• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.11a
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• pp.306-312
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• 1996

The performance of the failure detection algorithm may be greatly influenced by the model uncertainty. It is very important to design a robust failure detection system to the model uncertainty. In this paper, a design procedure to generate failure detection algorithm is proposed. The design procedure suggested is based on the concept of the‘threshold selector［1］’. The H$\infty$ control algorithm is used to derive a threshold selector which is robust to the model uncertainty, The threshold selector derived can be used to develop a failure detection system together with the weighted cumulative sum algorithm［3］. Computer simulation study showed that the failure detection system designed for an ISA(Integrated Servo Actuator) system by using the proposed method is robust to the model uncertainty.

• Nuclear Engineering and Technology
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• v.39 no.5
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• pp.591-602
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• 2007

The results of Reactivity-Initiated Accidents (RIA) experiments have been analysed and the main variables affecting the fuel failure propensity identified. Fuel burn-up aggravates the mechanical loading of the cladding, while corrosion, or better the hydrogen absorbed in the cladding as a consequence of corrosion, may under some conditions make the cladding brittle and more susceptible to failure. Experiments point out that corrosion impairs the fuel resistance for RIA transient occurring at cold conditions, whereas there is no evidence of important embrittlement effects at hot conditions, unless the cladding was degraded by oxide spalling. A fuel failure threshold correlation has been derived and compared with experimental data relevant for BWR and PWR fuel. The correlation can be applied to both cold and hot RIA transients, account taken for the lower ductility at cold conditions and for the different initial enthalpy. It can also be used for non-zero power transients, provided that a term accounting for the start-up power is incorporated. The proposed threshold is easy to use and reproduces the results obtained in the CABRI and NSRR tests in a rather satisfactory manner. The behaviour of advanced PWR alloys and of MOX fuel is discussed in light of the correlation predictions. Finally, a probabilistic approach has been developed in order to account for the small scatter of the failure predictions. This approach completes the RIA failure assessment in that after determining a best estimate failure threshold, a failure probability is inferred based on the spreading of data around the calculated best estimate value.

• ETRI Journal
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• v.28 no.5
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• pp.555-560
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• 2006

A PIN photodiode having a low dark current of 1.35 nA and a high external quantum efficiency of 95.3% fabricated for a passive optical network receiver. As the current was increased under a high voltage of 38 V and a temperature of $190^{\circ}C$, it was observed that there is a threshold current at 11 mA which induces a junction failure. Experimental data suggest that the junction failure occurs due to the crystal breaking at the end facet as a result of thermal heat or energetic carriers. This threshold behavior of junction failure is a valuable observation for the safe treatment of photodiodes. As long as the current is limited below the threshold currents, we have not observed failure events of our photodiodes.

• Smart Structures and Systems
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• v.22 no.2
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• pp.151-159
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• 2018

Maintenance activities are regarded as a key part of the repairable deteriorating system because they maintain the equipment in good condition. In practice, many maintenance policies are used in engineering fields to reduce unexpected failures and slow down the deterioration of the system. However, in traditional maintenance policies, maintenance activities have often been assumed to be performed at the same time interval, which may result in higher operational costs and more system failures. Thus, this study presents two non-periodic preventive maintenance (PM) policies for repairable deteriorating systems, employing the failure rate of the system as a conditional variable. In the proposed PM models, the failure rate of the system was restored via the failure rate reduction factors after imperfect PM activities. Operational costs were also considered, which increased along with the operating time of the system and the frequency of PM activities to reflect the deterioration process of the system. A numerical example was provided to illustrate the proposed PM policy. The results showed that PM activities performed at a low failure rate threshold slowed down the degradation of the system and thus extended the system lifetime. Moreover, when the operational cost was considered in the proposed maintenance scheme, the system replacement was more cost-effective than frequent PM activities in the severely degraded system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.4
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• pp.748-760
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• 1997

The handoff failure probability has to be enhanced efficiently to enhance the performance of PCS system. In this paper a new scheme called velocity adaptive handoff algorithm for reducing handoff failure probability and maintaining the carried traffic constantly in PCS systems, by assigning low handoff threshold value for high mobility calls, and assigning high handoff threshold value for low mobility calls, is presented. The performance of evaluation of this new scheme is carried out in terms of tranffic characteristics. Also velocity estimation algorithm for this new scheme is presented. According to the result, the handoff failure probability of velocity adaptive handoff algorithm is enhanced about 60%.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.5
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• pp.1181-1185
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• 1990

