• Journal of the Korea Institute of Military Science and Technology
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• v.21 no.2
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• pp.195-203
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• 2018

Among the techniques of reducing the drag to increase the speed of underwater moving bodies, we studied on the drag reduction method by gas injection. Researches on gas injection method have been paid much attention to reduce the drag of vessels or pipe inner walls. In this study, we used a sintered metal mesh that can uniformly distribute fine bubbles by gas injection method, and applied it to a cylindrical underwater moving body. Using the KRISO medium-sized cavitation tunnel, we measured both the bubble size on the surface of the sintered mesh and the bubble distribution in the boundary layer. Then, drag reduction tests were performed on the cylinder type underwater moving models with cylindrical or round type tail shape. Experiments were carried out based on the presence or absence of tail jet injection. In the experiments, we changed the gas injection amount using the sintered mesh gas injector, and changed flow rate accordingly. As a result of the test, we observed increased bubbles around the body and confirmed the drag reduction as air injection flow rate increased.

• Journal of Ocean Engineering and Technology
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• v.32 no.4
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• pp.222-227
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• 2018

Most underwater acoustic arrays for low frequency operation are deployed vertically, but a mid-range frequency horizontal array system is being developed by the Korea Research Institute of Ships and Ocean Engineering (KRISO). The horizontal array platform is deployed underwater and kept in place by weather vaning mooring. This is essential because it is nearly impossible to keep a submerged body at a given position in the water without any external force. Hence, the horizontal array platform can maintain the desired position in the presence of a weak tidal current. The objective of this study is to design an underwater platform that can maintain its horizontal position in a weak current. First, the authors investigated various virtual models, selected one of the models, and performed a small model test of the selected model at a basin. We calculated the external forces associated with the 2D motion, and then we conducted a large basin test followed by a circulation water channel test for the manufactured array platform. The results of the simplified 2D motion calculation essentially matched the results of the underwater test.

• 제어로봇시스템학회:학술대회논문집
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• 2003.10a
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• pp.1580-1586
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• 2003

This paper presents the design and the analysis of a "fish-like underwater robot". In order to develop swimming robot like a real fish, extensive hydrodynamic analysis were made followed by the study of biology of the fishes especially its maneuverability and propel styles. Swimming mode is achieved by mimicking fish-swimming of carangiform. This is the swimming mode of the fast motion using its tail and peduncle for propulsion. In order to generate configurations of vortices that gives efficient propulsion yawing and surging with a caudal fin has applied and in order to submerge and maintain the body balance pitching and heaving motion with a pair of pectoral fin is used. We have derived the equation of motion of PoTuna by two methods. In first method, we use the equation of motion of underwater vehicle with the potential flow theory for the power of propulsion. In second method, we apply the method of the equation of motion of UVM(Underwater Vehicle-Manipulator). Then, we compare these results.

• International Journal of Ocean System Engineering
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• v.1 no.2
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• pp.102-109
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• 2011

This paper describes the implementation of a precise underwater navigation solution using a multiple sensor fusion technique based on USBL, GPS, DVL and AHRS measurements for the operation of a remotely operated mine disposal vehicle (MDV). The estimation of accurate 6DOF positions and attitudes is the key factor in executing dangerous and complicated missions. To implement the precise underwater navigation, two strategies are chosen in this paper. Firstly, the sensor frame alignment to the body frame is conducted to enhance the performance of a standalone dead-reckoning algorithm. Secondly, absolute position data measured by USBL is fused to prevent cumulative integration error. The heading alignment error is identified by comparing the measured absolute positions with the DR algorithm results. The performance of the developed approach is evaluated with the experimental data acquired by MDV in the South-sea trial.

