• International Journal of Naval Architecture and Ocean Engineering
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• v.10 no.1
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• pp.48-59
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• 2018

This paper is mainly concerned with developing the formulae of predicting thermal deformation of steel plate due to multi-line heating. By investigating the results of line heating test and numerical analysis, reasonable heat flux model has been defined. Formulae of predicting the transverse shrinkage and the angular distortion as the dominant thermal deformation types in plate forming by line heating have been derived based on the results of line heating test and numerical analysis with varying plate thickness, heating speed and distance between torches. This paper illustrates how the derived formulae are used in investigating the effect of multi-line heating upon the thermal deformation and how they can be used in defining the limit distance with that there is no interacted effect between torches. This paper ends with describing the extension of the present study.

• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.1165-1167
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• 2005

본 논문은 냉각기 등에 적용 가능한 소형 압축기용 영구자석 여자 횡자속 선형 전동기 개발에 관한 내용이다. 3차원 등가 자기 회로망법을 이용하여 전동기의 특성을 해석하고 상용화 되어 사용되고 있는 선형 압축기의 특성과 서로 비교하여 그 성능을 평가 하였다.

• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.921-923
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• 2005

본 논문은 LCD 제조 공정라인에서 LCD 원판을 이송하기 위한 영구자석 여자 횡자속형 선형 진동기 개발에 관한 내용이다. 3차원 등가 자기 회로망법과 2차원 유한 요소법을 사용하여 이동자의 단부 효과를 고려하여 전동기 특성을 해석하였으며 정특성 실험을 통하여 설계 및 해석의 타당성을 검증하였다.

• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.1159-1161
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• 2005

This study uses a design of experiments to explain correlations between the objective function and design variables. Analysis of means, analysis of variance and table of orthogonal array were carried out. The change of shape design variable for TFLM based on the table of orthogonal array is made. Therefore this study carried to decide design variables for maximizing thrust force of TFLM. we showed improved design variables.

• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.1135-1137
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• 2005

단위 무게당 추력특성이 다른 전동기에 비해 우수한 것으로 나타나 있는 횡축형 선형전동기에 대한 연구가 많이 진행되고 있다. 본 논문에서는 횡축형 선형 전동기의 동적 시뮬레이션을 수행할 수 있는 시뮬레이션 모델을 개발하였다. 전동기의 설계단계에서는 주로 정적인 특성만을 고려하여 설계가 진행되지만, 이렇게 설계된 전동기는 실제 실험 결과와 설계 명세간의 차이가 많이 발생하는 경우가 있다. 본 논문에서 개발된 동적 시뮬레이션 모델을 이용한 결과를 설계 단계에서 적용한다면 좀 더 실제적인 전동기 설계를 할 수 있을것으로 기대된다. 또한 제작된 전동기의 성능 평가를 하는 경우 성능의 기준으로 활용할 수 있을 것으로 생각된다.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.2
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• pp.70.3-70.3
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• 2019

We present a method to estimate 3-component plasma velocity (Vx, Vy and Vz) at solar photosphere near solar disk center, using the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) called Space-weather HMI Active Region Patch (SHARP). In Heliocentric-Cartesian Coordinates, the component of Vz is obtained from Dopplergram while the components of Vx and Vy are derived from the relation of $B_z{\overrightarrow{u}}=B_z{\overrightarrow{{\nu}_t}}-{\nu}_z{\overrightarrow{B_t}}$ (Demoulin & Berger 2003) using a series of vector magnetograms by an optical flow technique NAVE (Nonlinear Affine Velocity Estimator). This velocity measurement method is applied to AR 12158 producing an X1.6 flare along with a coronal mass ejection. We find noticeable upflow motions at both ends of flux ropes which become a major eruption part, and strong transverse motions nearby them before the eruption. We will discuss the change of plasma motions and magnetic fields before and after the eruption.

