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Dong Ho Park - One of the best experts on this subject based on the ideXlab platform.
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Warranty cost analysis for second hand products under a two stage repair or full refund policy
Reliability Engineering & System Safety, 2020Co-Authors: Minjae Park, Ki-mun Jung, Dong Ho ParkAbstract:Abstract With this paper, we consider an optimal Warranty policy for second-hand products based on a two-stage repair-or-full-refund maintenance strategy to determine an optimal length of Warranty Period from the dealer's point of view. Because replacing failed products may not be an option with second-hand products, we newly introduce in this paper the concept of full refund rather than replacement. We pre-specify a repair time threshold and define the length of maintenance Period during which the dealer will maintain the product as the product maintenance cycle. Following this policy, if the product failure cannot be repaired within the repair time threshold during the Warranty Period, the user receives a full refund and the maintenance cycle ends. Otherwise, the user receives only minimal repairs to the product, and if the dealer does not issue a full refund during the Warranty Period, the maintenance cycle ends when the Warranty expires. Given a certain cost structure charged to the dealer, we derive mathematical formulas to evaluate the expected length of a maintenance cycle and the expected total maintenance cost during the cycle. As a criterion for the optimality of the Warranty policy, we utilize the expected cost during the product maintenance cycle to propose the optimal Warranty policy. Assuming the power law model for product failures and a two-parameter Weibull distribution for the repair times, we illustrate our proposed Warranty policy numerically and conduct sensitivity analysis to study the impacts of several relevant parameters on the optimal Warranty policy.
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cost optimization model following extended renewing two phase Warranty
Computers & Industrial Engineering, 2015Co-Authors: Ki-mun Jung, Minjae Park, Dong Ho ParkAbstract:Abstract In this paper, we study an extended Warranty model under which the customer is offered an additional Warranty Period after the original two-phase Warranty expires. Under the original two-phase Warranty, the Warranty Period is divided into two non-overlapping subintervals, one of which is for replacement Warranty, and the other is for minimal repair Warranty. If the system failure occurs during the original Warranty Period, the failed system is either replaced or minimally repaired by the manufacturer, and if the failure occurs during the extended Warranty Period, only the minimal repair is conducted. For the system failure during the replacement Warranty Period, the failed system is replaced by a new one, and the Warranty term is renewed anew. Following the expiration of extended Warranty, the customer is solely responsible for maintaining the system for a fixed length of time Period and replaces the system at the end of such a maintenance Period. During the maintenance Period, only the minimal repair is given for each system failure. Such a maintenance model can be considered as a generalization of several existing maintenance models which can be obtained as special cases. The main purpose of this article is to determine, from the customer’s perspective, the optimal length of maintenance Period after the extended Warranty expires. As the criterion to determine the optimal replacement strategy, we adopt the expected cost rate per unit time during the life cycle of the system. Given the cost structures incurred during the life cycle of the system, we formulate the expected cost and the expected length of life cycle to obtain the expected cost rate. The uniqueness of optimal solution for the decision variable is verified when the life distribution of the system shows an increasing failure rate. Numerical examples are provided to illustrate the proposed optimal replacement strategy.
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optimal post Warranty maintenance policy with repair time threshold for minimal repair
Reliability Engineering & System Safety, 2013Co-Authors: Minjae Park, Ki-mun Jung, Dong Ho ParkAbstract:Abstract In this paper, we consider a renewable minimal repair–replacement Warranty policy and propose an optimal maintenance model after the Warranty is expired. Such model adopts the repair time threshold during the Warranty Period and follows with a certain type of system maintenance policy during the post-Warranty Period. As for the criteria for optimality, we utilize the expected cost rate per unit time during the life cycle of the system, which has been frequently used in many existing maintenance models. Based on the cost structure defined for each failure of the system, we formulate the expected cost rate during the life cycle of the system, assuming that a renewable minimal repair–replacement Warranty policy with the repair time threshold is provided to the user during the Warranty Period. Once the Warranty is expired, the maintenance of the system is the user's sole responsibility. The life cycle of the system is defined on the perspective of the user and the expected cost rate per unit time is derived in this context. We obtain the optimal maintenance policy during the maintenance Period following the expiration of the Warranty Period by minimizing such a cost rate. Numerical examples using actual failure data are presented to exemplify the applicability of the methodologies proposed in this paper.
