• Journal of the Society of Naval Architects of Korea
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• v.30 no.2
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• pp.76-85
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• 1993

In order to predict the free surface signature of turbulent ship wakes two things are essential; a basic understanding of the mechanism of turbulent vortical flow/free surface interactions and a mathematical model to accurately predict the signature. The goal of the study described here is both to supplement experimental work to obtain basic understanding, as well as to condense this understanding in a model(or models) that captures the essential phenomena and thus allows predictions. To do so we followed two main paths guided by experimental observations. One is full simulations of the flow using the clavier-Stokes equations. The other is a vortex modeling, where the vortical structures of the flows are approximated by idealized structures, an the interaction assumed to be essentially inviscid. These approaches complement each other. Full simulations are only applicable to small scale phenomena, where the system is simple, and the Reynolds number is low. The vortex modeling, on the other hand, cannot represent essentially viscous aspects of the problem such as the effect of contamination gradient. Obviously, the modeling is what may eventually lead to a prediction method; the full simulations-too limited to mimic all but the simplest circumstances-are to aid and support the construction of realistic models. We address two-dimensional aspects of the vortex/free surface interaction first. Secondly we obtain some basic understanding of the interaction process through an experiment and then talk about several three-dimensional problems hoping to develop a successful prediction model.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2004.05b
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• pp.506-510
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• 2004

A torque transmission system composed of several gears and couplings is flexible. In order to get an exact response of motor, the torsional vibration due to an unexpected change of motor speed must be suppressed. Therefore, it is very important that motor control suppress vibration. Various methods to control it including dual inertia system are proposed. Specially, the method of vibration suppression is that vibration can be suppressed to fee㏈ack the estimated torsion torque via the disturbance observer filter being of normal filter. The suitable Proportional controller and coefficient parameter can be designed using CDM and the torsional vibration also be suppressed, but it has a low degree of adaptability to disturbance. The PID controller can be designed easily, but makes the excessive overshoot and oscillation for system response in the early period. To resolve these problems, simple and practical PID controller with two degree of freedom is proposed recently that it ran improve performance of obeying the reference unconcerned in any disturbance by changing the proportional gain by two degree of freedom parameter. But it has also the defect that parameter a must be changed to obtain the ideal Proportional parameter. On this paper, we design the controller which automatically adjusts parameter u using fuzzy Algorithm to overcome such defects. Also, we compare the proposed method with established one and evaluate them to confirm performance of the designed controller.

• Journal of the Korean Society of Marine Environment & Safety
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• v.24 no.7
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• pp.930-938
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• 2018

Underwater noise radiated from submarines is directly related to the probability of being detected by the sonar of an enemy vessel. Therefore, minimizing the noise of a submarine is essential for improving survival outcomes. For modern submarines, as the speed and size of a submarine increase and noise reduction technology is developed, interest in flow noise around the hull has been increasing. In this study, a noise analysis technique was developed to predict flow noise generated around a submarine shape considering the free surface effect. When a submarine is operated near a free surface, turbulence-induced noise due to the turbulence of the flow and bubble noise from breaking waves arise. First, to analyze the flow around a submarine, VOF-based incompressible two-phase flow analysis was performed to derive flow field data and the shape of the free surface around the submarine. Turbulence-induced noise was analyzed by applying permeable FW-H, which is an acoustic analogy technique. Bubble noise was derived through a noise model for breaking waves based on the turbulent kinetic energy distribution results obtained from the CFD results. The analysis method developed was verified by comparison with experimental results for a submarine model measured in a Large Cavitation Tunnel (LCT).

• The Journal of Korean Philosophical History
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• no.32
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• pp.277-308
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• 2011

The purpose of this study is to show that there are textual similarities between philosophy of Zhuangzi(莊子) and what Jacques Derrida' concepts such as 'differance', 'trace', and 'play', etc. Through our comparative study, we have established a philosophical affinity between Taoist thinking of Zhuangzi and Derridian deconstructive thinking. Zhuangzi and Derrida deconstruct all kinds of traditional and metaphysical thoughts. Zhuangzi's saying of "There is Tao(道) for Thievery(盜)". I call this philosophical tendency 'the logic of cohabitation and coexistence' of the Taoist philosophy. Derrida and Zhuangzi suggest that the logic of cohabitation and coexistence recognizes and affirms differences between opposites. In these thoughts of double affirmation, there is no violence of dichotomous thinking. In other words, their ways of thinking challenge the value system that suggests a single truth, and propose that all human values necessarily carry half-values. They give us to create an enjoyable play-space for human beings in this world. Zhuangzi's suggestions for moral theory provide us with a chance for making question as what is the better life with the others, with a fresh and new perspectives to understand differently the human beings along the category of universe in the 21st century.

