• Journal of Korean Society of Industrial and Systems Engineering
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• v.22 no.52
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• pp.171-180
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• 1999

Industrial equipment reliability improvement and maintenance is gaining attention as the next great opportunity for manufacturing productivity improvement. Reactive maintenance is expensive because of extensive unplanned downtime and damage to machinery. To avoid such an unplanned machine downtime, it is needed to use proactive maintenance approach by either using historical maintenance data or by sensing machine conditions. This paper discusses failure diagonosis and prediction based on the condition-based maintenance and reliability technique. Thus, by enabling such a framework, it can bring us more efficient planning and execution of maintenance to reduce costs and/or increase profits.

• Journal of the Korean Data and Information Science Society
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• v.21 no.5
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• pp.873-882
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• 2010

This paper considers a Bayesian approach to replacement policy following the expiration of non-renewing combination warranty. The non-renewing combination warranty is the combination of the non-renewing free replacement warranty and the non-renewing pro-rata replacement warranty. We use the criterion based on the expected cost and the expected downtime to determine the optimal replacement period. To do so, we obtain the expected cost rate per unit time and the expected downtime per unit time, respectively. When the failure times are assumed to follow a Weibull distribution with uncertain parameters, we propose the optimal replacement policy based on the Bayesian approach. The overall value function suggested by Jiang and Ji (2002) is utilized to determine the optimal replacement period. Also, the numerical examples are presented for illustrative purpose.

• Communications for Statistical Applications and Methods
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• v.15 no.6
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• pp.909-923
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• 2008

This paper considers the replacement model and the preventive maintenance model following the expiration of combination warranty for a repairable system. If the system fails after the combination warranty is expired, then it is minimally repaired at each failure. The criterion used to determine the optimal replacement policy and the optimal preventive maintenance policy is the overall value function based on the expected cost rate per unit time and the expected downtime per unit time. The numerical examples are presented for illustrative purpose when the failure time follows a Weibull distribution.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.37 no.3
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• pp.16-23
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• 2014

Most of metal cutting and processing companies are going through the difficulties such as frequent downtime and high failure rates by missing times to replace parts of CNC equipment. The reason is that the correct operation times of expensive CNC equipment can't be calculated. In this paper, to solve this problem, we try to construct the intelligent production information system for a case company and analyze its expected effects. The effects are as follows. First, it saves money about 3 million won each year during the useful life of three years by reducing downtime and failure rates, and increasing production rates etc. Second, it makes easily find and fix the cause of faulty through traceability of the production process, and enables to perform a systematic facility management through the calculation of reliable equipment's overall efficiency. This case can be easily applied in similar industries, and will contribute greatly to enhancing the competitiveness of related industries.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.4
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• pp.287-293
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• 2002

The unexpected failure of the induction motor makes the downtime of production, and the cost of the process cessation enormous. To reduce the downtime and increase the reliability of the motor, the vibration measurements for the fault detection have been used previously. Recently motor current signature analysis(MCSA) has been adapted for the fault detection and diagnosis of the motors. MCSA provides a powerful analysis tool for detecting the presence of mechanical and electrical faults in both the motor and driven equipment. In this paper, the fault severity of the rotor bar has been derived in terms of the resistance change which is calculated from the equivalent circuit model. Results show that the fault of the rotor can be easily detected and the measured value of the resistance change is verified by the detected fault from on-site tests using MCSA for the induction motors in an iron foundry.

• Proceedings of the Korean Reliability Society Conference
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• 2000.11a
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• pp.329-333
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• 2000

Delay time analysis is a pragmatic mathematical concept readily embraced by engineers which has been developed as a means to model maintenance decision problem. This paper considers an inspection period using delay time analysis for fishing vessel equipment. We assume that delay time distribution is Weibull and inspections are perfect. In this paper, we determine the optimal inspection period which minimize the expected downtime per unit time.

• Journal of Korean Society for Quality Management
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• v.22 no.4
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• pp.40-58
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• 1994

Some systems such as early warning system should be inspected occasionally in order to detect failures. If the system is inspected too frequently, inspection cost increases. On the other hand, if the number of inspections is reduced too much, the undetected system downtime cost increases. Thus, it is of interest to find effective inspection schedule, which minimizes the sum of inspection and downtime costs. When the system has increasing failure rate, inspection intervals get shorter as time goes on. But a common practice is to inspect the system at predetermined periodic intervals. In this paper, periodic inspection policy and a modified periodic inspection policy are considered. The modified policy is easily applicable and cost-effective. Some numerical examples are included in order to explain the modified inspection ploicy and its cost performance.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2003.09a
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• pp.462-466
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• 2003

This study was conducted to examine the potential of biosparging process in removing diesel contaminated soil and groundwater. The experiment was carried out lab-scale biosparging reactor and the biodegradation rate of diesel was evaluated as function of air injection rate and pattern. When renter was operated as air injection rate of 1000$m\ell$/min and pulsed air injection(15min pulse, 15min downtime), DO concentration in the renter was higher than another operating condition. The evidence for biodegradation of diesel was the $O_2$ utilization and $CO_2$ product following the cessation of sparging. Especially, air injection rate of 2000$m\ell$/min and pulsed air injection(15min pulse, 15min downtime) enhanced the diesel biodegradation during the operating. After 120day, the biodegradation rate of diesel was decreased as the lack of carbon source.

• Tunnel and Underground Space
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• v.29 no.6
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• pp.394-406
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• 2019

Difficult ground conditions (e.g., fault zone and mixed grounds) are highly probable to appear in subsea and urban tunnels because of the shallow working depth and alluvial characteristics. TBM usually experienced decrease of penetration rate and increase of downtime when it meets these difficult ground conditions. The problems are usually caused by the adverse geological conditions, and it is preferable to determine the optimal operational parameters of TBM based on the previous operational data obtained while excavating a preceding tunnel. This study carried out for efficient TBM excavation in fault zone and mixed grounds. TBM excavation data from the tunnel site in Singapore and the characteristics of the TBM excavation data was analyzed. The key operational parameters (i.e., thrust, torque, and RPM), penetration rate, and downtime were highly influenced by the presence of fault zones and mixed grounds, and the features was discussed. It is expected that the results and main discussions will be useful information for future tunneling projects in similar geological conditions.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.23 no.3
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• pp.226-235
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• 2011

Field measurements of the winds and waves were carried out for one year at multiple locations inside and outside of the Pohang New Harbor in order to clarify the reason of downtimes frequently occurring at most of the harbor quays and to establish an efficient countermeasure. In addition, the downtime records of the quays and precipitation data provided by Korea Meteorological Agency were acquired for mutual comparison and comprehensive analysis of the cause of downtimes. Except the influence of precipitation, it was found that the downtimes occurred when the height of waves entering into the harbor incurred by either one of swell, wind seas, or mixture of both, exceeded a threshold. The seiche whose period ranges from 5 to 80 minutes, which was suspected as a possible cause of the downtimes, is shown to have no direct relation with the downtimes. Meanwhile, the height of far-infra-gravity waves whose period ranges between 0.5 and 3 minutes, propagating to the harbor mouth forced by short period waves, showed almost proportional relationship with the height of short period waves. Based on the result of this study, it is concluded that the downtime problems of Pohang New Harbor can be greatly improved by effectively preventing the entrance of short period waves such as swell or wind seas.