• Journal of Applied Reliability
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• v.9 no.2
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• pp.131-148
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• 2009

An organic light emitting diode (OLED), also light emitting polymer (LEP) and organic electro luminescence (OEL), is any light emitting diode (LED) whose emissive electroluminescent layer is composed of a film of organic compounds. The layer usually contains a polymer substance that allows suitable organic compounds to be deposited. They are deposited in rows and columns onto a flat carrier by a simple "printing" process. The resulting matrix of pixels can emit light of different colors. Such systems can be used in television screens, computer displays, small, portable system screens such as cell phones and PDAs, advertising, information and indication. OLEDs can also be used in light sources for general space illumination, and large-area light-emitting elements. In this paper, we develop the general guide line of the accelerated life test for assuring B10 life of AMOLED(Active Matrix Organic Light Emitting Diode) and PMOLED(Passive Matrix Organic Light Emitting Diode) which are widely used for display monitor less than 115 mm.

• Journal of the Society of Naval Architects of Korea
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• v.51 no.4
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• pp.300-310
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• 2014

This paper presents a mooring design procedure of a floating offshore wind turbine. The environment data of south offshore area of Jeju collected from Korea Hydrographic and Oceanographic Administration(KHOA) are used for hydrodynamic analyses as environmental conditions. We considered a semi-submersible type floating wind turbine based on Offshore Code Comparison Collaborative Continuation(OC4) DeepCWind platform and National Renewable Energy Laboratory(NREL) 5 MW class wind turbine. Catenary mooring with studless chain is chosen as the mooring system. Important design decisions such as how large the nomial sizes are, how long the mooring lines are, how far the anchor points are located, are demonstrated in detail. Considering ultimate limit state and fatigue limit state based on 100-year return period and 50-year design life, respectively, longterm predictions of breaking strength and fatigue are proposed.

• Journal of the Korean Data and Information Science Society
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• v.25 no.4
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• pp.893-901
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• 2014

A certain number of products are sold each month and some of them are returned for repair. In this study both return rate and cumulative return rate are shown on the graph to show the general trend of how many products are returned as time goes by. Next this type of summary data can be considered as a conglomeration of both left and right censored data. So reliability analysis is attempted for this type of summary data. Lastly, left censored data can be traced to find the exact time period during which the product has been claimed. In that case the left censored data can be taken as failure data. So similar type of reliability analysis is attempted for the resulting right censored data.

• Journal of Hydrogen and New Energy
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• v.14 no.1
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• pp.61-68
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• 2003

This paper presents the methodology to analyze flow duration characteristics and performance prediction technique for small hydro power(SHP) Plants and its application. The flow duration curve can be decided by using monthly rainfall data at the most of the SHP sites with no useful hydrological data. It was proved that the monthly rainfall data can be characterized by using the cumulative density function of Weibull distribution and Thiessen method were adopted to decide flow duration curve at SHP plants. And, the performance prediction technique has been studied and development. One SHP plant was selected and performance characteristics was analyzed by using the developed technique, Primary design specfications such as design flowrate, plant capacity, operational rate and annual electricity production for the SHP plant were estimated, It was found that the methodology developed in this study can be a useful tool to predict the performance of SHP plants and candidate sites in Korea.

• Earthquakes and Structures
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• v.18 no.3
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• pp.285-296
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• 2020

Dams are important structures for management of water supply for irrigation or drinking, flood control, and electricity generation. In seismic regions, the structural safety of concrete gravity dams is important due to the high potential of life and economic loss if they fail. Therefore, the seismic analysis of existing dams in seismically active regions is crucial for predicting responses of dams to ground motions. In this paper, earthquake response of concrete gravity dams is investigated using the finite element (FE) method. The FE model accounts for dam-water-foundation rock interaction by considering compressible water, flexible foundation effects, and absorptive reservoir bottom materials. Several uncertainties regarding structural attributes of the dam and external actions are considered to obtain the fragility curves of the dam-water-foundation rock system. The structural uncertainties are sampled using the Latin Hypercube Sampling method. The Pine Flat Dam in the Central Valley of Fresno County, California, is selected to demonstrate the methodology for several limit states. The fragility curves for base sliding, and excessive deformation limit states are obtained by performing non-linear time history analyses. Tensile cracking including the complex state of stress that occurs in dams was also considered. Normal, Log-Normal and Weibull distribution types are considered as possible fits for fragility curves. It was found that the effect of the minimum principal stress on tensile strength is insignificant. It is also found that the probability of failure of tensile cracking is higher than that for base sliding of the dam. Furthermore, the loss of reservoir control is unlikely for a moderate earthquake.

