• International Journal of Aeronautical and Space Sciences
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• v.16 no.4
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• pp.548-559
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• 2015

We performed a numerical simulation based on the two-dimensional (2-D) unsteady Euler's equation with a single-step Arrhenius reaction model in order to investigate the detonation wave front propagation of an Argon (Ar) diluted oxy-hydrogen mixture ($2H_2+O_2+12Ar$). This simulation operates in the detonation frame of reference. We examine the effect of grid size and the performance impact of integrated quantities such as mass flow. For a given set of baseline conditions, the minimal and maximum grid resolutions required to simulate the respective detonation waves and the detonation cell structures are determined. Tertiary shock wave behavior for various grids and pre-exponential factors are analyzed. We found that particle fluctuation can be weakened by controlling the mass flow going through the oblique shock waves.

• Nuclear Engineering and Technology
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• v.42 no.3
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• pp.259-270
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• 2010

New generation nuclear reactors are designed using advanced safety analysis methods. A thorough understanding of different interacting physical phenomena is necessary to avoid underestimation and overestimation of consequences of off-normal transients in the reactor safety analysis results. This feature requires a multiphysics reactor simulation model. In this context, a coupled dynamics model based on a multiphysics formulation is developed indigenously for the transient analysis of large pressurized VVER reactors. Major simplifications are employed in the model by making several assumptions based on the physics of individual phenomenon. Space and time grids are optimized to minimize the computational bulk. The capability of the model is demonstrated by solving a series of international (AER) benchmark problems for VVER reactors. The developed model was used to analyze a number of reactivity transients that are likely to occur in VVER reactors.

• Bulletin of the Korean Space Science Society
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• 2010.04a
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• pp.35.1-35.1
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• 2010

Using the spectroscopic analysis and the theoretical modeling, physical properties of the nearby astrometric binary $\mu$ Cas have been determined. In spite of the well-defined parallax and astrometric orbit, there has been a chronic mass ratio problem between components. Recently, the radius of the primary component has been detected from the optical interferometric observation of the CHARA array. Using the high resolution spectroscopic analysis, we found that $\mu$ Cas have $\alpha$-enhanced chemical composition with respect to the scaled solar abundance by a factor of two. Combining our abundance analysis with recently determined physical properties, the consistent models for $\mu$ Cas have been constructed within the frame work of standard stellar theory. Through a statistical minimization between theoretical model grids, a reliable set of physical dimensions has been defined. Furthermore, the mode oscillation frequency of the best model has been calculated.

• Structural Engineering and Mechanics
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• v.55 no.3
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• pp.461-472
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• 2015

The existence of initial imperfections in manufacturing or assembly of double-layer space structures having hundreds or thousands of members is inevitable. Many of the imperfections, such as the initial curvature of the members and residual stresses in members, are all random in nature. In this paper, the probabilistic effect of initial curvature imperfections in the load bearing capacity of double-layer grid space structures with different types of supports have been investigated. First, for the initial curvature imperfection of each member, a random number is generated from a gamma distribution. Then, by employing the same probabilistic model, the imperfections are randomly distributed amongst the members of the structure. Afterwards, the collapse behavior and the ultimate bearing capacity of the structure are determined by using nonlinear push down analysis and this procedure is frequently repeated. Ultimately, based on the maximum values of bearing capacity acquired from the analysis of different samples, structure's reliability is obtained by using Monte Carlo simulation method. The results show the sensitivity of the collapse behavior of double-layer grid space structures to the random distribution of initial imperfections and supports type.

• Nuclear Engineering and Technology
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• v.49 no.6
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• pp.1125-1134
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• 2017

In this paper, we present a new multilevel in space and energy diffusion (MSED) method for solving multigroup diffusion eigenvalue problems. The MSED method can be described as a PI scheme with three additional features: (1) a grey (one-group) diffusion equation used to efficiently converge the fission source and eigenvalue, (2) a space-dependent Wielandt shift technique used to reduce the number of PIs required, and (3) a multigrid-in-space linear solver for the linear solves required by each PI step. In MSED, the convergence of the solution of the multigroup diffusion eigenvalue problem is accelerated by performing work on lower-order equations with only one group and/or coarser spatial grids. Results from several Fourier analyses and a one-dimensional test code are provided to verify the efficiency of the MSED method and to justify the incorporation of the grey diffusion equation and the multigrid linear solver. These results highlight the potential efficiency of the MSED method as a solver for multidimensional multigroup diffusion eigenvalue problems, and they serve as a proof of principle for future work. Our ultimate goal is to implement the MSED method as an efficient solver for the two-dimensional/three-dimensional coarse mesh finite difference diffusion system in the Michigan parallel characteristics transport code. The work in this paper represents a necessary step towards that goal.

