• Journal of Electrical Engineering and Technology
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• v.8 no.3
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• pp.421-427
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• 2013

The dependence between wind speeds in multiple wind sites has a considerable impact on the reliability of power systems containing wind energy. This paper presents a new method to generate dependent wind speed time series (WSTS) based on copulas theory. The basic feature of the method lies in separating multivariate WSTS into dependence structure and univariate time series. The dependence structure is modeled through the use of copulas, which, unlike the cross-correlation matrix, give a complete description of the joint distribution. An autoregressive moving average (ARMA) model is applied to represent univariate time series of wind speed. The proposed model is illustrated using wind data from two sites in Canada. The IEEE Reliability Test System (IEEE-RTS) is used to examine the proposed model and the impact of wind speed dependence between different wind regimes on the generation system reliability. The results confirm that the wind speed dependence has a negative effect on the generation system reliability.

• Journal of Applied Reliability
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• v.17 no.4
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• pp.316-324
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• 2017

Purpose: The purpose of this study is to determine the replacement cycle applied age replacement policy by reliability analysis based on railway vehicle contactor's failure history data. Method: We performed reliability analysis based on railway vehicle contactor's failure history data. We found a suitable distribution by goodness of fit test and predicted the reliability through estimation of scale & shape parameter. Considering cost information we determined the replacement cycle that minimize the opportunity cost. Result: Suitable distribution was the Weibull and scale parameter & shape parameter are estimated by reliability analysis. The replacement cycle was predicted and MTTF, $B_6$ percentile life were suggested additionally. Conclusion: We confirmed that failure rate type of railway vehicle contactor is degradation model having a time dependent characteristic and examined the replacement cycle in our country's operating environment. We expect that this study result contribute to railway operation agency for maintenance policy decision.

• International Journal of Reliability and Applications
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• v.12 no.2
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• pp.117-122
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• 2011

In this paper, we suggest the optimal replacement policy following the expiration of repair warranty when the cost of minimal repair depends on the age of system. To do so, we first explain the replacement model under repair warranty. And then the optimal replacement policy following the expiration of repair warranty is discussed from the user's point of view. The criterion used to determine the optimality of the replacement model is the expected cost rate per unit time, which is obtained from the expected cycle length and the expected total cost for our replacement model. The numerical examples are given for illustrative purpose.

• Journal of the Semiconductor & Display Technology
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• v.20 no.4
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• pp.141-145
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• 2021

The brightness of the Organic Light Emitting Diode (OLED) display is controlled by thin-film transistors (TFTs). Regardless of the materials and the structures of TFTs, an OLED suffers from the instable threshold voltage (V_th) of a TFT during operation. When designing an OLED pixel with circuit simulation tool such as SPICE, a designer needs to take V_th shift into account to improve the reliability of the circuit and various compensation methods have been proposed. In this paper, the effect of the compensation circuits from two typical OLED pixel circuits proposed in the literature are studied by the transient simulation with a SPICE tool in which the stretched-exponential time dependent V_th shift function is implemented. The simulation results show that the compensation circuits improve the reliability at the beginning of each frame, but V_th shifts from all TFTs in a pixel need to be considered to improve long-time reliability.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.5
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• pp.539-547
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• 1985

The low-cycle fatigue crack growth behavior of SUS 304 Stainless steel was investigated at 650.deg. C by the nonlinear fracture mechanics. Crack Propagation can be separated in to cycle-dependent and time-dependent, the former is correlated with .DELTA. $J_{f}$ , J-intergral range and the latter is correlated with J', modified J integral. Transition from cycle-dependent to time-dependent crack growth was successfully predicted using the .betha. hypothesis, which was proposed by the authors on the basis of an analysis on the interaction of elastic and creep strain. To investigate the reliability of .betha.-hypothesis, experimenting by the change of stress-level, stress rate and frequency, following conclusions were obtained. (1) High temperature fatigue crack propagation was separated into cycle-dependent and time-dependent. (2) Transition of crack propagation was predicted by .DELTA. $J_{c}$/.DELTA.$_{f}$ or .betha. (3) Lower limit in cycle-dependent crack propagation was obtained..

