• Proceedings of the KIEE Conference
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• 1999.07d
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• pp.1529-1531
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• 1999

The main functions of AC railroad vehicles arresters is to protect the main transformer from lightening impulse or switching impulse surge, then the MOV(metal oxide varistor) elements rated of 10kA is applied. The residual voltage and surge energy absorption are important parameters in designing arrester, these must be carefully decided with considering protecting level of impulse environment of system. The purpose of this study is to discuss the residual voltages and the energy absorption capability by impulse currents on MOV elements for railroad vehicles, and to introduce design factors which act as optimal protecting condition against impulse currents.

• Steel and Composite Structures
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• v.36 no.6
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• pp.657-669
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• 2020

This study investigates the fire resistance characteristics of reactive powder concrete according to changes in the cement content per unit area, mixing ratio of metakaolin (MK), and content of polypropylene fiber. A fire test was conducted, and the resulting residual strength characteristics were investigated through flexural and compressive strength measurements, as well as condition rating classification based on visual evaluation. MK effectively reduced the initial high content of calcium hydroxide, thereby reducing the water vapor pressure generated during pyrolysis and slowing spalling. Furthermore, the pore structure and loose tissue were effective for relieving the water vapor pressure in the event of a fire.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.6
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• pp.1363-1370
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• 1995

A nonlinear dynamic modeling method for simply supported structures undergoing large overall motion is suggested. The modeling method employs Rayleigh-Ritz mode technique and Von Karman nonlinear strain measures. Numerical study shows that the suggested modeling method provides qualitatively different results from those of the Classical Linear Cartesian modeling method. Especially, natural frequency variations and residual deformation due to membrane strain effects are observed in the numerical results obtained by the suggested modeling method.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.6
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• pp.1402-1410
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• 1995

An influence coefficient method with an optimal correction balancing algorithm is developed for balancing a high-speed flexible rotor system. Conventional flexible balancing algorithms such as least square and weighted least square algorithms may not satisfy allowable residual vibration levels in certain speed ranges, while the optimal correction balancing method can be more effective in controlling vibration levels in a target speed. Related analyses were reviewed and applied to a test rig to show the effectiveness of the optimal correction balancing method.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.4
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• pp.59-67
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• 2006

Recently, application of friction welded SUH35/SUH3 is increasing in the manufacturing process of automotive engine valves For securing its reliability and a reasonable strength evaluation method, it is necessary to assess stress singularity under the residual stress condition on the friction welded interface between dissimilar materials. In this paper, strength evaluation method of friction welded materials was investigated by boundary element method and static tensile testing. An advanced method of quantitative strength evaluation for SUH35/SUH3 friction welded material is to be suggested by establishing fracture criterion by using stress singularity factors.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.2 s.173
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• pp.378-385
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• 2000

Fracture resistance (J-R) curves, which are used for elastic-plastic fracture mechanics analyses, decreased under tension-compression loading condition. This phenomenon was proved by several former researches, but the causes have not been clear yet. The objective of this paper is to investigate the cause of this phenomenon. On the basis of fracture resistance curve test results, strain hardening hypothesis, stress redistribution hypothesis and crack opening hypothesis were built. In this study, hardness tests, Automated Ball Indentation(ABI) tests, theoretical stress field analyses, and crack opening analyses were performed to prove the hypotheses. From this study, strain-hardening of material, generation of tensile residual stress at crack tip, and crack opening effects are proved as the causes of the decrease hypothesis.

• Proceedings of the KWS Conference
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• v.43
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• pp.61-63
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• 2004

Recently many research works are going on in the field of application of Laser-Arc hybrid welding for superstructures such as shipstructures. However, the study on heat distribution and welding residual stress of hybrid weld by numerical simulation loaves much to be desired. Therefore in this study an optimized welding condition and numerical simulation for hybrid welding by using Previous numerical analysis which was used to calculate the kent source for hybrid welding has been analyzed.

• Journal of Chest Surgery
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• v.20 no.3
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• pp.603-609
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• 1987

The clinical, investigative, and surgical experiences were reviewed in four patients with congenitally corrected transposition of the great arteries who presented to the National Medical Center between August 1983 and August 1985. This condition is very rare congenital anomaly defined as the combination of atrioventricular discordance and transposition of the great arteries. Examples of primitive [single] ventricle inverted [that is, left sided in situs solitus] with outflow chamber were excluded in this paper. According to the sequential arrangement of the hearts there were two cases of [S,L,L] and two cases of [I,D,D]. The surgical approach should be focused on minimizing the risk of heart block and increasing the degree of relief of pulmonary outflow tract obstruction [POTO]. We experienced complete heart block in two cases of [S,L,L] and significant residual POTO in one case of [S,L,L] and one case of [I,D,D] postoperatively. There were one hospital mortality caused by complete heart block and residual POTO and two delayed mortalities caused by congestive heart failure and sepsis respectively.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.8
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• pp.157-163
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• 2001

This paper presents the new linear notion device so called \"inch-werm\" which gets large displacement by incrementally summing small displacements of PZT actuators. Dynamic stiffness of inch-worm is generally low compared to its driving condition due to the requirement of inch-worm like small size and light weight. This low stiffness may degenerate the positional precision of inch-worm. An inch-worm is realized using three PZT actuators, a monolithic moving device and a guide way frame. Finite element method and experimental approach are used to analyse the static and dynamic motion of the designed inch-worm. Command reference input is shaped to reduce the residual vibration of inch-worm. The practical feasibility of inch-worm is also examined by running tests.ing tests.

• Proceedings of the Korea Concrete Institute Conference
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• 1994.10a
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• pp.285-290
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• 1994

The influence of elevated temperatures on the mechanical properties of concrete is important for fire-resistance studies and also for understanding the behavior of containment vessel, such as nuclear reactor pressure vessels, during service and ultimate condition. The present study is to clarify the damage/deterioration of concrete structures that are subjected to high temperature exposure. To this end, comprehensive experiments are conducted. The major test variables are the peak temperatures, rate of temperature increase, and sustained duration at peak temperature. The results include weight loss residual compressive strength and stress-strain curve. From those results, residua compressive strength formula and stress-strain relationship are proposed.