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optimal maintenance policies during the post Warranty Period for second hand item
International Conference on Quality Reliability Risk Maintenance and Safety Engineering, 2011Co-Authors: Daekyung Kim, Jaehak Lim, Dong Ho ParkAbstract:This paper studies the optimal Periodic PM policies of a second-hand item following the expiration of Warranty. The criterion used to determine the optimality of the PM is the expected maintenance cost rate per unit time from the customer's perspective. The Periodic PM of the item starts right after the Warranty is expired and all maintenance costs are paid by the customer. Given the cost structures of maintaining the item, we determine the optimal number of PM's before replacing the item by a new one and the optimal length of Period for the Periodic PM following the expiration of Warranty.
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a bayesian approach to maintenance policy based on cost and downtime after non renewing Warranty
Communications in Statistics-theory and Methods, 2010Co-Authors: Ki-mun Jung, Dong Ho ParkAbstract:This article adopts a Bayesian approach to derive an optimal maintenance policy following the expiration of non renewing Warranty. If the system fails during its Warranty Period, it is replaced with a new one. If the system failure occurs after the Warranty Period is expired, then it is minimally repaired at each failure. As the criteria to determine the optimal replacement Period, we use the expected cost and the expected downtime during the life cycle of the system. Under the replacement model considered, we first derive the formulas to compute the expected downtime per unit time and the expected cost rate per unit time in general. When the failure times are assumed to follow a Weibull distribution with unknown parameters, we propose an optimal maintenance policy based on the Bayesian approach, under which such unknown parameters are updated using the observed data. The overall value function suggested by Jiang and Ji (2002) is utilized to combine the expected downtime and the expected cost rate and to ...
Minjae Park - One of the best experts on this subject based on the ideXlab platform.
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determination of optimal Warranty Period with preventive maintenance actions for items from heterogeneous populations
Mathematical Problems in Engineering, 2020Co-Authors: Minjae ParkAbstract:In this study, we develop an optimal maintenance policy with replacement service and minimal repair service for items from heterogeneous populations and determine the optimal Warranty length and repair time threshold. We consider the information-based repair-replacement policy model and develop the formula to evaluate the expected cost rate during the product life cycle. A general formulation is derived for the expected cost rate under a Warranty policy for items of heterogeneous populations. When a replacement service and minimal repair service are provided for a failed item, then an item from a weak population has the property of an item from a weak population after service. Similarly, an item from a strong population has the property of an item from a strong population after service. We define the optimal maintenance strategies to minimize the expected cost rate with failure time and repair time for items with heterogeneous reliability characteristics. The effects of parameters of the intensity function for the failure times on the optimal length of the Warranty Period are studied numerically. Assuming that the product deteriorates, we illustrate the proposed approach using numerical applications and observe the impacts of relevant parameters on the optimal length of the Warranty Period.
