• Title/Summary/Keyword: Multiple failure model

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Field data analyses for repairable products (수리가능한 제품의 사용현장 데이터 분석)

  • 배도선;윤형제;최인수
    • The Korean Journal of Applied Statistics
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    • v.8 no.2
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    • pp.133-145
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    • 1995
  • This paper is concerned with the method of estimating lifetime distribution from field data for repairable products with multiple modes of failure, and is an extension of Bai et al.(1995). The log linear function is considered as a model for describing the relation between failure time of a product and covariates. Using the nonhomogeneous poisson process, general methods for obtaining pseudo maximum likelihood estimators(PMLEs) for the parameters are outlined and specific formulas for Weibull distribution are obtained. Effects of follow-up percentage on the PMLEs are investigated. Extension to case-cohort design is also considered.

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A Study on the Simulation about Operation Availability under Maintenance Capacity and Repair Part Constraints (정비능력, 예비품 수량 제약조건 하에서의 운용가용도 시뮬레이션 연구)

  • Park, Se-Hoon;Moon, Seong-Am;Lee, Jung-Hwan
    • Korean System Dynamics Review
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    • v.11 no.2
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    • pp.119-138
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    • 2010
  • This study introduces the system dynamics model that simulate total operational availability when 10 equipments made of 3 major components are serviced under the constrains of the maintenance capacity level and the number of spare parts. This simulation is designed on the base of reliability engineering concept so failures of components happens with the rule of engineering factors like the mean time between failure(MTBF) of component and the next failure time of one component is effected by the conditions of other components. We analysed availability of 10 equipments under 121 constrains and executed multiple regression analysis with the simulation result. The analysis provide the managerial insight in the service fields with operation many equipments.

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Estimation of Freund Model for System Level Life Testing Using Component Life Data (체계수명시험에서 얻어진 부품의 수명자료를 이용한 Freund 모형의 추정)

  • 홍연웅
    • Journal of Korean Society for Quality Management
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    • v.26 no.2
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    • pp.27-38
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    • 1998
  • Consider a life testing experiment in which multiple two-component shared parallel systems are put on test, and the test is terminated at a specified number of system failures. The bivariate data obtained from such a system-level life testing can be classified into three classes: 1) the case of failed two components with known failure times, 2) the case of censored two components, and 3) the case of one censored component and the other failed component of which the failure time might be known or unknown. Under this censoring scheme and the assumption of Freund's bivariate exponential life distribution, the maximum likelihood estimators are obtained. Results of comparative studies based on Monte Carlo simulation are presented.

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Two-phase Finite Volume Analysis Method of Debris Flows in Regional-scale Areas (2상 유한체적모델 기반의 광역적 토석류 유동해석기법)

  • Jeong, Sangseom;Hong, Moonhyun
    • Journal of the Korean Geotechnical Society
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    • v.38 no.4
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    • pp.5-20
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    • 2022
  • To analyze the flow and density variations in debris flows, a two-phase finite volume model simplified with momentum equations was constructed in this study. The Hershel-Buckley rheology model was employed in this model to account for the internal and basal friction of debris flows and was utilized to analyze complex topography and entrainments of basal soil beds. In order to numerically solve the debris flow analysis model, a finite volume model with the Harten-Lax-van Leer-Contact method was used to solve the conservation equation for the debris flow interface. Case studies of circular dam failure, non-Newtonian fluid dam failure, and multiple debris flows were analyzed using the proposed model to evaluate shock absorption capacity, numerical isotropy, model accuracy, and mass conservation. The numerical stability and correctness of the debris flow analysis of this analysis model were proven by the analysis results. Additionally, the rate of debris flow with various rheological properties was systematically simulated, and the effect of debris flow rheological properties on behavior was analyzed.

Analysis of Success and Failure Factors of OTT Service Contents According to the Rating: Focus on Netflix (평점에 따른 OTT 서비스 콘텐츠의 성공과 실패 요인 분석: 넷플릭스를 중심으로)

  • Hong, Ji-Soo;Park, Jin-Soo;Kang, Sung-Woo
    • Journal of Korean Society of Industrial and Systems Engineering
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    • v.44 no.4
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    • pp.65-75
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    • 2021
  • This study explores multiple variables of an OTT service for discovering hidden relationship between rating and the other variables of each successful and failed content, respectively. In order to extract key variables that are strongly correlated to the rating across the contents, this work analyzes 170 Netflix original dramas and 419 movies. These contents are classified as success and failure by using the rating site IMDb, respectively. The correlation between the contents, which are classified via rating, and variables such as violence, lewdness and running time are analyzed to determine whether a certain variable appears or not in each successful and failure content. This study employs a regression analysis to discover correlations across the variables as a main analysis method. Since the correlation between independent variables should be low, check multicollinearity and select the variable. Cook's distance is used to detect and remove outliers. To improve the accuracy of the model, a variable selection based on AIC(Akaike Information Criterion) is performed. Finally, the basic assumptions of regression analysis are identified by residual diagnosis and Dubin Watson test. According to the whole analysis process, it is concluded that the more director awards exist and the less immatatable tend to be successful in movies. On the contrary, lower fear tend to be failure in movies. In case of dramas, there are close correlations between failure dramas and lower violence, higher fear, higher drugs.

