Modeling Expected Failure Considering Repair Time and Degradation: A Rail System Case Study

The repeated failures of any equipment or systems are modeled as a renewal process. The management needs an assessment of the number of future failures to allocate the resources needed for fast repairs. Based on the idea of expectation by conditioning, special Volterra-type integral equations are derived for general types of repairs, considering the length of repair and reduced degradation of the idle object. In addition to minimal repair and failure replacement, partial repairs are also discussed when the repair results in reduction of the number of future failures or decreases the effective age of the object. Numerical integration-based algorithm and simulation study are performed to solve the resulting integral equation. Since the geometry degradation in different dimensions of a rail track and controlling and maintaining defects are of importance, a numerical example using the rail industry data is conducted. Expected number of failures of different failure type modes in rail track is calculated within a two-year interval. Results show that within a two-year period, anticipated occurrences of cross level failures, surface failures, and DPI failures are 2.4, 3.8, and 5.8, respectively.

Optimal replacement policy of products with repair-cost threshold after the extended warranty

The reliability of the product sold under a warranty is usually maintained by the manufacturer during the warranty period. After the expiry of the warranty, however, the consumer confronts a problem about how to maintain the reliability of the product. This paper proposes, from the consumer's perspective, a replacement policy after the extended warranty, under the assumption that the product is sold under the renewable free replacement warranty (RFRW) policy in which the replacement is dependent on the repair-cost threshold. The proposed replacement policy is the replacement after the extended warranty is performed by the consumer based on the repair-cost threshold or preventive replacement (PR) age, which are decision variables. The expected cost rate model is derived from the consumer's perspective. The existence and uniqueness of the optimal solution that minimizes the expected cost rate per unit time are offered. Finally, a numerical example is presented to exemplify the proposed model.

Two-stage optimization model for renewing warranty considering warranty deadline

Renewing warranty can provide customers with better service,and thus help manufacturers to gain market opportunities.In engineering practice,the cost for replacement is usually higher than the cost for maintenance,hence manufacturers often face huge challenge to reduce the warranty service cost.With consideration of the warranty deadline,we propose a two-stage optimization model for renewing warranty.In the first stage,a renewing warranty with deadline(RWD)policy is implemented,where the deadline represents the cumulative uptime threshold.When the cumulative uptime exceeds the deadline,the product will be minimally repaired and kept to the residual warranty period.When RWD is expired,the replacement warranty with limited repairs(RWLR)policy is applied.Under the free replacement and pro-rata warranty policy,the corresponding two-stage cost optimization model is established from the manufacturer’s perspective,the aim is to minimize the cost rate and obtain the optimal warranty period.A numerical example is provided to illustrate the validity of the proposed model,and the sensitivity analysis is also carried out.

Component reallocation and system replacement maintenance based on availability and cost in series systems

Component reallocation(CR)is receiving increasing attention in many engineering systems with functionally interchangeable and unbalanced degradation components.This paper studies a CR and system replacement maintenance policy of series repairable systems,which undergoes minimal repairs for each emergency failure of components,and considers constant downtime and cost of minimal repair,CR and system replacement.Two binary mixed integer nonlinear programming models are respectively established to determine the assignment of CR,and the uptime right before CR and system replacement with the objective of minimizing the system average maintenance cost and maximizing the system availability.Further,we derive the optimal uptime right before system replacement with maximization of the system availability,and then give the relationship between the system availability and the component failure rate.Finally,numerical examples show that the CR and system replacement maintenance policy can effectively reduce the system average maintenance cost and improve the system availability,and further give the sensitivity analysis and insights of the CR and system replacement maintenance policy.

“A Prospective Randomized Case-Control Study To Evaluate Mini Right Thoracotomy versus Conventional Sternotomy For Mitral Valve Repair In Rheumatic Heart Disease.”

Purpose: Right mini thoracotomy has been evaluated in many studies for mitral valve repair mainly in degenerative valvular disease but not in rheumatic heart disease. Mitral valve repair is more challenging in rheumatic etiology due to complexity of lesions. This prospective randomized case control study was designed to evaluate repair through mini right thoracotomy and to compare the clinical and echocardiographic outcomes with sternotomy in rheumatic patients. Methods: 25 patients of rheumatic heart disease underwent mitral valve repair through mini right thoracotomy (group I). Various clinical and functional parameters were compared with 25 patients of mitral valve repair through sternotomy (group II). On follow up the results were compared in both groups for clinical and echocardiographic parameters. Results: The various pre-operative demographic parameters were comparable in two groups. Equal rate of mitral valve repair (group I-21/25, 84% and group II-21/25, 84%) was achieved in both groups. The various intra-operative and post-operative clinical parameters were better in group I .There were equivalent functional and valve related outcomes in both groups in term of NYHA class (1.28 ± 0.613 vs 1.08 ± 0.276, P = 0.144), post-operative mitral valve area (2.43 ± 0.891 vs 2.82 ± 0.662, P = 0.090), incidence of more than mild mitral regurgitation (0) and mean pressure gradient across mitral valve (4.98 ± 3.33 vs 4.23 ± 1.5, P = 0.309). Conclusion: Mitral valve repair through mini right thoracotomy approach in rheumatic etiology is feasible and safe with equivalent rate of successful repair as compared to median sternotomy. It is associated with lesser morbidity, cosmetic advantage and lesser resource utilization.

Right Axillary Thoracotomy Should Be the Standard of Care for Repair of Non-Complex Congenital Heart Defects in Infants and Children

Minimally invasive approaches for cardiac surgery in children have been lagging in comparison to the adult world.A wide range of the most common congenital heart defects in infants and children can be repaired suc-cessfully through a variety of non-sternotomy incisions.This has been shown to be associated with superior cos-metic results,shorter hospital stays,and rapid return to full activity compared to sternotomy.These approaches have been around for decades,but they have not been widely adopted for a variety of reasons.Right axillary thor-acotomy is one of these approaches that we believe should be the new standard for the repair of a wide variety of heart defects in children and will be the focus of our current review.

OPTIMUM ORDERING POLICY FOR PREVENTIVE AGE REPLACEMENT

Most of the spare ordering policies treated up to now have assumed that preventive and corrective replacement costs are equal, which implies in essential that there is no significant need for preventive replacement. This paper presents an ordering policy for preventive age replacement with minimal repair. Introducing the replacement, repair, inventory holding and shortage costs, the expected cost rate is derived. A procedure to determine jointly the ordering time for a spare and the preventive replacement time for the operating unit so as to minimize the expected cost rate is proposed. To explain the ordering policy and the optimization procedure, a numerical example is also included.

SOME RESULTS ON COMPARISON OF MAINTENANCE POLICIES

In this paper, we study the stochastic comparisons of minimal repair replacement policies in repairable case. We give some results on comparisons of the same unit for different policies and on comparisons of the same policies for different units.