Efficient monolithic projection method with staggered time discretization for natural convection problems

Pan, Xiaomin,Kim, Ki-Ha,Choi, Jung-Il Elsevier 2019 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.144 No.-

<P><B>Abstract</B></P> <P>For a more efficient algorithm, we introduce staggered time discretization to improve the previous method (Pan et al., 2017), fully decoupled monolithic projection method with one Poisson equation (FDMPM-1P), to solve time-dependent natural convection problems. The momentum and energy equations are discretized using the Crank–Nicolson scheme at the staggered time grids, in which temperature and pressure fields are evaluated at half-integer time levels ( n + 1 2 ), while the velocity fields are evaluated at integer time levels ( n + 1 ). Numerical simulations of two-dimensional (2D) Rayleigh–Bénard convection show that the proposed method is more computationally efficient and stable than FDMPM-1P, while preserving the second-order spatial and temporal accuracy. Further, the proposed method provides accurate predictions of 2D Rayleigh–Bénard convection under different thermal boundary conditions for a Rayleigh number up to <SUP> 10 10 </SUP> , three-dimensional turbulent Rayleigh–Bénard convection in the range of 1 × <SUP> 10 5 </SUP> – 2 × <SUP> 10 7 </SUP> in horizontal periodic domain, and three-dimensional turbulent Rayleigh–Bénard convection in the range of 1 × <SUP> 10 6 </SUP> – 1 × <SUP> 10 7 </SUP> in bounded domain. Finally, we theoretically confirmed that the proposed method is second-order in time and it is more stable than FDMPM-1P for small <I>Ra</I>.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We propose VDMPM-STD by improving FDMPM-1P using staggered time discretization. </LI> <LI> The VDMPM-STD allows an explicit decoupling of momentum and energy equations. </LI> <LI> The VDMPM-STD is computationally efficient with the second-order accuracy. </LI> <LI> The VDMPM-STD provides accurate predictions of 2D and 3D RBC problems. </LI> </UL> </P>

A decoupled monolithic projection method for natural convection problems

Pan, Xiaomin,Kim, Kyoungyoun,Lee, Changhoon,Choi, Jung-Il Elsevier 2016 Journal of computational physics Vol.314 No.-

<P><B>Abstract</B></P> <P>We propose an efficient monolithic numerical procedure based on a projection method for solving natural convection problems. In the present monolithic method, the buoyancy, linear diffusion, and nonlinear convection terms are implicitly advanced by applying the Crank–Nicolson scheme in time. To avoid an otherwise inevitable iterative procedure in solving the monolithic discretized system, we use a linearization of the nonlinear convection terms and approximate block lower–upper (LU) decompositions along with approximate factorization. Numerical simulations demonstrate that the proposed method is more stable and computationally efficient than other semi-implicit methods, preserving temporal second-order accuracy.</P>

Efficient monolithic projection method for time-dependent conjugate heat transfer problems

Pan, Xiaomin,Lee, Changhoon,Choi, Jung-Il Elsevier 2018 Journal of computational physics Vol.369 No.-