A failure evaluation diagram to evaluate fatigue fracture was developed. The relation between the fatigue limit and the threshold stress intensity factor for the short-cracked specimens of various materials including a piping carbon steel can be rationally predicted by the proposed method. It is shown that the coupled failure evaluation diagram for fatigue and ductile fracture is expecially useful for evaluation of the flaw tolerance as well as the margin of the safety of the pressure vessel and piping. Further, accumulation of fatigue data will be needed to construct an accurate fatigue failure evaluation diagram.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.15 no.12
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• pp.4617-4632
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• 2021

IEEE 802.11ax is a protocol being developed for high-density Wireless Local Area Networks (WLAN). Several algorithms have been proposed to improve the level of spatial reuse applied in IEEE 802.11ax. However, these algorithms are tentative and do not specify how to select the transmit power and carrier sense threshold in practice; It is unclear when and why the tuned parameters lead to better network performance. In this paper, we restricted the scale of transmit power tuning to prevent the case of backfire in which spatial reuse will result in transmission failure. If the restrictions cannot be satisfied, spatial reuse will be abandoned. This is why we named the proposed scheme as Arbitration based Spatial Reuse (ASR). We quantified the network performance after spatial reuse, and formulate a corresponding maximum problem whose solution is the optimal carrier sense threshold and transmit power. We verified our theoretical analysis by simulation and compared it with previous studies, and the results show that ASR improves the throughput up to 8.6% compared with 802.11ax. ASR can avoid failure of spatial reuse, while the spatial reuse failure rate of existing schemes can up to 36%. To use the ASR scheme in practice, we investigate the relation between the optimal carrier sense threshold and transmit power. Based on the relations got from ASR, the proposed Relation based Spatial Reuse (RSR) scheme can get a satisfactory performance by using only the interference perceived and the previously found relations.

• Journal of Positioning, Navigation, and Timing
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• v.4 no.4
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• pp.195-203
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• 2015

In this study, the carrier acceleration-ramp-step test was applied to GPS carrier phase measurements, and the results were compared and analyzed. In the carrier acceleration-ramp-step test, the acceleration, ramp, and measurements are estimated using 10 consecutive carrier phase measurements for satellites observed at the same time based on the least square method. As for the characteristic of this test, if failure occurs in the measurement, the value jumps significantly compared to the previous result; but it judges that failure has occurred in all the satellites although failure has occurred in one satellite. Therefore, in this study, a method that eliminates a satellite with failure was suggested, and thresholds of the carrier acceleration, ramp, and step were suggested. The evaluation of the failure detection performance of carrier phase measurement using the suggested thresholds showed that failure could be detected when the carrier phase measurement changed abruptly by more than about 0.1 cycles.

• 한국정보디스플레이학회:학술대회논문집
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• 2007.08b
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• pp.1172-1175
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• 2007

We have investigated the threshold voltage shifts(${\Delta}Vth$) and drain current level shift (${\Delta}Ids$) in subthreshold region of a-Si:H TFTs induced by DC Bias (Vgs and Vds) - Temperature stress (BTS) condition. We plotted the transfer curves and the ${\Delta}Vth$ contour maps as Vds-Vds stress bias and Temperature to examine the severe damage cases on TFTs. Also, by drawing out the time-dependent transfer curve (Ids-Vgs) in the region of $10^{-8}\;{\sim}\;10^{-13}$ (A) current level, we can estimate the failure time of TFTs in a operating condition.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.36 no.9
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• pp.678-684
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• 1987

The identification problem of instrument faults in PWR pressurizer is considered. The instrument failure detection technique in this paper consists of two filters, a normal-mode Kalman filter which estimates plant states in normal operation and a bias estimator which estimates the magnitudes and directions of bias faults. The concept of threshold based on the residual of a Kalman filter in normal operation is introduced. The bias estimator is driven when the absolute value of residual exceeds the threshold. The suggested failure detection algorithm is applied to a PWR pressurizer. Computer simulations show that the prompt detection of bias fault can be performed very successfully when there exist instrument faults.