A new δ-shock model for systems subject to multiple failure types and its optimal order-replacement policy

2019 ◽  
Vol 234 (1) ◽  
pp. 138-150
Author(s):  
Yi Jiang
Keyword(s):  
Operating Time ◽  
Replacement Policy ◽  
Sensitivity Analyses ◽  
Optimal Order ◽  
Shock Model ◽  
Cost Rate ◽  
Long Run ◽  
Average Operating ◽  
Average Operating Time ◽  
Average Cost Rate

In this article, a generalized δ-shock model with multi-failure thresholds is studied. For the new model, the system fails depending on the interval times between two consecutive shocks which arrive according to a Poisson process. The shorter interval times may cause more serious failures and thus result in longer down times and more costs for repair. Assuming that the repair is imperfect, an order-replacement policy N is adopted. Explicitly, the spare system for replacement is ordered at the end of ( N – 1)th repair and the aging system is replaced at the Nth failure or at an unrepairable failure, whichever occurs first. In addition, the system must meet the requirement of availability, that is, the long-run average operating time per unit time should not be lower than a certain level. The average cost rate C( N) and the stationary availability A( N) are derived analytically. Some convergence properties of A( N) and C( N) are also investigated. The optimal order-replacement policy N* can be obtained numerically with the constraint of availability. Finally, an illustrative example is given and some sensitivity analyses are conducted to demonstrate the proposed shock model.

scholarly journals Determining Optimal Replacement Policy with an Availability Constraint via Genetic Algorithms

2017 ◽  
Vol 2017 ◽  
pp. 1-8 ◽  
Author(s):  
Shengliang Zong ◽  
Guorong Chai ◽  
Yana Su
Keyword(s):  
Genetic Algorithm ◽  
Average Cost ◽  
Operating Time ◽  
Threshold Value ◽  
Replacement Policy ◽  
Time Interval ◽  
Cost Rate ◽  
Optimal Replacement ◽  
Optimal Replacement Policy ◽  
Average Cost Rate

We develop a model and a genetic algorithm for determining an optimal replacement policy for power equipment subject to Poisson shocks. If the time interval of two consecutive shocks is less than a threshold value, the failed equipment can be repaired. We assume that the operating time after repair is stochastically nonincreasing and the repair time is exponentially distributed with a geometric increasing mean. Our objective is to minimize the expected average cost under an availability requirement. Based on this average cost function, we propose the genetic algorithm to locate the optimal replacement policyNto minimize the average cost rate. The results show that the GA is effective and efficient in finding the optimal solutions. The availability of equipment has significance effect on the optimal replacement policy. Many practical systems fit the model developed in this paper.

Geometric process repair model for an unreliable production system with an intermediate buffer

2016 ◽  
Vol 231 (4) ◽  
pp. 747-759 ◽  
Author(s):  
Guoqing Cheng ◽  
Binghai Zhou ◽  
Ling Li
Keyword(s):  
Production System ◽  
Buffer Stock ◽  
Sensitivity Analyses ◽  
Cost Rate ◽  
Long Run ◽  
Proposed Model ◽  
Joint Policy ◽  
Traditional Assumption ◽  
Average Cost Rate ◽  
Continuous Demand

In this paper, we consider an unreliable production system consisting of two machines (M1 and M2) in which M1 produces a single product type to satisfy a constant and continuous demand of M2 and it is subjected to random failures. In order to palliate perturbations caused by failures, a buffer stock is built up to satisfy the demand during the production unavailability of M1. A traditional assumption made in the previous research is that repairs can restore the failed machines to as good as new state. To develop a more realistic mathematical model of the system, we relax this assumption by assuming that the working times of M1 after repairs are geometrically decreasing, which means M1 cannot be repaired as good as new. Undergoing a specified number of repairs, M1 will be replaced by an identical new one. A bivariate policy [Formula: see text] is considered, where S is the buffer stock level and N is the number of failures at which M1 is replaced. We derive the long-run average cost rate [Formula: see text] used as the basis for optimal determination of the bivariate policy. The optimal policies [Formula: see text] and [Formula: see text] are derived, respectively. Then, an algorithm is presented to find the optimal joint policy [Formula: see text]. Finally, an illustrative example is given to validate the proposed model. Sensitivity analyses are also carried out to illustrate the effectiveness and robustness of the proposed methodology.

A bivariate replacement policy for an imperfect repair system based on geometric processes

2018 ◽  
Vol 233 (4) ◽  
pp. 670-681
Author(s):  
Qinglai Dong ◽  
Lirong Cui ◽  
Hongda Gao
Keyword(s):  
Optimal Solution ◽  
Working Time ◽  
Repair Time ◽  
Replacement Policy ◽  
Repair System ◽  
Cost Rate ◽  
Delayed Repair ◽  
Long Run ◽  
Average Cost Rate ◽  
Geometric Processes

A repair replacement model for a deteriorating system with delayed repair is studied, in which the successive working times after repair and the consecutive repair times of the system are described by geometric processes. The instantaneous availability is studied in the case of general distributions for the working time, repair time and delayed repair time. A bivariate replacement policy is considered, that is, the system is replaced whenever the working age of the system reaches T or at the first hitting time of the working time after repair with respect to the working time threshold τ, whichever occurs first. The explicit expression of the long-run average cost rate under the replacement policies is derived. The corresponding optimal replacement policy can be determined numerically, and numerical examples are presented to demonstrate the application of the developed model and approach. It is shown that the optimal solution and optimal value are sensitive to the tiny change in the ratios of the Geometric processes and the expectation of the delayed repair time.

