• Journal of the Korean Society for Industrial and Applied Mathematics
• /
• v.22 no.3
• /
• pp.137-154
• /
• 2018

We investigate the condensation transition of a zero range process with jump rate g given by $g(k)=\left\{\frac{M}{k^{\alpha}},\;if\;k{\leq}an\\{\frac{1}{k^{\alpha}}},\;if\;k>an,$ (0.1), where ${\alpha}$ > 0 and a(0 < a < 1/2) is a rational number. We show that for any ${\epsilon}$ > 0, there exists $M^*$ > 0 such that, for any 0<$M{\leq}M^*$, the maximum cluster size is between ($a-{\epsilon}$)n and ($a+{\epsilon}$)n for large n.

• Journal of the Korean Mathematical Society
• /
• v.58 no.4
• /
• pp.819-833
• /
• 2021

Hawkes process is a self-exciting simple point process with clustering effect whose jump rate depends on its entire past history and has been widely applied in insurance, finance, queueing theory, statistics, and many other fields. Seol [27] proposed the inverse Markovian Hawkes processes and studied some asymptotic behaviors. In this paper, we consider an extended inverse Markovian Hawkes process which combines a Markovian Hawkes process and inverse Markovian Hawkes process with features of several existing models of self-exciting processes. We study the limit theorems for an extended inverse Markovian Hawkes process. In particular, we obtain a law of large number and central limit theorems.

• Journal of the Society of Naval Architects of Korea
• /
• v.37 no.3
• /
• pp.27-36
• /
• 2000

A higher order panel method based on B-spline representation for both the geometry and the velocity potential is developed for the solution of the flow around two-dimensional lifting bodies. Unlike Lee/Kerwin, who placed multiple control points on each panel and solved the overdetermined system of equation by the least square approach, the present method places only as many number of control points as required by the unknowns of the problem. Especially, a null pressure jump Kutta condition at the trailing edge is found to be effective in stabilizing the solution process and in predicting the correct solution. The new approach, is validated to be accurate through comparison with the analytic solution for a 2-D airfoil and to be less time-consuming due to fewer number of panels required than that used in Lee/Kerwin.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.28 no.1
• /
• pp.1-8
• /
• 2015

In this paper, computational evaluation method for fatigue crack growth rate(FCGR) based on material viscoplastic-damage model is proposed. Viscoplastic-damage model expressing material constitutive behavior of 7% nickel steel is introduced and is implemented into commercial finite element analysis(FEA) code, ABAQUS, as a user defined material subroutine(UMAT) for application in the FEA environments. Verification of developed UMAT and material parameters of material model are carried out by uniaxial tensile test simulations of 7% nickel steel. Moreover, jump-in-cycles procedure and rearrangement of critical damage are employed and also implemented to the ABAQUS UMAT for fatigue damage analysis. Typical FCGR test results such as relationship between crack length and number of cycles and relationship between da/dN and ${\Delta}K$ could be obtained from FCGR test simulation using developed UMAT and these results are compared with experimental results in order to verify of proposed computational method.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.13 no.1
• /
• pp.105-114
• /
• 1993

The ciculation due to bottom density current produced by a dense inflow into a small reservoir is analysed by numerical scheme. Before the front of the density current arrives at the downstream end, the mixing in the reservoir is mainly caused by the anticlockwise vortex formed at the downstream of plunging point along the movement of bottom density current. Upon the arrival of the front of the density current at the downstream end an internal surge is created through an internal hydraulic jump. With repeated propagation of the internal surge back and forth the mixing in the reservoir is progressed and the thickness of dense layer is increased upward. The dilution of the overflow at downstream end is found to depend on inflow densimetric Froude number, reservoir length and elapsed time. The time required for the overflow to attain a specified dilution increases as reservoir length increases and Fre decreases.

• Journal of Advanced Marine Engineering and Technology
• /
• v.35 no.4
• /
• pp.468-474
• /
• 2011

The flow field around baffle located sudden expansion and contraction channel was measured by PIV method and the effect according to height change of baffle built in the flow field was evaluated. The inlet flow velocity and the baffle height influence mutually to the size and flow pattern of the recycle flow of the back of the baffle and the size of the area of the water power jump passing the upper part of the baffle. In case of Reynolds number $Re=4{\times}10^3$, the critical value of baffle height is estimated around h/H=1.6 and there was a decreasing tendency as the inlet flow velocity was increased.

