• The Journal of Korea Robotics Society
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• v.6 no.3
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• pp.274-283
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• 2011

A simplified linearized dynamic equation for the propulsion force generation of an Ostraciiform fish robot with elastically jointed double caudal fins is derived in this paper. The caudal fin is divided into two segments and connected using an elastic joint. The second part of the caudal fin is actuated passively via the elastic joint connection by the actuation of the first part of it. It is demonstrated that the derived equation can be utilized for the design of effective caudal fins because the equation is given as an explicit form with several physical parameters. A simple Ostraciiform fish robot was designed and fabricated using a microprocessor, a servo motor, and acrylic plastics. Through the experiment with the fish robot, it is demonstrated that the propulsion force generated in the experiment matches well with the proposed equation, and the propulsion speed can be greatly improved using the elastically jointed double fins, improving the average speed more than 80%. Through numerical simulation and frequency domain analysis of the derived dynamic equations, it is concluded that the main reason of the performance improvement is resonance between two parts of the caudal fins.

• Journal of Advanced Marine Engineering and Technology
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• v.33 no.1
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• pp.52-61
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• 2009

This experiment was conducted in attempt of improving hydrodynamic efficiency of the propulsion mechanism by installing a spring to the wing so that the opening angle of the wing in one stroke can be changed automatically, compared to the existing method of fixed maximum opening angle in Weis-Fogh type ship propulsion mechanism. Average thrust coefficient was almost fixed with all velocity ratio with the prototype, but with the spring type, thrust coefficient increased sharply as velocity ratio increased. Average propulsive efficiency was larger with bigger opening angle in the prototype, but in the spring type, the one with smaller spring coefficient had larger value. In the range over 1.0 in velocity ratio where big thrust can be generated, spring type had more than twice of propulsive efficiency increase compared to the prototype.

• Journal of Magnetics
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• v.16 no.3
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• pp.263-267
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• 2011

The present paper proposes a novel cableless magnetic actuator with a new propulsion module that exhibits a very high thrusting force. This actuator contains an electrical inverter that directly transforms DC from button batteries into AC. The electrical DC-AC inverter incorporates a mass-spring system, a reed switch, and a curved permanent magnet that switches under an electromagnetic force. The actuator is moved by the inertial force of the mass-spring system due to mechanical resonance energy. The experimental results show that the actuator is able to move upward at a speed of 33 mm/s when using 10 button batteries when pulling a 10 g load mass. This cableless magnetic actuator has several possible applications, including narrow-pipe inspection and maintenance.

• Journal of the Korea Institute of Military Science and Technology
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• v.10 no.3
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• pp.189-199
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• 2007

The present survey paper introduces the research history, characteristics of body and fin shapes, basic principles of various locomotions and propulsion-generation mechanism of aquatic animals in nature, which utilize unsteady flow through a noble mechanism that is different in paradigm from the propulsion generation mechanism of man-made marine vehicles, and so have excellent performance and efficiency. The authors hope that the present paper helps to activate the domestic research interest on the fields of swimming in nature, which is expected to provide great ideas for improvement and innovation of today's marine vehicles.

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.1191-1198
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• 2011

The railway business was began at England in 1767. Since then, it has been changed for configuration of rail over the years and made in the form of I. The train propulsion has been developed in a engine of steam, diesel, motor, electromagnetic force and a pneumatic engine, continuously. also, the friction has been improved in a steel-wheel, rubber tire, frictionless maglev system and railless system. In consequence, the efficiency and improvement speed for train have been accomplished. In this paper, it is investigated for the structure with lightweight using the change for supporting the form of lateral pressure by centrifugal force in the substructure supporting load for railway vehicles.

• Journal of Advanced Marine Engineering and Technology
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• v.12 no.4
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• pp.53-61
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• 1988

Speed of a diesel engine is usually controlled by the hydraulic governor which uses the centrifugal force of rotating fly balls for sensing the error speed. But for a recently developed high efficient, low speed and long stroke 2 cycle marine diesel engine, this governor doesn't work well enough because of too much changes of toraring force during one revolution of engine and too long uncontrollable time due to small numbers of cylinder. For improvement of jiggling phenomena and unstability various studies are being carried out, but they are not enough for a steep load change in a small ship's generator plant or at rough sea condition in a propulsion engine. In this paper, authors propose a new method to control a fuel before the change of angular velocity due to load change by feedforward the change of load, and find that the proposed method shows quite a good control performance in comparision to the customary PID control method by simulation using a digital computer for the various load change.

• Bulletin of the Society of Naval Architects of Korea
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• v.26 no.2
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• pp.13-24
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• 1989

The geometrical characteristics of sculls which are in use for propulsion of Korean traditional row boats were briefly surveyed. A typical dimension of the scull was selected and prototype for test was prepared. Angular displacements and the force components at handle and pivoting point were measured when the scull was operated in moored condition by skilled fisherman. Time histories and trajectories of motion were analyzed with the force generated at the scull blade. It was found out that the thrust of the scull was generated mainly by reaction force. The direction of improvement for better rowing motion could be also suggested. Continued study on this topic in a self-propulsion condition will provide us another interesting informations and prepare a possibility of application in evaluating rowing motion of oar.

• Journal of the Korean Society of Marine Environment & Safety
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• v.25 no.6
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• pp.802-808
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• 2019

DC motors are used extensively on shipboard, including as the ship's winch operating motor, owing to their simple speed control and excellent output torque characteristics. Moreover, they were used as propulsion motors in the early days of electric propulsion ships. However, mechanical rectifiers, such as brushes, used in DC motors have certain disadvantages. Hence, brushless DC (BLDC) motors are increasingly being used instead. While the electrical characteristics of both types of motors are similar, BLDC motors employ electronic rectifying devices, which use semiconductor elements, instead of mechanical rectifying devices. The inverter system for driving conventional BLDC motors uses a two-phase excitation method so that the waveform of the back electromotive force becomes trapezoidal. This causes harmonics and torque ripple in the phase current switching period in which the winding wire through which the current flows is changed. Researchers have studied and presented various methods to reduce the harmonics and torque ripple. This study applies a cascaded H-bridge multilevel inverter, which implements a proportional-integral speed current controller algorithm in the driving circuit of the BLDC motor for electric propulsion ships using a power analysis program. The simulation results of the modeled BLDC motor show that the driving method of the proposed BLDC motor improves the voltage waveform of the input side of the motor and remarkably reduces the harmonics and torque ripple compared with the conventional driving method.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.10
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• pp.791-799
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• 2020

Launched in October 2019, Northrop Grumman's MEV-1 was the world's first unmanned mission demonstrating the practical feasibility of on-orbit servicing. Although the concept of on-orbit servicing was proposed several decades ago, it has been developed to various mission concepts providing services such as orbit change, station keeping, propellant and equipment supply, upgrade, repair, on-orbit assembly and production, and space debris removal. The historical success of MEV-1 is expected to expand the market of on-orbit servicing for government agencies and commercial sectors worldwide. The on-orbit servicing essentially requires the utilization of a highly propellant efficient electric propulsion system due to the nature of the mission. In this study, the space mission analysis for a simple on-orbit mission involving Hall thruster is conducted, which is life extension mission for geostationary orbit satellites. In order to analyze the mission, design space exploration for various Hall thruster design variable combinations is performed. The values of design variables and operational parameters of Hall thruster suitable for the mission are proposed through design space analysis and optimization, and mission performance is derived. In addition, the direction of further improvement for the current on-orbit mission analysis process and space mission analysis involving Hall thruster is reviewed.