Holographic thin-beam reconstruction technique for the study of 3-D refractive-index field

A thin-beam holographic reconstruction technique to study the 3-D refractive index field of a phase object is described. The advantages and drawbacks of this method are discussed.     

基于阻尼LSQR-LMBC的火焰三维温度场重建

光场相机可以解决辐射测温多相机系统光路复杂、同步触发难等问题,在辐射成像三维温度重建时有其独特优势. LSQR是求解基于大型稀疏矩阵最小二乘问题的经典算法,该算法用于重建三维温度场时对温度初值依赖较大,在信噪比较低的情况下重建精度不理想.本文提出阻尼LSQR-LMBC重建算法,通过在LSQR方法中添加阻尼正则化项,提高火焰三维温度场重建的抗噪性能,并结合LMBC算法,实现吸收系数和三维温度场同时求解.在数值模拟部分,随着信噪比逐渐降低,阻尼LSQR的重建效果比LSQR更加稳定,在信噪比达到13.86 d B时,重建精度大约提高30%.阻尼LSQR-LMBC的平均重建误差为6.63%.用丁烷火焰进行了实验,重建的丁烷火焰三维温度场分布符合辐射火焰燃烧的特征,和热电偶的测温数据结果进行对比,相对误差在6.8%左右.     

Quantitative visualization of temperature field in non-luminous flame by flame reaction technique

Abstract  

An experimental technique for measuring a temperature field in an axisymmetric non-luminous flame is developed using the flame reaction technique combined with the inverse Abel transformation. Flame visualization is carried out using alkali metal solution of Potassium (K), which is supplied to a premixed methane/air flame in a form of spray mist. The basic principle of this technique is based on the measurement of local emission intensity distribution visualized by the flame reaction, which is a function of temperature according to the Maxwell–Boltzmann statistics of thermodynamics. The relationship between the local intensity and the temperature is obtained from the calibration study, in which the local intensity is evaluated from the line of sight intensity by the inverse Abel transformation, and the temperature is measured by thermocouple. This technique is successfully applied to the measurement of local temperature distribution in steady and flickering premixed methane/air flame. The temperature field in the flickering flame indicates that the local temperature oscillates periodically with the flickering frequency, and the highest temperature is found along the flame front and in the merging region.     

炉膛三维温度场重建中Tikhonov正则化和截断奇异值分解算法比较

在煤粉锅炉诊断中火焰辐射能图像扮演着越来越重要的角色, 通过电荷耦合器件(CCD)获得的辐射能图像可以重建出炉内火焰三维温度场, CCD 用于获取视场角内的辐射能图像. 温度场重建的矩阵方程是一个严重病态的方程, 本文使用两种算法(Tikhonov正则化算法和截断奇异值分解(TSVD)算法)来重建温度场. 应用广义交叉检验算法来选取正确的正则化参数. 数值模拟的环境为一个10 m×10 m×10 m的三维炉膛, 系统被划分为10×10×10的1000个网格, 每个网格单元都是边长为1 m的立方体. 在正问题求解所得到的CCD接受信号基础上加上不同随机误差以模拟测量时的CCD接受信号. 研究两种算法重建后的温度重建误差、两者的重建时间, 以及最高温度的重建效果. 初步的研究结果显示, 一般情况下基于Tikhonov算法重建的温度场比基于TSVD算法重建的温度场误差要小, 计算所需时间短, 最高温度重建更准确.     