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Warranty cost analysis for second hand products under a two stage repair or full refund policy
Reliability Engineering & System Safety, 2020Co-Authors: Minjae Park, Ki-mun Jung, Dong Ho ParkAbstract:Abstract With this paper, we consider an optimal Warranty policy for second-hand products based on a two-stage repair-or-full-refund maintenance strategy to determine an optimal length of Warranty Period from the dealer's point of view. Because replacing failed products may not be an option with second-hand products, we newly introduce in this paper the concept of full refund rather than replacement. We pre-specify a repair time threshold and define the length of maintenance Period during which the dealer will maintain the product as the product maintenance cycle. Following this policy, if the product failure cannot be repaired within the repair time threshold during the Warranty Period, the user receives a full refund and the maintenance cycle ends. Otherwise, the user receives only minimal repairs to the product, and if the dealer does not issue a full refund during the Warranty Period, the maintenance cycle ends when the Warranty expires. Given a certain cost structure charged to the dealer, we derive mathematical formulas to evaluate the expected length of a maintenance cycle and the expected total maintenance cost during the cycle. As a criterion for the optimality of the Warranty policy, we utilize the expected cost during the product maintenance cycle to propose the optimal Warranty policy. Assuming the power law model for product failures and a two-parameter Weibull distribution for the repair times, we illustrate our proposed Warranty policy numerically and conduct sensitivity analysis to study the impacts of several relevant parameters on the optimal Warranty policy.
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cost models for age replacement policies and block replacement policies under Warranty
Applied Mathematical Modelling, 2016Co-Authors: Minjae Park, Hoang PhamAbstract:Abstract In this paper, we elaborate on cost models by examining the renewable and non-renewable Warranty policies subject to minimal repair within the Warranty Period and the post-Warranty Period. Among various maintenance policies, the block replacement policy and the age replacement policy have been investigated and compared under the broader Warranty perspective. The cost model is developed from the perspective of the customer. This analytical model should provide manufacturers with a better understanding of customer behavior. We consider failure time and repair time simultaneously instead of the traditional two dimensions such as age and usage because it may be difficult to obtain usage information. For the customer's satisfaction, the repair time threshold, which has several types based on the properties of a product, is fixed. However, if the repair time exceeds the repair time threshold, the decision is to discontinue providing the repair service and to provide a replacement service. We obtain and compare the differences between maintenance policies using the expected cost rate, both under the non-renewable Warranty policy and the renewable Warranty policy. The suggested model provides better guidance for finding an optimal maintenance policy. Numerical examples are discussed to demonstrate the applicability of the methodology derived in the paper.
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cost optimization model following extended renewing two phase Warranty
Computers & Industrial Engineering, 2015Co-Authors: Ki-mun Jung, Minjae Park, Dong Ho ParkAbstract:Abstract In this paper, we study an extended Warranty model under which the customer is offered an additional Warranty Period after the original two-phase Warranty expires. Under the original two-phase Warranty, the Warranty Period is divided into two non-overlapping subintervals, one of which is for replacement Warranty, and the other is for minimal repair Warranty. If the system failure occurs during the original Warranty Period, the failed system is either replaced or minimally repaired by the manufacturer, and if the failure occurs during the extended Warranty Period, only the minimal repair is conducted. For the system failure during the replacement Warranty Period, the failed system is replaced by a new one, and the Warranty term is renewed anew. Following the expiration of extended Warranty, the customer is solely responsible for maintaining the system for a fixed length of time Period and replaces the system at the end of such a maintenance Period. During the maintenance Period, only the minimal repair is given for each system failure. Such a maintenance model can be considered as a generalization of several existing maintenance models which can be obtained as special cases. The main purpose of this article is to determine, from the customer’s perspective, the optimal length of maintenance Period after the extended Warranty expires. As the criterion to determine the optimal replacement strategy, we adopt the expected cost rate per unit time during the life cycle of the system. Given the cost structures incurred during the life cycle of the system, we formulate the expected cost and the expected length of life cycle to obtain the expected cost rate. The uniqueness of optimal solution for the decision variable is verified when the life distribution of the system shows an increasing failure rate. Numerical examples are provided to illustrate the proposed optimal replacement strategy.
