• Smart Structures and Systems
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• 제15권3호
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• pp.699-715
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• 2015

A modal parameter based damage sensitive feature (DSF) is defined to mimic the relative change in any diagonal element of the stiffness matrix of a model of a structure. The damage assessment is performed in a statistical pattern recognition framework using empirical complementary cumulative distribution functions (ECCDFs) of the DSFs extracted from measured operational vibration response data. Methods are discussed to perform probabilistic structural health assessment with respect to the following questions: (a) "Is there a change in the current state of the structure compared to the baseline state?", (b) "Does the change indicate a localized stiffness reduction or increase?", with the latter representing a situation of retrofitting operations, and (c) "What is the severity of the change in a probabilistic sense?". To identify a range of normal structural variations due to environmental and operational conditions, lower and upper bound ECCDFs are used to define the baseline structural state. Such an approach attempts to decouple "non-damage" related variations from damage induced changes, and account for the unknown environmental/operational conditions of the current state. The damage assessment procedure is discussed using numerical simulations of ambient vibration testing of a bridge deck system, as well as shake table experimental data from a 4-story steel frame.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 추계학술대회 논문집(제1권)
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• pp.261-267
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• 2006

소요장치량은 컨테이너터미널의 장치능력을 결정짓는 매우 중요한 의사결정 변수이다. 일반적으로 소요장치량은 모선의 배선간격, 장치허용기간, 본선작업시간 등 여러 요인들에 좌우된다. 그러나 지금까지는 이들 요인이 확정적이라는 가정 하에 다양한 방법들을 소요장치량 산정에 적용해왔다. 본 연구는 본선작업 물량이 확률적인 것으로 가정하고 서비스수준을 만족시키는 소요장치량의 산정 방법을 제시했다. 시뮬레이션을 이용한 수치실험은 제시된 방법이 다른 방법들에 비해 확률적 상황에서 더욱 정확한 소요장치량을 산정할 수 있음을 보여주었다.

• 전기학회논문지
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• 제66권12호
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• pp.1712-1720
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• 2017

In South Korea, minimum reserve rate, which is to satisfy reliability standard, has been determined by simulation result using WASP. But, it is still controversial whether the level of minimum reserve rate is adequate. Thus, in this study, various analyses of minimum reserve rate are being conducted. WASP uses the probabilistic simulation technique to evaluate whether reliability standard is satisfied. In this process, forced outage rate and maintenance periods of each generator play important roles. Especially, the long-term plan can be varied depending on how maintenance periods deal with. In order to model maintenance periods in the probabilistic simulation technique, WASP uses derating method. However, broad analyses have to be conducted because there are various ways including derating method to model maintenance periods which result in different results. Therefore, in this paper, 3 different maintenance outage rate modeling methods are applied to arbitrarily modeled system based on the basic plan for long-term electricity supply and demand of South Korea. Results show impact of each modeling method on minimum reserve rate.

• 정보과학회 논문지
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• 제42권7호
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• pp.868-877
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• 2015

영상에서 바코드 영역을 검출하는 다양한 방식들이 연구되어 왔다. 기존 방식들은 주파수 성분 특징을 이용하거나, Hough transform (HT)을 이용하여 바코드 영역을 검출한다. 하지만 이 방식들은 바코드의 기울기와 노이즈에 영향을 받는다. 또한 여러 개의 바코드가 있는 경우 정확히 검출하지 못한다. 본 논문에서는 바코드의 기울기와 노이즈에 강인하고, 복수 개의 바코드를 검출할 수 있는 방식을 제안한다. 우리는 전처리 단계로 Probabilistic Hough transform (PHT)를 이용하여 바코드 기울기, 노이즈, 그리고 개수에 상관없이 바코드가 존재할 가능성이 높은 영역을 추출한 후, 주파수 성분 분석을 통해 바코드를 찾아낸다. 구현된 시스템의 성능분석을 통해 다양한 환경에서 바코드 추출이 가능함을 확인했다.

• Nuclear Engineering and Technology
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• 제51권1호
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• pp.138-145
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• 2019

With the application of digital technology to safety-critical infrastructures, cyber-attacks have emerged as one of the new dangerous threats. In safety-critical infrastructures such as a nuclear power plant (NPP), a cyber-attack could have serious consequences by initiating dangerous events or rendering important safety systems unavailable. Since a cyber-attack is conducted intentionally, numerous possible cases should be considered for developing a cyber security system, such as the attack paths, methods, and potential target systems. Therefore, prior to developing a risk-informed cyber security strategy, the importance of cyber-attacks and significant critical digital assets (CDAs) should be analyzed. In this work, an importance analysis method for cyber-attacks on an NPP was proposed using the probabilistic safety assessment (PSA) method. To develop an importance analysis framework for cyber-attacks, possible cyber-attacks were identified with failure modes, and a PSA model for cyber-attacks was developed. For case studies, the quantitative evaluations of cyber-attack scenarios were performed using the proposed method. By using quantitative importance of cyber-attacks and identifying significant CDAs that must be defended against cyber-attacks, it is possible to develop an efficient and reliable defense strategy against cyber-attacks on NPPs.

