• The Transactions of the Korean Institute of Electrical Engineers A
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• v.55 no.11
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• pp.468-475
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• 2006

This paper reviews the energy characteristics of oil filled cables in transient state such as grounding fault and lightning surge. Artificial grounding fault test was firstly performed in 2003 for the analysis of arc voltage and breakdown energy according to the fault current. In this paper, energy of OF cable is variously analysed at joint box based on the actual test. Then more various conditions such as installation types, section lengths and CCPU(Cable Covering Protection Unit) connection types are applied for the simulation using EMTP when the single line to ground fault and direct lightning stroke are occurred on actual underground power cable systems and combined power cable systems, respectively. Finally, the energy by the length of crossbonded lead and grounding lead as well as fault lasting time is also calculated using EMTP simulation.

• Proceedings of the KIPE Conference
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• 2007.07a
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• pp.479-481
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• 2007

This paper presented a actual conditions on a false-tripping of ELB(Earth Leakage Breakers) and an assessment of the harmonics due to non-linear electronic equipment such as personal computers, rectifier, electric furnace and test equipments in plant installations. Actual conditions on a failure of ELB were surveyed and analyzed by making up a question to safety managers of plant installations. Also, power quality measurements such as harmonic currents, voltage and current waveform and current imbalance were made at various plant installations where nuisance tripping of ELB is often occurred. The results of this study can be used in making decisions regarding cause of ELB trip and operating and tripping characteristics test of ELB when subjected to distorted current waveform.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.28 no.4
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• pp.82-88
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• 2020

Currently, flight training is not only a technical instruction that teaches maneuvering operations, but has expertise equal to that of general disciplines. Therefore, flight instructors must have academic knowledge and flight skills. As flight instructors are the first teacher in flight training for students who have never experienced actual flight control, the behavior of flight instructors will affect the students' flight education. Therefore, the influence of flight instructors for students are quite large compared to other educational institutions. In this study, the factors of instructional behavior were determined, and the actual state of instructional behavior of flight instructors were confirmed through students' survey. Improvements were derived to solve the problems identified in the survey results. For the follow-up analysis, improvements were applied to the flight instructors for 8 months, and then re-question was conducted to the same students who responded to the first questionnaire to find out the difference in results before and after through a paired t-test.

• Journal of the Korea Safety Management & Science
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• v.15 no.1
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• pp.109-120
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• 2013

As information-oriented industry has been developed and electronic devices has come to be smaller, lighter, multifunctional, and high speed, the components used to the devices need to be much high density and should have find pattern due to high integration. Also, diverse reliability problems happen as user environment is getting harsher. For this reasons, establishing and securing products and components reliability comes to key factor in company's competitiveness. It makes accelerated test important to check product reliability in fast way. Out of fine pattern failure modes, failure of Electrochemical Migration(ECM) is kind of degradation of insulation resistance by electro-chemical reaction, which it comes to be accelerated by biased voltage in high temperature and high humidity environment. In this thesis, the accelerated life test for failure caused by ECM on fine pattern substrate, $20/20{\mu}m$ pattern width/space applied by Semi Additive Process, was performed, and through this test, the investigation of failure mechanism and the life-time prediction evaluation under actual user environment was implemented. The result of accelerated test has been compared and estimated with life distribution and life stress relatively by using Minitab software and its acceleration rate was also tested. Through estimated weibull distribution, B10 life has been estimated under 95% confidence level of failure data happened in each test conditions. And the life in actual usage environment has been predicted by using generalized Eyring model considering temperature and humidity by developing Arrhenius reaction rate theory, and acceleration factors by test conditions have been calculated.

• Journal of the Korea Institute of Building Construction
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• v.19 no.3
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• pp.229-237
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• 2019

This study examines the estimation of strength through a ultra-high strength concrete mock-up specimen using the rock compressive strength test hammer. According to the test result, the commonly used strength estimation formulae showed differences among them when the data of this test were applied. In additional, it show that these formulae underestimated the actual measurements further when the compressive strength was 30MPa or greater and deviated the distribution range of actual measurements in all strength ranges. The rock test hammer showed a higher correlation than type N Schmidt hammer regardless of the direction of hit for each type of W/B and the inclusion of coarse aggregate, and mortar showed a little higher correlation than concrete. As a result, it can be suggested that the coefficient of variation and the standard deviation of the mortar(2.26%/1.36) are lower than those of the concrete(4.06%/2.5), and the smaller the size of the coarse aggregate, the smaller the coefficient of variation and the more accurate the value.

• Korean Journal of Metals and Materials
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• v.50 no.12
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• pp.873-882
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• 2012

Dual Phase (DP) steel which has a soft ferrite phase and a hard martensite phase reveals both high strength and high ductility and has received increased attention for use in automotive applications. To conduct structural analysis to verify vehicle safety, highly credible experimental results are required. In this study, tensile tests were performed in a strain rate range from $10^{-4}/s$ to 300/s for Sink Roll-Less (SRL) hot-dip metal coated sheets. Collision properties were estimated through simulation by LS-DYNA using the stress-strain curve obtained from the tensile test. The simulation results were compared with the actual crash test results to confirm the credibility of the simulation. In addition, a tensile test and a crash test with 2% prestrain and a baking (PB) specimen were evaluated identically because automotive steel is used after forming and painting. The mechanical behaviors were improved with an increasing strain rate regardless of the PB treatment. Thus, plastic deformation with an appropriate strain rate is expected to result in better formability and crash characteristics than plastic deformation with a static strain rate. The ultimate tensile strength (UTS) and absorbed energy up to 10% strain were improved even though the total elongation decreased after PB treatment, The results of the experimental crash test and computer simulation were slightly different but generally, a similar propensity was seen.

• Proceedings of the Korean Nuclear Society Conference
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• 1999.10a
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• pp.189-189
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• 1999

• Tunnel and Underground Space
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• v.3 no.2
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• pp.109-117
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• 1993

The existence and exact location of cavity is very important for the stability of the large underground storage house or building. Numerical method such as finite element method and finite diference methods are widely used because of model's complexity. Preliminary tests such as calculation step test, mesh size test and model size test were tried. Upper shadow zone and lower shadow zone can be calculated from 50% amplitude level of measuring data. From these statistical methods, the calculatied position of cavity coincided nearly with actual position of model testing cavity.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.575-578
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• 1999

The main objective of this study was to examine structural behavior of reinforced concrete column and steel beam joint. composite specimens about 3/4 of the actual beam column connection assembly were tested by applying cyclic load through actuators. Test variables include face bearing plate(FBP), extended face bearing plate(E-FBP), VIR, U-bar and sub beam. There is not much differenced between specimens with sub beam and without sub beam. Test results also show that the joint strength of test specimen is close to the predicted strength by ASCE guideline.

• Journal of the Korean Data and Information Science Society
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• v.9 no.2
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• pp.263-273
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• 1998

In this paper, we consider some approximate testings for the reliability of the stress-strength model when the stress X and strength Y each depends linearly on some explanatory variables z and w, respectively. We construct a bootstrap procedure for testing for various values of the reliability and compare the power of the bootstrap test with the test based on Mann-Whitney type estimator by Park et.al.(1996) for small and moderate sample size.