• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.9
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• pp.667-674
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• 2014

A ship's propulsion shafting system is subjected to varying magnitudes of intermittent loadings that pose great risks such as failure. Consequently, the dynamic characteristic of a propulsion shafting system must be designed to withstand the resonance that occurs during operation. This resonance results from hydrodynamic interaction between the propeller and fluid. For ice-class vessels, this interaction takes place between the propeller and ice. Producing load- and resonance-induced stresses, the propeller-ice interaction is the primary source of excitation, making it a major focus in the design requirements of propulsion shafting systems. This paper examines the transient torsional vibration response of the propulsion shafting system of an ice-class research vessel. The propulsion train is composed of an electric motor, flexible coupling, spherical gears, and a propeller configuration. In this paper, the theoretical analysis of transient torsional vibration and propeller-ice interaction loading is first discussed, followed by an explanation of the actual transient torsional vibration measurements. Measurement data for the analysis were compared with an applied estimation factor for the propulsion shafting design torque limit, and they were evaluated using an existing international standard. Addressing the transient torsional vibration of a propulsion shafting system with an electric motor, this paper also illustrates the influence of flexible coupling stiffness design on resulting resonance. Lastly, the paper concludes with a proposal to further study the existence of negative torque on a gear train and its overall effect on propulsion shafting systems.

• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.7
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• pp.1124-1128
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• 2021

As regulations of emissions from ships become more stringent, electric propulsion systems have been increasingly used to solve this problem in vessels ranging from large merchant ships to small and medium-sized ships. Methods for improving the efficiency of the electric propulsion system include the improvement of power sources; the use of a system linked to environmentally friendly power sources, such as batteries, fuel cells, and solar power; and the development of hardware and control methodology for rectifiers, power conversion devices, and propulsion motors. The method using a phase-shifting transformer with diodes has been widely used for rectification. Power semiconductor devices with grid connection to an environmentally friendly power source using DC distribution, a variable speed power source, and the application of small and medium-sized electric propulsion systems have been developed. Accordingly, the demand for active front-end (AFE) rectifiers is increasing. In this study, a method using a neural network rather than a conventional proportional-integral controller was proposed to control the AFE rectifier. Tested controller data were used to design a neural network controller trained through MATLAB/Simulink. The neural network controller was applied to a rectification system designed using PSIM software. The results indicated the effectiveness of improving the waveform and power factor DC output stage according to the load variation. The proposed system can be applied as a rectification system for small and medium-sized environmentally friendly ships.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.10
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• pp.2230-2236
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• 2012

Currently, the AC-to-DC power conversion system using diode rectifiers is mainly used in large vessels. Also, to reduce the total harmonic distortion(THD) of current and voltage, this system requires an additional phase-shifting transformer which can be powered multi-pulses. In this case, due to the installation of the transformer, the spatial or economic loss occurs. This paper presents a novel active rectification scheme using silicon controlled rectifier(SCR) or insulated gate bipolar transistor(IGBT) devices on behalf of the diode rectifiers which are currently operating in large vessels such as LNG Carrier(LNGC). The proposed system can use the low voltage source and reduce current and voltage harmonics generated by nonlinear loads connected to the power distribution bus and save economic costs by removing the phase-shifting transformers which are used in conventional system. Computer simulations are performed under the electric propulsion system which is operating in current large vessel. The results are shown in support of the improvement of THD included in the current and voltage wave forms of propulsion motor.

• Journal of Ocean Engineering and Technology
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• v.16 no.6
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• pp.60-64
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• 2002

This paper describes the machining characteristics of the MoSi$_2$--based composites through the process of electric discharge drilling with various tubular electrodes. In addition to hardness characteristics, microstructures of Nb/MoSi$_2$laminate composites were evaluated from the variation of fabricating conditions, such as preparation temperature, applied pressure, and pressure holding time. MoSi$_2$-based composites have been developed in new materials for jet engines of supersonic-speed airplanes and gas turbines for high-temperature generators. These high performance engines may require new hard materials with high strength and high temperature-resistance. Also, with the exception of grinding, traditional machining methods are not applicable to these new materials. Electric discharge machining (EDM) is a thermal process that utilizes a spark discharge to melt a conductive material. The tool electrode is almost -unloaded, because there is n direct contact between the tool electrode and the work piece. By combining a non-conducting ceramic with more conducting ceramic, it was possible to raise the electrical conductivity. From experimental results, it was found that the lamination from Nb sheet and MoSi$_2$ powder was an excellent strategy to improve hardness characteristics of monolithic MoSi$_2$. However, interfacial reaction products, like (Nb, Mo)SiO$_2$and Nb$_2$Si$_3$formed at the interface of Nb/MoSi$_2$, and increased with fabricating temperature. MoSi$_2$composites, with which a hole drilling was not possible through the conventional machining process, enhanced the capacity of ED-drilling by adding MbSi$_2$, relative to that of SiC or ZrO$_2$reinforcements.