• The Korean Journal of Applied Statistics
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• v.23 no.5
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• pp.943-953
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• 2010

From a mixture distribution of the score random variable for credit evaluation, there are many methods of estimating optimal thresholds. Most the research news is based on the assumption of normal distributions. In this paper, we extend non-normal distributions such as Weibull, Logistic and Gamma distributions to estimate an optimal threshold by using a hypotheses test method and other methods maximizing the total accuracy and the true rate. The type I and II errors are obtained and compared with their sums. Finally we discuss their e ciency and derive conclusions for non-normal distributions.

• Proceedings of the KIEE Conference
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• 1996.07c
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• pp.1526-1528
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• 1996

The dielectric reliability of a polycrystalline and a multilayered $BaTiO_3$ thin films was evaluated using a time-zero dielectric breakdown (TZDB) and a time-dependent dielectric breakdown (TDDB) techniques. The $BaTiO_3$ thin films were prepared by rf-magnetron sputtering technique on ITO-coated glass substrates. In case of the multilayered $BaTiO_3$ thin film, the dielectric breakdown histogram, which was obtained from the TZDB measurements, showed a typical Weibull distribution. While in case of polycrystalIine $BaTiO_3$ thin film, a randomly distributed dielectric breakdown histogram was observed. The TDDB results of the multilayered $BaTiO_3$ thin film guaranteed about $10^5$ hours-operation under the stress field of 1 MV/cm.

• Journal of Electrical Engineering and Technology
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• v.3 no.4
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• pp.571-575
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• 2008

Stator insulation quality assessment for high voltage motors is a major issue for the reliable maintenance of industrial and power plants. To assess the condition of stator insulation, nondestructive tests were performed on the sixty coil groups of twelve motors. After completing the nondestructive tests, the AC voltage applied to the stator winding was gradually increased until insulation failure in order to obtain the breakdown voltage. The stator winding of each motor was classified into five coil groups; one group with healthy insulation and four groups with four different types of artificial defects. To analyze the breakdown voltage statistically, Weibull distribution was employed for the tests on the fifty coil groups of ten motors. The 50th percentile values of the measured breakdown voltages based on the statistical data of the five coil groups of ten motors were 26.1kV, 25.0kV, 24.4kV, 26.7kV and 30.5kV, respectively. Almost all of the failures were located in the line-end coil at the exit of the core slot. The breakdown voltages and the types of defects showed strong relation to the stator insulation tests such as in the case of dissipation factor and ac current. It is shown that the condition of the motor insulation can be determined from the relationship between the probability of failure and the type of defect.

• Journal of Mechanical Science and Technology
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• v.15 no.1
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• pp.44-51
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• 2001

One of the recent issues in design of the spot-welded structure such as the automobile body is to develop an economical prediction method of the fatigue design criterion without additional fatigue test. In this paper, as one of basic investigation for developing such methods, fracture mechanical approach was investigated. First, the Model I, Mode II and Mode III, stress intensity factors were analyzed. Second, strain energy density factor (S) synthetically including them was calculated. And finally, in order to decide the systematic fatigue design criterion by using this strain energy density factor, fatigue data of the ΔP-N(sub)f obtained on the various in-plane bending type spot-welded lap joints were systematically re-arranged in the ΔS-N(sub)f relation. And its utility and reliability were verified by the theory of Weibull probability distribution function. The reliability of the proposed fatigue life prediction value at 10(sup)7 cycles by the strain energy density factor was estimated by 85%. Therefore, it is possible to decide the fatigue design criterion of spot-welded lap joint instead of the ΔP-N(sub)f relation.

• Journal of Electrical Engineering and Technology
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• v.9 no.1
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• pp.60-70
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• 2014

This paper discusses the impacts of large scale grid-connected wind farm equipped with permanent magnet synchronous generator (PMSG) on power system small signal stability (SSS) incorporating wind generation uncertainty and volatility. Firstly, a practical simplified PMSG model with rotor-flux-oriented control strategy applied is derived. In modeling PMSG generator side converter, the generator-voltage-oriented control strategy is utilized to implement the decoupled control of active and reactive power output. In modeling PMSG grid side converter, the grid-voltage-oriented control strategy is applied to realize the control of DC link voltage and the reactive power regulation. Based on the Weibull distribution of wind speed, the Monte Carlo simulation technique based is carried out on the IEEE 16-generator-68-bus test system as benchmark to study the impacts of wind generation uncertainty and volatility on small signal stability. Finally, some preliminary conclusions and comments are given.