• Journal of the Society of Naval Architects of Korea
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• v.46 no.2
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• pp.105-113
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• 2009

A theoretical study on the pressure fluctuation induced by a propeller was carried out in this study. The main objective of this study is to analyze the source mechanism of the pressure fluctuation induced by propeller sheet cavitation. To analyze the pressure fluctuation induced by propeller sheet cavitation, modern acoustic theory was applied. Governing equation of pressure fluctuation induced by sheet cavitation was derived using Ffowcs Williams proposed time domain acoustic approaches. Several factors affecting pressure fluctuation were analyzed based on the derived governing equation. Pressure fluctuation result was represented by combined results of the far field term and near field term. Finally, the physical mechanism of pressure fluctuation at the blade rate frequency was analyzed using numerically generated cavitation volume variation.

• International Journal of Fluid Machinery and Systems
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• v.3 no.4
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• pp.360-368
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• 2010

This paper describes the flow field and the blade pressure distribution of a horizontal axis wind turbine in various yawed flow conditions. These measurements were carried out with 2.4m-diameter rotor with pressure sensors and a 2-dimensional laser Doppler velocimeter for each azimuth angle in a wind tunnel. The results show that aerodynamic forces of the blade based on the pressure measurements change according to the local angle of attack during rotation. Therefore the wake of the yawed rotor becomes asymmetric for the rotor axis. Furthermore, the relations between aerodynamic forces and azimuth angles change according to tip speed ratio. By the experimental analysis, the flow field and the aerodynamic forces for each azimuth angle in yawed flow condition were clarified.

• Journal of Mechanical Science and Technology
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• v.14 no.8
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• pp.851-860
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• 2000

Temperature field and cooling rate are important parameters to influence the properties of clad layer and the heat affected zone. In this paper the temperature field and cooling rate of laser cladding are studied by a two-dimensional time-dependent finite element model. Experiment has been carried out by Nd:YAG laser cladding with wire feeding. Research results indicate that at the beginning of cladding, the width and depth of melt pool increase with cladding time. The cooling rate is related to position, cladding time, cladding speed, and preheating temperature. The temperature near melt pool changes rapidly while the temperature far from melt pool changes slowly. With the increase of cladding time, cooling rate decreases. The further the distance from the melt pool, the lower the temperature and the slower the cooling rate. The faster the cladding speed, the faster the cooling rate. The higher the preheating temperature, the slower the cooling rate. The FEM results coincide well with the experiment results.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2005.05a
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• pp.235-239
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• 2005

This paper gives a field-test method and result of PQM(Power Quality Meter) and PQMS(Power Quality Management System). The field-test was carried out as our own method. So, the test method has several kinds of improvement in this paper because it is first time to try the field-test of the equipment. However, we expect that the test result of PQM & PQMS has been used as a reference data which makes a scheme of evaluating performance of the equipment that has been used or is developed.

• Journal of Mechanical Science and Technology
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• v.18 no.11
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• pp.2042-2048
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• 2004

A molecular dynamics study has been conducted on an external-force-field-induced isothermal crystallization process of amorphous structures as a new low-temperature athermal crystallization process. An external cyclic-force field with a dc bias is imposed on molecules selected randomly in an amorphous-phase of argon. Multiple peaks smoothed out in the radial distribution functions for amorphous states appear very clearly during the crystallization process that cannot be achieved otherwise. When the amorphous material is locally exposed to an external force field, crystallization starts and propagates from the interfacial region and crystallization growth rates can be estimated.

• Proceedings of the Korean Geotechical Society Conference
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• 2004.03b
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• pp.897-903
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• 2004

Waste lime used in this study is producted as a by-product in the manufacturing process of making $Na_2CO_3$ from local chemical factory in Incheon. Currently about 320 millon tons of waste lime are accumulated and annually 100,000 tons are producted. Reuse of waste lime mixed with soil for banking and backfill materia in civil works was analysed in this study. This study was Carried out to investigate the geotechnical and environmental characteristics on field application. Field investigations were conducted on the road construction site in Incheon. This study presents the results of the engineering characteristics in field test and the leaching characteristic of waste lime in laboratory column tests. Countermeasure for reduction of environmental effects was suggested from the test results.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2000.02a
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• pp.170-172
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• 2000

This paper deals with the characteristic analysis of the flux damper with respect to the load, and the stability of Ag/Bi-2223 tapes in a high-Tc superconducting (HTS) synchronous motor. To find out the magnetic field distribution in a detailed model of the actual motor, the experimentally measured currents of the armature and the field windings are used as input parameters. The simulation results show that the flux damper shields the time varying field up to 10%, reduces armature reactance during the motor operation and during load changes, improving the stable motor operation. And it was observed that the flux damper generates loss by means of leakage flux, but this is not significant and it doesn't degrade the performance of the TS synchronous motor.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 1996.06c
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• pp.999-1008
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• 1996

The development and improvement of the originally designed direct rice sowing machine were carried out for the specific purpose of saving labor and increasing the efficiency of field operations in rice cultivation in the northern part of Japan. the prototype super wide spreader has a unique mechanism which propels rice seeds by compressed air and spreads them from the pivoting nozzle while the machine is in motion. The effective field capacity of sowing operation is about 6 ha/h. This spreader can also handle granular chemicals such as fertilizers, herbicides, pesticides and insecticides.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.48 no.7
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• pp.832-838
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• 1999

Recently, there are growing concerns about power frequency electric and magnetic fields coming out from the high voltage transmission lines, because of the wide spread perception of their probable harmful effect on human body. In connection with this trend, this paper describes the electric and magnetic fields measurement result around 154 kV and 345 kV transmission lines, a comparison of measured EMF to calculated one and the correlations between transmission lines currents and measured magnetic fields. Daily maximum and minimum magnetic field quantities under the selected 154 kV and 345 kV transmission lines had been measured for 1 year of 1997 and the average value of magnetic field exposure under the lines were calculated and presented based on the measured data.

• Proceedings of the KIEE Conference
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• 1997.07e
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• pp.1871-1873
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• 1997

The conventional current transformers are often take faults and out of order that for detect to over current of electric power lines because electromagnetic interference. But, it is possible to implement protection relay of high reliability using optical magnetic field sensor which are immunity and small size. The optical magnetic field sensor is possible to rapidly detect to over current and recover when electric power line have fault. And it is not necessary to make with capacitance of electric power lines as optical magnetic field sensor is have linearity from 0 to about 20kA. In this study, we designed and constructed compensative feedback circuit in order to minimize of optical power intensity variation with environ- mental variations(temperature, drive current) of light source. And this system have highest optical advantages and reliability.