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optimal post Warranty maintenance policy with repair time threshold for minimal repair
Reliability Engineering & System Safety, 2013Co-Authors: Minjae Park, Ki-mun Jung, Dong Ho ParkAbstract:Abstract In this paper, we consider a renewable minimal repair–replacement Warranty policy and propose an optimal maintenance model after the Warranty is expired. Such model adopts the repair time threshold during the Warranty Period and follows with a certain type of system maintenance policy during the post-Warranty Period. As for the criteria for optimality, we utilize the expected cost rate per unit time during the life cycle of the system, which has been frequently used in many existing maintenance models. Based on the cost structure defined for each failure of the system, we formulate the expected cost rate during the life cycle of the system, assuming that a renewable minimal repair–replacement Warranty policy with the repair time threshold is provided to the user during the Warranty Period. Once the Warranty is expired, the maintenance of the system is the user's sole responsibility. The life cycle of the system is defined on the perspective of the user and the expected cost rate per unit time is derived in this context. We obtain the optimal maintenance policy during the maintenance Period following the expiration of the Warranty Period by minimizing such a cost rate. Numerical examples using actual failure data are presented to exemplify the applicability of the methodologies proposed in this paper.
Alberto Cuocolo - One of the best experts on this subject based on the ideXlab platform.
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Warranty Period of normal stress myocardial perfusion imaging in hypertensive patients a parametric survival analysis
Journal of Nuclear Cardiology, 2020Co-Authors: Wanda Acampa, Francesco Rozza, Emilia Zampella, Roberta Assante, Teresa Mannarino, C Nappi, Ciro Mainolfi, Mario Petretta, Bruno Trimarco, Alberto CuocoloAbstract:We evaluated the Warranty Period of a normal stress myocardial perfusion single-photon emission computed tomography (MPS) in hypertensive patients. A total of 471 consecutive hypertensive patients with suspected coronary artery disease and normal perfusion at stress MPS were followed for a mean of 76 ± 21 months. Endpoint events were cardiac death or nonfatal myocardial infarction. With Cox analysis, age (hazard ratio 1.1, P 60 years old who underwent pharmacologic stress test. In patients undergoing exercise test, peak systolic blood pressure (BP; hazard ratio 1.1, P < .005) emerged as predictor of events, and only subjects with peak systolic BP < 160 mmHg remained at low risk for the entire length of follow-up. In contrast, for patients with peak systolic BP ≥180 mmHg, the time to achieve a cumulative cardiac risk level of 3% was 18 months. In hypertensive patients, the Warranty Period of a normal stress MPS varies according to stress type and peak systolic BP. A normal stress MPS can be considered reassuring in subjects ≤60 years old who performed exercise stress test and a peak systolic BP < 160 mmHg.
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Warranty Period of normal stress myocardial perfusion imaging in diabetic patients a propensity score analysis
Journal of Nuclear Cardiology, 2014Co-Authors: Wanda Acampa, Mario Petretta, Renato Cuocolo, Stefania Daniele, Valeria Cantoni, Alberto CuocoloAbstract:We evaluated the relationship between diabetes and temporal characteristics of cardiac risk at long-term follow-up in a propensity score-matched cohort of diabetic and non-diabetic patients with normal stress myocardial perfusion single-photon emission computed tomography (MPS). We studied 828 consecutive patients with suspected or known coronary artery disease and normal perfusion at stress MPS. To account for differences in baseline characteristics between diabetics and non-diabetics, we created a propensity score-matched cohort considering clinical variables and stress type. After matching, clinical characteristics were comparable in 260 diabetic and 260 non-diabetic patients. All patients were followed for at least 1 year (median 53 months). End-point events were cardiac death or nonfatal myocardial infarction. At Cox analysis, diabetes (hazard ratio 3.9, P 45% remained at low risk for the entire length of follow-up, while the highest probability of events and the major risk acceleration was observed in patients with diabetes and post-stress LVEF ≤45%. After a normal stress MPS, diabetic patients are at higher risk for cardiac events than non-diabetic subjects also after balancing clinical characteristics and stress type by propensity score analysis. The Warranty Period of a normal stress MPS varies according to diabetic status and post-stress LVEF.
Gi Mun Jung - One of the best experts on this subject based on the ideXlab platform.
