Replacement Schedule Research Articles

Optimizing preventive replacement schedule in standby systems with time consuming task transfers

In many industrial and technological systems, due to factors such as deterioration, corrosion, attacks, etc., preventive replacement is typically performed according to a predetermined schedule to renew the worn or aged online element using a standby element, enhancing the mission success probability. This paper models such a standby system with its mission time being divided into a certain number of mission parts (MPs). During different MPs, according to a pre-specified sequence, different system elements are activated to perform the mission operation. Upon completing each MP, following the preventive element replacement, a time-consuming transfer procedure must be conducted to start the new MP. The mission is successful when the last MP can be accomplished by an available system element. An event transition-based method is proposed to evaluate the mission success probability (MSP). The optimal preventive replacement scheduling problem is then solved, which finds the number of MPs and their durations maximizing the MSP. In the case of heterogeneous system elements, a combined optimization problem that finds the optimal element activation sequence and the optimal preventive replacement schedule to maximize the MSP is formulated and solved. Effects of several model parameters (the number of MPs, the number of system elements, task transfer time) are investigated through examples.

Ensuring consistency between strategic plans and equipment replacement decisions

ABSTRACT Strategic business plans are based upon assumptions of future wood costs. Future wood costs are affected by future equipment cost inputs and technological change. Equipment replacement decisions react to future cost inputs and technological change, taking advantage of opportunities to reduce future wood costs. By explicitly defining future equipment cost inputs and technological change, and their effect on equipment replacement decisions, future wood costs used in strategic planning have a rational and consistent basis. To ensure consistency between strategic plans and equipment replacement decisions we developed a forward reaching dynamic programming algorithm that recognizes the special structure of the equipment replacement problem. The output is an equipment replacement schedule that can be used to project equipment investment needs, operational costs, and tree harvesting costs. The results show that when we compare the proposed algorithm with the classic infinite series machine replacement approach under constant costs, both of them presented an optimal life with 52 months and a discounted cost of 5.691 USD million. Considering a 1200 month planning horizon under technological changes, the economic life policy proved optimum with 80 months of use for the first machine, while the next generations varied between 69 and 71 months of use with a discounted cost value of 4.617 USD million. Under the estimates of future costs and technological improvements, production costs decline and production rises. The algorithm is intuitive, flexible, easy to calculate, and yields the exact solution. No restrictions are needed on cost inputs over time, technologies, or discount rates.

Effects of Aqueous-Supplementing Artificial Tears in Wearers of Biweekly Replacement Contact Lenses vs Wearers of Daily Disposable Contact Lenses.

PurposeTo compare the effects of artificial tears (ATs) in wearers of biweekly replacement silicone hydrogel contact lenses (BW-Ws) and wearers of daily disposable contact lenses (DD-Ws) of the same material.Materials and MethodsThe aqueous-supplementing ATs, OPTOyalA and OPTOidro, were assigned to be used for 2 weeks to healthy and young subjects: 1) 20 (8 and 12, respectively) BW-Ws wearing silicone hydrogel somofilcon A CLs (Clariti Elite), 2) 18 (9 and 9, respectively) DD-Ws wearing silicone hydrogel somofilcon A CLs (Clarity 1 Day), and 3) a control group of 33 (16 and 17, respectively) N-Ws. Ocular symptoms and comfort, tear volume and stability, and ocular surface condition were assessed by Ocular Surface Disease Index (OSDI), 5-Item Dry Eye Questionnaire (DEQ5), tear meniscus height (TMH), non-invasive tear break-up time (NIBUT), and evaluation of ocular redness (OR). The assessment was performed before and after 15 days of use of the ATs in the 3 groups (BW-Ws, DD-Ws, and N-Ws).ResultsNo clear significant difference was noted in symptoms and signs between OPTOyalA and OPTOidro irrespectively of the group of people studied. ATs use for 15 days produced a significant improvement in DEQ5 and OR in DD-Ws (Δ=−34%, p=0.006; Δ=−23%, p<0.001) and in N-Ws (Δ=−21%, p=0.001; Δ=−10%, p=0.006) but not in BW-Ws (Δ=−5%, p=0.072; Δ=−2%, p=0.257). No significant change was noted for TMH.ConclusionIn young and healthy subjects, the aqueous-supplementing effect of the ATs under consideration is more a rinsing and tear replacem ent effect than an increase in tear volume, and it produces an improvement of the eye redness and ocular symptoms. Contact lens wear influenced the effectiveness of ATs in a way which is correlated with the CL replacement schedule.

