• The Journal of the Acoustical Society of Korea
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• v.39 no.2
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• pp.69-76
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• 2020

This paper deals with a method of transmitting depth information of a high-speed underwater vehicle. The depth information signal transmitted from the high-speed mobile object is received with high frequency variability. In the proposed method, we apply not only frequency synchronization but also additional synchronization on the time axis like the existing method. In the case of a Doppler frequency bank with less resolution than the conventional method through simulations performed in the environment moving up to 50 kn, and the depth information is recovered using the proposed method, the error rate of 6 % ~ 9 % is reduced to 0.2 % ~ 1 %.

• The Journal of Korea Robotics Society
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• v.18 no.1
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• pp.53-58
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• 2023

In general, in order to operate an autonomous underwater vehicle (AUV) in an underwater environment, a navigation system such as a Doppler Log (DVL) using a Doppler phenomenon of ultrasonic waves is used for speed and direction estimation. However, most of the ultrasonic sensors in underwater is large for long-distance sensing and the cost is very high. In this study, not only canal neuromast on the fish's lateral lines but also superficial neuromast are studied on the simulation to obtain pressure values for each pressure sensor, and the obtained pressure data is supervised using spherical CNN. To this end, through supervised learning using pressure data obtained from a pressure sensor attached to an underwater vehicle, we can estimate the speed and angle of the underwater vehicle in a quasi-static underwater environment and propose a method for a non-ultrasonic based navigation system.

• Journal of computational fluids engineering
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• v.18 no.1
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• pp.13-21
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• 2013

Cavitating flow is usually formed on the surface of a high speed underwater object. When a object moves near a free surface at very high speed, the cavity signature becomes one of the major factors to be overcome by sensors of military satellite. The present work was to study the free surface effect on the ventilated cavitation. The governing equations were Navier-Stokes equations based on a homogeneous mixture model. The multiphase flow solver used an implicit preconditioning method in the curvilinear coordinate system. The cavitation model used here was the one first presented by Merkle et al.(2006) and redeveloped by Park & Ha(2009). Computations considered the free surface effects were carried out with a NACA0012 hydrofoil and the corresponding results were compared with the experimental data to have a good agreement. Calculations were then performed considering the ventilated cavitation, including the effect of non-condensable gas under the free surface effects.

• The Journal of the Acoustical Society of Korea
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• v.42 no.4
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• pp.370-376
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• 2023

In the underwater image, it is not clear to distinguish the shape of the target due to underwater noise and low resolution. In addition, as an input of deep learning, underwater images require pre-processing and segmentation must be preceded. Even after pre-processing, the target is not clear, and the performance of detection and identification by deep learning may not be high. Therefore, it is necessary to distinguish and clarify the target. In this study, the importance of target shadows is confirmed in underwater images, object detection and target area acquisition by shadows, and data containing only the shape of targets and shadows without underwater background are generated. We present the process of converting the shadow image into a 3-mode image in which the target is white, the shadow is black, and the background is gray. Through this, it is possible to provide an image that is clearly pre-processed and easily discriminated as an input of deep learning. In addition, if the image processing code using Open Source Computer Vision (OpenCV)Library was used for processing, the processing speed was also suitable for real-time processing.

• Journal of the Korea Institute of Military Science and Technology
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• v.24 no.2
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• pp.237-244
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• 2021

In recent years, the maturity of the technology for a high speed underwater vehicle using supercavitation increase, it is entering the stage of applied research for practical use. In this study, hydrodynamic performance of the supercavitating object was evaluated by using a Viscous-Potential based Boundary Element Method(VP-BEM). 27 models with different shape parameters such as body diameter, length and fore-body shape were considered. The process of the supercavity development of each model was simulated, and drag generated according to operating conditions such as changes in water depth was analyzed.

• Journal of Korean Physical Therapy Science
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• v.16 no.4
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• pp.67-74
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• 2009

Background: This study had been carried out with 20 elderly subjects as its object for about one month from November 3, 2008 to December 14, 2008 in order to observe the effect of Underwater Treadmill on the elderly's walking and balance ability. Methods: Subjects were assigned either experimental group (n=10) or the control group (n=10), experimental group received Underwater Treadmill program (30 min per course, 3days a week for 6weeks). Subjects were assessed for muscle power (Nicolas Manual Muscle Test), balance (Functional Reach Test), gait ability (Time Up and Go, 10M walking test) before experiments and after experiments. Results: The results of this study were as follows; 1. After underwater treadmill exercise, the change of isometric contraction indicated a beneficial increase on lower extremity muscle power of experimental group and functional test of balance function; FRT, TUG indicated beneficial difference between groups. 2. beneficial difference between groups in walking speed of hourly index change of walking function. 3. between muscle power and balance, gait ability, we could find out there's high correlation ship between lower extremity muscle power increasing and balance and gait ability of the elderly. Conclusion: Aerobic exercise using underwater treadmill effects on muscle power strengthening of the elderly, and because of this, increase of lower extremity muscle power is very helpful not only to improvement of balance ability, but also to improvement of gait ability, so it will be used as a physical therapy program on clinic and used as an exercise program for protecting the elderly from falling down very well.

• Journal of the Korea Institute of Military Science and Technology
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• v.18 no.3
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• pp.300-308
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• 2015

Recently supercavitating underwater torpedo moving at high speed (over 200 knots) has been interested for their practical advantage of the dramatic drag reduction. Cavitator located in front of the torpedo plays an important role to generate a natural supercavity and control the motion of the object. Supercavity can be created artificially by injection of compressed gas from the rear of the cavitator at a relatively low speed. In this paper, we investigated physical characteristics of artificial supercavities through cavitation tunnel experiments. One of the main focuses of the study was to measure pressure inside the cavity, and examined variation of the gravity effects appearing according to different amount of injected air. It was also found that a stable supercavity could be sustained at injection rates less than that required to form the stable supercavity because of hysteresis effect.

• Proceedings of the Korea Contents Association Conference
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• 2009.05a
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• pp.759-764
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• 2009

With its rapid growth, the digital contents-related industry is drawing attention as an industry generating a high value added. Specifically, the 3D morphing technology often used in the appearance or movement of each object comprising contents makes it possible to compose various contents by inferring the appearance and movement of the object. For a realistic swimming appearance of fish by using fish that swim in the water, this paper proposes a technique that applies the same speed concept as a physical pendulum to a swimming cycle and applies a frame morphing technique that is able to express the growth process from fry to adult fish. This article is capable of realistically reviving the fish growth process, and can through magnified applying can be applied to in 3D fishes encyclopedias or virtual underwater expressions etc. in the viewpoint which is oceanography.