• The Bulletin of The Korean Astronomical Society
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• v.45 no.1
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• pp.55.1-55.1
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• 2020

In an attempt to investigate the nonlinear dynamics such as shock, shear, and turbulence associated with ultra-relativistic jets, we develop a new relativistic hydrodynamics (RHD) code based on the weighted essentially non-oscillatory (WENO) scheme. It is a 5th-order accurate, finite-difference scheme, which has been widely used for solving hyperbolic systems of conservation equations. The code is parallelized with MPI and OpenMP. Through an extensive set of tests, the accuracy and efficiency of different WENO reconstructions, and different time discretizations are assessed. Different implementations of the equation of state (EOS) for relativistic fluid are incorporated, As the fiducial setup for simulations of ultra-relativistic jets, we adopt the EOS in Ryu et al. (2006) to treat arbitrary adiabatic index of relativistic fluid, the WENO-Z reconstructions to minimize numerical dissipation without loss of stability, and the strong stability preserving Runge-Kutta (SSPRK) method to achieve stable time stepping with large CFL numbers. In addition, the code includes a high-order flux averaging along the transverse directions for multi-dimensional problems, and the modified eigenvalues for the acoustic modes to effectively control the carbuncle instability. We find that the new code performs satisfactorily simulations of ultra-relativistic jets.

• Nuclear Engineering and Technology
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• v.26 no.3
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• pp.440-452
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• 1994

Nuclear fuel bundles are designed such that the heat flux at a-fuel pin surface should not exceed the critical heat flux (CHF) during normal operation and anticipated transient. Therefore, evaluation of the CHF for fuel bundle is demanded in an exact and reliable manner. One of the major concerns with the current application of CHF correlations is that the CHF based on circular tubes is applied to the fuel bundle subchannel analysis, mainly in terms of the hydraulic diameter with correction factors which may result in a source of possibly large uncertainties in CHF prediction. The hydraulic diameter does not recognize the local properties of fluid nor such effect as the surface curvature; the turbulence action on the convex surface is much more pronounced than that on the concave surface. Even for the tube having concave curvature, the effect of tube diameter on CHF becomes important with decreasing diameter. These facts imply that the convex curvature effect is significant and crucial to the reliable CHF prediction. This paper reviews and discusses analytical and experimental aspects of effect of transverse convex curvature in incompressible turbulent flow and heat transfer, and on CHF. Flow models to quantify this effect are briefly mentioned and future works are recommended.

• Journal of the Korean Society of Propulsion Engineers
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• v.12 no.2
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• pp.24-32
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• 2008

A non-reacting experimental study on a normal injection into a Mach 1.92 crossflow which flows over various geometries(flat plate, small cavity, large cavity) was carried out to investigate the effect of the momentum flux ratio(J). The aft ramp of the cavity advances the increase of the penetration height and the strong two-dimensional shock from recompression region mainly affects the shock structure and mixing layer at the downstream flow. As flow runs downward, the transverse penetration height increases with increasing J(J = 0.9, 1.7, 3.4). However, above some critical ratio, jet penetration height growth with increasing J is not appeared in flow-field. Large scale cavity has a good mixing efficiency but it increases the drag loss in the combustor.

• Journal of The Korean Astronomical Society
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• v.41 no.6
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• pp.173-180
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• 2008

Using the MHD coronal seismology technique, we estimated the magnetic field for three spicules observed in 2008 June. For this study, we used the high resolution Ca II H line ($3968.5\;{\AA}$) images observed by the Hinode SOT and considered a vertical thin flux tube as a spicule model. To our knowledge, this is the first attempt to estimate the spicule magnetic field using the Hinode observation. From the observed oscillation properties, we determined the periods, amplitudes, minimum wavelengths, and wave speeds. We interpreted the observed oscillations as MHD kink waves propagating through a vertical thin flux tube embedded in a uniform field environment. Then we estimated spicule magnetic field assuming spicule densities. Major results from this study are as follows : (1) we observed three oscillating spicules having durations of 5-7 minutes, oscillating periods of 2-3 minutes, and transverse displacements of 700-1000 km. (2) The estimated magnetic field in spicules is about 10-18 G for lower density limit and about 43-76 G for upper density limit. (3) In this analysis, we can estimate the minimum wavelength of the oscillations, such as 60000 km, 56000 km, and 45000 km. This may be due to the much longer wavelength comparing with the height of spicules. (4) In the first event occurred on 2008 June 03, the oscillation existed during limited time (about 250 s). This means that the oscillation may be triggered by an impulsive mechanism (like low atmospheric reconnection), not continuous. Being compared with the ground-based observations of spicule oscillations, our observation indicates quite different one, i.e., more than one order longer in wavelength, a factor of 3-4 larger in wave speed, and 2-3 times longer in period.