Risk-based life cycle cost analysis using a two-level multi-objective genetic algorithm

ABSTRACT The aim of this study has been to develop a two-level multi-objective genetic algorithm (MOGA) to optimize risk-based LCC analysis to find the optimal maintenance replacement time for road tunnel ventilation fans. Level 1 uses a MOGA based on a financial risk model to provide different risk percentages, while level 2 uses a MOGA based on an LCC model to estimate the optimal fan replacement time. Our method is compared with the approach of using a risk-based LCC model. The results are promising, showing that the risk-based LCC offers the possibility of significantly reducing the maintenance costs of the ventilation system by optimising the replacement schedule by considering the risk costs. The risk-based LCC can be used with repairable components, making it applicable, useful and implementable within Swedish Transport Administration (Trafikverket). In this study, MOGA operators have selected the cost of maintenance and risk data through the previous levels using different ways to provide different possible solutions. A drawback of the MOGA based on a risk-based LCC model with regard to its estimation is that a late replacement period over 20-year period might increase the maintenance cost. Therefore, the MOGA does not provide a good solution for a risk-based LCC.

Perbandingan Algoritma Fitness of Spring dan Algoritma Tabu Search pada Kasus Penjadwalan Perkuliahan

The compilation of lecture schedules is very important at universities for the continuity of the teaching and learning process of study programs. Such as at Andi Djemma Palopo University, Informatics Engineering Study Program. Frequently occurring alternate lectures to change course schedules is a complex thing considering the pre-existing schedule is well organized. But with the lectures, it is usually difficult to determine schedules, days, hours, rooms, and classes so that, no alternate lectures are coinciding with other subjects. so that in this Case Study, the researcher compared two methods namely the Fitness Method and the Taboo Search Algorithm to see the performance when determining the replacement schedule. The values obtained from the results of the implementation of the two methods above, are with using the fitness method is 40 while for the taboo search the maximum value obtained is 15, based on the order of the schedule of previous courses and courses that will be replaced. Thus, the value obtained by using the taboo search method is in the normal category compared to the changing fitness method. Thus, the researcher can conclude that the value obtained by the taboo search is smaller so that, it is good to be used to determine scheduling.

Optimal Age-Replacement in Anticipation of Time-Dependent, Unpunctual Policy Implementation

In many maintenance settings, it is assumed that the preventive maintenance policy prescribed by the maintenance planner is implemented without error. However, in practice, the party who implements the policy often deviates from the intended maintenance times. We study an age-replacement setting in which the maintenance worker may be unpunctual. That is, the actual preventive replacement times may deviate from the prescribed replacement times in a probabilistic manner. Previous work on this problem assumes that the degree of unpunctuality is not influenced by the length of time between scheduled replacements. We relax this assumption and let the degree of deviation depend on the prescribed replacement time. In this article, we formulate a long-run cost-rate minimization model and present analytical and numerical results that compare its optimal solution and performance to those when the unpunctual behavior is assumed to be either absent or independent of the prescribed replacement time. We also provide insights that can help maintenance planners adjust their policies in anticipation of nonstationary, unpunctual implementation.

Analysis of the Age Replacement Method to Reduce Tool Downtime

A manufacturing company engaged in the manufacturing of diesel engines in Indonesia has a problem with high downtime. The most frequent replacement frequency is in the cylinder liner line which in April - June 2018 has 1254 units of replacements, besides that the cylinder liner line also has the highest downtime of 7243.94 minutes. To overcome this problem, it is necessary to schedule tool replacement using the Age Replacement method, where this method is to determine the tool replacement schedule with the least downtime. After that the calculation is done using the Availability method, where the higher the Availability value of a tool, the better the condition of the tool to operate according to its function. And finally the calculation is done using the Reliability method, where the higher the value of the reliability of a tool, the less likely the damage will occur to the tool.