• Journal of the Korean Institute of Telematics and Electronics D
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• v.34D no.6
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• pp.43-49
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• 1997

Tungsten poycide has studied gate oxide reliability and dielectric strength charactristics as the composition of gate electrode which applied submicron on CMOS and MOS device for optimizing gate electrode resistivity. The gate oxide reliability has been tested using the TDDB(time dependent dielectric breakdwon) and SCTDDB (stepped current TDDB) and corelation between polysilicon and WSi$_{2}$ layer. iN the case of high intrinsic reliability and good breakdown chracteristics on polysilicon, confirmed that tungsten polycide layer is a better reliabilify properities than polysilicon layer. Also, hole trap is detected on the polysilicon structure meanwhile electron trap is detected on polycide structure. In the case of electron trap, the WSi$_{2}$ layer is larger interface trap genration than polysilicon on large POCL$_{3}$ doping time and high POCL$_{3}$ doping temperature condition. WSi$_{2}$ layer's leakage current is less than 1 order and dielectric strength is a larger than 2MV/cm.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.27 no.2
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• pp.93-101
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• 2004

This paper is intended to assess a dynamic system reliability. Bayesian networks, however, have difficulties in their application for assessing the system reliability especially when the system consists of dependent components and the probability of failure of each component varies over time. Hence, we suggest a method for resolving the difficulties by considering a hoist system composed of two wires. Firstly, we explain the method of calculating the failure probability of the system components. Secondly, we show how to calculate the failure probability of the system for two cases that failure probability of each wire is constant and varying in time, respectively. finally, based on the calculated failure probability of the system, we infer the probability that two interesting events occur.

• Computers and Concrete
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• v.20 no.5
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• pp.511-519
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• 2017

The reliability of reinforced concrete structures is frequently compromised by the deterioration caused by reinforcement corrosion. Evaluating the effect caused by reinforcement corrosion on structural behaviour of corrosion damaged concrete structures is essential for effective and reliable infrastructure management. In lifecycle management of corrosion affected reinforced concrete structures, it is difficult to correctly assess the lifecycle performance due to the uncertainties associated with structural resistance deterioration. This paper presents a stochastic deterioration modelling approach to evaluate the performance deterioration of corroded concrete structures during their service life. The flexural strength deterioration is analytically predicted on the basis of bond strength evolution caused by reinforcement corrosion, which is examined by the experimental and field data available. An assessment criterion is defined to evaluate the flexural strength deterioration for the time-dependent reliability analysis. The results from the worked examples show that the proposed approach is capable of evaluating the structural reliability of corrosion damaged concrete structures.

• The Journal of Engineering Research
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• v.6 no.2
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• pp.33-38
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• 2004

To investigate the reliability of the MTJs on the roughness of insulating tunnel barrier, we prepared two MTJs with the different uniformity of barrier thickness. Namely, the one has uniform insulating barrier thickness; the other has non-uniform insulating barrier thickness as compared to different thing. As to depositing amorphous layer CoZrNb under the pinning layer IrMn, we achieved MTJ with uniform barrier thickness. Toinvestigate the reliability of the MTJs dependent on the bottom electrode, time-dependent dielectric breakdown (TDDB) measurements were carried out under constant voltage stress. The Weibull fit of out data shows clearly that $t_{BD}$ scales with the thickness uniformity of MTJs tunnel barrier. Assuming a linear dependence of log($t_{BD}$) on stress voltages, we obtained the lifetime of $10^4$years at a operating voltage of 0.4 V at MTJs comprising CoNbZr layers. This study shows that the reliabilityof new MTJs structure was improved due to the ultra smooth barrier, because the surface roughness of the bottom electrode influenced the uniformity of tunnel barrier.

• Journal of Applied Reliability
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• v.14 no.3
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• pp.203-207
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• 2014

Electrodeless lamp is famous for its long life. But its reliability is dependent not only on electrodes but also on materials and structures. To evaluate end product's reliability, we studied high temperature durability by $60^{\circ}C$, $75^{\circ}C$ and $90^{\circ}C$ temperature tests, and predicted failure times by an exponential model through regression analysis. However, the test showed that temperature does not affect degradation of electrodeless lamps. Their luminous outputs degrade during the early time of the test (till 250 hours) and then converge to a saturation points. Also, '410nm ~ 530nm' spectrum degrades more than other spectra.