【摘要】：壓力容器在日常生活和工業(yè)生產(chǎn)很多領域中都得到廣泛的應用,為了使其安全、正常運行,對于其內(nèi)部壓力的檢測至關重要。傳統(tǒng)的壓力測量方法往往需要進行開孔等可能破壞容器完整性的操作。非介入式壓力檢測方法具有安全、便攜等優(yōu)點,應用前景良好。基于超聲波的非介入式壓力檢測,其主要的理論基礎是聲彈性效應和薄殼理論。在對相關領域的文獻和成果的研究基礎之上,本論文建立了基于臨界折射縱波、反射縱波的線性和非線性壓力測量模型,對模型的波形選擇進行了研究,并對各個模型進行了分析和比較。本論文的主要研究成果和創(chuàng)新之處在于:(1)提出了基于最佳子集回歸和逐步回歸算法的多變量壓力測量模型輸入波形的選擇方法。之前多變量壓力測量模型輸入波形的選擇只是簡單的根據(jù)輸入波形的區(qū)分度和信噪比。用于建立模型的波形的選擇至關重要:一方面,越多的解釋變量更多的自變量可以使信息更加完整、全面,使預測更加精確,但也可能造成"過擬合"的現(xiàn)象,同時需要估計的參數(shù)個數(shù)增加會導致方差提高;另一方面,過少的解釋變量可能造成"欠擬合"的現(xiàn)象,預測準確度降低。本文將最佳子集回歸和逐步回歸算法應用于輸入信號波形的選擇,可以建立更優(yōu)、更符合選定準則的模型。(2)針對線性壓力測量模型精度不高的問題,提出并建立了基于臨界折射縱波、反射縱波的非線性壓力測量模型。根據(jù)聲彈性效應和薄殼理論,壓力與臨界折射縱波、反射縱波呈線性關系,但實驗數(shù)據(jù)表明在某些壓力范圍內(nèi),二者存在非線性關系。本論文嘗試使用非線性方法進行建模,包括將傳播時延的二次項加入測量模型以及基于神經(jīng)網(wǎng)絡的測量模型,實驗結(jié)果表明,非線性壓力測量模型比線性壓力測量模型的測量精度更高,非線性模型中基于BFGS神經(jīng)網(wǎng)絡的模型測量精度最高。(3)對超聲波在容器壁中的傳播過程的信號幅值變化機理進行了理論分析。超聲波從發(fā)射探頭到接收探頭傳播過程中,由于反射、折射等會引起波型轉(zhuǎn)換和能量分配,另外,在傳播過程中由于散射、擴散和吸收也會引起能量的衰減,綜合表現(xiàn)為幅值的變化。為了確定合適的探頭間距,以獲取信噪比更高的波形,本論文對超聲波在圓柱型壓力容器壁的傳播過程中的幅值變化進行了理論分析。
[Abstract]:Pressure vessels are widely used in many fields of daily life and industrial production. In order to make them safe and normal operation, it is very important to detect the internal pressure. Traditional pressure measurement methods often require operations such as opening holes that may damage the integrity of the vessel. The non-interventional pressure detection method has the advantages of safety and portability, and has a good prospect in application. The main theoretical basis of non-interventional pressure measurement based on ultrasonic wave is acoustic elastic effect and thin shell theory. Based on the research of literature and achievements in related fields, the linear and nonlinear pressure measurement models based on critical refraction P-wave and reflected P-wave are established in this paper, and the waveform selection of the model is studied. The models are analyzed and compared. The main achievements and innovations of this thesis are as follows: (1) an input waveform selection method based on optimal subset regression and stepwise regression algorithm for multivariable pressure measurement model is proposed. The selection of input waveform of multivariable pressure measurement model is simply based on the discrimination and signal-to-noise ratio of the input waveform. The choice of waveforms used to build models is crucial: on the one hand, more explanatory variables and more independent variables can make information more complete, more comprehensive, and more accurate predictions, but may also result in "overfitting". On the other hand, too few explanatory variables may cause the phenomenon of "under-fitting", and the accuracy of prediction will be reduced. In this paper, the optimal subset regression and stepwise regression algorithms are applied to the selection of input signal waveforms, which can set up a better model, which is more consistent with the selected criteria. (2) the accuracy of the linear pressure measurement model is not high enough. A nonlinear pressure measurement model based on critical refraction P-wave and reflected P-wave is proposed and established. According to the acoustoelastic effect and thin shell theory, the pressure is linearly related to the critical refraction longitudinal wave and the reflected longitudinal wave, but the experimental data show that there is a nonlinear relationship between them in some pressure range. This thesis attempts to use nonlinear method to model the model, including adding the quadratic term of propagation delay into the measurement model and the measurement model based on neural network. The experimental results show that, The accuracy of nonlinear pressure measurement model is higher than that of linear pressure measurement model. In the nonlinear model, the model based on BFGS neural network has the highest measurement accuracy. (3) the mechanism of signal amplitude variation in the process of ultrasonic wave propagation in the vessel wall is analyzed theoretically. In the process of ultrasonic wave propagation from transmitting probe to receiving probe, wave type conversion and energy distribution will be caused by reflection and refraction. In addition, energy attenuation will also be caused by scattering, diffusion and absorption during the propagation process. The comprehensive performance is the change of amplitude. In order to determine the appropriate probe spacing and obtain the higher signal-to-noise ratio (SNR) waveform, the amplitude variation of ultrasonic wave during the propagation of cylindrical pressure vessel wall is theoretically analyzed in this paper.
【學位授予單位】：浙江大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TH49;TB559

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本文編號：2190134