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optimal maintenance policies during the post Warranty Period
Reliability Engineering & System Safety, 2003Co-Authors: Gi Mun Jung, Dong Ho ParkAbstract:Abstract This paper develops the optimal Periodic preventive maintenance policies following the expiration of Warranty. We consider two types of Warranty policies to discuss such optimum maintenance policies: renewing Warranty and non-renewing Warranty. From the user's perspective, the product is maintained free of charge or with prorated cost on failure during the Warranty Period. However, the users will have to repair or replace the failed product at their own expenses during the post-Warranty Period. Given the cost structure to the user during the cycle of the product, we derive the expressions for the expected maintenance costs for the Periodic preventive maintenance following the expiration of Warranty when applying two types of Warranty policies and obtain the optimal number and the optimal Period for such post-Warranty maintenance policies by minimizing the expected long-run maintenance cost per unit time. Explicit solutions for the optimal Periodic preventive maintenance are presented for illustrative purposes.
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a bayesian approach to optimal replacement policy for a repairable system with Warranty Period
Communications for Statistical Applications and Methods, 2002Co-Authors: Gi Mun Jung, Sungsil HanAbstract:This paper considers a Bayesian approach to determine an optimal replacement policy for a repairable system with Warranty Period. The mathematical formula of the expected cost rate per unit time is obtained for two cases : RFRW(renewing free-replacement Warranty) and RPRW(renewing pro-rata Warranty). When the failure time is Weibull distribution with uncertain parameters, a Bayesian approach is established to formally express and update the uncertain parameters for determining an optimal replacement policy. Some numerical examples are presented for illustrative purpose.
Ki-mun Jung - One of the best experts on this subject based on the ideXlab platform.
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Warranty cost analysis for second hand products under a two stage repair or full refund policy
Reliability Engineering & System Safety, 2020Co-Authors: Minjae Park, Ki-mun Jung, Dong Ho ParkAbstract:Abstract With this paper, we consider an optimal Warranty policy for second-hand products based on a two-stage repair-or-full-refund maintenance strategy to determine an optimal length of Warranty Period from the dealer's point of view. Because replacing failed products may not be an option with second-hand products, we newly introduce in this paper the concept of full refund rather than replacement. We pre-specify a repair time threshold and define the length of maintenance Period during which the dealer will maintain the product as the product maintenance cycle. Following this policy, if the product failure cannot be repaired within the repair time threshold during the Warranty Period, the user receives a full refund and the maintenance cycle ends. Otherwise, the user receives only minimal repairs to the product, and if the dealer does not issue a full refund during the Warranty Period, the maintenance cycle ends when the Warranty expires. Given a certain cost structure charged to the dealer, we derive mathematical formulas to evaluate the expected length of a maintenance cycle and the expected total maintenance cost during the cycle. As a criterion for the optimality of the Warranty policy, we utilize the expected cost during the product maintenance cycle to propose the optimal Warranty policy. Assuming the power law model for product failures and a two-parameter Weibull distribution for the repair times, we illustrate our proposed Warranty policy numerically and conduct sensitivity analysis to study the impacts of several relevant parameters on the optimal Warranty policy.
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cost optimization model following extended renewing two phase Warranty
Computers & Industrial Engineering, 2015Co-Authors: Ki-mun Jung, Minjae Park, Dong Ho ParkAbstract:Abstract In this paper, we study an extended Warranty model under which the customer is offered an additional Warranty Period after the original two-phase Warranty expires. Under the original two-phase Warranty, the Warranty Period is divided into two non-overlapping subintervals, one of which is for replacement Warranty, and the other is for minimal repair Warranty. If the system failure occurs during the original Warranty Period, the failed system is either replaced or minimally repaired by the manufacturer, and if the failure occurs during the extended Warranty Period, only the minimal repair is conducted. For the system failure during the replacement Warranty Period, the failed system is replaced by a new one, and the Warranty term is renewed anew. Following the expiration of extended Warranty, the customer is solely responsible for maintaining the system for a fixed length of time Period and replaces the system at the end of such a maintenance Period. During the maintenance Period, only the minimal repair is given for each system failure. Such a maintenance model can be considered as a generalization of several existing maintenance models which can be obtained as special cases. The main purpose of this article is to determine, from the customer’s perspective, the optimal length of maintenance Period after the extended Warranty expires. As the criterion to determine the optimal replacement strategy, we adopt the expected cost rate per unit time during the life cycle of the system. Given the cost structures incurred during the life cycle of the system, we formulate the expected cost and the expected length of life cycle to obtain the expected cost rate. The uniqueness of optimal solution for the decision variable is verified when the life distribution of the system shows an increasing failure rate. Numerical examples are provided to illustrate the proposed optimal replacement strategy.