<P><B>Abstract</B></P> <P>We propose herein an efficient monolithic projection method (MPM) to solve time-dependent conjugate heat transfer problems involving not only natural convection in the fluid domain and heat conduction in the solid domain, but also the thermal interaction between solid and fluid domains across the solid–fluid interface. We obtain a global discretized linearized system by advancing the buoyancy, nonlinear convection, and linear diffusion terms in time using the Crank–Nicolson scheme and introducing the second-order central finite difference in space along with linearizing the nonlinear convection terms in both momentum and energy equations. The energy equations are simultaneously and implicitly discretized in both solid and fluid domains with the implemented Taylor series expansion for thermal interaction normal to the interface without an involved sub-time step iteration. Approximated lower–upper decompositions and an approximate factorization are also imposed to speed up the computation. Thus, we obtain a non-iterative monolithic projection method over the entire domain. Numerical simulations of two-dimensional (2D) conjugate natural convection and 2D conjugate Rayleigh–Bénard convection and periodic forced flows are performed to investigate the numerical performance of the proposed method. Consequently, the MPM correctly predicts the solution of the conjugate natural convection problem involving strong thermal interactions and provides a more stable and efficient computation than the semi-implicit projection method proposed by Kim and Moin (1985) with a loosely or strongly coupled algorithm for the solid–fluid interface, while preserving the second-order temporal and spatial accuracy. Finally, the proposed method reasonably simulates a typical real-world problem, namely conjugate heat transfer through double-pane windows, by considering 2D heat conduction in each pane of glass for three different climatic conditions. Using the proposed MPM, we also investigate the effects of the air layer thickness ranging from 5 mm to 40 mm on the averaged Nusselt number and the distribution of temperature as well as fluid motion.</P> <P><B>Highlights</B></P> <P> <UL> <LI> An efficient monolithic projection method is proposed for solving time-dependent conjugate heat transfer (CHT) problems. </LI> <LI> Buoyancy, convection, and diffusion terms are advanced using the Crank–Nicolson scheme in time with second-order central difference in space. </LI> <LI> We investigate the numerical performance of the proposed method based on 2D CHT problems. </LI> <LI> We also perform 2D CHT through double-pane windows to assess the capability of the proposed method in solving real-world problems. </LI> </UL> </P>

Fully decoupled monolithic projection method for natural convection problems

Pan, Xiaomin,Kim, Kyoungyoun,Lee, Changhoon,Choi, Jung-Il Elsevier 2017 Journal of computational physics Vol.334 No.-

<P><B>Abstract</B></P> <P>To solve time-dependent natural convection problems, we propose a fully decoupled monolithic projection method. The proposed method applies the Crank–Nicolson scheme in time and the second-order central finite difference in space. To obtain a non-iterative monolithic method from the fully discretized nonlinear system, we first adopt linearizations of the nonlinear convection terms and the general buoyancy term with incurring second-order errors in time. Approximate block lower-upper decompositions, along with an approximate factorization technique, are additionally employed to a global linearly coupled system, which leads to several decoupled subsystems, i.e., a fully decoupled monolithic procedure. We establish global error estimates to verify the second-order temporal accuracy of the proposed method for velocity, pressure, and temperature in terms of a discrete <SUP> l 2 </SUP> -norm. Moreover, according to the energy evolution, the proposed method is proved to be stable if the time step is less than or equal to a constant. In addition, we provide numerical simulations of two-dimensional Rayleigh–Bénard convection and periodic forced flow. The results demonstrate that the proposed method significantly mitigates the time step limitation, reduces the computational cost because only one Poisson equation is required to be solved, and preserves the second-order temporal accuracy for velocity, pressure, and temperature. Finally, the proposed method reasonably predicts a three-dimensional Rayleigh–Bénard convection for different Rayleigh numbers.</P>

FULLY DECOUPLED MONOLITHIC PROJECTION METHOD FOR CONJUGATE HEAT TRANSFER PROBLEMS

Xiaomin Pan,C. Lee(이창훈),J.-I. Choi(최정일) 한국전산유체공학회 2017 한국전산유체공학회 학술대회논문집 Vol.2017 No.11

Image Quality Assessment with Saliency Map in Nonsubsampled Contourlet Transform Domain

Pan Wang,Wei Wu,Xiaomin Yang,Kai Liu,Gwanggil Jeon 보안공학연구지원센터 2016 International Journal of Multimedia and Ubiquitous Vol.11 No.6

Many researchers evaluate images by objective image quality assessments instead of subjective ones. Objective image quality assessment sets up mathematical model according to the human visual system, and it evaluates the image quality through the reference image and the distorted image. The Structural Similarity Index (SSIM) is one of the most classical methods in image quality assessment. However, SSIM has several inherent shortcomings. First, SSIM does not take spatial position, spatial frequency, or direction into account. Second, SSIM considers that different regions in an image have equal importance for overall image quality assessment. Third, it is unreasonable to use fixed parameters for various images. To overcome these shortcomings, we propose a new method of image quality assessment based on Nonsubsampled Contourlet Transform (NSCT). Firstly, NSCT is performed to decompose the image into a low-pass map and high-pass ones. Then, low-pass and high-pass maps are respectively assessed with different strategies. In addition, saliency map is added to describe the importance of different regions in an image. Last, we proposed an approach to calculate the adaptive parameters for various images. Experimental comparisons among five public benchmark databases demonstrate that the proposed method is better than other competing methods.

