• Journal of the Korea Institute of Military Science and Technology
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• v.21 no.2
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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.

• Journal of the Society of Naval Architects of Korea
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• v.58 no.1
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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.

• Journal of the Society of Naval Architects of Korea
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• v.56 no.4
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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.

• Journal of the Society of Naval Architects of Korea
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• v.55 no.1
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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.

• Journal of Christian Education in Korea
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• v.67
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• pp.377-414
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• 2021

Since Schwab mentioned the Fourth Industrial Revolution at the World Economic Forum Annual Meeting 2016, discussions have been ongoing about it and the future society. The Fourth Industrial Revolution exceeds the development of technology and influences society, culture, and lifestyle. Moreover, in the face of the COVID-19 crisis, society continues to experience and realize the era of the Fourth Industrial Revolution. Although we hope that this era will surely improve human life, we are also concerned about human alienation and social and economic polarization that may emerge as a consequence. How, then, does Christianity contribute to the public space and set the direction for education in this day and age? This study focused on the role of Christianity and the direction of education during the Fourth Industrial Revolution. First, I examine problems in terms of the inner and outer aspects of individuals and communities that may occur during the Fourth Industrial Revolution through the perspectives of Mitchell, a psychologist, Bellah, a sociologist, McGrath, a theologian, and Bostrom, a philosopher. Through their theories, we can view the lives of individuals in the real, virtual, and transcendental worlds of this era. I find that Christianity can provide a transcendent norm in this world, give meaning to life, and change people and the world. Therefore, I suggest the creation and expression of symbols as a direction for education. For this form of education, I recommend five steps, namely, observing, entering, discovering, participating, and making symbols. In this manner, people can represent the kingdom of God in the real world.