【作者】 朱明；

【导师】 王殊；

【作者基本信息】 华中科技大学 ， 信息与通信工程， 2008， 博士

【摘要】 在现代社会生活和工业生产中,气体浓度检测有着广泛的需求和应用前景,实时检测混合气体中多种成分的浓度更是被人们广泛研究。传统又年轻的弛豫声学方法混合气体浓度检测,以成本较低、寿命较长、功耗较小、响应速度较快、测量浓度范围不受限、能同时检测出具有不同特性的多种气体浓度等优点,正在被学者们大力研究。混合气体浓度检测的弛豫声学方法是,利用声速、声衰减等声学参量随气体成分浓度的改变而变化的特性,寻找和建立声速、声衰减、声频率、气体成分浓度之间关系的模型,研究如何利用声速、声衰减系数、有效弛豫频率等具体声学参数与气体浓度之间的模型检测混合气体成分浓度的理论和技术,属于数学、物理学、电子学、信号处理等学科的交叉前沿成果。本论文根据弛豫声学方法混合气体浓度检测的特点,对经典声速理论、经典声衰减理论、弛豫声衰减理论、分子碰撞能量转移理论等众多气体声学理论进行研究、扩展和创新,分析并解决了弛豫声学方法检测三种成分、四种成分混合气体浓度的关键技术。本论文所开展的研究工作主要有以下内容: 1.在分子碰撞能量转移模型和有效弛豫频率算法方面,本论文证明了有效弛豫频率作为第三个气体声学参数的合理性;通过在气体分子碰撞能量转移概率的计算中忽略近似共振振动模式,重新界定了参与分子碰撞能量转移模型的气体分子振动频率;推导了四种成分混合气体有效弛豫频率的弛豫矩阵算法,从弛豫理论上统一了弛豫矩阵算法和最大声衰减系数算法的结果,使得有效弛豫频率用于弛豫声学方法检测混合气体浓度成为可能。2.在四种成分混合气体浓度的弛豫声学检测算法方面,本论文首次将有效弛豫频率引入弛豫声学方法检测混合气体浓度,结合弛豫衰减系数和声速,完成了用三种参数检测四种成分混合气体浓度的弛豫声学算法,同时验证了该算法的精确度,以及不同浓度时该算法对声频率偏移的线性性和健壮性,证明了该算法存在通过多次测量的平均值减少实验误差的可能性,使该算法在实际中可行。3.在三种成分混合气体浓度的弛豫声学检测算法方面,本论文确定了声速和经典声衰减理论在声学方法混合气体浓度检测中的相关性,并将经典声衰减从声衰减模型中去掉,分析了弛豫衰减系数和声速与混合气体各成分浓度和声频率之间的依赖关系,分别建立了弛豫衰减系数与声频率的二维模型,以及弛豫衰减系数和声速与气体浓度的三维模型,完成了通过测量弛豫声衰减系数和声速计算三种成份混合气体浓度的算法;通过分析气体分子碰撞能量转移理论,找到了微弱浓度时弛豫衰减系数与混合气体浓度的三维曲面变为崎岖不平的原因,利用信号处理中的滤波思想,使用平滑窗处理弛豫声衰减结果,将三种成分混合气体浓度检测算法扩展到了微弱气体浓度检测,检测浓度达到0.001%;通过仿真实验还发现了三种成分混合气体浓度弛豫声学检测算法的最佳适用声频率范围——小于有效弛豫频率的一个10倍频程,以及该算法具有的线性声频率偏移特性,同样证明了该算法存在通过多次测量的平均值减少实验误差的可能性,使该算法在实际中可行。4.在弛豫声衰减理论方面,本论文阐述了气体弛豫声学的基础定义和理论,阐明了气体弛豫声衰减源于气体分子碰撞能量转移的关系,讨论了现有气体分子碰撞和能量转移模型,并详细推导和求解了现有弛豫声衰减理论,利用其他研究者的理论计算结果和实验测量数据验证了本论文建立的弛豫声衰减模型的正确性。5.在气体声学实验装置方面,本论文总结和借鉴了国外众多现有气体声学实验装置的结构优点和实现方法,设计并制作了一个气体声学实验装置原型,目前该实验装置原型正在最后完成中,其设计思想和实现方法都具有一定的参考价值。本论文的研究成果既是对气体弛豫声衰减理论的扩展和创新,又是对混合气体浓度检测的弛豫声学方法技术的扩展和创新,得到的具体检测算法考虑了将其应用于实验的问题,具有实际可行性。更多还原

