• 수산해양기술연구
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• 제58권1호
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• pp.68-74
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• 2022

This study analyzed the wake characteristics of the rim-driven propeller (RDP) used in an underwater robot. For underwater robots to perform specific missions, not only propulsion characteristics but also wake characteristics must be considered. In this study, a blade was designed based on NAC 0012 with a symmetrical cross-section. The RDP was hubless with three or four blades. The influence of both the free water surface and the bottom was considered, and the wake was measured using a particle image velocimetry in the advance ratio of 0.2 to 1. Model 1 showed symmetrical wakes in the entire advance ratio section. Model 2 showed asymmetric wakes due to the influence of the free water surface and the bottom at low advance ratio.

• 한국잠사곤충학회지
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• 제32권1호
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• pp.8-16
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• 1990

누에 7개 품종을 이면교잡하여 얻은 F$_1$, 세대에 대한 잡종강세, 선발지수 그리고 유전적 진전 등을 분석한 결과는 다음과 같다. 잡종강세는 F$_1$세대에서 5령경과, 견층연감율의 자웅이 부의 방향을 나타냈고 견층비율을 제외한 전 형질이 20.90-37.60%로 정의 높은 강세율을 나타내었다. F$_2$에서는 견층비율, 견층연감율의 자웅이 부로, 그 외의 전 형질이 정의 강세율을 나타내었다. 선발지수는 선발의 최종대상형질을 견사량으로 하였을 때 F$_1$, F$_2$세대 모두 단일형질에서 단견중이 높았다. 선발대상형질을 5령경과, 단견중 견층중, fibroin량 등의 4개 형질로 하여 2, 3, 4형질을 조합하였을 때, 5령 경과와 단견중의 조합에서 선발가중치가 가장 크게 나타났다. 유전진전은 F$_1$, F$_2$세대에서 한일형질에서는 모두 견층중이 가장 높았고, 각 형질간의 조합에서는 전 형질을 조합하였을 때가 가장 높았다. 관계효율도 전 형질을 조합하였을 때가 가장 높았다.

• 에너지공학
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• 제15권3호
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• pp.139-145
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• 2006

The purpose of this study is to obtain low-emission and high-efficiency in LPG engine with hydrogen enrichment. The objective of this paper is to clarify the effects of hydrogen enrichment in LPG fuelled engine on exhaust emission, thermal efficiency and performance. The compression ratio of 8 was selected to avoid abnormal combustion. To maintain equal heating value of fuel blend, the amount of LPG was decreased as hydrogen was gradually added. The relative air-fuel ratio was increased from 0.8 to 1.3, and the ignition timing was controlled to be at MBT (minimum spark advance for best torque)

• 의료법학
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• 제11권2호
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• pp.239-274
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• 2010

Advance directive refers to a description of the treatment method a patient wants to be provided with in case where the person is unconscious or lacks an ability to decision making in a future period or a declaration of intention that delegates and appoints another person who makes a decision regarding a treatment method on behalf of the person. Advance directive is usually a document form, but oral statement is acceptable as well. Advance directive may have a variety of forms though, it basically consists of two basic forms. That is, one is a living will, and the other is a surrogate decision making. Though the importance of advance directive has been emphasized, and the necessity of adopting the system has been strongly argued for so far, the debates on criteria, method, and procedure alike have not yet reached an agreement. It is because even the concept of advance directive is more or less ambiguous, and each specific method has its own theoretical limitations and practical constraints. Thus the inquiries on advance directive raised in the study are summarized as the meaning, practicability, and philosophical foundation of the advance directive. Firstly, the theoretical limitations of Advance directive may be categorized into conceptual and moral limitations. In case of conceptual limitations, authors of advance directives may not be well aware, in advance, of the particular situation in which he or her will experience in the future, and patients may experience the change in his or her values and lack the understanding and information about the future situation due to the changes in treatment methods. In case of moral limitations, a patient has a limited moral autonomy right and self identity that have an impact on his or her preference. Secondly, in case of practical constraints for advance directive, there exist cultural features, low ratio of documentation, as patients themselves admit, and low predictability and stability of patient's own preference regarding life-sustaining care. And the problem of validity and accuracy in proxy's decision making is also raised. Those who administer a living will, especially, may have a difficulty in understanding the directive by a patient, so that the accuracy of execution cannot be secured. In the sense, it is needed to implement a legal device in order to solve such problems. In summary, it is urgently required to understand the limitations and explore desired alternatives to overcome the relevant problems in advance, which must contribute to successfully adopting and effectively operating the advance directive system in Korea.