• Journal of the Korean Society of Marine Environment & Safety
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• v.29 no.6
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• pp.688-696
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• 2023

In the present study, free roll decay and resistance performances of fishing vessels were evaluated with the combinations and variations of in the parameters of appendages which are attached to improve motion performance of fishing vessels. Computational Ffluid Ddynamics was used to perform free roll decay and resistance analysis. The roll period and decay coefficient were derived by the variations in the combination and dimensions of the primary appendages of the bilge keel and the under keel. It was observed thatThe variations of in the length of the under keel did not significantly impact to the roll damping coefficient. Conversely, for the bilge keel, an increase in the length and angle resulted in an increase in the roll damping coefficient. Comparison of resistance performance was additionally assessed among the selected hulls with the appendages and bare hull. The resistance of the hull with the appendages was higher than that of the bare hull due owing to the changes of in the pressure on the surface of the hull and trim angle. Throughout the present study, the impact of appendage parameter and arrangement on the free roll decay and resistance performance of fishing vessels were was assessed,. which This will be beneficial for the application of appendages to fishing vessels.

• The Journal of Korean Society for Radiation Therapy
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• v.24 no.2
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• pp.167-174
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• 2012

Purpose: The respiration is one of the most important factors in respiratory gating radiation therapy (RGRT). We have developed an unique respiratory guidance system using an audio-visual system in order to support and stabilize individual patient's respiration and evaluated the usefulness of this system. Materials and Methods: Seven patients received the RGRT at our clinic from June 2011 to April 2012. After breathing exercise with the audio-visual system, we measured their spontaneous respiration and their respiration with the audio-visual system respectively. With the measured data, we yielded standard deviations by the superficial contents of respiratory cycles and functions, and analyzed them to examine changes in their breathing before and after the therapy. Results: The PTP (peak to peak) of the standard deviations of the free breathing, the audio guidance system, and the respiratory guidance system were 0.343, 0.148, and 0.078 respectively. The respiratory cycles were 0.645, 0.345, and 0.171 respectively and the superficial contents of the respiratory functions were 2.591, 1.008, and 0.877 respectively. The average values of the differences in the standard deviations among the whole patients at the CT room and therapy room were 0.425 for the PTP, 1.566 for the respiratory cycles, and 3.671 for the respiratory superficial contents. As for the standard deviations before and after the application of the PTP respiratory guidance system, that of the PTP was 0.265, that of the respiratory cycles was 0.474, and that of the respiratory superficial contents. The results of t-test of the values before and after free breathing and the audio-visual guidance system showed that the P-value of the PTP was 0.035, that of the cycles 0.009, and that of the respiratory superficial contents 0.010. Conclusion: The respiratory control could be one of the most important factors in the RGRT which determines the success or failure of a treatment. We were able to get more stable breathing with the audio-visual respiratory guidance system than free breathing or breathing with auditory guidance alone. In particular, the above system was excellent at the reproduction of respiratory cycles in care units. Such a system enables to reduce time due to unstable breathing and to perform more precise and detailed treatment.

• Journal of The Korean Society of Grassland and Forage Science
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• v.33 no.4
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• pp.298-303
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• 2013

This study investigates the effect of a feed concentrate on the growth performance, feed requirement, and rearing expenses of growing black goats. Forty female growing black goats were divided into four groups and fed rice straw (ad libitum) mixed with different levels of the feed concentrate: T1 (1.5%), T2 (1.8%), T3 (2.1%), and T4 (0%, control). The average daily weight gain (body weight per day) was as follows: T1 < T2 < T3 < T4 (50.23, 60.37, 71.46 and 98.90 g/day, respectively) (p<0.05). The intake of rice straw decreased significantly with increase in the concentrate level (p<0.05). Rearing expenses amounted to 46,704, 49,998, 54,701, and 74,613 won for feed concentrate levels of 1.5%, 1.8%, 2.1%, and ad libitum, respectively. Increase in feed concentrate levels led to an increase in rearing expenses. In conclusion, a concentrate level of 2.1% was determined to be idea for a rice-straw-based feed for growing black goats.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1993.04a
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• pp.86-92
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• 1993

