• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.6
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• pp.767-776
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• 1985

Unsteady thermally stratified flow caused by two-dimensional surface discharge of warm water into a oblong channel was investigated. Experimental study was focused on the rapidly developing thermal diffusion at small Richardson number. The basic objective were to study the interfacial mixing between a flowing layer of warm water and an underlying body of cold water and to accumulate experimental data to test computational turbulence models. Mean velocity field measurements were carried out by using NMR-CT (Nuclear Magnetic Resonance-Computerized Tomography). It detects quantitative flow image of any desired section in any direction of flow in short time. Results show that at small Richardson number warm layer rapidly penetrates into the cold layer because of strong turbulent mixing and instability between the two layers. It is found that the transfer ofheat across the interface is more vigorous than that of momentum. It is also proved that the NMR-CT technique is a very valuable tool to measure unsteady three dimensional flow field.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.05a
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• pp.99-102
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• 2009

LES(Large eddy simulation) of breakup and atomization of a liquid jet into cross turbulent flow was performed. Two phase flow between a gas phase and a liquid phase was modeled by a mixed numerical scheme of both Eulerian and Lagrangian methods for gas and liquid phases respectively. The first and second breakup of liquid column was observed. The penetration depth in cross flow was comparable with experimental data for several variant of a liquid-gas momentum flux ratio by varying liquid injection velocities. SMD(Sauter Mean Diameter) distribution downstream of jet was analyzed.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.9
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• pp.879-888
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• 2009

Unsteady three-dimensional reacting flowfield generated by transverse hydrogen injection into a supersonic mainstream is numerically investigated using DES and finite-rate chemistry model. Comparisons are made with experimental results to investigate the turbulent reacting flow physics. The numerical OH distribution describes well the experimental OH-PLIF result, while the numerical ignition delay time shows some disparity due to the restricted available experimental data. The intermittency phenomena are identified by the comparative analysis between RANS and DES. Those effects are also quantified by the temperature distributions along streamlines and superimposed OH mass fraction along with time.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.9
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• pp.863-878
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• 2009

Unsteady three-dimensional flowfield generated by transverse fuel injection into a supersonic mainstream is simulated with a DES turbulence model. Comparisons are made with experimental results in terms of the temporal eddy position and eddy formation frequency. The vorticity field around the jet exit is also analyzed to understand the formation mechanism of the large eddy structures. Results indicate that the DES model correctly predicts the convection characteristics of the large scale eddies. However, it is also observed that the numerical results slightly over-predict the eddy formation frequency. The large eddy structures are generated as the counter-rotating vortices are detached alternately in the upstream recirculation region.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.28 no.1
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• pp.94-99
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• 1983

This experiment was conducted to study a cause of lodging on culm internode. The rice varieties were undergone on injuries by typo on 'Agnes' on Jeonbug Provincial in 1981 year. Long-culmed varieties had extreme lodging injury but short-culmed varieties were not serious. The lodging had weaken tolerance when culm internode was long, weight of internode per unit length was light, and culm diameter and culm wall were thin. The breaking weight of internode was light in lodging rice field. The internode length and the weight of internode per unit length between the breaking weight of internode had significant correlation. Lodging had high tolerance when the total nitrogen was low, phosphate, silica, cellulose and starch contents were high in internode. The difference of culm length and the weight of internode per unit length was high relationship with lodging.h lodging.

• Journal of Ocean Engineering and Technology
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• v.7 no.1
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• pp.13-24
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• 1993

The dispersion in the oscillatory flow generated by gravitational waves above the spatially periodic repples is studied. The steady parts of equations describing the orbit of the passive particle in a two dimensional field are assumed to be simply trigonometric functions. From the view point of nonlinear dynamics, the motion of the particle is chaotic under externally time-periodic perturbations which come from the wave motion. Two cases considered here are; (i) shallow water, and (ii) deep water approximation.

• Aerospace Engineering and Technology
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• v.4 no.2
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• pp.101-106
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• 2005