• Journal of Advanced Marine Engineering and Technology
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• v.41 no.3
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• pp.245-250
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• 2017

Worldwide environmental regulations have been enhanced for emission reduction of greenhouse gases and air pollutants; accordingly, some measures were prepared. Furthermore, the need for effective and reasonable energy-saving methods is growing in accordance with that for environmental pollution minimization. In the case of marine engineering, techniques for the development of eco-friendly vessels have been actively studied, including reduction of exhaust gas emissions, development of alternative fuel, and development of a new propulsion system. In this study, we presented the basic concepts and analyzed the speed, current, voltage, and output power characteristics of each operating mode, i.e., operating mode of battery, generator, and full power.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2021.10a
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• pp.59-61
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• 2021

The electric propulsion development is underway to minimize pollutants and greenhous gas emissions during the operation of ships / offshore installation vessels. The importance of the use and efficient management of batteries, which is an ESS system in ships / offshore installation vessels, is increasing. Generally, in ESS where battery is applied, cell balancing and life span are monitored in real time by BMS. Ships / offshore installation vessel are equipped with several ESS rooms, and ESS rooms with ESS systems of the same specification are being constructed due to the recent demand for electric propulsion development. In this paper, we propose an algorithm to additionally predict and diagnose battery pack and cell balancing failures by comparing BMS data for each rooms. The proposed algorithm compares the BMS data of each ESS Room according to the environmental change of the ship / offshore installation vessels, measures accurate status information, and reliably monitors it to prevent accidents in advance.

• Journal of the Society of Disaster Information
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• v.3 no.2
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• pp.79-93
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• 2007

With international urgence of terror situation, many methods of terror techniques and skills are appearing and more intense and threatening terror is braking out not only in the air(plane), but also in the sea(ship). Korea is surrounded by 3 sides of sea and is a proud maritime nation that should advance to foreign country through the sea because South Korea and North Korea are confronting. Korea depend on the maritime transportation, 99.7% of exporting, importing material resources. Therefore, acquisition of the marine safety has the great affect on national security and economical life. On the high tension of situation about threat and possibility of maritime terroism, the potential ways of the improvement policy for counter-tactics against big maritime terror are the following. First, we should construct clear and well-organized network for accurate information about maritime terrorism Second, we should have the information of all domestic, foreign passenger's ships Third, national important facilities such as atomic energy plant, thermo-electric power plant, shipyard need policies to manage all emergency situation Fourth, government authorities should improve tactic abilitities by competing with support and budget inside of nation as well as outside of nation. To develop big maritime terror of our country, we will have to hold cooperative training & tactics contest of big maritime terror by cooperating educational industry organization with similar institute, improve the ability of members of big terror and acquire tactics information by excavating and exchanging a new technique through tactics seminar and public hearing.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.3
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• pp.309-316
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• 2011

This paper deals with the experimental study of the vibration suppression of the smart structures. First, a new high-speed active control system is presented using the DSP320C6713 microprocessor. A peripheral system developed is composed of a data acquisition system, A/D and D/A converters, piezoelectric (PZT) actuator/sensors, and drivers using PA 95 for fast data processing. Next, the processing time of the peripheral device is tested and the corresponding test results are provided. Since fast data processing is very important in the active vibration control of the structures, achieving the fast loop times of the control system is focused. The control algorithm using PPF in addition to FIR filter is implemented. Finally, numerous experiments were carried out on the aluminum plate to validate the superior performance of the vibration control system at different control loop times.

• Journal of the Korea Safety Management & Science
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• v.12 no.1
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• pp.11-18
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• 2010

In the steel industry, steel is manufactured and processed to produce a variety of steel products. The industry provides fundamental materials to the whole range of industries including car, ship, electric appliance and construction industries, so that it is very important as an infrastructure industry. The steel manufacture process involves aerial work, many danger factors caused by the treatment with hazardous gases including BFG and COG and by high pressure gases including $H_2$, $O_2$, $N_2$ and LPG. It requires the management over the large area because many workers work in a plant. The potential dangers in the steel plant were identified and the effect of the danger assessment was verified through the analysis of the danger assessment for the steel plant. The allowed degree of danger was lowered after the improvement through the danger assessment in the plant where the case studies were conducted, which indicates that the danger assessment is highly effective.

• Journal of Power Electronics
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• v.13 no.1
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• pp.70-76
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• 2013

For high power high step-down dc-dc conversion applications, conventional three-level dc-dc converters are subject to extreme duty cycles or increased volume and cost due to the use of transformers. In this paper, a transformerless three-level dc-dc buck converter with a high step-down conversion ratio is proposed. The converter comprises two asymmetrical half bridges, which are of the neutral point clamped structures. Therefore, the output pulse voltage of the converter can be obtained in terms of the voltage difference between the two half bridges. In order to realize harmonious switching of the converter, a modulation strategy with capacitor voltages self balance is presented. According to the deduced output dc voltage function, transformerless operation without extreme duty cycles can be implemented. Experimental results from a 1kW prototype verify the validity of the proposed converter. It is suitable for ship electric power distribution systems.