• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.739-742
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• 1997

Continuously variable transmission(CVT) mechanisms are proposed, which can offer a backward mode, a geared neutral, an underdrive mode and an overdriver mode. They are not required of a starting device as a torque converter. CVT mechanisms developed here present two distinct operating modes which are a power circulation mode and a power split mode. The transition of two modes takes place at the particular CVU speed ratio. For these CVT mechanisms, performance analysis related to speed ratio, power ratio and theoretical efficiency are executed.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.2
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• pp.199-208
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• 2003

Continuously variable transmission (CVT) mechanisms considered here combine the functions of a K-H-V type differential gear unit and a V-belt type continuously variable unit (CVU). As combining the functions of a K-H-V type differential gear unit and a V-belt type CVU, 24 different mechanisms are presented. Some useful theoretical formula related to speed ratio, power flow and efficiency are derived and analyzed. These mechanisms have many advantages which are the decrease of CVT size, the increase of overall efficiency, the extension of speed ratio range, and the generation of geared neutral.

• Journal of Power System Engineering
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• v.11 no.2
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• pp.26-31
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• 2007

통신용 전자기기에서 대부분의 열은 증폭기에서 발생한다. 일반적으로 증폭기를 냉각하기 위하여 공랭식을 사용하여 발생하는 많은 열을 냉각하였다. 그러나 전통적인 방법은 고성능 콤팩트화 되어가는 추세에서 발열되는 열을 충분히 냉각하기는 부족하다. 본 논문은 고발열 전자부품 냉각을 위해서 수냉식 방법을 사용하였다. 열전달 효율을 높이기 위하여 냉각판에 직접 냉각수를 흐르게하여 접촉저항을 줄였다. 그리고 냉각판의 유로에 대한 배열과 유량의 비의 효과를 조사하였다. 연구를 수행한 결과, 다음과 같은 결론을 얻을 수 있었다. 냉각수 순환량이 $3{\iota}/min$인 경우, 유로 직경이 8 mm일 때의 냉각 성능이 10 mm일 때보다 우수한 것으로 나타났다. 냉각수 순환량이 $3{\iota}/min$인 경우, 유로 직경이 8 mm일 때의 발열 소자 표면 온도 분포가 더욱 안정적으로 나타났으며, 상하부에 설치된 발열 소자 표면 온도가 더 낮게 나타났다. 동일한 유로 직경의 냉각판에서, 열유속 증가에 따른 냉각수의 전열 성능 증가로 인해 전체 발열량의 증가율보다 발열 소자의 온도 증가율이 낮게 나타났다.

• Journal of Power System Engineering
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• v.16 no.4
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• pp.24-29
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• 2012

The numerical analysis by using CFX 11.0 commercial code was done for prediction of fluid flow and thermal field in the vertical heat exchanger. The present experimental studies were also conducted to investigate the effects of circulating solid particles on the fluid flow and temperatures in the fluidized bed vertical shell and tube type heat exchanger with counterflow, at which the solid particles of glasses (3 $mm{\Phi}$) were used in the fluidized bed with a smooth tube. The effect of circulation on the distance(L) of tube inlet and baffle plate was also examined. The present experimental and numerical results showed that the particles in the distance (Ds) of 15 mm showed a more efficient circulation without stacked the space and the LMTD(Log Mean Temperature Difference) in the fluidized bed type was much lower than that in the typical type shell and tube heat exchanger.

• Journal of Power System Engineering
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• v.14 no.5
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• pp.41-47
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• 2010

티타늄과 티타늄 합금은 재료적 특이성 때문에 심장 혈관 임플란트에서 일반적으로 사용되어 왔다. 일찍이 적용된 예로는 인공심장판막, 심박조율기의 보호케이스, 혈액 순환 장치 등이 있다. 하지만 물질유도혈전증(Material-induced thrombosis)은 혈전폐색에 의해 기인한 기능 손실로 심장혈관 임플란트 장치의 주된 합병증으로 존재하고 있으며, 심장혈관 임플란트의 혈전유전자는 심장혈관장치의 발달에 주된 난관 중 하나로 남아있다. 그리고 텍스처 혈액 접합 물질(Textured blood-contacting material)은 1960년대 초반 이후부터 혈액순환 보조 장치의 임상실험에 사용되고 있다. 접합 물질에 내장된 텍스처 섬유조직 표면은 형성, 성장, 안정적 부착, 생물학적 내벽(neointimal layer) 등 유도 혈액(entrapping blood) 성분에 의해 형성된다. 공동(cavity) 형상의 용해 가능한 미립자를 사용하는 SCPL법(Solvent casting/particulate leaching method)은 티타늄 기질 이전에 형성된 폴리우레탄 위에 텍스처(texture)를 생성하기 위해 사용되었다. 또한 콜라겐의 부동화(不動化)에 의한 공동(cavity)은 혈액 접합면에 잔존하기 위한 내피세포를 고정할 수 있는 효과가 있다. cpTi로 층화된 PU 기소공성(microporous)은 구조적 특성과 혈전증 감소를 위한 생물학적 내벽 사용의 잠재성을 평가하기 위한 세포 공동체 실험을 통해서 평가되었다.