Minimum life-cycle cost design of ice-resistant offshore platforms

  • Li, Gang;Zhang, Da-Yong;Yue, Qian-Jin
    • Structural Engineering and Mechanics
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    • v.31 no.1
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    • pp.11-24
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    • 2009
  • In China, the oil and natural gas resources of Bohai Bay are mainly marginal oil fields. It is necessary to build both ice-resistant and economical offshore platforms. However, risk is involved in the design, construction, utilization, maintenance of offshore platforms as uncertain events may occur within the life-cycle of a platform under the extreme ice load. In this study, the optimum design model of the expected life-cycle cost for ice-resistant platforms based on cost-effectiveness criterion is proposed. Multiple performance demands of the structure, facilities and crew members, associated with the failure assessment criteria and evaluation functions of costs of construction, consequences of structural failure modes including damage, revenue loss, death and injury as well as discounting cost over time are considered. An efficient approximate method of the global reliability analysis for the offshore platforms is provided, which converts the implicit nonlinear performance function in the conventional reliability analysis to linear explicit one. The proposed life-cycle optimum design formula are applied to a typical ice-resistant platform in Bohai Bay, and the results demonstrate that the life-cycle cost-effective optimum design model is more rational compared to the conventional design.

Cumulative survival rate and associated risk factors of Implantium implants: A 10-year retrospective clinical study

  • Park, Jin-Hong;Kim, Young-Soo;Ryu, Jae-Jun;Shin, Sang-Wan;Lee, Jeong-Yol
    • The Journal of Advanced Prosthodontics
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    • v.9 no.3
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    • pp.195-199
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    • 2017
  • PURPOSE. The objective of this study was to determine the cumulative survival rate (CSR) and associated risk factors of Implantium implants by retrospective clinical study. MATERIALS AND METHODS. Patients who received Implantium implants (Dentium Co., Seoul, Korea) at Korea University Guro Hospital from 2004 to 2011 were included. The period between the first surgery and the last hospital visit until December 2015 was set as the observation period for this study. Clinical and radiographic data were collected from patient records, including all complications observed during the follow-up period. Kaplan-Meier analysis was performed to examine CSR. Multiple Cox proportional hazard model was employed to assess the associations between potential risk factors and CSR. RESULTS. A total of 370 implants were placed in 121 patients (mean age, 56.1 years; range, 19 to 75 years). Of the 370 implants, 13 failed, including 7 implants that were lost before loading. The 10-year cumulative survival rate of implants was 94.8%. The multiple Cox proportional hazard model revealed that significant risk factor of implant failure were smoking and maxillary implant (P<.05). CONCLUSION. The 10-year CSR of Implantium implants was 94.8%. Risk factors of implant failure were smoking and maxillary implant.

Influence of Social Support and Negative Emotional Status on Self-care Adherence in Symptomatic Patients with Heart Failure (심부전 환자의 사회적 지지와 부정적 정서상태가 자가간호 이행에 미치는 영향)

  • Yang, In-Suk
    • Korean Journal of Adult Nursing
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    • v.28 no.3
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    • pp.302-313
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    • 2016
  • Purpose: The objective of this study was to identify factors related to self-care adherence in symptomatic patients with heart failure (HF). Methods: Using a cross-sectional design, a convenience sample 209 outpatient clinic patients were recruited at two medical centers. Between October 2011 and August 2012, data were collected using the structured questionnaire. Factors related to self-care adherence were examined using hierarchical multiple regression. Results: Mean age of participants was 67.71 years and a half of them (53.6%) were female. They showed relatively low self-care adherence with mean scores of $61.88{\pm}12.92$. Lower self-care adherence was reported in asking for low sodium items, weighing oneself, checking for ankle edema, and exercising for 30 minutes. The overall model significantly explained 23.9% of variance in self-care adherence. Among the predictors, education, New York Heart Association functional classification, and social support were statistically significant in influencing self-care adherence. The variable of negative emotional status such as anxiety and depression were not found to be significant. Conclusion: These findings demonstrate that social support could help self-care adherence among symptomatic patients with HF. Thus, programs targeting self-care adherence in this population should consider the strategies improving social support.