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optimal post Warranty maintenance policy with repair time threshold for minimal repair
Reliability Engineering & System Safety, 2013Co-Authors: Minjae Park, Ki-mun Jung, Dong Ho ParkAbstract:Abstract In this paper, we consider a renewable minimal repair–replacement Warranty policy and propose an optimal maintenance model after the Warranty is expired. Such model adopts the repair time threshold during the Warranty Period and follows with a certain type of system maintenance policy during the post-Warranty Period. As for the criteria for optimality, we utilize the expected cost rate per unit time during the life cycle of the system, which has been frequently used in many existing maintenance models. Based on the cost structure defined for each failure of the system, we formulate the expected cost rate during the life cycle of the system, assuming that a renewable minimal repair–replacement Warranty policy with the repair time threshold is provided to the user during the Warranty Period. Once the Warranty is expired, the maintenance of the system is the user's sole responsibility. The life cycle of the system is defined on the perspective of the user and the expected cost rate per unit time is derived in this context. We obtain the optimal maintenance policy during the maintenance Period following the expiration of the Warranty Period by minimizing such a cost rate. Numerical examples using actual failure data are presented to exemplify the applicability of the methodologies proposed in this paper.
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a bayesian approach to maintenance policy based on cost and downtime after non renewing Warranty
Communications in Statistics-theory and Methods, 2010Co-Authors: Ki-mun Jung, Dong Ho ParkAbstract:This article adopts a Bayesian approach to derive an optimal maintenance policy following the expiration of non renewing Warranty. If the system fails during its Warranty Period, it is replaced with a new one. If the system failure occurs after the Warranty Period is expired, then it is minimally repaired at each failure. As the criteria to determine the optimal replacement Period, we use the expected cost and the expected downtime during the life cycle of the system. Under the replacement model considered, we first derive the formulas to compute the expected downtime per unit time and the expected cost rate per unit time in general. When the failure times are assumed to follow a Weibull distribution with unknown parameters, we propose an optimal maintenance policy based on the Bayesian approach, under which such unknown parameters are updated using the observed data. The overall value function suggested by Jiang and Ji (2002) is utilized to combine the expected downtime and the expected cost rate and to ...
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optimization of cost and downtime for replacement model following the expiration of Warranty
Reliability Engineering & System Safety, 2008Co-Authors: Ki-mun Jung, Dong Ho ParkAbstract:Abstract This paper deals with the optimal replacement policies following the expiration of Warranty: renewing Warranty and non-renewing Warranty. If the system fails during its Warranty Period, it is replaced with a new one and if the system fails after the Warranty Period is expired, then it is minimally repaired at each failure. The criterion used to determine the optimality of the replacement Period is the overall value function, which is established based on the expected downtime and the expected cost rate combined. Firstly, we develop the expected downtime per unit time and the expected cost rate per unit time for our replacement model when the cost and downtime structures of maintaining the system are given. The overall value function suggested by Jiang and Ji [Age replacement policy: a multi-attribute value model. Reliab Eng Syst Saf 2002;76:311–8] is then utilized to determine the optimal maintenance Period based on the expected downtime and the expected cost rate. Numerical examples are presented for illustrative purpose.