Engine replacement scheduling optimization using Data Mining

Engine overhaul activity in heavy duty equipment takes long shutdown duration, while unscheduled replacement is impacted on process delay, increasing man power cost, and production loss. One main cause of these problems is the scheduling performed just based on mechanics’ intuition and experience. On the other side, condition monitoring data are available in a large number. Reliable data processing methods are needed to disclose hidden information from the data. For the purpose, this research used three data mining methods on condition monitoring data and external factors of heavy equipment engine to get an optimized engine replacement scheduling. Clustering method was used to classify condition monitoring data, association rule was used to analyze the interrelationship between variables and time series analysis was used to predict the value of condition monitoring. The result showed that data mining methods can be used to perform scheduling optimization. Unscheduled replacement engine or engine failed in service was reduced from 31% to 13%.

Enzymes as Parts in Need of Replacement - and How to Extend Their Working Life.

Enzymes catalyze reactions in vivo at different rates and each enzyme molecule has a lifetime limit before it is degraded and replaced to enable catalysis to continue. Considering these rates together as a unitless ratio of catalytic cycles until replacement (CCR) provides a new quantitative tool to assess the replacement schedule of and energy investment into enzymes as they relate to function. Here, we outline the challenges of determining CCRs and new approaches to overcome them and then assess the CCRs of selected enzymes in bacteria and plants to reveal a range of seven orders of magnitude for this ratio. Modifying CCRs in plants holds promise to lower cellular costs, to tailor enzymes for particular environments, and to breed enzyme improvements for crop productivity.

Assessment of compliance with contact lens wear and care among university-based population in Jordan

Purposethis survey aimed to assess levels of compliance with contact lens wear and care among university student’s population in Jordan. MethodsAn interviewer-administered questionnaire was used to assess the extent of compliance among contact lens wearers toward contact lens care in a university population. The questionnaire included 12 questions regarding compliance with contact lens care, lens case/solution replacement, general hygiene procedures related to contact lens and adherence to aftercare visits. Results210 contact lens wearers were interviewed. Of the study population 187 (89 %) were females and 23 (11 %) were males. The average age of the study group was 22.35 (± 3.77) years and all the study population were students (undergraduate or postgraduate).The average compliance rate of the study population was 75 %. High level of compliance was noticeable in the following aspects; not sharing lenses with others, not sleeping while wearing lenses, hand washing before lens use and not using water to clean lenses. Moderate level of compliance was reported in the following aspects; showering/swimming with lenses, using lenses longer than recommended replacement schedule and all behaviours related to contact lens care solution. However, low levels of compliance were reported in relation to cleaning and rinsing lens case and adherence to aftercare visits. ConclusionHigh to moderate levels of compliance were reported generally by participants. However, better strategies are recommended to further increase levels of compliance among contact lens wearers in Jordan related to adherence to aftercare visits. While this study is targeted contact lens wearers from a university student’s population, a future study is recommended to include larger sample of contact lens wearers from the general lay population.

Probabilistic Health Index-Based Apparent Age Estimation for Power Transformers

This paper proposes a probabilistic health index-based method for estimating the apparent age of power transformer. Compared with the conventional weighted-score-sum based health index, the probabilistic health index is calculated as a data fusion result of kinds of transformer condition monitoring data through a constructed Bayesian belief network. The regression result of such a probabilistic health index is then applied to estimate the apparent age of the transformer through a few steps listed in the paper. The apparent age not only embodies an overall health status a transformer but also helpful for sorting a transformer fleet based on the estimated apparent age or even make it easy to make comparisons between transformer fleets. The estimated apparent age can be taken as a reference for power utilities to prioritize transformers and pay attention to the unit who owns the maximum apparent age among a fleet, thus helps to schedule replacement plans. Case studies with different transformers verify the usability and prove the advantages of the proposed method.