• Journal of Science of Art and Design
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• v.1
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• pp.125-164
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• 1999

The Grid, a lattice structure adapted in paintings, is one of thesimplest plastic structures based on the intersection of horizontal and perpendicular lines. Though mankind has, from the pre-history to the present day, put it to good use in everyday life as a traditional practice or a magical, esoteric, religious emblem in the case of the teciform of primitve art, it was in the paintings of Piet Mondrian that the Grid showed its modern, artistic transformation. As we suggest in the title, before I state the Grid as a plastic construction of modern painting, this dissertation inquires the Grid structure that extends over paintings through the ages as a painterly conept, especially focused on their formation and deconstruction. To begin with, my dissertation investigates, as a historical background, a general idea of the geometrical structure and phases of its transition in art, prior to dealing with the Grids as plastic strures in modern painting. the core of my study on formal Grids is permeated through the third chapter. The first chapter concentrates on, firstly, difining the notion of the Grid and geometrical structure, secondly, searching for a historical backgrounb with whict the so- called modern Grid-paintings come in, inquiring into the formation of the illusion-Grid as aresult of discovering the linear perpective and the situation of the conflict and reconciliaton between reality and illusion. Based on these considerations, the second cecond chapter will examine the various sitations of formation and adaptation of the paintery Grids in the Literalism-Grid, as we have already seen in the chapter one. And the cardinal third chapter devotes itself to the process of the formation of the so-called Object-Grid and Literal-Grid in the Literalism or Minimalism as its logical extension of the Painterly Grid. With it we can get to an interpretation and understanding of the meaning and qualites of Grid dwelt in Modernism thst transformed the structure of Painterly Grid originally as a plane concept to the third dimentionl structure. And then, the fourth chapter, we try to draw a new meaning andre-interpretation of the Formal-Grid as a representatuinnal structure appeared in the post-modernist paintings, going with its deconstructional situation. Therefore, we can, in our study on Grids, see the various points of view in the interpretation of them as illusion-structure, as plane-structure, and as cubic-structure; its concept differs form times, oscillating between its formation and deconstruction. The Grid, as we have seen in my dissertation, contains various problems and significations in art that deserve to investigate throughly, including some important plastic problem such as space and plane, and, in the case of do-grid, time. We may expect new concepts of it that will have difference meanings. 1 hope my study makes some contributions to understanding the coordination of the abstruse modern and contemporary art.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.85.2-85.2
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• 2012

In this paper, we introduce the 3D modeling of the coronal magnetic field in the solar active region by extrapolating from the 2D observational data numerically. First, we introduce a nonlinear force-free field (NLFFF) extrapolation code based on the MHD-like relaxation method implementing the cleaning a numerical error for Div B proposed by Dedner et al. 2002 and the multi-grid method. We are able to reconstruct the ideal force-free field, which was introduced by Low & Lou (1990), in high accuracy and achieve the faster speed in the high-resolution calculation (512^3 grids). Next we applied our NLFFF extrapolation to the solar active region NOAA 10930. First of all, we compare the 3D NLFFF with the flare ribbons of Ca II images observed by the Solar Optical Telescope (SOT) aboard on the Hinode. As a result, it was found that the location of the two foot-points of the magnetic field lines well correspond to the flare ribbon. The result indicates that the NLFFF well capture the 3D structure of magnetic field in the flaring region. We further report the stability of the magnetic field by estimating the twist value of the field line and finally suggest the flare onset mechanism.

• International Journal of Aeronautical and Space Sciences
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• v.2 no.2
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• pp.1-18
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• 2001

A numerical technique for simulating the separation dynamics of strap-on boosters jettisoned in the dense atmosphere is presented. Six degree of freedom rigid body equations of motion are integrated into the three-dimensional unsteady Navier-Stokes solution procedure to determine the dynamic motions of strap-ons. An automated Chimera overlaid grid technique is introduced to achieve maximum efficiency for multi-body dynamic motion and a domain division technique is implemented in order to reduce the computational cost required to find interpolation points in the Chimera grids. The flow solver is validated by comparing the computed results around the Titan IV launch vehicle with experimental data. The complete analysis process is then applied to the. H-II launch vehicle, the central rocket in japans space program, the CZ-3C launch vehicle developed in China and the KSR-III, a three-stage sounding rocket being developed in Korea. From the analyses, separation trajectories of strap-on boosters are predicted and aerodynamic characteristics around the vehicles at every time interval are examined. In addition, separation-impulse devices generally introduced for safe separation of strap-ons are properly modeled in the present paper and the jettisoning force requirements are examined quantitatively.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.139.1-139.1
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• 2012

Wilson and Bappu (1957) found a significant relationship (WBR) between the absolute magnitude ($M_v$) and the width of the Ca II K emission line (W) for late type stars. In this study, we revisit the WBR to claim that WBR can be an excellent indicator of stellar surface gravity. We analyze 95 high-resolution spectra of G, K and M type stars obtained with UVES and BOES. WBR found in this work is $M_v$=34.22-18.34logW. In addition, stellar atmospheric parameters ($T_{eff}$, logg, [Fe/H], ${\xi}_{tur}$) are determined with the MOOG code and the Kurucz ATLAS9 model grids for G and K type stars. For M type stars, the method of Belle et al. (1999) is used to derive effective temperature which shows good agreement with other methods. Using the derived $T_{eff}$ and the measured logW,we find the relationship between logg and [logW, logT]; ${\log}g-_{fit}=-25.051-5.527{\log}W+10.254{\log}T_{eff}$. This relation can be applied to estimate the surface gravity of M type stars, which is difficult to be determined by other methods.

• Journal of Korean Society of Steel Construction
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• v.28 no.6
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• pp.395-402
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• 2016

Space frame structures considering the components such as forms, layers, grids, etc. are possible to form a large space without interior columns. Here, steels having the yield strengths of 210 MPa to 450 MPa are generally used. The high strength steel (i.e., yield strength of 690 MPa) having suitable weldability, aseismicity and economics have been recently developed. In this paper, the high strength steel is applied to the space frame structures in order to analytically find out their transient responses considering the material and geometric nonlinearities. For various circular dome types of space frame structures, the modal analysis and nonlinear transient analysis are carried out using nonlinear three dimensional finite element analysis.