• Journal of Applied Reliability
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• v.9 no.4
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• pp.319-329
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• 2009

The airbag module is an inflatable restraint system that inflates within 0.05 seconds automatically in a collision to protect the occupants. The airbag fabrics used in the module are required to have the good resilience and strength and also to have retained at least 80% of mechanical properties after using longer than 10 years. In this study, we develop an accelerated test method in order to predict the lifetimes of airbag. In this test, we select temperature and humidity as environmental stresses by analyzing the failure mechanisms of coated and uncoated nylon 66 fabrics. It is found that the degradation of airbag fabrics is effectively accelerated under the combined conditions of high temperature and humidity. Analyzing the results of the accelerated test, the lifetimes of airbag fabrics are predicted to be longer than 10 years.

• Wind and Structures
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• v.27 no.5
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• pp.283-291
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• 2018

This study presents the reliability assessment of a 100.5 m tall reinforced concrete chimney at a glass factory under wind loading by using vibration-based identified modal values. Ambient vibration measurements were recorded and modal values such as frequencies, shapes and damping ratios were identified by using Enhanced Frequency Domain Decomposition (EFDD) method. Afterwards, Finite Element Model (FEM) of the chimney was verified based on identified modal parameters. Reliability assessment of the chimney under wind loading was performed by obtaining the exceedance probability of demand to capacity distribution. Demand distribution of the chimney was developed under repetitive seeds of multivariate stochastic wind fields generated along the height of chimney. Capacity distribution of the chimney was developed by Monte Carlo simulation. Finally, it was found that reliability of the chimney is lower than code suggested limit values.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.52 no.1
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• pp.9-16
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• 2003

In this paper, we propose a reliability evaluation method considering the momentary interruptions of power distribution systems. The results of research are concentrated on two parts. One is the analytic and probabilistic reliability evaluation of power distribution system considering the momentary interruptions and the other is the reliability cost evaluation that unifies the cost of sustained and momentary interruptions. This proposed reliability cost evaluation methodology is also divided into the analytic and probabilistic approach and the time sequential Monte Carlo method is used for the probabilistic method. The proposed methods are tested using the modified RBTS (Roy Billinton Test System) form and historical reliability data of KEPCO (Korea Electric Power Corporation) system. Through the case studies, it is verified that the proposed reliability evaluation and its cost/worth assessment methodologies can be applied to the actual reliability studies.

• Journal of Applied Reliability
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• v.13 no.3
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• pp.217-227
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• 2013

Reliability growth is defined as the positive improvement in a reliability parameter over a period of time due to implementation of corrective actions to system design, operation or maintenance procedures, or the associated manufacturing process. In recent, the importance of reliability growth management has emerged in the military authority and industries. For effective application of reliability growth models, it is necessary to understand their characteristics and differences. This paper presents the concepts of reliability growth management and compares the features of reliability tracking and projection models centered on MIL-HDBK-189C for selecting the appropriate model for an one-shot system under development.

• Physical Therapy Korea
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• v.21 no.3
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• pp.73-79
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• 2014

The purposes of the current study were to (1) estimate the inter-rater agreement for visual assessment of scapular downward rotation (SDR), (2) develop the scapular downward rotation index (SDRI) as a method to measure SDR objectively and quantitatively, and (3) analyze the intra- and inter-rater reliability of the SDRI. Twenty subjects with scapular downward rotation syndrome (SDRS) were recruited for this study. The visual assessment and the measurement for the SDRI were conducted by two examiners in two sessions each. The SDRI [$(a-b){\div}a{\times}100$] is calculated with the measurement of two linear distances: One is a perpendicular distance from the root of the scapular spine to the thoracic mid-line (a), and the other is a perpendicular distance from the inferior angle of the scapula to the thoracic mid-line (b). Cohen's kappa coefficient was calculated to estimate the inter-rater agreement for visual assessment. Intra-class correlation coefficients (ICCs) with a 95% confidence interval (CI), the standard error of measurement, and minimal detectable differences were calculated to assess intra- and inter-rater reliability of SDR measurement using the SDRI. The results indicated that the kappa coefficient of inter-rater agreement for visual assessment was fair (${\kappa}=.21$). The intra-rater reliability of SDR measurement using the SDRI was excellent for examiner 1 (ICC=.92, 95% CI=.78~.97) and good for examiner 2 (ICC=.82, 95% CI=.55~.93). The inter-rater reliability was moderate (ICC=.73, 95% CI=.32~.89). These findings showed that SDR measurement using the SDRI for subjects with SDRS may be considered reliable and better than the visual assessment.

