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Khambampati, Anil Kumar,Kim, Kyung Youn,Lee, Yeon-Gun,Kim, Sin Elsevier 2016 Applied mathematical modelling Vol.40 No.2
<P><B>Abstract</B></P> <P>Flow of immiscible liquids through horizontal pipe is observed in many industrial process applications. The flow is mainly characterized by its flow regime, relative phase velocities, liquid fraction and water holdup. Electrical resistance tomography (ERT) that provides a cross-sectional image of flow distribution is helpful in monitoring the process. In this paper, the moving interfacial boundary between the immiscible liquids of stratified flow is estimated based on the measured voltages on the pipe surface. Determining the time-varying shape and location of the interfacial boundary has a practical significance. It gives us the cross-sectional liquid fraction which is a key parameter to analyze the hydrodynamic properties of flow. The interfacial boundary shape and location is parameterized with discrete front points and the forward solution is formulated using analytical boundary element method (BEM). The analytic formulation of BEM is simple with less number of unknowns therefore it is computationally efficient. Moreover, BEM discretizes the boundaries alone and is therefore appropriate choice for interfacial boundary estimation. To estimate the time-varying boundary, conventional methods that assume no change in flow distribution within the measurement time of full frame of voltage data are inadequate. Dynamic imaging methods that use one or few sets of data can improve the temporal resolution and hence they are more accurate and practical in realistic situations. Inverse problem is treated as a state estimation problem where the front points are considered as state variables and are estimated using extended Kalman filter. Numerical simulations and phantom experiments are performed to validate the performance of the proposed method.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A numerical solution based on BEM is formulated for moving interfacial boundary. </LI> <LI> Boundary between immiscible liquids is parameterized using discrete front points. </LI> <LI> Analytic BEM is formulated for ERT boundary estimation problem. </LI> <LI> The moving front points that determine the boundary shape are estimated using EKF. </LI> <LI> Number of front points and contrast ratio of liquids affects estimation performance. </LI> </UL> </P>
Khambampati, Anil Kumar,Lee, Bo An,Kim, Kyung Youn,Kim, Sin IOP Pub 2012 Measurement Science and Technology Vol.23 No.3
<P>This paper is about locating the boundary of a moving cavity within a homogeneous background from the voltage measurements recorded on the outer boundary. An inverse boundary problem of a moving cavity is formulated by considering a two-phase vapor–liquid flow in a pipe. The conductivity of the flow components (vapor and liquid) is assumed to be constant and known a priori while the location and shape of the inclusion (vapor) are the unknowns to be estimated. The forward problem is solved using the boundary element method (BEM) with the integral equations solved analytically. A special situation is considered such that the cavity changes its location and shape during the time taken to acquire a full set of independent measurement data. The boundary of a cavity is assumed to be elliptic and is parameterized with Fourier series. The inverse problem is treated as a state estimation problem with the Fourier coefficients that represent the center and radii of the cavity as the unknowns to be estimated. An extended Kalman filter (EKF) is used as an inverse algorithm to estimate the time varying Fourier coefficients. Numerical experiments are shown to evaluate the performance of the proposed method. Through the results, it can be noticed that the proposed BEM with EKF method is successful in estimating the boundary of a moving cavity.</P>
Khambampati, Anil Kumar,Ijaz, Umer Zeeshan,Lee, Jeong Seong,Kim, Sin,Kim, Kyung Youn IOP Pub 2010 Measurement Science and Technology Vol.21 No.3
<P>In industrial processes, monitoring of heterogeneous phases is crucial to the safety and operation of the engineering structures. Particularly, the visualization of voids and air bubbles is advantageous. As a result many studies have appeared in the literature that offer varying degrees of functionality. Electrical impedance tomography (EIT) has already been proved to be a hallmark for process monitoring and offers not only the visualization of the resistivity profile for a given flow mixture but is also used for detection of phase boundaries. Iterative image reconstruction algorithms, such as the modified Newton–Raphson (mNR) method, are commonly used as inverse solvers. However, their utility is problematic in a sense that they require the initial solution in close proximity of the ground truth. Furthermore, they also rely on the gradient information of the objective function to be minimized. Therefore, in this paper, we address all these issues by employing a direct search algorithm, namely the Hooke and Jeeves pattern search method, to estimate the phase boundaries that directly minimizes the cost function and does not require the gradient information. It is assumed that the resistivity profile is known a <I>priori</I> and therefore the unknown information will be the size and location of the object. The boundary coefficients are parameterized using truncated Fourier series and are estimated using the relationship between the measured voltages and injected currents. Through extensive simulation and experimental result and by comparison with mNR, we show that the Hooke and Jeeves pattern search method offers a promising prospect for process monitoring.</P>