Solid support flame synthesis of 1-D and 3-D tungsten-oxide nanostructures

In this paper we report the growth of 1-D and 3-D tungsten-oxide nanostructures on tungsten wire probes inserted in an opposed-flow oxy-fuel flame. The probe diameter and oxygen content in the oxidizer were varied to study their influence on the growth of tungsten-oxide nanostructures. The introduction of a 1-mm diameter W probe into the flame environment with an oxidizer composition of 50%O₂ + 50%N₂, resulted in the formation of 1-D nanorods on the upper surface of the probe. The formation of triangular, rectangular, square, and cylindrical 3-D channels with completely hollow or semi-hollow morphology was achieved by reducing the probe diameter to 0.5 mm. Whereas, the increase of the O₂ content to 100% and the employment of a 1-mm probe resulted in the growth of ribbon-like micron-sized structures. The lattice spacing of ∼0.38 nm measured for the 1-D W-oxides closely matches a monoclinic WO₃ structure. X-ray photoelectron spectroscopy analysis revealed that the larger 3-D structures also consist of WO₃ confirming that the chemical composition of the structures remains the same while varying the probe and flame parameters. The proposed growth mechanism states that the 3-D WO₃ structures are formed through the lateral coalescence of 1-D W-oxide nanorods.     

Mean field theory for nonequilibrium network reconstruction

There has been recent progress on inferring the structure of interactions in complex networks when they are in stationary states satisfying detailed balance, but little has been done for nonequilibrium systems. Here we introduce an approach to this problem, considering, as an example, the question of recovering the interactions in an asymmetrically coupled, synchronously updated Sherrington-Kirkpatrick model. We derive an exact iterative inversion algorithm and develop efficient approximations based on dynamical mean-field and Thouless-Anderson-Palmer equations that express the interactions in terms of equal-time and one-time-step-delayed correlation functions.     

无需系统标定的三维视觉重建

为了解决传统三维重建需要依赖系统标定信息的问题,提出了一种基于相位图的不需要系统标定信息的三维视觉重建算法。首先使用结构光测量技术获得被测物体表面的相位图,再利用相位图的横向和纵向空间扭曲特性计算物体表面相对深度信息,最后实现被测物体的三维视觉重建。这种方法可以用在无法进行标定或无法获取标定信息的场合。实验结果表明,当被测物体表面结构简单时,这种方法的三维视觉重建效果较好。并通过对比传统三维重建结果验证了该方法的有效性。     

无需系统标定的三维视觉重建北大核心CSCD

为了解决传统三维重建需要依赖系统标定信息的问题,提出了一种基于相位图的不需要系统标定信息的三维视觉重建算法。首先使用结构光测量技术获得被测物体表面的相位图,再利用相位图的横向和纵向空间扭曲特性计算物体表面相对深度信息,最后实现被测物体的三维视觉重建。这种方法可以用在无法进行标定或无法获取标定信息的场合。实验结果表明,当被测物体表面结构简单时,这种方法的三维视觉重建效果较好。并通过对比传统三维重建结果验证了该方法的有效性。     

A deep neural network surrogate modeling benchmark for temperature field prediction of heat source layout

The thermal issue is of great importance during the layout design of heat source components in systems engineering, especially for high functional-density products. Thermal analysis requires complex simulation, which leads to an unaffordable computational burden to layout optimization as it iteratively evaluates different schemes. Surrogate modeling is an effective method for alleviating computation complexity. However, the temperature field prediction(TFP) with complex heat source layout(HSL) input is an ultra-high dimensional nonlinear regression problem, which brings great difficulty to traditional regression models. The deep neural network(DNN) regression method is a feasible way for its good approximation performance. However, it faces great challenges in data preparation for sample diversity and uniformity in the layout space with physical constraints and proper DNN model selection and training for good generality, which necessitates the efforts of layout designers and DNN experts. To advance this cross-domain research, this paper proposes a DNN-based HSL-TFP surrogate modeling task benchmark. With consideration for engineering applicability, sample generation, dataset evaluation, DNN model, and surrogate performance metrics are thoroughly investigated. Experiments are conducted with ten representative state-of-the-art DNN models. A detailed discussion on baseline results is provided, and future prospects are analyzed for DNN-based HSL-TFP tasks.     

Fourier transform moiré tomography for high-sensitivity mapping asymmetric 3-D temperature field

Fourier transform evaluation for moiré deflectogram is proposed to automatically map the temperature field. The moiré deflectogram is generated by conventional deflectometer and is analyzed by means of Fourier transform algorithm. The convolution backprojection algorithm is used for the optical tomography. Asymmetric 3-D gas temperature distribution for a given layer is reconstructed.     

