• Journal of the Korean Institute of Gas
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• v.22 no.3
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• pp.7-12
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• 2018

Thermal NOx is generated in a high temperature environment in a combustion facilities. Exhaust gas recirculation method is widely used among various methods for reducing nitrogen oxides in combustion devices. In the present study, the computational fluid dynamic analysis was accomplished to elucidate the cold flow characteristics in the flue gas recirculation burner with both outlets opening. Because the reciculation pipes is installed toward the tangential direction, the swirling flow is formulated in the burner and the phenomenon of the reverse flow creation is detected at the center area of circular burner. We are confirmed that this is the similar trend with the burner with one side outlet closed. From the present study, it was seen that the recirculated inflow from both recirculated burner outlets increased by about 5% compared to the burner with one side outlet opening. At the outlet located at the exhaust gas recirculation pipe inlet(gas exit 1), the inlet flow was formed in the entire region. At the opposite outlet(gas exit 2), the total flow was discharged, but the center part of the burner was observed to have a reverse flow. The flow rate at the gas exit 2 was 3 ~ 5 times larger than the flow rate at the gas exit 1.

• Journal of the Korean earth science society
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• v.18 no.6
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• pp.529-539
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• 1997

The circulations and movement of suspended materials by tidal residual current and seasonal surface wind in the Yellow Sea and the East China Sea are investigated by using a 2-dimensional barotropic model and a particle tracing technique. The tidal residual current is relatively strong around the south and west coast of Korea including the Cheju Island and southern coast of China. The current has a maximum speed of 10 cm/s in the vicinity of Cheju Island with a clockwise circulation. General tendency of the current, however, is to flow eastward along the southern coast of Korea. At the east coast of China from Shanghai to Tunghai, it also shows a eastward flow toward the South Sea of Korea. The anticyclonic circulation formed by wind-driven current and southward current prevails along the coast of Korea in the winter season(from October to April) when northerly wind is dominant. In summer(represented by July), however, the cyclonic circulation appears due to the influence of southerly wind. Suspended materials are advected by tidal residual current and wind-driven current. The long period(ten days) displacement by wind-driven current is bigger than that by tidal residual current. However, the tidal residual current would have the more important role for the advection of the suspended material considering longer period more than several months.

• Journal of the Korean earth science society
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• v.38 no.1
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• pp.35-48
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• 2017

This study analyzed the obvious increasing tendency of summer (June to August) rainfall in the region of Korea- and northern China ($35^{\circ}-40^{\circ}N$, $110^{\circ}-130^{\circ}E$) in the late 1990s. In order to investigate the causes of the increase in summer rainfall since 1998, we analyzed the difference of the rainfall average between 1998-2012 and 1981-1997. The analysis of the 850 hPa stream flows showed that the huge anomalous anticyclonic circulations were developed in North Pacific and eastern Australia. In both hemispheres, the anomalous easterlies (anomalous trade winds) were strengthened from the equatorial central Pacific to the tropical western Pacific by the anomalous circulations, which was an anomalous circulation pattern shown in La $Ni{\tilde{n}}a$ years. As for the 200 hPa stream flows, the huge anomalous cyclonic circulations were also developed in both South Pacific and North Pacific. These two anomalous circulations reinforced the anomalous westerlies in the equatorial central and western Pacific, leading to the increase in summer rainfall in the region of Korea- and northern China since the late 1990s in association with La $Ni{\tilde{n}}a$ pattern, which was resulted in strengthening the Walker circulation. Recently in East Asia, the local Hadley circulation has been strengthened in which upward flows in the equatorial western Pacific and mid-latitude region of East Asia have descended in the subtropical western Pacific.

• Journal of the Korean Society of Marine Environment & Safety
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• v.14 no.4
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• pp.333-338
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• 2008

The coastal zone is a delicate and dynamic area in which the majority of a water kinetic energy is dissipated. These processes are subsequent to the transport of the beach materials. In comparison to emerged breakwaters, submerged structures permit the passage of some wave energy and in turn allow for circulation along the shoreline zone. This research aims to examine the beach erosion prevention capability of submerged structure by laboratory model. The flow characteristics behind a submerged obstacle with bottom gap were experimentally investigated at Re = $1.2{\times}10^4$ using the two-frame PIV(CACTUS 2000) system. Streamline curvature field behind the obstacle has been obtained by using the data of time-averaged mean velocity information. And the large eddy structure in the separated shear layer seems to have signification influence on the development of the separated shear layer. As bottom gap size increases, the recirculation occurring behind the obstacle moves toward downstream and its strength is weakened.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.6 s.324
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• pp.9-15
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• 2004

In MIMO-OFDM systems, conventional channel estimation techniques using comb type training symbols give relatively large mean squared errors(MSEs) at the edge subcarriers. To reduce the MSEs at these subcarriers, a cyclic comb type training structure is proposed. In the proposed cyclic training structure, all types of training symbols are transmitted cyclically at each antenna. At the receiver, the channel frequency responses that are estimated using each training symbol are averaged with weights obtained from the corresponding MSEs. Computer simulations showed that the proposed cyclic training structure gives more SNR gain than the conventional training structure.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.9
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• pp.3289-3295
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• 2010

In business material management, as the number of products and their parts increases, the employment of databases becomes inevitable. Many researchers have tried to incorporate semantics in traditional models using logic programming, resulting in the deductive method. However, since the designer of this method does not overcome the traditional design concept of relational method, there have been not much successful implementations in deductive method. Therefore, this paper propose the new way designing the retrieval methods for deductive databases and using those relations the query that makes recursive retrievals possible and hypotheses test in business material management.

