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Long-time simulations of the Kelvin-Helmholtz instability using an adaptive vortex method.
Sohn, Sung-Ik,Yoon, Daeki,Hwang, Woonjae Published by the American Physical Society through 2010 Physical review. E, Statistical, nonlinear, and so Vol.82 No.4
<P>The nonlinear evolution of an interface subject to a parallel shear flow is studied by the vortex sheet model. We perform long-time computations for the vortex sheet in density-stratified fluids by using the point vortex method and investigate late-time dynamics of the Kelvin-Helmholtz instability. We apply an adaptive point insertion procedure and a high-order shock-capturing scheme to the vortex method to handle the nonuniform distribution of point vortices and enhance the resolution. Our adaptive vortex method successfully simulates chaotically distorted interfaces of the Kelvin-Helmholtz instability with fine resolutions. The numerical results show that the Kelvin-Helmholtz instability evolves a secondary instability at a late time, distorting the internal rollup, and eventually develops to a disordered structure.</P>
STABILITY ANALYSIS OF REGULARIZED VISCOUS VORTEX SHEETS
Sohn, Sung-Ik Korean Mathematical Society 2016 대한수학회보 Vol.53 No.3
A vortex sheet is susceptible to the Kelvin-Helmhotz instability, which leads to a singularity at finite time. The vortex blob model provided a regularization for the motion of vortex sheets in an inviscid fluid. In this paper, we consider the blob model for viscous vortex sheets and present a linear stability analysis for regularized sheets. We show that the diffusing viscous vortex sheet is unstable to small perturbations, regardless of the regularization, but the viscous sheet in the sharp limit becomes stable, when the regularization is applied. Both the regularization parameter and viscosity damp the growth rate of the sharp viscous vortex sheet for large wavenumbers, but the regularization parameter gives more significant effects than viscosity.
LATE-TIME VORTEX DYNAMICS OF HYDRODYNAMIC INSTABILITIES
Sung-Ik SOHN,Daeki YOON,Woonjae HWANG 한국산업응용수학회 2010 한국산업응용수학회 학술대회 논문집 Vol.5 No.2
The late-time nonlinear evolutions of interfaces subject to a parallel shear flow and the gravitational acceleration, known as the Kelvin-Helmholtz and Rayleigh-Taylor instabilities, are studied by the vortex sheet model. We perform long-time simulations for the vortex sheet by using the point vortex method, and investigate late-time dynamics of the unstable interfaces. We apply an adaptive point insertion procedure and the WENO scheme to the vortex method, to handle the nonuniform distribution of point vortices and enhance the resolution. Our adaptive vortex method successfully simulates chaotically distorted interfaces with fine resolutions. Various late-time dynamics such as a secondary instability and the reacceleration phenomena of the hydrodynamic instabilities are discussed.
Inviscid and viscous vortex models for Richtmyer–Meshkov instability
North-Holland 2011 Fluid dynamics research Vol.43 No.6
<P>We present simple inviscid and viscous vortex models for the Richtmyer–Meshkov (RM) instability, in the limit of fluids of the same densities. The evolution of the interface is driven by a row of alternating point vortices. A regularization method for the singular vortices is applied to the inviscid model for stable calculations. The regularized vortex model provides fine resolutions for the interface, improving previous results on the evolution of the RM instability. The point vortex model, for the inviscid fluid, is validated by comparing with the results of the full vortex sheet model. The viscous vortex model for the unstable interface is based on the multi-Lamb–Oseen vortices. We show that the viscous vortex model gives the main qualitative features of the evolution of the viscous RM instability.</P>
Restoring Effects of Natural Anti-Oxidant Quercetin on Cellular Senescent Human Dermal Fibroblasts
Sohn, Eun-Ju,Kim, Jung Min,Kang, Se-Hui,Kwon, Joseph,An, Hyun Joo,Sung, Jung-Suk,Cho, Kyung A,Jang, Ik-Soon,Choi, Jong-Soon World Scientific Publishing Company 2018 The American journal of Chinese medicine Vol.46 No.4
<P>The oxidative damage initiated by reactive oxygen species (ROS) is a major contributor to the functional decline and disability that characterizes aging. The anti-oxidant flavonoid, quercetin, is a plant polyphenol that may be beneficial for retarding the aging process. We examined the restoring properties of quercetin on human dermal fibroblasts (HDFs). Quercetin directly reduced either intracellular or extracellular ROS levels in aged HDFs. To find the aging-related target genes by quercetin, microarray analysis was performed and two up-regulated genes <I>LPL</I> and <I>KCNE2</I> were identified. Silencing <I>LPL</I> increased the expression levels of senescence proteins such as p16<SUP>INK4A</SUP> and p53 and silencing <I>KCNE2</I> reversed gene expressions of EGR1 and p-ERK in quercetin-treated aged HDFs. Silencing of <I>LPL</I> and <I>KCNE2</I> decreased the expression levels of anti-oxidant enzymes such as superoxide dismutase and catalase. Also, the mitochondrial dysfunction in aged HDFs was ameliorated by quercetin treatment. Taken together, these results suggest that quercetin has restoring effect on the cellular senescence by down-regulation of senescence activities and up-regulation of the gene expressions of anti-oxidant enzymes in aged HDFs.</P>
A new TVD-MUSCL scheme for hyperbolic conservation laws
Elsevier 2005 COMPUTERS & MATHEMATICS WITH APPLICATIONS - Vol.50 No.1
<P><B>Abstract</B></P><P>The second-order extension of Godunov's method for hyperbolic conservation laws, known as MUSCL schemes, is studied in this paper. We present a new type of Eulerian MUSCL scheme and oscillation-free algorithms. The intercell flux is computed from difference approximations of characteristic equations with the data influencing the values at half-time step. The data for characteristic equations are classified in several different types by the domain of dependence. The oscillation-free algorithm, based on TVD method, gives a general formulation for previously used method and provides a class of limiters including existing limiters. To validate the new TVD-MUSCL scheme, numerical experiments are performed for several model problems in one and two dimensions.</P>
HIGH-ORDER POTENTIAL FLOW MODELS FOR HYDRODYNAMIC UNSTABLE INTERFACE
SUNG-IK SOHN 한국산업응용수학회 2012 Journal of the Korean Society for Industrial and A Vol.16 No.4
We present two high-order potential flow models for the evolution of the interface in the Rayleigh-Taylor instability in two dimensions. One is the source-flow model and the other is the Layzer-type model which is based on an analytic potential. The late-time asymptotic solution of the source-flow model for arbitrary density jump is obtained. The asymptotic bubble curvature is found to be independent to the density jump of the fluids. We also give the timeevolution solutions of the two models by integrating equations numerically. We show that the two high-order models give more accurate solutions for the bubble evolution than their loworder models, but the solution of the source-flow model agrees much better with the numerical solution than the Layzer model.
A HIGH-ORDER MODEL FOR SPIKE AND BUBBLE IN IMPULSIVELY ACCELERATED INTERFACE
Sohn, Sung-Ik The Kangwon-Kyungki Mathematical Society 2012 한국수학논문집 Vol.20 No.3
We present a high-order potential ow model for the motion of the impulsively accelerated unstable interface of infinite density jump. The Layzer model for the evolution of the interface is extended to high-order. The time-evolution solutions of the bubble and the spike in the interface are obtained from the high-order model. We show that the high-order model gives improvement on the prediction of the evolution of the bubble and the spike.