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1.
为提高流场超声层析成像的图像重建质量,提出了一种迭代滤波反投影图像重建算法。该算法借鉴联合迭代重建算法的原理,将滤波反投影算法引入迭代重建过程。首先,利用滤波反投影算法,通过投影数据残差重建误差图像对流场图像进行修正,实现图像的迭代重建。然后,通过优化迭代步长,使每步迭代后投影数据残差均取得极小值以便加快收敛速度。最后,基于流场连续、紧支撑分布的特点,在迭代重建过程中引入投影数据的细分内插和流场图像的圆域修正。实验表明:相比于滤波反投影算法,迭代滤波反投影算法可使理论流场重建的图像误差平均减少26%,流量误差由1.77%减小至±0.25%以内;程序运行时间为0.63s,仅为联合迭代重建算法的0.89%。该算法可实现对直管段内和单弯管下游实际流场的可靠重建,满足流场高精度实时成像的要求。  相似文献   

2.
实时、准确的建筑室内温度分布信息反馈是暖通空调(HVAC)系统控制与室内热环境优化研究的难点。针对这一问题,提出了基于卡尔曼滤波-线性随机估计(KF-LSE)的室内温度场实时准确重建方法。该方法利用本征正交分解(POD)方法将室内温度场映射为与POD模式系数相关的低阶线性系统,采用LSE方法获取POD模式系数动态模型,基于KF算法构建POD模式系数估计器,最后通过估计器与在线采集的室内温度值进行POD模式系数最优估计,快速重建出温度场。对比传统的POD-LSE方法进行建筑室内仿真实验,结果表明本方法具有更好的噪声抑制能力和温度场重建精度。  相似文献   

3.
感应式磁声成像(MAT-MI)是一种融合磁感应技术和超声断层扫描技术的新型生物电阻抗成像方法,兼具电阻抗功能成像和超声技术高空间分辨率的优点.目前针对声源重建大都采用时间反转法,该方法存在的问题有:求导数后对数据噪声有放大作用;声压的边缘Gibbs效应导致重建图像的伪影重等.为此,本文对已有的格林函数积分解进行离散,提出一种矩阵投影格式,并在此基础上提出一种迭代求解的算法.为了验证新方法的正确性,我们使用电导率具有空间分布3Dphantom模型进行了数值模拟并获得了不同截面处的声压波形.最后使用本文提出的方法由获得的声压重建得到了高精度的声源分布和电导率分布.  相似文献   

4.
实时监测炉内燃烧温度场和烟气速度场是保证锅炉安全、经济运行的重要手段,声学法测物理场被认为是一种非侵入性和有效的测量方法。本文提出了一种基于声波法的炉内温度场和烟气速度场的协同测量新方法,建立了基于径向基函数的多物理场重建模型,采用Tikhonov正则化算法求解不适定问题,同时考虑了声波的折射效应对物理场的重建影响。采用典型的炉内物理场模型进行了数值模拟,模拟结果表明,本文方法能够很好的协同重建温度场和速度场。当考虑声线弯曲时能够显著提高各物理场的重建质量。算法具有较好的适应性和良好的抗噪性能,重建精度较高,标准均方根误差在10%以下。模拟实验平均计算时间为31.4 s,可保证炉内声学测量的实时性。声学法协同测量多物理场可为优化炉膛燃烧过程提供依据。  相似文献   

5.
针对在一些不能获取大量投影数据或者投影分布不均匀的实际情况下,重建大气痕量气体的二维空间分布问题,采用代数迭代重建算法(ART)和同步迭代重建算法(SIRT)2种重建算法对其进行重建。通过数值模拟的方式对2种重建算法的重建效果进行了比较研究,并建立了多轴差分吸收光谱层析系统,进行了外场试验。通过计算机模拟和外场实验研究,从成像效果中可以看出,2种迭代算法均能在数据不完善的情况下,精确地重建出大气痕量气体的二维空间分布;在不同的模型及评价指标下,通过对2种重建算法的重建误差的比较,可以发现SIRT算法的重建误差要小于ART算法的重建误差,尤其在测量数据波动比较大、受干扰的情况下。  相似文献   

