• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.4
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• pp.301-307
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• 2013

MRU(motor reduction unit) for KTX is a assembled complex structure that is equipped with a lot of parts at the express train KTX and that is the core power source operating variable speeds. This study is recorded the dynamic characteristics analysis results tested by EMA which is done through the parts and assembly test, transient analysis and stoped train test in order to design the online monitoring system for KTX MRU. And the mode shapes result from critical vibration frequency explain the relation with variable speeds of express train over 250 km/hr. Also these variable speeds make variable operational frequencies at pinion, axle gear mesh frequency and normal bearing fault frequencies. As the specified speed can make resonance with natural frequencies of the MRU, for the train operating stability, this study also presents the MRU's critical speeds calculated by the each train speed.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.12
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• pp.68-75
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• 2000

This paper presents the construction of an ultra-precision machining system and machining experiments using the developed system. The system is composed of air bearing system, granite bed, air pad, and linear feeding mechanism. The cutting conditions have great effect on the surface quality in ultra-precision machining. the ultra-precision machining is mainly processed by several ${\mu}{\textrm}{m}$ depth of cut and feed rate. For this, tools with sharper cutting edge and less tool wear are needed. To satisfy these requirement, diamond is generally used as a tool material for ultra-precision machining. In order to evaluate the cutting characteristics of the PCD and MCD tools on the aluminum alloy, the machining experiments performed using the developed system.

• 한국신재생에너지학회:학술대회논문집
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• 2006.11a
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• pp.515-518
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• 2006

This paper presents the friction and wear characteristics of contact type sealing unit for a water turbine of a small hydro-power generation, which Is to stop a leakage of a circulating water from a outside of an impeller to an inside of a rolling bearing. The surface wear strongly affect to the seal life of a mechanical face seal. In this study, the hardness of a stainless steel in which is a heat-treated is 892.8 in Vickers hardness and the hardness of silicone carbide of SiC is 714.1 in Vickers hardness. The surface hardness of a heat-treated stainless steel is 25% high compared with that of a ceramic material of SiC. The contact modes of rubbing surfaces aye a dry friction a water film friction and a mixed friction that is contaminated by a dust, silt and moistures, etc. These two factors of a contact rubbing modes and a material property are very important parameters on the tribological performance such as a friction and wear between a seal ring and a seal seat. The experimental result shows that the surface hardness of a seal material is very important on the friction coefficient and a wear volume. Thus, the results recommend higher hardness of a seal material, which may reduce a friction loss and increase a wear life of primary seal components

• Journal of Korea Foundry Society
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• v.22 no.4
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• pp.174-183
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• 2002

Twin-roll process is a relatively new continuous casting process which can produce high-quality strip products directly, and solidification rate can reach $10^3$ to $10^4$ K/s, leading to fine and uniform microstructures with enhanced mechanical properties. The strip casting condition for producing fine Al-Sn alloy strip was obtained experimentally, and defects appearing on the strip was examined. Crack formation and surface quality of the strip was found to depend mainly on process parameters such as melt temperature, roller gap and rolling speed. Sn structure of network type was observed in Al-20Sn and Al-40Sn alloy strips, and cell spacing of Al-40Sn alloy was smaller than that of Al-20Sn. Banding strength of the heat treated specimens increased with increasing of soaking time and temperature, and bonding strength of Al-20Sn alloy was more superior than that of Al-40Sn alloy. However wear resistance of Al-40Sn alloy contained large amount of soft Sn which possess good anti-friction characteristics was superior than that of Al-20Sn alloy.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.595-598
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• 2010

Many economical and efficient methods such as sand drain method(SD), plastic board drain(PBD), sand compaction pile, vacuum consolidation method, etc., have been used for soft grounds. The case of sand compaction pile has an effect on accelerating consolidation and increasing bearing capacity by penetration at regular intervals under soft grounds for reducing the drainage path. But, this method has caused not only the nature damage by extracting the sands indiscreetly but also the economical problem for importing the sands because it needs so much sand to make the sand compaction pile. Thus, this study choosed the bottom ash which has similar engineering characteristics with sand. It was performed that clogging test and large direct shear test changing the bottom ash replacement ratio in soft ground for studying strength characteristics of soft ground using bottom ash compaction pile. As a result of the test, the internal friction angle was largely increased and the cohesion was decreased as the replacement ratio increased.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.1100-1105
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• 2008

