• Structural Engineering and Mechanics
• /
• v.63 no.6
• /
• pp.703-712
• /
• 2017

The composite blades of offshore wind turbines accumulate structural damage such as fatigue cracking due to harsh operation environments during their service time, leading to premature structural failures. This paper investigates various fatigue crack models for reproducing crack development in composite blades and proposes a stochastic approach to predict fatigue crack evolution and to analyse failure probability for the composite blades. Three typical fatigue models for the propagation of fatigue cracks, i.e., Miner model, Paris model and Reifsnider model, are discussed to reproduce the fatigue crack evolution in composite blades subjected to cyclical loadings. The lifetime probability of fatigue failure of the composite blades is estimated by stochastic deterioration modelling such as gamma process. Based on time-dependent reliability analysis and lifecycle cost analysis, an optimised maintenance policy is determined to make the optimal decision for the composite blades during the service time. A numerical example is employed to investigate the effectiveness of predicting fatigue crack growth, estimating the probability of fatigue failure and evaluating an optimal maintenance policy. The results from the numerical study show that the stochastic gamma process together with the proper fatigue models can provide a useful tool for remaining useful life predictions and optimum maintenance strategies of the composite blades of offshore wind turbines.

• International Journal of Reliability and Applications
• /
• v.18 no.1
• /
• pp.9-20
• /
• 2017

In this paper, we consider a renewable repair-replacement warranty strategy with age-dependent minimal repair service and propose an optimal maintenance model during post-warranty period. Such model implements the repair time limit under warranty and follows with a certain form of system maintenance strategy when the warranty expires. The expected cost rate is investigated per unit time during the life period of the system as for the standard for optimality. Based on the cost design defined for each failure of the system, the expected cost rate is derived during the life period of the system, considering that a renewable minimal repair-replacement warranty strategy with the repair time limit is provided to the customer under warranty. When the warranty is finished, the maintenance of the system is the customer's responsibility. The life period of the system is defined and the expected cost rate is developed from the viewpoint of the customer's perspective. We obtain the optimal maintenance strategy during the maintenance period by minimizing such a cost rate after a warranty expires. Numerical examples using field data are shown to exemplify the application of the methodologies proposed in this paper.

• Proceedings of the KSR Conference
• /
• 2010.06a
• /
• pp.261-267
• /
• 2010

Present maintenance of a high speed railway is after the fack maintenance that executes a task when measured value goes over threshold value except some planned maintenance. It is difficult from efficient management of maintenance human resource and equipment commitment because it is difficult to predict quantity of maintenance targets. Corrective maintenance is pushed back on the repair priority of other target to need repair and it is exceeded repair cost potentially. For safety and dependable track management because track deterioration prediction is linked directly with track's life and safety of train service, it is very important that track management be based on preventive maintenance. In this study, we propose statistics model of track quality to use track inspection data and forecast model for track deterioration prediction.

• Journal of the Korean Institute of Landscape Architecture
• /
• v.36 no.5
• /
• pp.26-34
• /
• 2008

This study was conducted to investigate the correlation between golfer satisfaction and the diverse variables of golf course design and operation from the golfer's point of view. It was intended to reflect the various expectations and desires of golfers regarding golf course design and operation. The study was conducted on 119 golf courses in Korea, and 309 questionnaires were collected and analyzed. Results are summarized as follows. First, the most influential operational service variables on golfer satisfaction were "appearance of the golf courses", followed by "staff service", and "greens fee". Second, the most influential course design and maintenance factor variables on satisfaction were "course maintenance status", "teeing ground characteristics", and "landscape architecture". Third, based on the results shown in these two areas, a linear regression analysis was conducted to synthetically explain "operational service" variables and "course design and maintenance" variables. As a result, it was found that the explanation power of the synthetic model was 36.5%, and a model appropriateness test was found to be positive. As a result of a regression analysis of the synthetic model affecting golfer satisfaction, the most influential factors were "course maintenance status" followed by "landscape architecture", "tee characteristics", and "staff service". Regarding coefficient values, course maintenance status had an influence of 21.8% followed by landscape architecture at 20%, tee characteristics at 17.7%, and staff service at 15.5%. These results were found to be different from preceding studies that emphasized golf course operational service.

• Journal of Korean Institute of Industrial Engineers
• /
• v.33 no.4
• /
• pp.487-493
• /
• 2007

In this paper, we deal with an optimal software-release problem of determining the time to stop testing and release the software system to the user. The optimal release time problem is considered from maintenance like the periodic distribution of service packs and the unpredictable distribution of patches after the release. Moreover, the environment of software error-detection during operation differs from the environment during testing. This paper proposes the software reliability growth model which incorporates periodic service packs, unpredictable patches and operational environment. Based on the proposed model, we derive optimal release time to minimize total cost composed of fixing an error, testing and maintenance. Using numerical examples, optimal release time is determined and illustrated.

