基于激光吸收光谱技术的燃烧场气体温度和浓度二维分布重建研究

基于可调谐半导体激光吸收光谱技术和代数迭代算法（ART）实现燃烧场温度和浓度二维分布重建．采用时分复用技术,在1kHz扫描频率下分别扫描H2O的两条吸收谱线,7205．25和7416．05cm^-1,对温度分布在300-1100K范围内的气体温度场进行了重建．研究了投影角度和投影光线数目对温度场和浓度场重建结果的影响,并将温度场重建结果与热电偶测量结果进行比较,结果表明,采用四个投影方向时,温度场重建结果与热电偶测量结果除中心低温区域外基本符合．当光线数目减少时,通过在两条光线间增加虚拟光线,代入到迭代算法中,增加光线数目,提高了温度场和浓度场的重建效果．但此方法受到燃烧场温度梯度大小的影响,即在两条光线之间气体温度梯度较大,增加虚拟光线提高温度场重建效果不明显．     

基于多波长激光吸收光谱技术的气体浓度与温度二维分布遗传模拟退火重建研究

利用可调谐半导体激光吸收光谱技术实现气体浓度温度二维分布重建.设计了气体浓度温度二维分布重建测量系统,采用四路波分复用技术以减少投影光路布置数量和增加气体吸收测量信息.针对于图像重建过程中建立的非线性投影方程组,将遗传算法与模拟退火算法相结合进行求解,在实现全局最优搜索基础上提高算法搜索效率.建立燃烧环境下H2O浓度温度二维分布模型,借助于近红外波段1.3—1.5μm范围内4条H2O气体吸收谱线,利用数值模拟计算方法进行了气体分布重建,重建结果与模型符合得很好.通过在投影数据中添加不同比例的随机误差,考察其对气体分布重建结果的影响.研究表明,气体浓度分布重建结果对于投影误差不敏感,而增加投影误差幅值将导致温度分布重建均方误差增大。     

基于吸收光谱层析成像的气体摩尔分数和温度分布二维重建

基于可调谐二极管激光吸收光谱层析成像技术,采用代数迭代重建算法,实现对气体摩尔分数场和温度场二维分布的重建.利用半透半反镜,将激光束反复穿过被测区域,用多个探测器依序接收,固定光路瞬时测量.建立H2O蒸气摩尔分数和温度分布模型,数值分析了初始光线角度、光线数目、网格数目对重建结果的影响.通过对初始假定分布数据进行取样得到期望数据,将期望数据与重建数据的对比结果作为重建结果评价依据,通过插值与初始数据比较评判整个重建方案.结果表明新的光线分布能够较好地对被测区域进行重建,同时证明了期望数据描述方法可行.     

卷积反投影法重建温度场

电子散斑干涉技术是近年发展起来的一门新兴的测量技术,它由光干涉原理测量物理场的密度、温度分布等,这种测量技术是由物理场在不同截面、不同方向上的投影值反求场分布,这非常类似于CT技术。简述二维重建的基本原理,着重介绍卷积反投影重建算法。依此原理,模拟了双高斯分布函数的投影,并由平行束卷积法重建出模拟的温度场。为了指导电子散斑干涉实验,模拟了三种可能实验误差,并分别给出了重建结果。由于电子散斑干涉测量(投影)的方向个数小,提出了双线性滤波算法,使在测量值稀疏的条件下得到较好重建结果。     

声学CT复杂温度场重建研究

为提高声学CT复杂温度场重建能力,提出一种利用Markov径向基函数逼近和Tikhonov正则化的温度场重建算法,简称MTR算法。该算法首先用Markov径向基函数的线性组合,逼近介质中的复杂声速场分布,然后利用介质中多路径声波传播时间和Tikhonov正则化法,求解声速场分布,进而利用声速与温度的关系获得温度分布。对单热点、三热点和五热点温度场模型进行了仿真重建,结果表明MTR算法热点定位精度高,重建误差小。开发了声学CT温度场重建实验系统,用电加热器在内装1200 kg大豆的实验粮仓中形成热点,MTR重建结果能正确反映热点位置,热点温度重建误差1.3%。可见,MTR算法复杂温度场重建能力强,可望用于实际储粮温度分布监测。      