• The KIPS Transactions:PartA
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• v.16A no.4
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• pp.255-262
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• 2009

We present an autonomous entertainment dolphin robot system based on ubiquitous sensor networks(USN). Generally, It is impossible to apply to USN and GPS in underwater bio-mimetic robots. But An Entertainment dolphin robot which presented in this paper operates on the water not underwater. Navigation of the underwater robot in a given area is based on GPS data and the acquired position information from deployed USN motes with emphasis on user interaction. Body structures, sensors and actuators, governing microcontroller boards, and swimming and interaction features are described for a typical entertainment dolphin robot. Actions of mouth-opening, tail splash or water blow through a spout hole are typical responses of interaction when touch sensors on the body detect users' demand. Dolphin robots should turn towards people who demand to interact with them, while swimming autonomously. The functions that are relevant to human-robot interaction as well as robot movement such as path control, obstacle detection and avoidance are managed by microcontrollers on the robot for autonomy. Distance errors are calibrated periodically by the known position data of the deployed USN motes.

• Journal of the Society of Naval Architects of Korea
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• v.55 no.6
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• pp.482-489
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• 2018

Most of the numerical and experimental studies on supercavitating flows are focused on the cavitator only. However, the partial cavity growing into the supercavity is affected by the shape of the body placed behind the cavitator. In this paper, we develope a numerical method which is based on the boundary element method to predict supercavitating flow around three-dimensional axisymmetric bodies. We estimate the influence of the body shape on the supercavity growth. Here, we consider various parameters of the body such as cavitator shape, shoulder length and body diameter, and compare the results with the case of the cavitator only. In summary, it is found that the body may impede the cavity growth, the shoulder mainly affects the cavity length, and the supercavity occurring in the cone type cavitator is strongly influenced rather than that of the disk type cavitator.

• Journal of Ocean Engineering and Technology
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• v.28 no.5
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• pp.466-473
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• 2014

Underwater gliders do not have any external propulsion systems that can generate and control their motion. Generally, underwater gliders would obtain a propulsive force through the lift force generated on the body by a fluid. Underwater gliders should be equipped with mechanisms that can induce heave and pitch motions. In this study, an inner movable and rotatable mass mechanism was proposed to generate the pitch and roll motions of an underwater glider. In addition, a buoyancy control unit was presented to adjust the displacement of the underwater glider. The buoyancy control unit could generate the heave motion of the underwater glider. In order to analyze the underwater dynamic behavior of this system, nonlinear 6-DOF dynamic equations that included mathematical models of the inner movable mass and buoyancy control unit were derived. Only kinematic characteristics such as the location of the inner movable mass and the piston position of the buoyancy control unit were considered because the velocities of these systems are very slow. The effectiveness of the proposed dynamic modeling was verified through sawtooth and spiraling motion simulations.

• The Journal of the Convergence on Culture Technology
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• v.6 no.1
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• pp.433-439
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• 2020

This study compared and analyzed the change of air consumption according to water depth with human characteristics and theoretical values. The experimental results are as follows. First, subjects A and B showed similar rise rates depending on the water depth. Second, subject C had a significantly higher rate of increase in air consumption at 25m underwater because the body responded sensitively to deep water pressure, which increased air consumption because breathing was faster than other participants. Third, the subjects D and E showed significantly lower overall air consumption. D and E were 37 and 35 years of age, respectively, the youngest, strongest and most experienced in deep sea diving at the time of military service. Fourth, the average air consumption per minute of the test subjects increased from 5m in water to 1.45 times, 10m in water to 1.85 times, and 20m in water to 2.8 times. This seems to be a result of different experiences, physical fitness, the degree of adaptation of the body to underwater, and different breathing techniques. Lastly, the difference between the experimental average value and the theoretical value appears to be the result of using more or less air than the theoretical value depending on the experiences and physical strength of each of the 5 rescuers, the degree of adaptation of the body underwater, and the method of underwater breathing.

• Journal of Ocean Engineering and Technology
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• v.26 no.5
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• pp.47-54
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• 2012

In this study, numerical simulations were performed to evaluate the current loads acting on the multi-legged underwater robot "Crabster" with a variety of incident angles using the ANSYS-CFX package. The Reynolds-averaged Navier-Stokes equations were solved to simulate the fluid flow around Crabster to calculate the forces and moments induced by incoming currents with various angles. First, to assess the posture stability of the body, the forces and moments were calculated with various incident angles when the current acted in the vertical and horizontal directions. Next, two forms of legs (box and foil types) were evaluated to determine the hydrodynamic force variation. Finally, the current forces and moments acting on the Crabster body with the legs attached were estimated.

• 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.