자동차의 현가장치에 대한 능동제어연구는 국내외적으로 활발히 진행되어 왔다. 수동식현가장치는 단순히 스프링과 감쇠기로 차체의 진동을 수동 제어 하므로 성능 향상에 한계가 존재하게 된다. 수동식 현가장치가 강성계수와 감쇠계수를 조절함으로써 차체로 들어오는 진동을 억제하는 반면, 능동식제 어는 보통 유압을 이용하여 효율적으로 차체에 들어오는 진동을 억제시키게 된다. 일반적으로 자동차가 능동현가장치 설계시 요구되는 사항은 탑승자의 승차감, 조종성, 현가장치의 공간확보 문제, 경제성(제어력), 실제적으로 자동 차에 적용할 수 있는 능동제어기법인가 하는 문제이다. 자동차 능동식 현가 장치는 보통 1/4 car (2자유도계), Full-car 모델 (7자유도계) 등으로 모델링 을 하여 능동제어기를 설계한다. 1/4 car 모델의 특징은 해석이 비교적 단순 하고 현가장치의 동적거동을 이해하는데 유용하고 실험을 하거나 실제 자동 차에 적용하기 쉬운 반면에 Full-car 모델에 비해 제어력의 효율이 떨어진다 는 단점이 있다. 그 이유는 1/4 car 모델은 차체의 동역학적 특성을 고려하 여 설계하지 않았기 때문에 4개의 독립현가차축에서는 오직 그 현가축방향 으로 발생하는 수직방향의 진동만을 제어하기 때문이다. 따라서 동역학적 역 성에 기인하는 운동을 제어하는 비효율적인 제어력이 공급된다는 단점을 갖 는다. 이에 비해 full-car 모델은 주행모드(수직, 롤링, 피칭운동)간의 연성을 고려하여 제어기를 설계할 수 있기 때문에 1/4 car 모델에 비해 제어력의 효 율이 높다는 장점이 있는 반면에 모델이 수학적으로 복잡하므로 제어력을 구하는데 계산량이 많고, 실제 자동차에 적용하기에 복잡하다는 단점을 갖고 있다. 따라서 본 논문에서는 쉽게 실험할 수 있고, 실용화할 수 있는 1/4 car 모델에 대하여 능동제어기를 설계하여 실제자동차에 능동제어기를 적용할 때 참고가 될 수 있도록 하였다. 자동차는 저주파영역의 밴드통과필터 역할 을 하므로 저주파에서의 성능, 특히 탑승자가 민감하게 느끼는 0.5Hz - 10Hz 부근의 주파수성능은 승차감, 조종성에 상당히 중요하다. 이에 본 논문 에서는 0.5Hz - 10Hz 부근의 승차감, 조종성의 향상에 초점을 두고 차체의 속도를 출력변수로 한 LQG/LTR 제어기를 설계하였다. LQG/LTR 설계기법 은 안정도-강인성이 좋은 체계적인 설계기법으로서 전 상태를 측정할 필요 가 없으므로 실제 적용시 효과적이다. 또한 자동차의 제원의 변화에 대한 고 유치의 민감도해석과 새로운 개념으로 안정도-강인성(Robustness)해석을 하 여 수동시스템과 능동시스템의 강인성을 비교하였다.

• The Journal of Engineering Geology
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• v.15 no.4 s.42
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• pp.407-421
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• 2005

This study aims to investigate hydrogeological properties of the central area from Yangjeong-Dong to Sujeong-Dong in Busan Metropolitan City. For this study, pumping tests were carried out in the bedrock aquifer of Yangjeong-Dong and the unconsolidated aquifer near Busanjin railway station. The pumping test in the bedrock aquifer containing the Dongrae fault revealed specific hydraulic characteristics with respect to the fault. The pumping test in the unconsolidated aquifer revealed the hydrogeologic properties of both coastal landfill and fine sediments. It was found that the Moench's sphere-shaped dual-porosity model fits the bedrock aquifer, whereas the Neuman's uncofined aquifer model accords with the unconsolidated aquifer. The average transmissivity and storage coefficient of the bedrock aquifer are $2.75{\times}10^{-5}m^2/s\;and\;6.41{\times}10^{-5}$ and those of the unconsolidated aquifer are $8.24{\times}10^{-4}m^2/s\;and\;3.70{\times}10^{-3}$, respectively. On the other hand, slug tests gave average transmissivity and storage coefficient values of $9.84{\times}10^{-4}m^2/s\;and\;1.21{\times}10^{-2}$, respectively.

• Journal of KIISE:Computing Practices and Letters
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• v.9 no.6
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• pp.623-634
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• 2003

In this paper, we propose a collaborative multimedia authoring system. Our authoring system represents a multimedia presentation in a 3D coordinate system. One axis represents the traditional timeline information (T-zone), and the other two axes represent spatial coordinates (XY-zone). Our system represents a visual media objects as a 3D parallelepipeds and audio media objects as cylinders. This interface allows for simultaneous authoring and manipulation of both the temporal and the spatial aspects of a presentation. Using our system, users can design multimedia presentations collaboratively in the unified spatio-temporal space while freely traversing the spatial domain and the temporal domain without changing the context of authoring. In addition, we suggest an efficient mechanism of concurrency control for shared objects generated by our collaborative writing system. The mechanism is mainly based on the user awareness, the multiple versions, and the access permission of shared objects. Our concurrency control mechanism is designed to keep data consistency by minimizing the collision due to the delay or the failure of network communication and to allow maximum responsiveness for users using optimistic concurrency control. Also, the mechanism maximize the responsiveness by refining the locking granularity and applying different concurrency control mechanisms to each.