In most drilled shafts construction sites, it is common, depending on the site condition, to use either water or slurry as fluids for maintaining stability of the holes, however, there are yet no design manuals by hole stability fluids. In this paper, in order to evaluate load transfer characteristics of the drilled shafts by hole stability fluids, two test piles are constructed over the soft ground of the lower Busan Bay based on the Bi-directional Pile Load Test. The test results showed that no ultimate states has found under the condition of applied loads with fresh water and slurry as hole fluids for drilled shafts. Then, the load transfer behavior were estimated with the data measured in fields and the effect of hole stability fluids were compared. All these results are presented in the paper.

• Aerospace Engineering and Technology
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• v.8 no.1
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• pp.98-107
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• 2009

Vibration analysis of a turbo compressor test rig was carried out in order to investigate the vibrational characteristics of the compressor facility in KARI before conducting the compressor performance test of 5MW-class gas turbine engine for generation. The overall compressor test facility consists largely of inlet and exit ducts, a test section and a driving part. Vibration was measured with accelerometers at the test section and the driving part, especially at a main housing, a collector, a bearing carrier, a torquemeter, a gearbox, and an electric motor. Gap sensors are also installed to measure the rotordynamic characteristics of compressor shaft.

• Journal of the Korean GEO-environmental Society
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• v.3 no.2
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• pp.15-21
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• 2002

Because of the environmental problem during the pile driving, the use of low noise-vibration auger-drilled pilling is increasing to solve noise and vibration problem in pilling. In Korea, SIP (Soil-Cement Injected Precast Pile) method is mainly used as auger-drilled pilling. But, a proper bearing capacity evaluation formula has not been suggested, yet. To improve and supplement this situation, direct shear tests between SIP pile skin interface and soil were executed under various conditions. Through the analysis of test results, skin resistance characteristics of SIP were investigated thoroughly. Also, the maximum unit skin resistance capacity evaluation formulae on SM, SC soil was suggested.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2010.05a
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• pp.153-157
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• 2010

As the recent economic downturn continues to undermine the profits of construction industry in Korea, it has become ever more pressing to improve productivity of the industry. Since construction site management manpower staffing plan has close bearing on the productivity of construction projects, it is essential to estimate and mobilize adequate number of resources as per conditions and characteristics of each construction site. However, there are no reference approaches in practice to provide baseline for site management manpower staffing plan or estimation of manpower requirement. Therefore, this study aims to examine factors affecting productivity that warrants first and foremost consideration in development of site management manpower staffing plan during the initial phase of building construction project by conducting survey on industry stakehoders with hands-on responsibilities in construction sites and analyzing their responses. Conclusions herein will provide basic inputs for subsequent studies on development of site management manpower staffing plan as per project characteristics.

• Aerospace Engineering and Technology
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• v.3 no.2
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• pp.25-33
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• 2004

In this paper, we briefly introduce the micro-vibration test bench of KARI and the test and analysis method of RWA(Reaction Wheel Assembly) micro-vibration. The micro-vibration of RWA is measured on a KISTLER dynamic plate which can measure the time signal of 6 DOF simultaneously up to 400Hz. Measured data are extensively evaluated with respect to the wheel spin rate to identify the complicate wheel dynamic characteristics, and the static/dynamic unbalances are estimated from the extracted first harmonic component as a part of evaluation process. The estimated static and dynamic unbalances. 0.79gcm and 17.4gcm² respectively. The structural resonance mode and two rocking modes observed as a results of its frequency analysis. Several higher order harmonic components observed, which come from its rotor shape as well as the wheel bearing characteristics.