【Abstract】 In the modern world and industrial production, gas concentration detection has widely demands and application prospects. The real-time concentration measurement of multi-component gas mixture has been extensively developed by many researchers. The concentration detection for gas mixtures based on acoustic relaxation theory, which both has solid theoretical background and brightly developing orientation, is being studied vigorously by the researchers, because it has the numerous advantages, such as lower cost, longer service duration, smaller power loss, faster response speed, considerably wide concentration scope for detecting, as well as simultaneously gaining results of multiple gases with different characteristics. The concentration detection for gas mixtures based on acoustic relaxation theory is a novel theory and technology. It utilizes the characteristics of acoustic attenuation and sound speed along with the changes of concentrations of gaseous components, and founds models of acoustic attenuation and sound speed depending on acoustic frequencies and concentrations of gases components. The detection is conducted by using sound speed, acoustic attenuation coefficients, effective relaxation frequency and these models. It is an interdisciplinary study based on mathematics, physics, electronics, signal processing.In this thesis, according to the natures of gases relaxation acoustics, we studied the classical acoustic velocity theory, the classical acoustic attenuation theory, the acoustic relaxation attenuation theory, and the gas molecular collision and energy transfer theory. Through researching, expanding and innovating of these theories, we have solved the key technologies of the concentration detection algorithms for three-component and four-component gas mixtures.For the gas molecular collision and energy transfer model and the algorithm of effective relaxation frequency, this thesis demonstrated it is reasonable that effective relaxation frequency can be considered as a third gas acoustics parameter. By ignoring the near resonance modes in relaxation energy transitions of gas molecular collision process under normal temperature, we improve the gas molecular collision and energy transfer model. For the first time, we gain the relaxation matrix algorithm to calculate the effective relaxation frequency for four-component gas mixtures. The simulation results verify that two results of the effective relaxation frequency, which come from the relaxation matrix algorithm based on the developed acoustic multi-relaxation attenuation theory and the algorithm based on the maximal dimensionless relaxation attenuation coefficient per wavelength respectively, become consistent basically. Therefore, the effective relaxation frequency can be introduced to the concentration detection algorithms of four-component gas mixtures based on acoustic relaxation theory.For the concentration detection algorithms of four-component gas mixtures based on acoustic relaxation theory, in this thesis, the effective relaxation frequency is first applied to acoustic gas concentration detection for four-component gas mixtures. We establish several multidimensional models for the concentrations of the constituents versus the effective relaxation frequency, relaxation attenuation, and acoustic velocity, respectively. Based on these models, we can use the measured parameters: effective relaxation frequency, relaxation attenuation coefficient and acoustic velocity, to predict the concentration of each component in the mixture. Testing the simulation results of sample gas mixtures demonstrates that the algorithm has high accuracy, strong stability and robustness for a wide range of acoustic frequencies.In the concentration detection algorithm of three-component gas mixtures discussed here, we boldly remove the classical acoustic attenuation from the total attenuation due to the certain relativity between the classical acoustic velocity and the classical acoustic attenuation. Then we provided dependences between relaxation attenuation coefficients and other acoustic parameters when ultrasound propagates in gas mixtures, such as concentrations of constituents and acoustic frequencies, and established a three dimensional model between concentrations of mixture constituents and relaxation absorption, acoustic velocity, separately. Further more, we gave out the two dimension relationship between relaxation absorption and acoustic frequencies. We propose a simplified algorithm to calculate the carbon monoxide concentration by measuring relaxation absorption and acoustic velocity. By analyzing the models of the energy transfer in molecular collision process and the acoustic relaxation attenuation in gas, we find the reason why ruggedness appears when the gas constituents have weak concentrations. We use the smooth window, a typical method in signal processing, to address acoustic relaxation attenuation data, and develop the algorithm for weak gas concentration detection of three-component gas mixtures. The measuring accuracy of this algorithm achieves 0.001%. Simulation results not only prove the feasibility of this method, but also indicate the appropriate range of acoustic frequencies, which is one 10 octave under the effective relaxation frequency. The reasons of application errors can be reduced through mean tested value, because of linear acoustic frequency displacement characteristic of the algorithm.For the acoustic relaxation attenuation theory, in this thesis, we introduced the fundamental definition and theory of gases relaxation acoustics, and the acoustic relaxation attenuation theory resulted from the gas molecular collision and energy transfer theory. Then we completed the foundation and solution of the acoustic relaxation attenuation theory according to the existing gas molecular collision and energy transfer models, and confirmed the correctness of the acoustic relaxation attenuation model by using other researcher’s theoretical calculation result and experiment metrical data.For the gas acoustic experimental equipment, in this thesis, we summarized the structure merits and design proposals of overseas gas acoustic experimentation equipments, then designed and manufactured a prototype of gas acoustic experimentation equipment independently. Although the equipment is not finished, we still believe it has a high probability to be actualized. The design concepts of the prototype can be used for reference for other researchers.The achievements of the research work in this thesis are expansion and the innovation not only to theory of gas acoustic relaxation attenuation, but also to technologies of the concentration detection for gas mixtures based on acoustic relaxation theory. The algorithm of the concentration detection for gas mixtures based on acoustic relaxation theory had been considered to be applied in experiment, and it has a strong feasibility.更多还原