6.
FDS团队发展了剂量引导实时验证系统KylinRay-DGRT,该系统集射野透射影像采集、射野透射剂量标定、三维剂量重建、剂量评价、计划重优化等功能于一体,可进行强度和三维剂量验证,并引导物理师对放疗计划进行精确修正,从而有效地保证病人受照剂量的精准性。本文对KylinRay-DGRT的总体设计和关键技术方法进行了介绍;采用美国医学物理学家协会(AAPM)TG119号报告中的"模拟C形靶区"测试例题对KylinRay-DGRT进行正确性测试举例,结果表明KylinRay-DGRT重建的剂量与参考TPS计算的计划剂量,以及实测剂量的符合率达到94.8%以上;采用头颈部肿瘤病例对KylinRay-DGRT进行了临床验证,结果表明KylinRay-DGRT重建的剂量满足临床要求。  相似文献   

7.
谭永明 《中国机械》2014,(14):153-154
搅拌装置作为工程中常用的非标机械设备,工作原理为机械能转化为流体动能。合理的结构模式和运转情况是影响流体流场分布和决定能量转化效率的重要因素。本文基于CAE流体分析软件CFX通过工程实例对传统搅拌方式和导流筒搅拌方式进行比对,为搅拌装置的合理研发提供了数据依据。  相似文献   

8.
可调谐二极管激光吸收光谱层析成像(TDLAST)是一种重要的非侵入式燃烧检测技术。然而,TDLAST逆问题的欠定性使得传统算法重建的气体吸收密度存在较大误差。本文将期望块对数似然先验引入TDLAST逆问题的求解,提出基于高斯混合模型(GMM)正则化的温度重建算法(GMMTRT)。该方法利用GMM建模燃烧场气体吸收密度的局部分布特性,采用半二次分裂方法求解引入GMM正则化的TDLAST逆问题。利用火灾动力学模拟器生成的仿真数据与利用TDLAST实验系统获得的实际数据进行的重建实验均表明,GMMTRT重建的温度图像能够准确定位火焰位置,并清晰描述燃烧场感兴趣区域的温度分布。与现有的基于Tikhonov正则化的温度重建算法和同时代数重建算法相比,GMMTRT的重建误差分别能够降低15.42%~36.16%和23.10%~44.79%。  相似文献   

9.
电阻层析成像技术是近年来发展起来的一种截面分布式的检测技术.具有非侵入的,无辐射的,可视化的特点。在电阻层析成像技术中.图像重建是由测量到的边界电压重建出对象内部电阻率分布的过程.是最终实现ERT技术可视化测量的过程。图像重建算法.直接影响成像的效果。本文介绍了目前比较常用的图像重建算法的原理以及应用过程中的优缺点。  相似文献   

10.
电容层析成像(Electrical Capacitance Tomography,ECT)技术是目前最具发展前景的多相流参数检测方法,它可重建两相流在其流经管道横截面上的分布图像.对12电极的电容传感器进行了数学描述,建立了电容敏感场分布的数学模型及其有限元模型,分析了敏感场的算法,利用有限元法实现了敏感场的仿真,并且研究了敏感场分布的规律.在此基础上利用灰度图像重建的方法重现出不同流体分布状态下油管横截面的灰度图像,为两相流在线检测仪器的设计提供了理论依据.  相似文献   

11.
Gas/liquid two-phase flow regime identification by ultrasonic tomography   总被引:1,自引:0,他引:1  
A gas/liquid two-phase flow is considered as a strongly inhomogeneous medium with respect to high contrast in acoustic impedance distribution. Based upon a binary logic operation and a method of “time-of-propagation along straight path”, an ultrasonic facility for tomographic imaging of gas/liquid two-phase flow was developed. In this paper the principle and construction of this facility are briefly introduced. Emphasis is placed on the evaluation of its performance in flow regime identification and cross-sectional void fraction measurement. Several flow pattern models were used and the corresponding monitoring results given. Finally, limitations and possible future improvements of the system are discussed.  相似文献   

12.
Optical tomography provides a means for the determination of the spatial distribution of materials with different optical density in a volume by non-intrusive means. This paper presents results of concentration measurements of gas bubbles in a water column using an optical tomography system. A hydraulic flow rig is used to generate vertical air-water two-phase flows with controllable bubble flow rate. Two approaches are investigated. The first aims to obtain an average gas concentration at the measurement section, the second aims to obtain a gas distribution profile by using tomographic imaging. A hybrid back-projection algorithm is used to calculate concentration profiles from measured sensor values to provide a tomographic image of the measurement cross-section. The algorithm combines the characteristic of an optical sensor as a hard field sensor and the linear back projection algorithm.  相似文献   

