• The Journal of the Korea institute of electronic communication sciences
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• v.16 no.6
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• pp.1089-1094
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• 2021

In order to support the restoration and construction work of port infrastructure facilities damaged or damaged due to disasters and disasters, it is linked with work equipment based on the performance of duties such as regular patrol in the port, monitoring the underwater environment, and acquisition of underwater configuration information in the port, Define content related to AUV platform analysis and design that can support construction.

• Journal of Advanced Marine Engineering and Technology
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• v.33 no.8
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• pp.1203-1211
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• 2009

The dynamics of underwater vehicles can be greatly influenced by the dynamics of the vehicle thrusters. The control of the state of the hovering or very slow motion of the underwater vehicle is most important for automatic docking or control of the manipulator of the vehicle. The dynamics of the thruster based on the electric motor is nonlinear and has uncertain parameters. Since the dynamics of the vehicle coupled with the dynamics of the thruster is nonlinear and has uncertain parameters, a robust control is very effective for a desired motion tracking of the uncertain and nonlinear vehicle. In this paper a study was performed on the robust control scheme of the very slow motion or hovering motion of the underwater vehicle actuated by the electric motor. Also, a concurrent control on the state of the vehicle with nonlinearity and uncertain parameters was performed. A sliding mode control algorithm out of robust controllers was designed and applied, which compensates the nonlinear forces and uncertain parameters of the vehicle and actuator. Through a computer simulation, the proposed control scheme was compared with a linear PD controller and its superior performance was validated.

• Journal of the Korean Society of Marine Environment & Safety
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• v.25 no.6
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• pp.765-771
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• 2019

With the increase in the speed of ships and the size of ocean structures, the importance of flow noise has become increasingly critical in meeting regulatory standards. However, unlike active investigations in aeroacoustics fields for airplanes and trains, which are based on acoustic analogy methods for tonal and broadband frequency noise, only the discrete blade passing frequency noise from propellers is considered in marine fields. In this study, prediction methods for broadband noise in marine propellers and underwater appendages are investigated using FW-H Formulation1B, which can consider the mechanism of primary noise generation of trailing edge noise. The original FW-H Formulation 1B is based on the pressure correlation function tolackitsgeneralityandaccuracy. To overcome these limitations, wall-pressure spectrum models are adopted to improve the generality in fluid mediums. The comparison of the experimental results obtained in air reveals that the proposed model exhibits a higher accuracy within 5 dB. Furthermore, the prediction procedures for broadband noise for hydrofoils are established, and the estimation of broadband noise is conducted based on the results of the computational fluid dynamics.

• Journal of the Korean Society of Marine Environment & Safety
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• v.22 no.5
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• pp.389-401
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• 2016

This study attempted to present the monthly distribution of the inshore gill netters for the prevention of propeller failure caused by the damage of fishing gear by the merchant vessels in the West Sea. This study was conducted using the transmitting device of fishing location (V-Pass) data for 1 year in 2014. The grid intervals are $30minute{\times}30minute$ ($latitude{\times}longitude$) based on the section of the sea. A total of 56 sections were analyzed by constructing a grid. The results revealed that the section no. 194 with the highest density index showed no fishing gear damage accident. But the section no. 193 with a relatively lower density index showed more frequent fishing gear damage accident. It is because the section no. 193 is included in the main route of the merchant vessels. Based on this analysis, it is found that the fishing gears are not damaged in proportion to density index but risk of damage exists according to the main routes of merchant vessels. Therefore, for the safe navigation of the merchant vessels, notifying the waters of $34.5^{\circ}{\sim}35.5^{\circ}$ at latitude and $125.67^{\circ}{\sim}126^{\circ}$ at longitude, as a navigational warning area from May through September, will prevent marine accident, such as propeller failure and fishing gear damage. Accordingly, when the merchant vessels navigate in the section no. 193 and 203, the area of $34.5^{\circ}{\sim}35.5^{\circ}$ at latitude and $125.5^{\circ}{\sim}125.67^{\circ}$ at longitude is recommended for the safe navigation.

• Journal of the Society of Naval Architects of Korea
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• v.34 no.4
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• pp.31-41
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• 1997

This paper describes a potential-based panel method formulated for the prediction of the steady performance of a waterjet propulsor. The method employs normal dipoles and sources distributed on the solid surfaces such as the impeller/stator blades, hub and duct, and normal dipoles in the shed wakes trailing the impeller and stator to represent the potential flow around the waterjet propulsor. To define a closed boundary surface, the inlet and outlet open boundary surfaces are introduced where the sources and dipoles are distributed. The kinematic boundary condition on the solid boundary surface is satisfied by requiring that the normal component of the total velocity should vanish. On the inlet surface, the total inflow flux into the duct is specified, and on the outlet surface the conservation of mass principle is applied to evaluate the source strength. The solid surfaces are discretized into a set of quadrilateral panel elements and the strengths of sources and dipoles are assumed constant at each panel. Applying this approximation to the boundary conditions leads to a set of simultaneous equations. Systematic numerical tests show that the present numerical method is fast and stable. In order to validate the present method, sample computations are carried out first for the case of a conventional axial flow fan which has a similar geometry as the waterjet propulsor, and then for the case of a waterjet propulsor on which experiments are carried out at KRISO(Korea Research Institute of Ships and Ocean Engineering).

