• 한국군사과학기술학회지
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• 제21권2호
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• pp.188-194
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• 2018

Recently a supercavitating underwater vehicle moving at high speed over 200 knots has been of interest for its practical advantage of the dramatic drag reduction. Many experimental and numerical studies have been explored, however most of the studies deal with the case of uniform flows. In this paper, we investigated physical behaviors of the artificial supercavity in a periodic gust flow. Experiments were carried out at a cavitation tunnel of the Chungnam National University(CNUCT), which is equipped to remove the gas supplied from outside of the tunnel. We devised an experimental apparatus generating vertical and horizontal gust flows, and investigated the supercavity formations at different periodic mode of the incoming flow.

• 대한조선학회논문집
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• 제58권1호
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• pp.24-31
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• 2021

In this study, we present experimental observations of artificial supercavitation generated by the injection of compressed air at multiple locations on the body. Experiments were conducted at a cavitation tunnel equipped with a special facility to remove injected air before returning to the test section. Artificial supercavitation, which is generated at a relatively low speed compared to natural supercavitation, is formed asymmetrically on the axis of the body due to the buoyancy effect. In order to accelerate the development of the supercavity and increase the area covering the body, an experimental device capable of additional injection from the body was designed and its performance was evaluated through the model test. The shapes of the supercavity generated by multi-injections of different combinations according to different flow speeds were analyzed using high-speed shadow images. The results show that multiple injections at suitable locations can effectively increase the length of the supercavity and consequently improve propulsion efficiency.

• 대한조선학회논문집
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• 제56권4호
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• pp.327-334
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• 2019

Recently, there has been a growing interest in artificial supercavitation as a way to reduce friction drag of submerged vehicles. A cavitator plays an important role to generate the supercavity, so many studies have focused on the case of cavitator only. However, the body shape behind the cavitator affects the growth of the supercavity and this effect must be considered for evaluating the overall performance of the system. In this work, we conducted experimental investigation on artificial supercavitation generated by different combinations of the cavitator and body. We observed the supercavity pattern by using a high-speed camera and measured the pressure inside the cavity by using an absolute pressure transducer. We estimated the relation between the amount of injected air and the supercavity shape for different combinations. In summary, the disk type cavitator generates larger supercavity than that of the cone and ellipsoidal cavitators, but cavity development speed is relatively slower rather than the others. Furthermore, fore body angle plays an important role to generate the supercavity enveloping the entire body.

• 대한조선학회논문집
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• 제55권1호
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• pp.75-82
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• 2018

Wedge-shaped fins are generally used to provide sufficient forces and moments to control and maneuver a supercavitating vehicle. There are four fins placed along the girth of the vehicle, near he tail: two of the fins are horizontal and the other two fins are vertical. In a fully developed supercavitating flow condition, a part of the fin is in a cavity pocket and the other is exposed to water. In this paper, experimental investigations of hydrodynamic characteristics of the wedge-shaped fin models are presented. Experiments were conducted at a cavitation tunnel of the Chungnam National University. We first closely observed the typical formation of wake cavitation and measured lift and drag forces acting on two different test models. Next, using a special device for generating natural and artificial supercavities, we investigated hydrodynamic forces at different cavitation number conditions. This work provides a basis for interpreting the cavity stability and hydrodynamic characteristics of the wedge-shaped control fin for a supercavitating vehicle.

• 기독교교육논총
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• 제67권
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• pp.377-414
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• 2021

슈밥(Schwab)이 2016년 다보스 포럼에서 4차 산업혁명을 언급하면서 많은 이들이 4차 산업혁명과 미래사회에 대하여 논하였다. 4차 산업혁명은 기술의 발달을 넘어서서 우리의 사회, 문화, 생활양식 전반에 영향을 주고 있으며, 우리는 코로나19 상황을 맞이하며 더욱더 실감을 하고 있다. 우리는 4차 산업혁명은 분명 인간의 삶을 증진시키며, 문명의 발달을 이루게 할 것이라 희망하지만, 인간소외나 양극화의 문제를 우려하게 된다. 이러한 때에 기독교가 어떻게 공적 영역에서 기여하며 교육의 방향을 설정할 것인가. 본 연구는 이러한 4차 산업혁명시대의 기독교의 역할과 교육방향에 관하여 연구한 논문이다. 먼저 4차 산업혁명시대에 일어날 개인과 공동체의 내면과 외면의 문제를 다각도로 조명하고자 심리학자 미첼(Mitchell), 사회학자 벨라(Bellah), 신학자 맥그래스(McGrath), 철학자 보스트롬(Bostrom)의 견해를 통해 접근하였다. 이들의 이론을 통해 4차 산업혁명시대의 현실 세계와 가상 세계, 초월적 세계에 사는 개인의 삶을 바라보았다. 그리고 이러한 세계에 기독교가 초월적 규범을 제시하고, 의미를 부여하며, 개인과 세계의 변화를 일으킬 수 있다고 보며, 교육의 방향을 "상징을 만들고 표현하는 교육"으로 보았다. 이를 위하여 관찰하기, 들어가기, 발견하기, 참여하기, 상징 만들기의 5단계를 제시하여, 이를 통해 현실 세계 안에서 하나님 나라를 이뤄갈 수 있도록 하였다.