An Automatic Detection of the ROI Using Otsu Thresholding in Nonlinear Difference EIT Imaging
Khambampati, A. K.,Liu, D.,Konki, S. K.,Kim, K. Y. IEEE 2018 IEEE SENSORS JOURNAL Vol.18 No.12
<P>Inverse problem of electrical impedance tomography is highly ill-posed therefore often prior information is used to have a satisfactory and stable solution. Recently, introduced non-linear differential imaging method estimates the initial and difference in conductivities simultaneously and is efficient in handling modeling errors. The non-linear parameterization of conductivity enables to use different regularization schemes for background and region of interest (ROI). Identifying the ROI without any prior information can be beneficial in improving the reconstruction performance. Therefore, in this paper, automatic detection of ROI is introduced using Otsu thresholding method and is then used with non-linear differential imaging. The proposed non-linear differential imaging with Otsu method (NDIWO) considers different regularization methods, i.e., total variational approach with ROI and smoothness prior with background regions during reconstruction. Numerical and experimental studies are performed to test NDIWO method for two-phase flow and thorax imaging and the performance is compared with absolute and linear difference imaging. The results indicate that the proposed NDIWO method has improved reconstruction performance compared with conventional absolute and linear difference imaging.</P>
Khambampati, Anil Kumar,Kim, Kyung Youn,Hur, Seop,Kim, Sung Joong,Kim, Jung Taek Korean Nuclear Society 2021 Nuclear Engineering and Technology Vol.53 No.2
Nuclear power plants contain several monitoring systems that can identify the in-vessel phenomena of a severe accident (SA). Though a lot of analysis and research is carried out on SA, right from the development of the nuclear industry, not all the possible circumstances are taken into consideration. Therefore, to improve the efficacy of the safety of nuclear power plants, additional analytical studies are needed that can directly monitor severe accident phenomena. This paper presents an interacting multiple model (IMM) based fault detection and diagnosis (FDD) approach for the identification of in-vessel phenomena to provide the accident propagation information using reactor vessel (RV) out-wall temperature distribution during severe accidents in a nuclear power plant. The estimation of wall temperature is treated as a state estimation problem where the time-varying wall temperature is estimated using IMM employing three multiple models for temperature evolution. From the estimated RV out-wall temperature and rate of temperature, the in-vessel phenomena are identified such as core meltdown, corium relocation, reactor vessel damage, reflooding, etc. We tested the proposed method with five different types of SA scenarios and the results show that the proposed method has estimated the outer wall temperature with good accuracy.
Khambampati, Anil Kumar,Rashid, Ahmar,Ijaz, Umer Zeeshan,Kim, Sin,Soleimani, Manuchehr,Kim, Kyung Youn The Royal Society 2009 Philosophical transactions. Series A, Mathematical Vol.367 No.1900
<P>The monitoring of solid-fluid suspensions under the influence of gravity is widely used in industrial processes. By considering sedimentation layers with different electrical properties, non-invasive methods such as electrical impedance tomography (EIT) can be used to estimate the settling curves and velocities. In recent EIT studies, the problem of estimating the locations of phase interfaces and phase conductivities has been treated as a nonlinear state estimation problem and the extended Kalman filter (EKF) has been successfully applied. However, the EKF is based on a Gaussian assumption and requires a linearized measurement model. The linearization (or derivation of the Jacobian) is possible when there are no discontinuities in the system. Furthermore, having a complex phase interface representation makes derivation of the Jacobian a tedious task. Therefore, in this paper, we explore the unscented Kalman filter (UKF) as an alternative approach for estimating phase interfaces and conductivities in sedimentation processes. The UKF uses a nonlinear measurement model and is therefore more accurate. In order to justify the proposed approach, extensive numerical experiments have been performed and a comparative analysis with the EKF is provided.</P>
Anil Kumar Khambampati,Ahmar Rashid,Jeong Seong Lee,Sin Kim,Kyung Youn Kim 대한전자공학회 2008 ITC-CSCC :International Technical Conference on Ci Vol.2008 No.7
This work is related to interfacial phase bounadry estimation in sedimentation monitoring using electrical impedance tomography. The fluid is assumed to settle into three different phases separated by sharp interfacial boundary. The time evolution of the phase interface gives important information about the sedimentation process which can be used to control and optimize the sedimentation process. Phase interface location and their corresponding conductivities estimation is treated as a stochastic nonlinear state estimation problem with the nonstationary interfacial phase boundary (state) being estimated online with the aid of unscented Kalman filter. Numerical experiments are performed to evaluate the performance of the proposed approach and is compared with conventional extended Kalman filter.