Spatially Driven Chemical Species Tomography With Size-Adaptive Hybrid Meshing Scheme

Abstract

This paper develops a size-adaptive hybrid meshing scheme for Chemical Species Tomography (CST) that is driven by the customized spatial resolution of the sensing region. Traditionally, the entire sensing region in CST is uniformly discretized with the empirically determined density of the meshes. Such a discretization results in a) waste of computational efforts on the less spatially resolved location; and b) much severer rank deficiency. To solve the above-mentioned issues, we introduce, for the first time, a size-adaptive hybrid meshing scheme for CST. Driven by the spatial resolution, dense meshes are deployed in the region of interest (RoI) to detail the target flow field while sparse ones are deployed out of the RoI to fully consider the physically existing laser absorption. The proposed scheme is numerically validated using a CST sensor with 128 laser beams. The visual and quantitative metric comparisons show that the proposed hybrid-size meshing scheme outperforms the traditionally uniform-size meshing scheme, giving 35% lower image error and 38% less significant dislocation at a typical 35 dB signal-to-noise ratio in the RoI. The proposed hybrid-size meshing scheme significantly facilitates the reconstruction of the industrial combustion processes where the combustion zone is bypassed by cooling flows. In these scenarios, the proposed scheme can adapt a finer resolution to detail the combustion zone, while maintaining the integrity of the physical model by less resolved reconstruction of the bypass flows.

FPGA-Accelerated Distributed Sensing System for Real-Time Industrial Laser Absorption Spectroscopy Tomography at Kilo-Hertz

“…9, the laser beams are arranged at 4 equiangular projection views with 8 parallel beams in each projection view. More details of the beam arrangement can be found in [28]. The target flames in the sensing region are generated by two identical burners with butane-propane mixed fuel.…”

Online tomography algorithm based on laser absorption spectroscopy

“…赵荣 1) 周宾 1) † 刘奇 1) 戴明露 1) 汪步斌 1) 王一红 1) 2) 第一作者.E-mail: zhaorong@seu.edu.cn 1 引 言 可调谐半导体激光吸收光谱(TDLAS)技术具有高灵敏度、非入侵、高测量 精度和工业普适性等优点，可实现对燃烧场和推进流场温度、组分浓度的实时测 量 [1,2] 。为了准确获得非均匀分布流场温度和浓度的空间分布，将 TDLAS 技术与 计算机层析成像(CT)技术相结合，即激光吸收光谱层析成像(LAST)技术 [3][4][5][6][7][8][9] 。LAST 对于研究燃烧过程和火焰结构等诊断工具具有十分重要的意义，是 流场 测量的理想方法之一。LAST 基本原理是将感兴趣区域(ROI)离散为一定数量 的网格，假设其物理参数不变，然后通过测量到的投影数据，建立参数方程求解 逆问题，从而获得网格中的参数 [10][11][12] 。在经典的吸收层析成像测量中，积分吸光 度(投影数据)是长度、浓度和压力的线性函数，这满足了重建算法的条件。因 此，准确的积分吸光度测量结果是 LAST 重建的一个重要因素 [13] 。 LAST 重建通常采用直接吸收光谱法(DAS)和波长调制光谱(WMS)两种 方案获得积分吸光度 [14] 。DAS 获得积分吸光度的一个关键步骤是确定基线，从透 射强度中计算出入射强度。然而，在恶劣的环境中，入射激光强度受振动和窗口 污损而发生变化，这在计算积分吸光度时引入了误差，进而这些误差被引入到层 析成像的重建中。即使对重建算法和模型进行优化，也很难消除积分吸光度中的 误差。相反 WMS 可以达到非常高的灵敏度，对背景噪声有很强的鲁棒性，被广 泛应用在恶劣的环境中。Rieker 等人 [15,9] 开发了一种免标定的 WMS 方法，并采用 一次谐波对二次谐波进行归一化(WMS-2f/1f)的方式消除光强波动的影响。Sun 等人 [16]…”

Reconstruction Algorithm Optimization Based on Multi-Iteration Adaptive Regularity for Laser Absorption Spectroscopy Tomography

“…i (i = 1, 2...., M) and j (j = 1, 2..., N) are the indexes of the laser beam and pixel, respectively. The spectrally integrated absorption area A v = {A v,1 , A v,2 , A v,N } T and the locally integrated absorption area α v = {α v,1 , α v,2 , α v,N } T are column vectors, where α v,j = P j X j S(T j ), from which the distribution of flame temperature and gas concentration parameters can be extracted [23][24][25].…”