13.
In bubbly two-phase flow, the gas phase and liquid phase have different flow fields. The relative velocity of the two phases depends on the motion characteristic of the bubbles. The mathematical expression for the motion of a small bubble at low Reynolds number is already established. Using the equation, the liquid velocity along the trajectory of the bubble is calculated inversely using the motion equation. Whole field liquid flow structure is also estimated using a spatial and/or temporal interpolation method. This paper proposes an algorithm for estimating the liquid phase flow field from measurement data on bubble motion. In order to verify this principle, Taylor–Green vortex flow and Karman vortex shedding from a square cylinder have been chosen. The results reveal that by combining the inverse analysis and PTV with the spatio-temporal post-processing algorithm one can reconstruct well the carrier phase flow of the gas–liquid two-phase flow.  相似文献   

14.
A real-time neutron radiography (RTNR) system and a high speed X-ray computed tomography (X-CT) system are compared for measurement of two-phase flow. Each system is used to determine the flow regime, and the void fraction distribution in a vertical annulus flow channel with particular attention on the temporal resolution of the systems and the time behaviour of the two-phase flow. The annulus flow channel is operated as a bubble column and measurements obtained for gas flow rates from 0.0 to 30.0 l/min. Both the RTNR and the X-CT systems show that the two-dimensional void fraction distribution can be obtained. The X-CT system is shown to have a superior temporal resolution capable of resolving the void fraction distribution in an (r,θ) plane in 4.0 ms. The RTNR system is shown to obtain void fraction distribution in a (r,z) plane in 33.0 ms. Void fraction distribution for bubbly flow and slug flow is determined.  相似文献   

15.
The void fraction is one of the key parameters in the measurement of gas/liquid two-phase flow. It can be derived from the absolute conductivity distribution based on Maxwell׳s theory. With Electrical Resistance Tomography (ERT) technology, the absolute conductivity distribution is obtained by multiplying the relative conductivity image with the reference conductivity which is conventionally the liquid conductivity of a gas/liquid flow. Unfortunately the liquid conductivity is not always available. Therefore, a conductivity fitting method is proposed in this paper, to find an optimal reference conductivity, which will be used in substituting the liquid conductivity to reconstruct the quasi-absolute conductivity image. The optimal reference conductivity fitting method is proposed and validated by simulation and experiments under certain flow regimes, e.g. slug flow, annular flow and bubbly flow. The simulation and experimental results show that, independent from prior-knowledge, the fitted quasi-homogenous conductivity is close to the average conductivity of the sensing field. It also leads to a much more accurate estimation of void fraction than the conventional method using liquid conductivity as the reference. With the proposed method, the ERT technique can play a more significant role in the measurement of multiphase flow (MPF).  相似文献   

16.
This paper proposes a measurement technique for two-phase bubbly and slug flows using ultrasound. In order to obtain both liquid and gas velocity distributions simultaneously, a new technique for separating liquid and gas velocity data is developed. The technique employs a unique ultrasonic transducer referred to as multi-wave transducer (TDX). The multi-wave TDX consists of two kinds of ultrasonic piezoelectric elements which have different resonant frequencies. The central element of 3 mm diameter has a basic frequency of 8 MHz and the outer element has a basic frequency of 2 MHz. The multi-wave TDX can emit the two ultrasonic frequencies independently. In our previous investigations, both elements were connected with two ultrasonic velocity profile (UVP) monitors to measure liquid and bubble velocity distributions. However, the technique was limited to the measurement of bubbly flows at low void-fraction. Furthermore, it was impossible to synchronize the instantaneous velocities of liquid and bubbles because of the facility limitation. In order to overcome these disadvantages, cross-correlation method is employed for the measurements in this study. In order to apply the technique to flow measurements, ultrasound pressure fields are measured. As a result, it is found that the TDX must be set 20 mm away from the test section. The technique is applied to measuring bubbly and slug flows. By the combination of 2 and 8 MHz ultrasonic echo signals, the echo signals are distinguished between reflected from particles and bubbles. Compared with the results of obtaining with the multi-wave method and a high-speed camera, it is confirmed that the technique can separate the information of liquid and gas phases at a sampling rate of 1000 Hz.  相似文献   