Collaborative Optimization of Replacement and Spare Ordering of a Deteriorating System with Two Failure Types

2012 ◽  
Vol 220-223 ◽  
pp. 210-214 ◽  
Author(s):  
Guo Qing Cheng ◽  
Ling Li
Keyword(s):  
Average Cost ◽  
Life Time ◽  
Collaborative Optimization ◽  
Replacement Policy ◽  
Cost Rate ◽  
Ordering Policy ◽  
Long Run ◽  
Proposed Model ◽  
Average Cost Rate ◽  
Optimal Ordering

This paper proposes a model to find optimal ordering and replacement policies for a deteriorating system. Assume that the life time of system has a normal distribution, and it has two failures types, typeⅠfailure is repairable, whereas typeⅡfailure is catastrophic which leads to replacement. A replacement policy N is adopted by which the system will be replaced by an identical new one if available at the time following the Nth typeⅠfailure or the 1st typeⅡfailure whichever occurs first. Furthermore, it considers an ordering policy M in which a spare unit is ordered at the time of the Mth typeⅠfailure or 1st typeⅡfailure, whichever occurs first. The objective is to derive the long-run average cost rate and then find the optimal policy (N,M) such that the average cost rate is minimized. Finally, a numerical example is provided to illustrate the proposed model.

Minilaparotomy Cholecystectomy as a Day Surgery Procedure: A Prospective Clinical Pilot Study

2007 ◽  
Vol 96 (3) ◽  
pp. 206-208 ◽  
Author(s):  
J. Harju ◽  
M. Pääkkönen ◽  
M. Eskelinen
Keyword(s):  
Randomised Trial ◽  
Operating Time ◽  
Day Surgery ◽  
Prospective Randomised Trial ◽  
Wound Pain ◽  
Average Operating ◽  
Average Operating Time ◽  
Study Support ◽  
The Mean

Background and Aims: In some studies minilaparotomy cholecystectomy (MC) has been shown to be as good as laparoscopic cholecystectomy (LC) in the surgical treatment of cholecystolithiasis. To our knowledge, the MC operation is rarely considered as a day surgery procedure. Patients and Methods: Thirty elective symptomatic non-complicated patients were included in the study during the end of the year 2004 to June 2005. The mean age of patients was 52 years (range 27–68), the mean body mass index 29 kg/m2 (range 19–41). Gallstones were confirmed with ultrasound and the pre-operative liver laboratory tests were normal in all patients. A five (+/-2) centimetre-long incision was used avoiding to split the rectus abdominis muscle. All patients were re-evaluated four weeks postoperatively with the follow-up letter. Results: The average operating time was 51 minutes (range 30–105 minutes). Day surgery was possible in 25 cases (83%). Five patients (17%) stayed over night at the hospital. There were four (13%) conversions to conventional cholecystectomy. The average postoperative sick leave was 16 days (range 14–30). Two patients returned to hospital. One patient had wound pain, but no complication was found, and the patient was not admitted. One patient had a wound infection and spent 6 days in the hospital. Twenty-nine (97%) patients were satisfied with the operation and were ready to recommend it for other patients. Conclusions: The results of this study support the suitability of MC as a day surgery procedure, but a prospective randomised trial is needed to evaluate the relative advantages of MC and LC.

Optimal repair/replacement policy for a general repair model

2001 ◽  
Vol 33 (1) ◽  
pp. 206-222 ◽  
Author(s):  
Xiaoyue Jiang ◽  
Viliam Makis ◽  
Andrew K. S. Jardine
Keyword(s):  
Average Cost ◽  
Failure Time ◽  
Operating Time ◽  
Replacement Policy ◽  
Repair Cost ◽  
Virtual Age ◽  
Preventive Replacement ◽  
Long Run ◽  
Special Cases ◽  
Cost Limit

In this paper, we study a maintenance model with general repair and two types of replacement: failure and preventive replacement. When the system fails a decision is made whether to replace or repair it. The repair degree that affects the virtual age of the system is assumed to be a random function of the repair-cost and the virtual age at failure time. The system can be preventively replaced at any time before failure. The objective is to find the repair/replacement policy minimizing the long-run expected average cost per unit time. It is shown that a generalized repair-cost-limit policy is optimal and the preventive replacement time depends on the virtual age of the system and on the length of the operating time since the last repair. Computational procedures for finding the optimal repair-cost limit and the optimal average cost are developed. This model includes many well-known models as special cases and the approach provides a unified treatment of a wide class of maintenance models.

scholarly journals Video assisted resections. Increasing access to minimally invasive liver surgery?