KOMPSAT-2 위성에서 사용되는 TAM의 정상적인 작동을 위해 각 유닛에서 생성되는 자기장(magnetic field) 값은 일정한 양 이하가 되도록 관리되고 있다. 자기장은 그 특성상 전장품 간의 거리에 반비례하며 전장품의 자기 모멘트에 비례하므로 위성체 유닛의 자기장 값을 관리하기 위해 우선 유닛의 magnetic moment 값을 구해야한다. KOMPSAT-2의 각 전장품들의 자기 모멘트 값은 기존 KOMPSAT-1의 값을 근거로 설정되었다. 이것은 KOMPSAT-2가 KOMPSAT-1의 heritage를 따라 설계되었으며 각 전장품 역시 KOMPSAT-1 전장품 설계를 대부분 따르고 있기 때문이다. 그리고 최근 EMC 해석 S/W중 magnetic moment를 전문적으로 해석해주는 tool이 출시되었다. 이 tool은 해석하고자 하는 유닛의 geometric 정보와 전류 패스를 설정하면 자기 모멘트 값을 구할 수 있는 수식을 풀어내 그 값을 알려준다. 본 논문에서는 magnetic moment 값을 구할 수 있는 수식이 이 tool에 어떻게 구현되었는지 살펴보고 실제 KOMPSAT-2의 전장품의 자기 모멘트 해석 결과를 보여준다.

• Proceedings of the KIEE Conference
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• 1999.07d
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• pp.1836-1838
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• 1999

다결정 실리콘 박막 트랜지스터(TFT)의 누설전류를 줄이기 위하여 채널의 중간에 선택적으로 도핑된 영역을 가진 새로운 다결정 실리콘 TFT를 제안한다. 제안된 TFT에서는 채널의 일부가 선택적으로 도핑되어 채널 전체에 걸리는 전기장이 재분배된다. 제안된 n-채널 TFT는 $V_{GS}$<0, $V_{DS}$>0인 조건에서, 대부분의 전기장이 드레인 접합에 형성되는 공핍영역과, 도핑된 영역 중 소오스 쪽과 도핑되지 않은 채널 사이에 형성되는 공핍영역에 각각 나뉘어 걸린다. 기존의 다결정 실리콘 TFT와 비교할 때 드레인 접합에서 걸리는 전기장은 1/2로 감소하였고, 이에 따라 드레인 접합에서 생성되는 전자-홀 쌍도 현저히 감소하였다. 더구나 제안된 TFT의 온-전류는 기존의 TFT와 비교했을 때 거의 같거나 약간 감소하였으며 이에 따른 온/오프 전류비가 현저히 향상되었음을 실험을 통해 확인할 수 있었다.

• Korean Journal of Ichthyology
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• v.9 no.1
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• pp.15-21
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• 1997

The influence of delayed(1, 2, 3, 4 days) feeding and starvation on morphological change and survival rate of the spotted sea bass larvae was examined at the KORDI laboratories which located at Poryong Power Plant, Poryong-gun, Chungchongnam-do in November, 1996. 1. The larvae of spotted sea bass began to feed on rotifers at 5 days after hatching. In case of non-feeding, all of the larvae died at 9 days after hatching. The larvae which fed 1 day after the normal first feeding schedule(1 day delayed) grew normally and 2 days delayed groups showed 5.3% in survival rate at 9 days after hatching. In case of non-feeding and 3 or 4 days delayed groups, all of the larvae died between 9 and 10 days after hatching. 2. In case of non-feeding, total length of the larvae decreased gradually. 3. The percente ratio of gut height and mytome height to standard length in starved larvae has declined most rapidly compare to other demensions during the non-feeding period. The percente ratio of gut height to mytome height had also difference between unfed and fed larvae. At 9 days after hatching, the ratio of that between fed and unfed larvae were 84.5 % and 52.4 %, respectively. 4. The morphology of starving larvae were characterized as sharpened jaw, projected edge of lower part of clavicle and bending trunk with slenger gut.

• Journal of the Korean Society of Propulsion Engineers
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• v.1 no.1
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• pp.8-23
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• 1997

Steady and unsteady numerical simulations are conducted for the comparison with the experiments performed to investigate the ram accelerator flow field by using an expansion tube facility in Stanford University. Wavier-Stokes equations for chemically reacting flows are analyzed by fully implicit and time accurate numerical methods with Jachimowski's detailed chemistry model for hydrogen-air combustion involving 9 species and 19 reaction steps. Although the steady state numerical simulation shows a good agreement with the experimental schlieren and OH PLIF images for the case of $2H_2$＋$O_2$＋$17N_2$ fails in reproducing the combustion region behind the shock intersection point shown in the case of $2H_2$＋$O_2$＋$12N_2$ mixture. Therefore, an unsteady numerical simulation is conducted for this case and the result shows all the detailed flow stabilization process. From the result of unsteady numerical simulation, the experimental result seems to be an instantaneous state during the flow stabilization process. The combustion behind the shock intersection point is the result of a normal detonation formed by the intersection of strong oblique shocks that exist at early stage of the stabilization process. At final stage, the combustion region behind the shock intersection point disappears and the steady state result is retained. The time required for stabilization of the reacting flow in the model ram accelerator is found to be very long in comparison with the experimental test time.