要地位。圆形活塞换能器、矩形活塞换能器是超声无损检测中常用的声源,而线列阵组合平面阵和矩形阵组合平面阵是相控阵换能器研究的基础,因而其声场的模拟在超声场模拟的研究中具有重要意义。 科学计算可视化(简称可视化),是计算机图形学的一个新领域,指的是运用计算机图形学和图像处理技术,将科学计算过程中产生的数据及计算结果转换成图形或图像,并在屏幕上显示出来等一系列交互处理的理论、方法和技术。本文根据积分法的理论基础——克希霍夫积分定理建立声场研究模型,推导出声场中声压分布和指向性的计算公式,利用MATLAB M语言对圆形活塞换能器和矩形活塞换能器辐射的声场进行模拟并将模拟结果可视化,利用可视化图形分析其声场分布及指向性特征,总结声场分布规律。对直径为10mm、20mm、50mm和发射频率为1MHz、2MHz、5MHz的圆形活塞换能器声场声压分布进行比较,发现频率不变声源尺寸增大或声源尺寸不变频率增大,声束的主瓣都会变窄,辐射范围缩小,副瓣增多,轴线上声压增高;对波数与声源尺寸的乘积对指向性的影响进行讨论,发现随着乘积数值的增大其声场变得尖锐,能量集中,指向性变好;在对圆形活塞换能器和矩形活塞换能器声场声压分布及指向性进行分析的基础上,进一步分析线列阵组合平面阵和矩形阵组合平面阵辐射声场的指向性特征,分别对M(行)×N(列)为2×2、3×3、3×8的线列阵组合平面阵和M(行)×N(列)为2×2、2×6的矩形阵组合平面阵的指向性分布特征进行分析,得到阵元个数及排列对指向性分布的影响规律为:阵元个数越多,指向性分布越复杂,M和N不等的阵列上阵元数较多的方向旁瓣会得到相应的抑制,主瓣比较突出;以水/钢界面为例对液/固界面对声压分布的影响进行讨论,得到声波从声阻抗较小的液体入射到声阻抗较大的固体中声压会突然变大,增大的幅度取决于透射系数。综上研究结果得出:声源尺寸、发射频率是影响声场分布及指向性特征的主要因素,对于换能器阵除了声源尺寸和发射频率之外,阵元个数及其排列情况也是影响其声场分布特征的重要因素;界面对声场的分布有较大影响,声压分布的变化取决于声阻抗及透射系数的大小。最后通过对部分声场模拟结果与已有文献进行比较,对本文研究方法及结果进行了初步验证。 对声场进行模拟并将模拟结果可视化,使抽象声场变为可见的图形图像,根据图形进行声场分析,有利于人们形象、直观地理解声场,同时可以避开烦琐的解析计算过程而降低研究难度,为分析和研究换能器辐射声场提供一种方便途径,也为检测过程中探头的选取、检测信号的接收、各种材料的超声无损表征与评价以及探头制造中参数的选取等提供参考。
Simulation of ultrasonic testing progress becomes a hot issue with the development of ultrasonic testing technology. Ultrasonic sound field has a close relation of detecting the defect, quantifying its size and accuracy and sensitivity of testing, thus understanding the structure and distribution of sound field plays an important role on improving reliablility and efficiency of ultrasonic testing. Round and rectangular piston transducers are the common sound source in ultrasonic nondestructive testing, and combination plane arrays of line and rectangular array are the foundation of investigating phased array technology, so simulating these sound field is significant for studying ultrasonic field simulation. Visualization of scientific computing (called visualization simply), is a new field of Computer Graphics. Visualization includes a series of interactive handling of the theory, methods and techniques which displayed on the screen. Using computer graphics and image processing technology, the data from scientific computing and the corresponding results will be converted into graphic or image. The sound pressure distribution and directivity formulas were deducted based on the sound field model built up by Kirchhoff integral theorem. Sound field of round and rectangular piston transducers were simulated and visualized by M-language of MATLAB. Visual graphics were applied to analyze distribution and directivity, summing up the rule of sound field. A comparison has carried out on the acoustic pressure distributions among the transducers with the diameter of 10 mm, 20mm, 50mm and exciting frequency of 1 MHz, 2MHz, 5MHz, respectively. Increasing size or frequency of the sound source will lead to that the main lobe of beam become narrow, deputy flap become more, acoustic pressure in the axis become larger and the radiation of sound field become smaller. The influence of product of wave number and sound source size on directivity was discussed, and it was found that the sound field become intense, energy become focused and its directivity become better with the increase of product value. A further analysis on the directivity character of radiation sound field of combination plane arrays of line and rectangular array was carried out on the basis of investigating directivity of round and rectangular piston transducers. Distribution and directivity character of M (row)×N (column) 2×2, 3×3, 3×8 array of line combinations plane arrays and M (row)×N (column) 2×2, 2×6 rectangular combination plane arrays were analyzed respectively. It was found that the more array number, the more complex for the distribution. In the direction (a row or column) of the more array number will make sidelobe suppression, the main lobe relatively prominent and energy more concentrated. The influence of liquid/solid interface on sound field distribution has been discussed, taking the water/steel interface for example, and it was found that the acoustic pressure in the solid will increase when the wave propagates from the small acoustic impendence medium to the large one. According to all discussions above, some effective results can be obtained: sound source size and transducer working frequency are the main factors of influencing sound field distribution and its directivity character. Also is the array number and situation. Interface has a great influence on sound field distribution, and its change depends on the value of acoustic impendence and transmission coefficient. Finally, the method in our work was verified by comparing parts of the simulation results in this paper with some previous studies. Nonrepresentational sound field was converted into eyeable images on the basis of simulation and visualization. It is conducive to analyze and comprehend sound field by an image directly. At the same time, it can avoid the complex analytic calculating process so as to reduce the difficulty of investigating the sound field. Sound field simulation and visualization provide a convenient method for analyzing and researching transducer radiation field, and selecting the transducer in various testing situation, signal reception. It is also able to provide the reference for ultrasonic characterization and evaluation, and select manufacturing parameters of transducers.
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