火焰烟黑三维温度场和浓度场同时重建实验研究

利用电荷耦合器件摄像机采用烟黑温度场和浓度场同时重建模型对自由火焰烟黑的三维温度场和浓度场进行了同时重建实验研究,所利用的重建模型是基于区域重建的方法.将重建的烟黑温度场和浓度场与文献结果进行了对比,而且还将重建温度场与热电偶所测量的温度场进行了对比.结果表明,重建的烟黑温度场和浓度场与文献结果趋势相一致,重建温度值与热电偶测量值符合较好.因此,同时重建模型可以较好地重建出火焰烟黑的三维温度场和浓度场. 关键词： 火焰烟黑 温度场 浓度场 三维同时重建     

一种少投影光学层析新算法及其应用

研究少投影数情况下等离子体温度场重建问题。结合光学层析重建算法及等离子体光谱诊断中的谱线绝对强度法进行自由电弧等离子体温度场重建实验。理论上，详细讨论了一种基于最大熵准则及最优化原理的光学层析图像重建新算法。通过计算机数值模拟，考察了该算法对非对称温度场分布的重建效果。详细分析了投影噪声、投影方向数、场分布性质对重建精度的影响，并与代数迭代重建算法结果进行对比．结果表明，该算法以两个正交方向投影数据重建单峰余弦模拟场平均误差仅为0.3％，而代数迭代重建算法为3．81％；该算法以四个均匀角度间隔投影数据重建三峰随机高斯模拟场平均误差为1．77％，而代数迭代重建算法为2．02％。实验中，运用该算法结合谱线绝对强度法重建了自由电弧等离子体的温度分布。     

非对称碳氢扩散火焰内烟黑浓度与温度联合重建模型研究

基于烟黑热辐射传递过程,提出了非对称碳氢扩散火焰断面内烟黑浓度和温度分布的联合层析重建模型.应用最小二乘QR矩阵分解算法模拟分析了传感器数量和布置方式对重建结果的影响以及模型的抗噪能力.计算结果表明,当4个320像素线阵电荷耦合辐射投影传感器(CCD)成非正对布置时,浓度场重建结果最大误差小于2.5%,温度场重建结果最大误差小于0.2%.此外CCD正对布置将导致重建误差向中心聚集.从对含噪声数据的重建结果看,应用联合层析重建模型,辐射能传感器的信噪比不应低于60dB. 关键词： 非对称火焰 层析重建 最小二乘QR矩阵分解算法 联合重建     

二维弥散介质温度场的快速重建

提出了一种利用电荷耦合器件摄像机获取的辐射信息进行二维弥散介质温度场快速重建的新模型. 与现有的温度场重建模型相比,该模型是以逆向Monte Carlo方法为基础,重建速度更快、效率更高,能更好地描述散射介质. 采用了一个精确的二维温度场作为重建对象,结果表明,即使在存在测量误差的情况下,利用此模型重建出的温度场仍能重现原有精确温度场的特征. 关键词： 温度场重建 逆向Monte Carlo 电荷耦合器件摄像机 反问题     

基于超声波飞行时间的空气温度场重建

利用超声波在空气中的传播速度会随着空气温度的变化而变化这一特点,可测得空气中不同温度下的平均速度场,进而重建空气中的温度场。提出了一种非对称布置超声波传感器重建二维温度场的方法,在被测温度场周围布置8个收发一体的超声波传感器,并将被测温度场划分为24个小区间,以得到超声波通过每个小区间的平均温度值,以该温度值作为小区间中心点的温度并进行插值,从而重建整个被测区域的温度场。     

Algebraic tomographic reconstruction of two-dimensional gas temperature based on tunable diode laser absorption spectroscopy

Based on tunable diode laser absorption spectroscopy, the combustion gas temperature distribution was reconstructed using the algebraic iterative reconstruction technique. The effects of the projected angle and number of rays on the temperature reconstruction results for both fan beam and parallel beam were investigated. The flow field information was shown in detail. The reconstruction quality increased with increased ray number for both parallel- and fan-beam projections. The trend tended to be smooth when the total number of beams exceeded 100. A virtual ray method combined with the reconstruction algorithms was proposed. The virtual ray method is effective to improve the accuracy of reconstruction results for the symmetric and non-axisymmetric temperature distributions. Moreover, the temperature reconstruction of an infrared gas-field furnace is demonstrated, showing the virtual ray method can be applied to the combustion diagnostics.     