• Structural Monitoring and Maintenance
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• v.1 no.4
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• pp.357-369
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• 2014

In the existing bridge management systems, assessment of the structural behavior is based on the results of visual inspections in which corresponding condition states are assigned to individual elements. In this process, limited attention is given to the correlation between bridge elements from structural perspective. Also, the uncertainty of parameters which affect the structural capacity is ignored. A system reliability-based assessment model is potentially an appropriate replacement for the existing procedures. The aim of this research is to evaluate the system reliability of existing conventional Steel-Reinforced bridge decks over time. The developed method utilizes the reliability theory and evaluates the structural safety for such bridges based on their failure mechanisms. System reliability analysis has been applied to simply-supported concrete bridge superstructures designed according to the Canadian Highway Bridge Design Code (CHBDC-S6) and the deterioration pattern is achieved based on the reliability estimates. Finally, the bridge condition index of an old existing bridge in Montreal has been estimated using the developed deterioration pattern. The results obtained from the developed reliability-based deterioration model and from the evaluation done by bridge engineers have been found to be in accordance.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2004.04a
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• pp.267-274
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• 2004

Since there is a large variation in measurements of the thickness of corroded elements, the thickness of corroded elements are considered as imprecise elements. There is also a considerable degree of uncertainty in a visual assessment of thickness loss. The remaining thickness of a severly corroded element may be represented by an imprecise which expresses the range over which there is uncertainty about the thickness. Therefore, the objective of this paper is to propose a new methodology to safety assessment using imprecise reliability into conventional safety assessment frameworks. For this purpose, this study presents a safety assessment model using Imprecise reliability for large civil structures and demonstrates the applicability of the approach to cable-stayed bridge projects.

• Journal of Advanced Research in Ocean Engineering
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• v.3 no.3
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• pp.125-135
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• 2017

The paper considers the practical application of the FMEA(Failure Mode and Effect Analysis) method to assess the operational reliability of the LNG(Liquefied Natural Gas) transfer system, which is a potential problem for the connection between the LNG FPSO and LNG carrier. Hazard Identification (HAZID) and Hazard operability (HAZOP) are applied to identify the risks and hazards during the operation of LNG transfer system. The approach is performed for the FMEA to assess the reliability based on the detection of defects typical to LNG transfer system. FTA and FMEA associated with a probabilistic risk database to the operation scenarios are applied to assess the risk. After providing an outline of the safety assessment procedure for the operational problems of system, safety assessment example is presented, providing details on the fault tree of operational accident, safety assessment, and risk measures.

• Journal of Applied Reliability
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• v.18 no.3
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• pp.193-200
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• 2018

Purpose: In this study, the life of the motor is investigated by performing the accelerated life test with the brush wear of the industrial cleaner motor as the main failure mode. Methods: The accelerating stress factor of the accelerated life test is a voltage, which can increase the number of revolutions of the motor to accelerate the brush wear due to the friction between the brush and the commutator. Also, the accelerating stress level was determined after determining the maximum allowable level of the voltage through the preliminary test. Results: The motor failure time at each accelerating stress level was predicted by regression analysis with brush wear length as performance degradation data. The main failure mode, which is brush wear, of the motor was reproduced by this test. The shape parameter of the Weibull distribution was confirmed to be the same statistically at all accelerating stress levels by the likelihood ratio test. Conclusion: The life of the motor was investigated by performing the accelerated life test with the brush wear of the industrial cleaner motor as the main failure mode. Through the accelerating test method of the cleaner motor, various life expectancy and life expectancy of the acceleration factor are predicted.

• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.4
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• pp.42-49
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• 2019

This paper presents a method to predict the storage reliability of springs for turbo engine components based on an accelerated degradation test. The reliability assessment procedure for springs is established to proceed with the accelerated degradation test. The spring constant is selected as the performance degradation characteristic, the temperature is determined to be the stress factor that deteriorates the spring constant. The storage tests are performed at three temperature test conditions. The spring constant is measured periodically to check the degradation status of the springs. Failure times of the springs are predicted by using the degradation model. Finally, the storage lifetime of the springs at normal use conditions is predicted using an accelerated model and failure times of all test conditions.