• Journal of Information Technology Services
• /
• v.13 no.1
• /
• pp.1-21
• /
• 2014

In IT service quality research, the relationship between the service quality and clients' satisfaction was the focus of many studies while in relationship quality research, the influence of trust and conflict on relationship commitment seems to be the focus. In this study, these two research streams are integrated and a theoretical research model is proposed consisting of IT service quality, satisfaction, trust and relationship commitment with conflict as a moderator for the overall psychological mechanism. As satisfaction represents emotional response while trust cognitive response, this research model integrated both emotional and cognitive aspects of relationship maintenance in the IT service context. Analysis of data collected from 262 employees of global IT service firm revealed the differential effects of reliability, responsiveness, assurance and empathy on satisfaction and trust. Also, depending upon the level of conflict, the effects of reliability and assurance were found to be moderated. Further analysis revealed more profound mechanism at work relating emotional and cognitive aspects in the psychology of relationship maintenance in IT service context. Practical implications are further discussed in the conclusion.

• Structural Monitoring and Maintenance
• /
• v.2 no.2
• /
• pp.133-143
• /
• 2015

Civil engineering infrastructure is aging and requires cost-effective maintenance strategies to enable infrastructure systems operate reliably and sustainably. This paper presents an approach for determining risk-cost balanced repair strategy of corrosion damaged reinforced concrete structures with consideration of uncertainty in structural resistance deterioration. On the basis of analytical models of cover concrete cracking evolution and bond strength degradation due to reinforcement corrosion, the effect of reinforcement corrosion on residual load carrying capacity of corroded reinforced concrete structures is investigated. A stochastic deterioration model based on gamma process is adopted to evaluate the probability of failure of structural bearing capacity over the lifetime. Optimal repair planning and maintenance strategies during the service life are determined by balancing the cost for maintenance and the risk of structural failure. The method proposed in this study is then demonstrated by numerical investigations for a concrete structure subjected to reinforcement corrosion. The obtained results show that the proposed method can provide a risk cost optimised repair schedule during the service life of corroded concrete structures.

• IE interfaces
• /
• v.3 no.1
• /
• pp.1-11
• /
• 1990

The purpose of this study is to develop the decision support model for the investment in the operation and maintenance in telecommunication networks. First, we analyze the relation between the cost of quality and the quality of service, and then establish and analysis tool of the investment alternatives for the improvement of the quality of service. This study will offer a decision tool to enhance an efficiency of the operation and maintenance for telecommunication facilities, and will contribute to shaping a policy of network performance management.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.18 no.11
• /
• pp.130-137
• /
• 2017

To maintain traffic safety during the target lifetime of bridges, it is essential to secure an appropriate maintenance budget and allocate that budget appropriately. This paper proposes a reasonable budget allocation system that considers various impact factors to improve the conventional budget allocation method simply considering the bridge scale. The maintenance action rate model and the unit cost model based on the prior maintenance history were developed to allocate appropriately the bridge maintenance budget for the total bridges of the management organization with the target management level. A method to determine the optimal budget allocation ratio for each management subject was proposed and case analysis was conducted using the proposed model. Proper budget allocation was made considering the bridge types, current safety level, and service life as well as the bridge size as an impact factor of the budget allocation of the bridge. The developed method can prevent budget waste and provide a rational basis for budget allocation by implementing the rational budget distribution.

• Journal of Korean Society of Water and Wastewater
• /
• v.31 no.1
• /
• pp.51-62
• /
• 2017

For the asset management of a water pipe network, it would be necessary to understand the extent of the maintenance cost required for the water pipe network for the future. This study would develop a method to draw the optimum cost required for the maintenance of the water pipe network in waterworks facilities to maintain the aim revenue water ratio and to achieve the target revenue water ratio, considering the water service providers' waterworks condition and revenue water ratio comprehensively. This study conducted a survey with 96 water service providers as of the early 2015 and developed models to estimate the optimum maintenance cost of the water pipe network, considering the characteristics of the water service providers. Since the correlation coefficient of all the developed models was higher than 0.95, it turned out that it had significant reliability, which was statistically significant. As a result of applying the developed models to the actual water service providers, it was drawn that increasing revenue water ratio to more than a certain level can reduce the maintenance cost of the water pipe network by a great deal. In other words, it is judged that it would be the most efficient to secure the reliability of waterworks management by increasing the short-term revenue water ratio to more than a certain level and gradually increase the revenue water ratio from the long-term perspective. It is expected that the proposed methodology proposed in this study and the results of the study will be used as a basic research for planning the maintenance of water pipe network or establishing a plan for waterworks facilities asset management.