【作者】 范迪；

【导师】 曹茂永；

【作者基本信息】 山东科技大学 ， 控制理论与控制工程， 2010， 博士

【摘要】 钻孔底部过厚的沉渣是影响钻孔灌注桩质量的主要因素,而目前尚缺乏先进准确的沉渣厚度检测仪器,针对这一现状,本文提出钻孔沉渣厚度的超声测量方法,并围绕其超声信号处理中的滤波、增强和声走时获取等问题展开了一系列的研究工作,主要包括：1、分析了超声检测系统的四种工作模式及超声换能器参数与检测指标间的关系,确定了钻孔沉渣厚度超声检测所用超声换能器的特性,并在模拟环境中进行实验,获得了比较清晰的沉渣界面回波。2、研究了时域和变换域Gabor滤波。分析了Gabor变换系数的特点,提出了基于首个大类间距概率的阈值选取方法,并给出了详细的处理步骤。基于首个大类间距概率阈值的Gabor变换滤波在仿真信号和实际超声检测信号的处理中都获得了很好的效果。3、把迭代被动时间反转镜(PTRM)技术用于超声检测信号的增强,分析了二次迭代PTRM的时变增强原理和增强倍数。实验表明,该增强方法在介质声波传播特性未知的情况下能够实现信号的盲时变增强,同时还具有一定的噪声抑制能力。4、把谱减和子带的概念引入到奇异谱熵中,并给出了奇异谱子带的划分方式。提出了谱减子带奇异谱熵并把它用于超声信号的首波检测和定位。试验表明,基于谱减子带奇异谱熵的首波定位精确度高、抗干扰能力强、鲁棒性好。5、提出虚拟阵MUSIC时延估计算法,并给出虚拟阵元信号的构造方法和最少虚拟真元个数。在超声信号的时延估计中,虚拟阵MUSIC时延估计算法获得了高精度、高分辨率的时延估计结果。6、把以上提出的方法应用到实验获得中的沉渣超声测量信号的处理中,得到获得了比较理想的结果,证实了沉渣厚度超声检测的可行性和所提出处理方法的有效性。更多还原

【Abstract】 Too thick sediment in the bottom of borehole is a main factor which much affects the quality of the bored pile. So far the advanced and exact instruments to measure the sediments thickness are deficient. Based on this status, a new method to measure the sediments thickness by ultrasonic technology has been proposed and a series of research work about the ultrasonic signal processing as filtering, signal enhancing and sound travel time obtaining has been developed. The major work of this dissertation includes six parts as the following:1. The four work modes of ultrasonic detection systems and the relations between the parameters of ultrasonic transducer and detection indexes have been analyzed. According to them, the characteristics of ultrasonic transducer needed in ultrasonic detection system to measure the sediments thickness in borehole has been determined. Using the specially made ultrasonic transducer and necessary instruments such as waveform generator, power amplifier, digital oscillograph and so on, experiments in simulation environments have been carried out and clear echoes of the sediments interfaces have been obtained.2. Gabor filtering in time domain and transform domain has been studied. According to the analysis of the features of Gabor expansion coefficients, a new method to select Gabor transform filter’s threshold based on the first larger probability in histogram of class separation distance, and its detail process steps have been given. Using the presented threshold, the Gabor transform filter can achieve good effect in processing both the simulation signal and the real ultrasonic detection signal.3. The iterative passive time reverse mirror (PTRM) has been used to enhance ultrasonic detection signal. As for iterative PTRM, its principle of time-varying enhancement and the enhancement multiple have been analyzed and deducted. The experiments results have shown that iterative PTRM can enhance signal with a time-varying gain even the characteristics of the ultrasonic transmitting in the media is unknown. In addition, iterative PTRM can de-noise to some extent.4. The concepts of band and spectral subtraction have been introduced into singular value spectrum entropy and the way how to plot out the bands has been given. On this base, spectral subtraction band singular value spectrum entropy (SS-B-SVSE) has been proposed and applied to detect and locate the wave head of ultrasonic signal. The experiments have shown SS-B-SVSE is a high precise, strongly anti-interference and robust method for locating wave head in ultrasonic signal.5. Virtual matrix MUSIC (VM-MUSIC) has been presented to estimate the time delays of the echoes. Furthermore, the way how to construct the signal of virtual matrix elements and the least matrix elements in virtual matrix have been discussed and determined. In the experiments of the ultrasonic detection signal, VM-MUSIC has gotten high precise and high resolution time delay estimation.6. The proposed signal processing algorithms above have been used to process the ultrasonic echoes which are obtained by experimenting in the simulation environments. The satisfied results have verified the feasibility of the method of measuring the sediments thickness in borehole by ultrasonic and the validity of the processing algorithms.更多还原