• 청정기술
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• 제19권2호
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• pp.156-164
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• 2013

본 연구에서는 등온반응기와 단열반응기로 구성된 0.25 MW 메탄합성 파일롯 공정 실험을 통한 운전 특성을 분석하였다. 등온반응기는 메탄합성 반응을 통해 발생하는 열을 포화수의 유량과 압력을 통해 강제적으로 제어할 수 있는 반응기로 등온반응기와 단열반응기를 조합할 경우 기존 단열반응기만으로 구성된 메탄합성 공정에 비해 반응기 개수를 줄일 수 있다. 또한 합성가스 재순환이 불필요하기 때문에 단열반응기 조합으로 구성된 메탄합성 공정에서 비용의 약 15~20%를 차지하는 재순환 압축기를 제거할 수 있다. 등온반응기로 유입되는 합성가스의 $H_2$/CO 비가 3보다 낮은 경우에는 튜브에 충진된 촉매에 탄소 침적 현상이 일어나 반응기의 차압이 증가하였으며, $H_2$/CO 비가 3으로 공급되는 경우에는 탄소 침적 현상이 일어나지 않고 메탄합성 반응이 안정적으로 유지되어 CO 전환율 99% 이상, $CH_4$선택도 97% 이상, $CH_4$생산성 최대 $695ml/h{\cdot}-cat$를 얻을 수 있었다.

• 한국전기전자재료학회논문지
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• 제35권4호
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• pp.407-411
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• 2022

Bulk-sized PbTiO₃ (PT), which is widely known as a high-performance ferroelectric oxide but cannot be fabricated into a monolithic ceramic due to its high c/a ratio, was successfully prepared with a high tetragonality by partially substituting Ni ions for Pb ions using a solid-state reaction method. We found that Ni-doped PT was well-fabricated as a bulk monolith with a significant c/a ratio of ~1.06. X-ray diffraction on as-sintered and crushed samples revealed that NiTiO₃ secondary phase was present at the doping level of more than 2 at.%. Scanning electron microscopic study showed that NiTiO₃ secondary phase grew on the surface of PT specimens regardless of the doping level possibly due to the evaporation of Pb during sintering. We demonstrated that an unconventional introduction of Ni ions into A-site plays a key role on the fabrication of bulk PT, though how Ni ion functions should be studied further. We expect that this study contributes to a further development of displacive ferroelectric oxides with a high c/a ratio.

• 한국항공우주학회지
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• 제39권6호
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• pp.498-504
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• 2011

속도와 샤프트각 그리고 피치 변화에 따른 토크 평형상태의 자동회전에서 플래핑 거동 특성과 전진비의 변화를 조사하였다. 속도 증가에 따른 압축성 효과를 모사하기 위해 압축성 Navier-Stokes 솔버로 해석된 2차원 데이터를 Pitt/Peters 유도흐름 이론과 함께 사용하였고 토크 평형상태에 대한 세 변수의 조합을 찾기 위해 과도모사법(TSM)을 이용하였다. 토크 평형상태에서 최대 플래핑각을 속도, 샤프트각, 피치와의 관계로 나타내고 전진비 변화와 비교함으로써 후진깃의 역풍영역 확대가 로터의 자동회전 특성에 관여하는 현상을 정성적으로 고찰하였다.

• 에너지공학
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• 제24권4호
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• pp.217-222
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• 2015

A computer simulation has been developed to predict and investigate the performance of the assumed hydrogen engine. The simulation has be come a powerful tool as it saves time and also economical when compared to experimental study. The effects of various parameters, such as equivalent ratio, spark advance, revolutions per minute were calculated and then the optimal parameters of assumed engine were determined. The effects of spark advance, revolutions per minute, cylinder pressure, rate of pressure rise, flame temperature, rate of heat release, and mass fraction burned were simulated. The objective of the research paper is to develop a internal combustion model with hydrogen as a fuel.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1994년도 춘계학술대회 논문집
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• pp.175-182
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• 1994

Effect of some process variables including area reduction, stroke advance, materials on the extrusion load, plastic flow and height ratio of upper to lower extruded parts in the cup-cup axisymmetric extrusion were experimentally investigated and analyzed. Deformed pattern is visualized by grid-marking technique using half-cut billets splitted. The influence of using split specimen and original specimen on the extrusion load and height ratio is examined by experiment.

• 지질공학
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• 제6권3호
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• pp.111-118
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• 1996

터널이 굴진될 때 주변지반은 3차원적으로 거동하게 되나 설계단계에서의 해석은 일반적으로 2차원적으로 수향하고 있다. 2차원적인 터널해석은 응력분배법 또는 강송 변화법에 의하여 3차원적인 터널굴진에 따른 다양한 조건하에서의 정규화된 지반 변위곡선을 구하고 이 곡선과 유사한 곡선이 유도되도록 시행착오법에 의하여 2차원 해석을 실시하므로 3차원 해석과 근사한 변위곡선을 가지도록 막장거리별 응력분배비율을 결정하였다. 따라서, 시간과 노력이 많이 소요되는 3차원 해석없이도 적절한 응력분배비율을 적용하는 경우 2차원 해석으로 터널굴진시의 3차원적인 지반거동을 평가할 수 있게 되었다.