Optimum replacement policy for cumulative damage models based on multi-attributes

In the present paper, we investigate a preventive replacement policy based on multiple attributes. A system is subject to two types of shocks which arrive according to a non-homogeneous Poisson process. Type 1 shocks are minor and cause a random amount of damage to the system. We use a minimal repair to fix type 1 shock. Type 2 shocks are catastrophic and the system is correctively replaced at its occurrence. The probabilities of type 1 shock and type 2 shock are assumed to depend on age. A system fails (in a catastrophic failure type) once the cumulative damage reaches a failure level K or a type 2 shock happens. In addition, the system with cumulative damage of level z may fail (in a minor failure type) with probability ωz at each type 1 shock occurrence and be rectified by a minimal repair. A replacement policy based on nature of failure, cumulative damage, system age and number of type 1 shocks is formulated. Under this policy, preventive replacement is made before catastrophic failure when the age of the system reaches T or the number of occurrences of type 1 shock achieves N or the accumulative damage exceeds a level Z but less than K, whichever occurs first, and corrective replacement is immediately carried out whenever the catastrophic failure of the system happens. We determine the optimum preventive replacement schedule such that the expected cost per unit time is minimized. The proposed model extends many existing models since the framework and analysis are general. Finally, the numerical example is provided.

Track grid health index for grid-based, data-driven railway track health evaluation

Railway managers must have accurate assessments of railway track health to optimize maintenance and replacement scheduling and allocate resources reasonably. A model for railway track health evaluation, in which a continuous track line is divided into adjacent segments of the same length, referred to as track grids, is proposed in this study. A condition-evaluation index system for track grids was established, and deep autoencoder networks were used to reduce the dimensions of data on multiple condition measures. The set of all possible health features of the track grids was obtained using the hybrid hierarchical k-means clustering method. The tree-augmented naïve Bayes algorithm was employed to obtain the track grid health index and evaluate the overall health of the track grids. The proposed model was verified using measurement data from the Lanxin Railway in China. The proposed model was found to be superior to conventional health evaluation methods used in railway management in China. These results will enhance railway management knowledge and enable accurate determination of track health on a smaller spatial scale.

A new model based on Artificial Bee Colony algorithm for preventive maintenance with replacement scheduling in continuous production lines

Rails are produced in continuous production lines and most of the equipment in this line are huge. Thus, preventive maintenance in these lines is performed by replacing the parts. Since the part replacement in this kind of production lines halts production, it decreases production outputs. An effective scheduling reduces the downtime to the lowest possible levels. In this study, we propose a replacement scheduling model for a rail production line. The replacement scheduling problem is discussed for 1349 parts annually. The problem was studied for the first time in the literature both in size and in the way, it was handled. A new model is proposed integrating Bin Packing solution method into the replacement scheduling problem assuming the replacements as an item. Bottom Left (BL) Bin Packing algorithm is used to assign the replacements in two solution methods. Firstly, the classical Time-Based Replacement (TBR) method was analysed and the downtime was calculated. Secondly, the Flexible Time-Based Replacement (FTBR) method was developed integrating Artificial Bee Colony (ABC) algorithm. When the results are examined for both solutions, FTBR provided a decrease of approximately 12% in downtime compared to TBR. This improvement means 21 328 tons of rail production. As a result, the proposed solution method can be easily applied for any replacement scheduling problem.

Epidemiology of contact lens-induced giant papillary conjunctivitis: a retrospective study

Purpose: The purpose of the study is to determine the correlation between the incidence of giant papillary conjunctivitis induced by the use of contact lenses (CLPC) and contact lens material, replacement schedule or wearing time. The emergence of new materials and designs of contact lenses along with modifications in the replacement and wearing schedule have changed the structure of complications in users of soft contact lenses (SCLs). At present, infectious and hypoxic complications are extremely rare; on the other hand, toxic-allergic reactions that arise in users of contact lenses (CLs) have come to the fore. Material and methods. A retrospective cohort clinical study involved 1 668 users of SCL of various materials and with different replacement and wearing schedules. Patients were monitored from 2008 to 2018. Results. As a result of the study, it was found that the CLPC incidence correlate with the wearing time and replacement schedule of the SCLs.