PLIF法定量测量甲烷-空气火焰二维温度场分布

利用平面激光诱导荧光(PLIF)技术,通过选择适合的OH自由基激励线,定量测量了甲烷-空气燃烧火焰的二维温度场分布。给出炉面中心上方火焰温度随离炉面高度的变化和距炉面12 mm高处沿炉面水平方向变化的实验测量结果并进行了讨论与分析。与利用相干反斯托克斯喇曼散射（CARS）技术进行测温的实验结果相比,该测量的相对不确定度优于5％。     

PLIF法定量测量甲烷-空气火焰二维温度场分布

利用平面激光诱导荧光(PLIF)技术,通过选择适合的OH自由基激励线,定量测量了甲烷-空气燃烧火焰的二维温度场分布。给出炉面中心上方火焰温度随离炉面高度的变化和距炉面12 mm高处沿炉面水平方向变化的实验测量结果并进行了讨论与分析。与利用相干反斯托克斯喇曼散射（CARS）技术进行测温的实验结果相比,该测量的相对不确定度优于5％。     

一种基于偏振解析的三维表面重建方法

提出用解析反射光偏振图像来重建透明物体表面形状的原理及实现方法。从物体表面反射的光具有一定的偏振特性,偏振特性的不同反映了物体的形状和反射特性的不同,这两者之间存在一种必然的联系。通过分析物体表面反射光的偏振分布,可以得到物体的表面形状。依据菲涅耳反射公式,推导出偏振度与物体表面法线间的函数关系,据此构建相应算法,对由CCD照相机拍得的被测物体的偏振灰度图像进行处理,重建出被测物体的表面形状。实验结果证明提出的方法是实用且有效的。     

The measurement of 3-D asymmetric temperature field by using real time laser interferometric tomography

A real time nondestructive temperature measurement technique based on laser holographic interference tomography technique is presented. An He–Ne laser is used as light source, and a CCD video camera is used to grab the interferogram. This laser holographic tomography technique is applied to the measurement of the temperature fields generated by two heated rods. Since data error is inevitable in engineering measurement, it is necessary to study the reconstruction techniques for reconstructing the temperature field. Three techniques including convolution back projection (CBP), algebra reconstruction technique (ART) and simultaneous iterative reconstruction technique (SIRT) are studied. Based on the reconstruction techniques and experimental situation, ART is used to reconstruct the asymmetric temperature fields. The thermocouples are used to measure the temperatures of the two heated rods. Comparing the reconstructed result with the measured temperature value, a satisfactory result is obtained.     

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     

利用迈克耳孙干涉仪重建蜡烛火焰温度场

利用教学实验中的迈克耳孙干涉仪,进行蜡烛火焰温度场的测量.对干涉条纹进行了处理和细化,并分别用阿贝尔变换法和环带法对蜡烛火焰的温度场进行了计算,得到蜡烛火焰横截面上温度场的定量结果.     

Digital holography-assisted 3-D bright-field image reconstruction and refocusing

Optical Review - We propose an image reconstruction technique of a color 3-D object to perform image refocusing by combining information from bright-field image and digital holography. The key...     

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     

基于截断奇异值分解的三维火焰温度场重建研究

利用CCD摄像机得到的火焰辐射能图像进行炉膛三维火焰温度场重建，但温度重建矩阵方程是一个不适定方程组，从而重建问题是一个不适定问题.应用截断奇异值分解(truncated singular value decomposition，TSVD)的正则化方法对该不适定方程组进行求解，并且采用了L曲线法对正则化参数进行选取.结合重建算例，采用奇异值分解(singular value decomposition，SVD)与离散Picard条件对这个不适定问题进行了分析.重建结果表明，在不同的模拟测量误差下，TSVD能够成功得到合理的解，重建温度场较好的再现了原始假设温度场的特征.