쇼트 클립 영업 방식에 대한 사용자 체험 연구

Zhou Xiaomin,Pan Young Hwan 한국서비스디자인학회 2020 한국서비스디자인학회 학술대회자료집 Vol.2020 No.-

노인 우울증 개선을위한 요양원 서비스 디자인 연구

Zhou Xiaomin,Pan Younghwan 한국서비스디자인학회 2021 한국서비스디자인학회 학술대회자료집 Vol.2021 No.-

A pre-conditioned implicit direct forcing based immersed boundary method for incompressible viscous flows

Park, Hyunwook,Pan, Xiaomin,Lee, Changhoon,Choi, Jung-Il Elsevier 2016 Journal of computational physics Vol.314 No.-

<P><B>Abstract</B></P> <P>A novel immersed boundary (IB) method based on an implicit direct forcing (IDF) scheme is developed for incompressible viscous flows. The key idea for the present IDF method is to use a block LU decomposition technique in momentum equations with Taylor series expansion to construct the implicit IB forcing in a recurrence form, which imposes more accurate no-slip boundary conditions on the IB surface. To accelerate the IB forcing convergence during the iterative procedure, a pre-conditioner matrix is introduced in the recurrence formulation of the IB forcing. A Jacobi-type parameter is determined in the pre-conditioner matrix by minimizing the Frobenius norm of the matrix function representing the difference between the IB forcing solution matrix and the pre-conditioner matrix. In addition, the pre-conditioning parameter is restricted due to the numerical stability in the recurrence formulation. Consequently, the present pre-conditioned IDF (PIDF) enables accurate calculation of the IB forcing within a few iterations. We perform numerical simulations of two-dimensional flows around a circular cylinder and three-dimensional flows around a sphere for low and moderate Reynolds numbers. The result shows that PIDF yields a better imposition of no-slip boundary conditions on the IB surfaces for low Reynolds number with a fairly larger time step than IB methods with different direct forcing schemes due to the implicit treatment of the diffusion term for determining the IB forcing. Finally, we demonstrate the robustness of the present PIDF scheme by numerical simulations of flow around a circular array of cylinders, flows around a falling sphere, and two sedimenting spheres in gravity.</P>

Acetylation of Smc3 by Eco1 Is Required for S Phase Sister Chromatid Cohesion in Both Human and Yeast

Zhang, Jinglan,Shi, Xiaomin,Li, Yehua,Kim, Beom-Jun,Jia, Junling,Huang, Zhiwei,Yang, Tao,Fu, Xiaoyong,Jung, Sung Yun,Wang, Yi,Zhang, Pumin,Kim, Seong-Tae,Pan, Xuewen,Qin, Jun Elsevier 2008 Molecular cell Vol.31 No.1

<P><B>Summary</B></P><P>Sister chromatid cohesion is normally established in S phase in a process that depends on the cohesion establishment factor Eco1, a conserved acetyltransferase. However, due to the lack of known in vivo substrates, how Eco1 regulates cohesion is not understood. Here we report that yeast Eco1 and its human ortholog, ESCO1, both acetylate Smc3, a component of the cohesin complex that physically holds the sister chromatid together, at two conserved lysine residues. Mutating these lysine residues to a nonacetylatable form leads to increased loss of sister chromatid cohesion and genome instability in both yeast and human. In addition, we clarified that the acetyltransferase activity of Eco1 is essential for its function. Our study thus identified a molecular target for the acetyltransferase Eco1 and revealed that Smc3 acetylation is a conserved mechanism in regulating sister chromatid cohesion.</P>