17.
Two-phase flow is closely linked with the efficiency and safety of industrial processes in many fields, and there are various instruments for measuring the two-phase distribution. Among them, γ-ray and ultrafast X-ray tomography systems are most promising to break the technical barrier of gas-liquid measurement in the flow channel of high-temperature and high-pressure (up to 15 MPa/342 °C) nuclear reactors. Hence, A CT measurement method has been developed for imaging a two-phase distribution of a central plane oriented in axial direction in a rectangular duct, which was tested theoretically using a numerical phantom and experimentally on a preliminary tomographic hardware with a mechanically traversed gamma source and a detector unit, as well as a static phantom simulating gas bubbles in the pipe. After completing experimental and numerical imaging of a multi-bubbles phantom, the two-phase contrast and locations of bubbles in the experimental and simulated reconstruction images showed a good agreement and supported the feasibility of applying the linear scanning technique to realize two-phase detection in rectangular channels. The sensitivity analyses of scanning range, photon-registering time and scanning step length conveyed the optimal experimental strategy for this system. Morphological operation has also been imposed on image processing achieving elimination of severe ringing artefacts.  相似文献   

18.
A new flowrate measurement method for gas–oil two-phase flow using an electrical capacitance tomography technique and a Venturi meter is reported in this paper. A hybrid image reconstruction algorithm combining the Tikhonov regularization and the Algebraic Reconstruction algorithm is used to obtain images. The cross-sectional void fraction is determined from the images. A Venturi meter is used as a velocity measurement device whilst five measurement models are introduced to predict the total mass flowrate of gas–oil two-phase flow. Experimental results obtained show that the performance of the proposed flowrate measurement system is effective.  相似文献   

19.
The accurate prediction of flow regimes is vital for the analysis of behaviour and operation of gas/liquid two-phase systems in industrial processes. This paper investigates the feasibility of a non-radioactive and non-intrusive method for the objective identification of two-phase gas/liquid flow regimes using a Doppler ultrasonic sensor and machine learning approaches. The experimental data is acquired from a 16.2-m long S-shaped riser, connected to a 40-m horizontal pipe with an internal diameter of 50.4 mm. The tests cover the bubbly, slug, churn and annular flow regimes. The power spectral density (PSD) method is applied to the flow modulated ultrasound signals in order to extract frequency-domain features of the two-phase flow. Principal Component Analysis (PCA) is then used to reduce the dimensionality of the data so as to enable visualisation in the form of a virtual flow regime map. Finally, a support vector machine (SVM) is deployed to develop an objective classifier in the reduced space. The classifier attained 85.7% accuracy on training samples and 84.6% accuracy on test samples. Our approach has shown the success of the ultrasound sensor, PCA-SVM, and virtual flow regime maps for objective two-phase flow regime classification on pipeline-riser systems, which is beneficial to operators in industrial practice. The use of a non-radioactive and non-intrusive sensor also makes it more favorable than other existing techniques.  相似文献   

20.
Compared to general room-temperature fluids, the characteristics of cryogenic fluids, as well as the complexity of the cryogenic environment, pose greater challenges for reconstruction algorithms for Electrical Capacitance Tomography (ECT). Based on deep learning, a hybrid model is proposed for cryogenic fluid ECT image reconstruction in this study. The multi-head self-attention mechanism is employed to initially establish the mapping of capacitance to the image, and then an improved U-net-like convolution neural network is presented to perform deep feature extraction and image reconstruction. The ConvNeXt block is adopted for multi-level feature extraction, and a separate downsampling layer is used to replace the pooling layer. A dataset covering a variety of two-phase typical flow patterns and irregular flow patterns is built for training. A capacitance vector and an image of phase distribution are included in each sample. Extensive numerical experiments are carried out on the trained model. The results show that the model can accurately predict phase distribution and produce a clear interface. Finally, the model was successfully applied in cryogenic experiment to obtain the phase distribution image of liquid nitrogen stratified flow.  相似文献   

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