• Proceedings of the Korean System Dynamics Society
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• 2000.02a
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• pp.61-96
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• 2000

“다운사이징은 조직의 기술혁신에 어떠한 영향관계를 형성하면서 순환하는가？” 80년대 미국의 기업들이 다운사이징의 열풍을 건너면서, 90년대에 들어 국내의 기업들도 다운사이징 및 해고에 대한 정당성을 지속적으로 피력해 나갔다. 사회적 거부감의 팽배로 인해 본격적인 실행조치를 취하지는 못하던 중에, IMF 체제로까지 물려나간 기업들은 마침내 본격적으로 다운사이징을 실행 화하기 시작하였다. 기업이 다운사이징을 한다는 것은 해당기업은 물론이고 이해관계자, 정치영역, 사회전반체계 등에 지대한 영향을 미친다. 특히 국민정서가 개인주의가 아닌 공동체의식이 발달해있는 문화권에 속한 우리의 사정에서 그 영향력은 훨씬 더 막대하다. 수많은 논쟁들이 다운사이징의 정당성을 놓고 치열하게 진행되고 있다. 국내의 기업들이 겪고 있는 상황은 구태여 어떠한 자료를 제시하지 않더라도 그 생존에 대한 절실함은 이미 잘 알려져 있다. 한보파동, 기아사태, 대우사태로 연결되고 있는 기업들의 생존문제는 다운사이징의 정당성 문제를 이미 공리 화시키고 있다.(중략)

• Proceedings of the Korean Information Science Society Conference
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• 2004.10c
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• pp.469-471
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• 2004

다중 지역 이동 에이전트 컴퓨팅 시스템에서는 단일 지역으로 구성된 시스템에 비해서 호스트의 결함이나 호스트 사이의 통신 결함 발생 확률이 높아, 안정된 시스템 설계에 있어서 이동 에이전트의 결함을 검출하고 이를 복구하는 결함 포용 기법은 매우 중요한 고려 사항이다. 이동 에이전트의 안정적인 연산 수행을 보장하기 위한 기존의 결함 포용 기법들은 크게 시간적 복제 기반 기법(Temporal Replication Based Approach: TRBA)와 공간적 복제 기반 기법(Spatial Replication Based Approach: SRBA)으로 구분 지을 수 있으나, 다중 지역으로 구성된 이동 에이전트 시스템과 같은 복잡한 시스템에서는 낮은 결함 포용 비용이 요구되는 TRBA가 보다 적합하다. 그러나 기존의 TRBA에서는 이동 에이전트의 비멱등(non-idempotent) 연산 수행을 지원하기 위해 단일 수행 (exactly-once execution) 특성을 보장했지만, 이동 에이전트가 순환적 작업 경로를 가지는 연산 수행 시에는 작업을 완결하지 못하는 복귀월산 문제(comeback-skip problem)가 발생한다. 본 논문에서는 플래그와, 히스토리 필드, 파손 길드를 도입하여 복귀월산 문제를 해결하는 시간적 복제 기반 결함 포용 기법을 제안한다. 이 기법은 이동 에이전트의 다양한 작업 수행을 지원함으로써 이동 에이전트의 작업 수행 영역을 확대한다.

• Journal of Industrial Technology
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• v.20 no.B
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• pp.55-62
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• 2000

The purpose of this research is to find out how the inlet angle of secondary air affects the formation of recirculation zone inside a small incinerator. A commercial code, PHOENICS, is used to simulate the flow field of an incinerator. The computational grid system is constructed by Multi-Block technique. Numerical experiments are done with the five different angles of secondary air inlet. The formation of recirculation zone is evaluated by checking velocity fields. The computational results show that recirculation zone is clearly formed from 60 degree of inlet angle and the zone of recirculation is widen as angle of recirculation is increased to $75^{\circ}$.

• Proceedings of the Korea Water Resources Association Conference
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• 2016.05a
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• pp.468-468
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• 2016

3차원 동수역학 모델을 이용하여 연안 순환에서 발생하는 이안류의 연직 분포를 조사하였다. 이안류 흐름은 변수심 위에서 발생하는 파의 쇄파와 모멘텀 전달에 의해 발생하는 외해방향의 흐름을 의미하는 것으로 해안의 보전, 유지 및 개발 측면에서 매우 중요한 역할을 한다. 지난 수십년동안 이안류와 관련된 현상을 해석하기 위해 많은 연구들이 수행되어 왔다. 하지만 대부분의 연구들은 수심적분된 2차원 모델을 사용하거나 위상 평균된 3차원 모델을 사용하여 이안류 흐름이 발생할 시 유속의 3차원 분포나 각 종 물리량의 시간적인 변화 등을 모의하기 어려웠다. 본 연구에서는 3차원 동수역학 모델 NHWAVE (Non-Hydrostatic WAVE model)을 이용하여 이안류의 연직분포를 조사하였다. 이안류를 발생시키기 위하여 이상적인 이안류 지형을 만들었으며 여러 지점에서 연직분포를 측정하여 수심적분된 Boussinesq 모델과 비교하여 특성을 파악하였다. 수치모의 수행결과, 두 모델 모두 이안류 현상을 잘 재현하였으나 Boussinesq 모델은 수평유속의 연직방향 변화를 잘 재현하지는 못하였다. 또한, 파고가 상대적으로 큰 경우에는 3차원 모델에서는 작은 순환류가 외해 영역에서 발생하였으나 Boussinesq 모델에서는 관측하지 못하였다.