• Earthquakes and Structures
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• 제16권5호
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• pp.523-532
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• 2019

Different types of gas reservoir such as Liquid Natural Gas (LNG) are among the strategic infrastructures, and have great importance for any government or their private owners. To keep the tank and its contents safe during earthquakes especially if the contents are of hazardous or flammable materials; using seismic protection systems such as base isolator can be considered as an effective solution. However, the major deficiency of this system can be the large deformation in the isolation level which may lead to the failure of bearing system. In this paper, as a solution, the efficacy of an optimally designed combined vibration control system, the combined laminated rubber isolator and rotational friction damper, is investigated to evaluate the enhancement of an existing metal tank response under both far- and near-field earthquakes. Responses like impulsive and convective accelerations, base shear, and sloshing height are studied herein. The probabilistic framework is used to consider the uncertainties in the structural modeling, as well as record-to-record variability. Due to the high calculation cost of probabilistic methods, a simplified structural model is used. By using the Mont-Carlo simulation approach, it is revealed that this combined isolation system is a highly reliable system which provides considerable enhancement in the performance of reservoir, not only leads to the reduction of probability of catastrophic failure of the tank but also decrease the reservoir damage during the earthquake. Moreover, the relative displacement of the isolation level is controlled very well by this combined system.

• Structural Engineering and Mechanics
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• 제81권4호
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• pp.429-441
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• 2022

A probabilistic assessment of the seismic-excited buildings with a multiple-tuned-mass-damper (MTMD) system is carried out in the presence of uncertainties of the structural model, MTMD system, and the stochastic model of the seismic excitations. A free search optimization procedure of the individual mass, stiffness and, damping parameters of the MTMD system based on the snap-drift cuckoo search (SDCS) optimization algorithm is proposed for the optimal design of the MTMD system. Considering a 10-story structure in three cases equipped with single tuned mass damper (STMS), 5-TMD and 10-TMD, sensitivity analyses are carried out using Sobol' indices based on the Monte Carlo simulation (MCS) method. Considering different seismic performance levels, the reliability analyses are done using MCS and kriging-based MCS methods. The results show the maximum structural responses are more affected by changes in the PGA and the stiffness coefficients of the structural floors and TMDs. The results indicate the kriging-based MCS method can estimate the accurate amount of failure probability by spending less time than the MCS. The results also show the MTMD gives a significant reduction in the structural failure probability. The effect of the MTMD on the reduction of the failure probability is remarkable in the performance levels of life safety and collapse prevention. The maximum drift of floors may be reduced for the nominal structural system by increasing the TMDs, however, the complexity of the MTMD model and increasing its corresponding uncertainty sources can be caused a slight increase in the failure probability of the structure.

• Nuclear Engineering and Technology
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• 제55권4호
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• pp.1420-1427
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• 2023

Seismic risk has received increased attention since the 2011 Fukushima accident in Japan. The seismic risk of a nuclear power plant is evaluated via seismic probabilistic safety assessment (PSA), for which several methods are available. Recently, the discrete approach has become widely used. This approximates the seismic risk by discretizing the ground motion level interval into a small number of subintervals with the expectation of providing a conservative result. The present study examines the effect of the number of subintervals upon the results of seismic risk quantification. It is demonstrated that a small number of subintervals may lead to either an underestimation or overestimation of the seismic risk depending on the ground motion level. The present paper also provides a method for finding the boundaries between overestimation and underestimation regions, and illustrates the effect of the number of subintervals upon the seismic risk evaluation with an example. By providing a method for determining the effect of a small number of subintervals upon the results of seismic risk quantification, the present study will assist seismic PSA analysts to determine the appropriate number of subintervals and to better understand seismic risk quantification.

• 한국음향학회지
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• 제27권2호
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• pp.75-79
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• 2008

본 논문에서는 support vector machine (SVM) 기반의 global soft decison (GSD)을 이용한 새로운 음성 향상 기법을 제시한다. 일반적으로 soft decision (SD) 이득 수정 및 잡음 전력 추정에 근거한 음성 향상 기법이 hard decision을 이용한 음성향상 기법 보다 우수한 성능을 보이는 것으로 알려져 있다. 특히, 각 프레임에서의 음성 부재에 대한 효과적인 척도인 전역음성 부재확률 (global speech absence probability, GSAP)을 SD 기반의 음성 향상 기법에 적용한 여러 연구가 진행되었다. 본 논문에서는 sigmoid 함수를 이용하여 얻어진 SVM의 확률 출력에 의해 추정된 새로운 GSAP를 음성 향상 기법에 적용한다. 제안된 알고리즘의 성능은 다양한 잡음 환경에 적용하여 PESQ 및 MOS 평가 방법을 바탕으로 기존의 GSD 기반의 스펙트럼 향상 기법과 비교하여 향상된 결과를 나타내었다.

• Nuclear Engineering and Technology
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• 제56권8호
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• pp.3359-3368
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• 2024

In the calculation of DCGLs using RESRAD code, the selection of input parameter values is paramount, which is basically possible when specific measures for selecting reuse scenarios and probabilistic evaluation methods are established. When referring to the impact of the age group considered in the environmental impact assessment among the existing operations of the plant, it may also need to be applied in the decommissioning project, and there will be considerations along with site reuse scenarios and probabilistic evaluations. Therefore, the main purpose of this study is to distinguish the types of exposure affected by residual radioactivity contamination during the process of deriving DCGL to be used in the final site release stage of NPPs and to evaluate them by reasonably assigning age group parameter values. In addition, the case of entering a single value for parameter values by age group and the case of entering probabilistic distributions were compared and analyzed.