• 한국전산유체공학회:학술대회논문집
• /
• 2003.10a
• /
• pp.294-298
• /
• 2003

The complex, unsteady, self-sustained pressure oscillations induced by supersonic flow past a rectangular cavity is investigated using numerical simulations. The present numerical study is performed using a parallel, multiblock solver for the two-dimensional, compressible Navier­Stokes equations. Open cavities with length-to-depth (L / D) ratio in the range 0.5 - 3.3 are considered. This paper sheds light on the cavity physics, cavity oscillatory mechanism, and the organisation of vortical structures inside the cavity. The vortex shedding phenomenon, the shear layer impingement event at the aft wall and the movement of the acoustic/compression wave within the cavity are well predicted. The vortical structures· and the source of the acoustic disturbances are found to be located near the aft wall of the cavity. With the increase in the cavity length, strong recompression of the flow near the aft wall leading to a sudden jump in the cavity form drag is observed. The estimated cavity tones are in good agreement with the available semi­empirical relation. Multiple peaks are noticed in deep and long cavities. For the present free­stream Mach number 1.71, it is observed that around L/D=2.0, the cavity oscillatory mechanism changes from the transverse to longitudinal oscillatory mode. The effects of this transition on various fluid dynamics and acoustic properties are also discussed.

• BMB Reports
• /
• v.43 no.6
• /
• pp.383-388
• /
• 2010

The number of cancer patients has increased due to longer life spans and treatment has become a universal problem. Since molecular-targeted therapies were introduced as a new developmental strategy, certain targets have been examined hundreds of times, with developers overlapping their research efforts. We need to focus our energy and resources on novel drug candidate identification and optimization, in order to enhance the entry of early-stage drug candidates into the therapeutics pipeline. This presents a major opportunity for Korea to jump the decades-old development gap between our programs and those that are more advanced in other countries. Although this country does not have a specific center for validation and development of cancer therapeutics, we do have cutting-edge scientists performing research in many institutions. In this paper, I will review cancer drug development in Korea and suggest future directions, while urging colleagues to utilize their networking expertise so we can move toward a new paradigm of novel therapeutics development. An example of such efforts has begun with the Drug Development Consortium, which was described in the KSBMB chapter. This consortium was launched in 2010 by biochemists, chemists, cell and molecular biologists and pharmacologists. It is clear that effective cancer therapeutics will be developed more efficiently when we all strive for the same goal.

• Nuclear Engineering and Technology
• /
• v.44 no.8
• /
• pp.871-888
• /
• 2012

This paper aims at presenting the state of the art, the recent progress, and the perspective for the future, in the modelling of two-phase flow in the horizontal legs of a PWR. All phenomena relevant for safety analysis are listed first. The selection of the modelling approach for system codes is then discussed, including the number of fluids or fields, the space and time resolution, and the use of flow regime maps. The classical two-fluid six-equation one-pressure model as it is implemented in the CATHARE code is then presented and its properties are described. It is shown that the axial effects of gravity forces may be correctly taken into account even in the case of change of the cross section area or of the pipe orientation. It is also shown that it can predict both fluvial and torrential flow with a possible hydraulic jump. Since phase stratification plays a dominant role, the Kelvin-Helmholtz instability and the stability of bubbly flow regime are discussed. A transition criterion based on a stability analysis of shallow water waves may be used to predict the Kelvin-Helmholtz instability. Recent experimental data obtained in the METERO test facility are analysed to model the transition from a bubbly to stratified flow regime. Finally, perspectives for further improvement of the modelling are drawn including dynamic modelling of turbulence and interfacial area and multi-field models.

• Journal of the Korean Society for Industrial and Applied Mathematics
• /
• v.23 no.2
• /
• pp.65-92
• /
• 2019

We survey a recently developed immersed finite element method (IFEM) for the interface problems. The IFEM uses structured grids such as uniform grids, even if the interface is a smooth curve. Instead of fitting the curved interface, the bases are modified so that they satisfy the jump conditions along the interface. The early versions of IFEM [1, 2] were suboptimal in convergence order [3]. Later, the consistency terms were added to the bilinear forms [4, 5], thus the scheme became optimal and the error estimates were proven. For elasticity problems with interfaces, we modify the Crouzeix-Raviart based element to satisfy the traction conditions along the interface [6], but the consistency terms are not needed. To satisfy the Korn's inequality, we add the stabilizing terms to the bilinear form. The optimal error estimate was shown for a triangular grid. Lastly, we describe the multigrid algorithms for the discretized system arising from IFEM. The prolongation operators are designed so that the prolongated function satisfy the flux continuity condition along the interface. The W-cycle convergence was proved, and the number of V-cycle is independent of the mesh size.