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.9
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• pp.3952-3958
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• 2011

This study was to investigate the difference in gait pattern between the visual handicap children and non handicap children in by analyze the biomechanical variation and pattern of lower limb. Therefore, we have made a choice of four visually handicapped children and two subjects, who had no medical disorder for the last six months. In order to collect the gait pattern data of each group, we have used six infrared cameras and one forceplate Also, we have used QTM program to collect the raw data and Visual3D program to calculate kinetic variable. The results were as follows, An/Posterior GRF of breaking phase and propulsion phase in stance phase was lower in visual handicapped children than that of non handicapped children and breaking phase was longer than propulsion phase. extension moment at the ankle was quite lower than general gait pattern and there was little variation at the knee joint which makes the results differ from the general gait pattern. However, hip joint moment was relatively higher than that of other joints. Mechanical variation of lower limb, in case of foot and shank, showed similar results. but generated very low mechanical energy. In thigh, the form of mechanical energy generation was slightly different in each group but generated more mechanical energy than other segments.

• Journal of the Korean Society of Marine Environment & Safety
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• v.24 no.4
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• pp.475-481
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• 2018

In this study, the safety and effectiveness of ope cutter, developed to prevent frequent accident propeller windingness at sea. First, we calculated the bolt strength of the three types of rope cutting devices used in the experiment and the torsional stresses on the shafting system theoretical equation and the finite element method. As a result, the bolts used in the rope cutter confirmed from the viewpoint of safety life design and fail safe design. Also, safety satisfactory because of the small effect on the shaft system when locking up. Experiments were carried out to cut ropes and fishing nets from the sea using the ships equipped with three types of rope cutters verified to be safe. As a result, ropes of 20 to 50 mm in thickness were generally cut. It was found that the cutting efficiency of a rope cutter attached to shafting decreased when cutting thick ropes.

• Bulletin of the Society of Naval Architects of Korea
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• v.27 no.3
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• pp.89-99
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• 1990

It is required to develop a hull form with low resistance and high propulsive efficiency for the improvement of the ship-board operational economy. Since the hull forms with low resistance frequently have lower propulsive efficiency and on the other hand the hull forms with higher propulsive efficiency don't show good resistance characteristics, it is always very difficult to obtain economical hull forms which require less propulsive power accordingly. Efforts have been made to pursue a stern form with excellent resistance and propulsion characteristics together by shaping the run of the so-called buttock-flow type stern, which is known to have good viscous resistance performance, like that of conventional aftbody(U-type or Hogner type) featured by high propulsive efficiency. First model tests confirmed that the above concept can be one of the alternative approaches to the design of the good stern form and by the continuing efforts thereafter for the refining of the concept, propelled by the first promising results, stern form of good resistance performance together with good propulsive efficiency has been realized to some extent. In addition, it is confirmed that the new new stern can have better cavitation and vibration characteristics due to uniform wake-fields and the compact engine room arrangement can be possible due to it's larger floor area in way of engine room double bottom as compared with usual barge stern.

• The Journal of the Acoustical Society of Korea
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• v.40 no.4
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• pp.261-269
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• 2021

Without any validation of the incompressible assumption, most of previous studies on cavitation flow and its noise have utilized numerical methods based on the incompressible Reynolds Average Navier-Stokes (RANS) equations because of advantage of its efficiency. In this study, to investigate the effects of the flow compressibility on the Tip Vortex Cavitation (TVC) flow and noise, both the incompressible and compressible simulations are performed to simulate the TVC flow, and the Ffowcs Williams and Hawkings (FW-H) integral equation is utilized to predict the TVC noise. The DARPA Suboff submarine body with an underwater propeller of a skew angle of 17 degree is targeted to account for the effects of upstream disturbance. The computation domain is set to be same as the test-section of the large cavitation tunnel in Korea Research Institute of Ships and Ocean Engineering to compare the prediction results with the measured ones. To predict the TVC accurately, the Delayed Detached Eddy Simulation (DDES) technique is used in combination with the adaptive grid techniques. The acoustic spectrum obtained using the compressible flow solver shows closer agreement with the measured one.

• Aerospace Engineering and Technology
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• v.4 no.2
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• pp.209-215
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• 2005

A qualification of propellant for a AKM(Apogee Kick Motor) has been conducted by firing standard motors. The Standard motor used in developing process of KSLV-I's AKM is ST-6 whose diameter is about six inches. HTPB composite propellant are used in these motors. Several standard motors are fired and compared with simulation results. A mean value of characteristic velocity is 1518 m/s. The characteristic value for prediction is 1516 m/s, and the thrust loss is about 5.9%. Differences between the measurements and prediction are less than 3%.