Numerical simulations to improve the performance of tunable diode laser absorption tomography in a harsh combustion environment

The impact of measurement noise and tomographic methods on reconstruction quality are investigated via simulation studies under a hypothesis harsh flow field environment. Computer tomographic methods based on direct absorption spectroscopy and wavelength modulation spectroscopy are conducted under different measurement noise levels to assess the noise effect quantitatively. It turns out that the wavelength modulation spectroscopy-based tomographic method shows efficient immunity to measurement noise. However, the direct absorption spectroscopy-based tomographic method is found to be susceptible to the measurement noise, which makes the reconstruction quality decline with the increasing noise level. In addition, two kinds of tomographic methods including linear and nonlinear method are investigated under a complex multimodal temperature distribution environment with limited projection data. The reconstructed distribution for the nonlinear tomographic method reveals great fidelity to the original value with a maximum deviation of 51.9?K, while the reconstructed distribution for the linear tomographic method under parallel beam arrangement shows an obvious distortion.     

Application of acoustic reflection tomography to sonar imaging

Computer-aided tomography is a technique for providing a two-dimensional cross-sectional view of a three-dimensional object through the digital processing of many one-dimensional views (or projections) taken at different look directions. In acoustic reflection tomography, insonifying the object and then recording the backscattered signal provides the projection information for a given look direction (or aspect angle). Processing the projection information for all possible aspect angles enables an image to be reconstructed that represents the two-dimensional spatial distribution of the object's acoustic reflectivity function when projected on the imaging plane. The shape of an idealized object, which is an elliptical cylinder, is reconstructed by applying standard backprojection, Radon transform inversion (using both convolution and filtered backprojections), and direct Fourier inversion to simulated projection data. The relative merits of the various reconstruction algorithms are assessed and the resulting shape estimates compared. For bandpass sonar data, however, the wave number components of the acoustic reflectivity function that are outside the passband are absent. This leads to the consideration of image reconstruction for bandpass data. Tomographic image reconstruction is applied to real data collected with an ultra-wideband sonar transducer to form high-resolution acoustic images of various underwater objects when the sonar and object are widely separated.     

多光谱辐射层析重建三维火焰温度场

提出一种基于多光谱辐射测温理论及光学层析技术的三维温度场重建方法。建立了基于参考温度的多光谱测温法数学模型，提出了一种基于模拟退火理论的变松弛因子的光学层析技术新算法，通过计算机数值模拟，详细考察了该算法对非对称温度场分布的重建效果并与传统的代数迭代重建算法及滤波反投影算法进行比较。计算结果表明，变弛豫因子重建算法重建精度最高。作为一个应用实例，用多光谱辐射变弛豫因子重建层析方法重建了四峰蜡烛火焰某一截面的温度分布。     

Flame four-dimensional deflection tomography with compressed-sensing-revision reconstruction

Deflection tomography with limited angle projections was investigated to visualize a premixed flame. A projection sampling system for deflection tomography was used to obtain chronological deflectogram arrays at six view angles with only a pair of gratings. A new iterative reconstruction algorithm with deflection angle compressed-sensing revision was developed to improve reconstruction-distribution quality from incomplete projection data. Numerical simulation and error analysis provided a good indication of algorithm precision and convergence. In the experiment, 150 fringes were processed, and temperature distributions in 20 cross-sections were reconstructed from projection data in four instants. Four-dimensional flame structures and temperature distributions in the flame interior were visualized using the visualization toolkit. The experimental reconstruction was then compared with the result obtained from computational fluid dynamic analysis.     

Quasi Monte Carlo-based isotropic distribution of gradient directions for improved reconstruction quality of 3D EPR imaging

In continuous wave (CW) electron paramagnetic resonance imaging (EPRI), high quality of reconstructed image along with fast and reliable data acquisition is highly desirable for many biological applications. An accurate representation of uniform distribution of projection data is necessary to ensure high reconstruction quality. The current techniques for data acquisition suffer from nonuniformities or local anisotropies in the distribution of projection data and present a poor approximation of a true uniform and isotropic distribution. In this work, we have implemented a technique based on Quasi-Monte Carlo method to acquire projections with more uniform and isotropic distribution of data over a 3D acquisition space. The proposed technique exhibits improvements in the reconstruction quality in terms of both mean-square-error and visual judgment. The effectiveness of the suggested technique is demonstrated using computer simulations and 3D EPRI experiments. The technique is robust and exhibits consistent performance for different object configurations and orientations.     

Measurement of the laser beam intensity distribution using optical tomography

Optical tomography is proposed as a method for studying the intensity distribution in the laser beam cross section. The tomographic projection of the beam cross section is obtained with the help of an optical fiber possessing a high radiation resistance, which makes it possible to employ this technique for studying high-power laser radiation. The results of tomographic reconstruction of the bean cross section from experimental projections are compared with the results of reconstruction from model projections.