• Water for future
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• v.27 no.3
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• pp.45-54
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• 1994

Basic theory of fractal dimension is introduced and performed for the generated time series using the water balance model. The water balance equation over a large area is analyzed at seasonal time scales. In the generation and modification of mesoscale circulation local recycling of precipitation and dynamic effects of soil moisture are explicitly included. Time delay is incorporated in the analysis. Depending on the parameter values, the system showed different senarios in the evolution such as fixed point, limit cycle, and chaotic types of behavior. The stochastic behavior of the generated time series is due to deterministic chaos which arises from a nonlinear dynamic system with a limited number of equations whose trajectories are highly sensitive to initial conditions. The presence of noise arose from the characterization of the incoming precipitation, destroys the organized structure of the attractor. The existence of the attractor although noise is present is very important to the short-term prediction of the evolution. The implications of this nonlinear dynamics are important for the interpretation and modeling of hydrologic records and phenomena.

• Land and Housing Review
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• v.3 no.3
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• pp.271-278
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• 2012

The climate change and global warming has been a world-wide issue. Also, the green growth has been a widely adopted strategy for national and regional development. In particular, after the Kyoto Protocol to United Nations Framework Convention on Climate Change was declared, the low carbon society was inevitable phenomenon. The hydrologic cycle in urban catchment has been changed due to the expansion of impervious area by rapid urban development. This paper has examined the Water cycle planning elements for green city in the scale of urban planning as well as site planning including housing site. In this study, the SWMM5-LID (Storm Water Management Model5-LID) model was used to simulate the hydrologic cycle of the test catchment as a typical urban catchment. We performed continuous simulation on urban runoff before and after the development of the test catchment and after the installation of Green city planning Elements.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.436-436
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• 2022

셀룰러 오토마타(Cellular Automata; CA)는 격자(cell)에 대해 사전 정의된 규칙을 바탕으로 이웃 격자 간 상호작용을 해석하여 복잡한 동력학적 현상을 효과적으로 재현할 수 있는 이산형(discrete) 모의 기법이다. CA 기법은 격자 구조에 수치표고 자료 및 토양수분 정보 등을 직접 매칭 후 상호관계를 해석하기 때문에 공간정보를 최대한 활용하여 불균질성을 나타내는 것이 가능하다. 따라서, 도시 유출해석에 있어서 높은 정확도와 빠른 계산속도를 기대할 수 있다. 본 연구에서는 CA 기반 고해상도 물순환·침수 연계 해석 framework 개발 방향 및 CA 기반 prototype 모형의 사면유출 적용 사례를 소개한다. 개발 중인 CA 모형에서는 격자별 침수 깊이, 침투, 토양수분 저류, 지표 유출 등의 물순환 요소를 모의할 수 있다. 기존의 집중형(lumped) 모형은 지표-지표하 유출에 대한 routing algorithm이 없고 각 셀의 물수지 모형 내 파라미터가 많은 단점이 있다. 따라서 개발 중인 CA 모형에서는 cell state 내 fast reservoir와 slow reservoir를 통해 지표-지표하 상태를 구현하고 단순화된 물수지 모형 및 흐름 방향 알고리즘을 적용함으로써 실제 현장에서 발생하는 다중 피크 형태의 지표 유출을 모사한다. 최적의 지표수 흐름 방향 알고리즘 선정을 위해 3개의 다중 흐름 방향 알고리즘(D4, D8, 4+4N)을 정량적으로 비교·분석한다. 이번 발표에서는 CA 모형을 소규모 산지 사면과 도심지 등 다양한 규모의 테스트베드에 적용하여 모형의 장단점을 평가한다.

• Journal of Aerospace System Engineering
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• v.16 no.3
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• pp.84-92
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• 2022

The electro-hydrostatic actuator (EHA) recently has been used in flight control fields for aircraft because of its benefits of minimizing oil leakage and weight, improving safety, and etc. while independently operating the hydraulic power source and eliminating complex hydraulic piping. The aircraft of which EHA is installed inside, has the thermal management issue of EHA, because of its limited cooling source as compared with the aircraft which installs the traditional central hydraulic system. So, the thermal analysis model which predicts the thermal characteristics of EHA, is required to resolve this thermal management issue. In this study, an oil circulation circuit inside the hydraulic power module comprised of hydraulic pump and electrical motor for EHA was applied. This is for the purpose of developing the internal rotary group of hydraulic power module, which operates under the conditions of high rotation speed and hydraulic pressure. After formulating an appropriate thermal analysis model, the thermal analysis results with oil cooled or no oil cooled hydraulic control module were compared and reviewed, for the purpose of predicting the thermal characteristics of EHA.

• Transactions of the Korean hydrogen and new energy society
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• v.33 no.6
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• pp.819-826
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• 2022

Fuel cell systems are being supplied to households and buildings to reduce greenhouse gases. The fuel cell systems have problems of high cost and slow startup due to fuel processors. Greenhouse gas reduction of the fuel cell systems is also limited by using natural gas. The problems can be solved by using a hydrogen generator consisting of a reformer and pressure swing adsorption (PSA). However, part load operation of the hydrogen generator is required depending on the hydrogen consumption. In this paper, PSA operation strategies are investigated for part load of the hydrogen generator. Adsorption and purge time were changed in the range of part load ratio between from 0.5 to 1.0. As adsorption time increased, hydrogen recovery increased from 29.09% to 48.34% at 0.5 of part load ratio. Hydrogen recovery and hydrogen purity were also improved by increasing adsorption and purge time. However, hydrogen recovery dramatically decreased to 35.01% at 0.5 of part load ratio.