Direct fault-tree modeling of human failure event dependency in probabilistic safety assessment

  • Ji Suk Kim;Sang Hoon Han;Man Cheol Kim
    • Nuclear Engineering and Technology
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    • v.55 no.1
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    • pp.119-130
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    • 2023
  • Among the various elements of probabilistic safety assessment (PSA), human failure events (HFEs) and their dependencies are major contributors to the quantification of risk of a nuclear power plant. Currently, the dependency among HFEs is reflected using a post-processing method in PSA, wherein several drawbacks, such as limited propagation of minimal cutsets through the fault tree and improper truncation of minimal cutsets exist. In this paper, we propose a method to model the HFE dependency directly in a fault tree using the if-then-else logic. The proposed method proved to be equivalent to the conventional post-processing method while addressing the drawbacks of the latter. We also developed a software tool to facilitate the implementation of the proposed method considering the need for modeling the dependency between multiple HFEs. We applied the proposed method to a specific case to demonstrate the drawbacks of the conventional post-processing method and the advantages of the proposed method. When applied appropriately under specific conditions, the direct fault-tree modeling of HFE dependency enhances the accuracy of the risk quantification and facilitates the analysis of minimal cutsets.

Development of a complex failure prediction system using Hierarchical Attention Network (Hierarchical Attention Network를 이용한 복합 장애 발생 예측 시스템 개발)

  • Park, Youngchan;An, Sangjun;Kim, Mintae;Kim, Wooju
    • Journal of Intelligence and Information Systems
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    • v.26 no.4
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    • pp.127-148
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    • 2020
  • The data center is a physical environment facility for accommodating computer systems and related components, and is an essential foundation technology for next-generation core industries such as big data, smart factories, wearables, and smart homes. In particular, with the growth of cloud computing, the proportional expansion of the data center infrastructure is inevitable. Monitoring the health of these data center facilities is a way to maintain and manage the system and prevent failure. If a failure occurs in some elements of the facility, it may affect not only the relevant equipment but also other connected equipment, and may cause enormous damage. In particular, IT facilities are irregular due to interdependence and it is difficult to know the cause. In the previous study predicting failure in data center, failure was predicted by looking at a single server as a single state without assuming that the devices were mixed. Therefore, in this study, data center failures were classified into failures occurring inside the server (Outage A) and failures occurring outside the server (Outage B), and focused on analyzing complex failures occurring within the server. Server external failures include power, cooling, user errors, etc. Since such failures can be prevented in the early stages of data center facility construction, various solutions are being developed. On the other hand, the cause of the failure occurring in the server is difficult to determine, and adequate prevention has not yet been achieved. In particular, this is the reason why server failures do not occur singularly, cause other server failures, or receive something that causes failures from other servers. In other words, while the existing studies assumed that it was a single server that did not affect the servers and analyzed the failure, in this study, the failure occurred on the assumption that it had an effect between servers. In order to define the complex failure situation in the data center, failure history data for each equipment existing in the data center was used. There are four major failures considered in this study: Network Node Down, Server Down, Windows Activation Services Down, and Database Management System Service Down. The failures that occur for each device are sorted in chronological order, and when a failure occurs in a specific equipment, if a failure occurs in a specific equipment within 5 minutes from the time of occurrence, it is defined that the failure occurs simultaneously. After configuring the sequence for the devices that have failed at the same time, 5 devices that frequently occur simultaneously within the configured sequence were selected, and the case where the selected devices failed at the same time was confirmed through visualization. Since the server resource information collected for failure analysis is in units of time series and has flow, we used Long Short-term Memory (LSTM), a deep learning algorithm that can predict the next state through the previous state. In addition, unlike a single server, the Hierarchical Attention Network deep learning model structure was used in consideration of the fact that the level of multiple failures for each server is different. This algorithm is a method of increasing the prediction accuracy by giving weight to the server as the impact on the failure increases. The study began with defining the type of failure and selecting the analysis target. In the first experiment, the same collected data was assumed as a single server state and a multiple server state, and compared and analyzed. The second experiment improved the prediction accuracy in the case of a complex server by optimizing each server threshold. In the first experiment, which assumed each of a single server and multiple servers, in the case of a single server, it was predicted that three of the five servers did not have a failure even though the actual failure occurred. However, assuming multiple servers, all five servers were predicted to have failed. As a result of the experiment, the hypothesis that there is an effect between servers is proven. As a result of this study, it was confirmed that the prediction performance was superior when the multiple servers were assumed than when the single server was assumed. In particular, applying the Hierarchical Attention Network algorithm, assuming that the effects of each server will be different, played a role in improving the analysis effect. In addition, by applying a different threshold for each server, the prediction accuracy could be improved. This study showed that failures that are difficult to determine the cause can be predicted through historical data, and a model that can predict failures occurring in servers in data centers is presented. It is expected that the occurrence of disability can be prevented in advance using the results of this study.