2015 ◽  
Vol 42 (5) ◽  
pp. 318-324 ◽  
Author(s):  
Fabricio Ferreira Coelho ◽  
Marcos Vinícius Perini ◽  
Jaime Arthur Pirola Kruger ◽  
Renato Micelli Lupinacci ◽  
Fábio Ferrari Makdissi ◽  
...  
Keyword(s):  
Operating Time ◽  
Perioperative Outcomes ◽  
Liver Lesions ◽  
Minimally Invasive Liver Surgery ◽  
Video Assisted ◽  
Average Operating ◽  
Average Operating Time ◽  
Average Size ◽  
Anesthesia Time ◽  
Prospective Database

Objective: To evaluate perioperative outcomes, safety and feasibility of video-assisted resection for primary and secondary liver lesions. Methods : From a prospective database, we analyzed the perioperative results (up to 90 days) of 25 consecutive patients undergoing video-assisted resections in the period between June 2007 and June 2013. Results : The mean age was 53.4 years (23-73) and 16 (64%) patients were female. Of the total, 84% were suffering from malignant diseases. We performed 33 resections (1 to 4 nodules per patient). The procedures performed were non-anatomical resections (n = 26), segmentectomy (n = 1), 2/3 bisegmentectomy (n = 1), 6/7 bisegmentectomy (n = 1), left hepatectomy (n = 2) and right hepatectomy (n = 2). The procedures contemplated postero-superior segments in 66.7%, requiring multiple or larger resections. The average operating time was 226 minutes (80-420), and anesthesia time, 360 minutes (200-630). The average size of resected nodes was 3.2 cm (0.8 to 10) and the surgical margins were free in all the analyzed specimens. Eight percent of patients needed blood transfusion and no case was converted to open surgery. The length of stay was 6.5 days (3-16). Postoperative complications occurred in 20% of patients, with no perioperative mortality. Conclusion : The video-assisted liver resection is feasible and safe and should be part of the liver surgeon armamentarium for resection of primary and secondary liver lesions.

A hybrid preventive maintenance model for systems with partially observable degradation

2020 ◽  
Vol 31 (3) ◽  
pp. 345-365 ◽  
Author(s):  
Maxim Finkelstein ◽  
Ji Hwan Cha ◽  
Gregory Levitin
Keyword(s):  
Preventive Maintenance ◽  
Replacement Policy ◽  
Hybrid Strategy ◽  
Cost Rate ◽  
Shot Noise Process ◽  
Shock Process ◽  
Long Run ◽  
Age Replacement ◽  
Partially Observable ◽  
Maintenance Model

Abstract A new model of hybrid preventive maintenance of systems with partially observable degradation is developed. This model combines condition-based maintenance with age replacement maintenance in the proposed, specific way. A system, subject to a shock process, is replaced on failure or at some time ${T}_S$ if the number of shocks experienced by this time is greater than or equal to m or at time $T>{T}_S$ otherwise, whichever occurs first. Each shock increases the failure rate of the system at the random time of its occurrence, thus forming a corresponding shot-noise process. The real deterioration of the system is partially observed via observation of the shock process at time ${T}_S$. The corresponding optimization problem is solved and a detailed numerical example demonstrates that the long-run cost rate for the proposed optimal hybrid strategy is smaller than that for the standard optimal age replacement policy.

Laparoscopic “en-bloc” ligation of spermatic veins

1996 ◽  
Vol 63 (3) ◽  
pp. 384-388
Author(s):  
C. Trombetta ◽  
G. Savoca ◽  
G. Liguori ◽  
A. Tamai ◽  
S. Siracusano ◽  
...  
Keyword(s):  
General Anaesthesia ◽  
Operating Time ◽  
Case Histories ◽  
En Bloc ◽  
Optical Magnification ◽  
Average Operating ◽  
Average Operating Time ◽  
The Right

Laparoscopic varicocelectomy is suggested only for II-III grade bilateral varicocele. The optical magnification granted by videosurgical techniques, prevents damaging testicular arteries; this possibility, however, requires a considerable amount of time. We performed a laparoscopic “en-bloc” ligation without sparing the artery on 13 patients with bilateral varicocele in order to assess eventual changes in gonadal volume. 10 patients underwent bilateral “en-bloc” ligation of spermatic vessels with an average operating time of 21 minutes. In 3 other patients, “en-bloc” ligation was performed on the right side while on the left side the artery was identified and saved; in these cases the average operating time was 33 minutes. After an average follow-up period of 19 months no cases of testicle atrophy nor of hydrocele were reported. ColorDoppler sonography, performed 3 months later on the 10 patients treated by bilateral “en-bloc” ligation, showed no persistent reflux. No case of homolateral persistent reflux was encountered in the 3 patients who underwent only right-side “en-bloc” ligation, but on the left side, where selective ligation had been performed, persistence of reflux was registered in one patient. Our experience has confirmed that laparoscopic “en-bloc” ligation of the internal spermatic pedicle, sparing vasa deferentia, prevents the persistence of reflux in all cases and allows a reduction in operating time. The opportunity of treating a pathology like bilateral varicocele by means of laparoscopy, which requires general anaesthesia, needs further confirmation and a larger number of case histories.

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