Healthy Contact Lens Behaviors Communicated by Eye Care Providers and Recalled by Patients - United States, 2018.

An estimated 45 million U.S. residents enjoy the benefits of contact lens wear, but many of them might be at increased risk for complications stemming from improper wear and care behaviors (1). One of the most serious complications of contact lens wear is a corneal infection known as microbial keratitis, which can sometimes result in reduced vision or blindness (2). In 2014, 50% of contact lens wearers reported ever sleeping in contact lenses, and 55% reported topping off* their contact lens solutions (3), which put them at greater risk for a contact lens-related eye infection (2,4). Data on communication between eye care providers and contact lens wearers on contact lens wear and care recommendations are limited. Two surveys were conducted to better understand and assess contact lens education about nine recommendations: the first assessed contact lens wearer experiences regarding recommendations received from eye care providers during their most recent appointment; the second evaluated provider-reported practices for communicating contact lens wear and care recommendations to their patients. One third (32.9%) of contact lens wearers aged ≥18 years recalled never hearing any lens wear and care recommendations. Fewer than half (47.9%) recalled hearing their provider recommend not sleeping in lenses at their last visit, and 19.8% recalled being told to avoid topping off their contact lens solution. A majority of providers reported sharing recommendations always or most of the time at initial visits, regular checkups, and complication-related visits. Providers reported sharing nearly all recommendations more frequently at initial and complication-related visits than at regular checkups. Of the nine recommendations for safe contact lens wear and care, eye care providers at regular checkups most often recommend complying with the recommended lens replacement schedules (85% of regular visits), not sleeping in lenses (79.0% of regular visits), and not topping off solutions (64.4% of regular visits). Eye care providers play an important role in the health of their contact lens-wearing patients and can share health communication messages with their patients to help educate them about healthy wear and care habits. These findings can assist in the creation of health communication messages to help encourage eye care providers to communicate more effectively with their patients.

Integrated Cache Scheduling Replacement Algorithm to Reduce Cache Pollution

Cache memory management has recently become one of the most crucial research topics in the area of high performance computing. The cache memory has gained popularity due to its capability to offer faster access compared to main memory so processor can access data directly through cache very efficiently. As processor execution speed is faster than accessing memory so the goal is to keep programs rapidly accessible for processing. Cache memory helps not only to access data quickly but also improves the performance of the system. Various cache management policies have been developed to improve the performance of the system. In this paper we focus the issues related with the existing replacement policies and present a new algorithm to overcome these issues. In this paper, we proposed Integrated Cache Scheduling Replacement Algorithm (ICSRA) that will remove the object on the basis of integration of all the parameters like size, frequency and recency if the cache is full. This algorithm consider all size of object to replace with the condition of frequency and timestamp parameter to reduce the cache pollution [1]. Cache pollution means the cache unnecessary waste its space by holding such an object which is no longer be accessed. ICSRA helps to enhance the utilization of cache memory in an efficient manner as well as maximize the cache hit ratio to improve the performance of the system. A detailed classification has also been included based on different parameters which are depending on the analysis of the existing techniques.

Multiyear Water Quality Performance and Mass Accumulation of PCBs, Mercury, Methylmercury, Copper, and Microplastics in a Bioretention Rain Garden

A multiyear water quality performance study of a bioretention rain garden located along a major urban transit corridor east of San Francisco Bay was conducted to assess the efficacy of bioretention rain gardens to remove pollutants. Based on data collected in three years between 2012 and 2017, polychlorinated biphenyls (PCBs) and suspended sediment concentrations (SSCs) were reduced (>90%), whereas total mercury (Hg), methylmercury (MeHg), and copper (Cu) were moderately captured (37%, 49%, and 68% concentration reduction, respectively). Anthropogenic microparticles including microplastics were retained by the bioretention rain garden, decreasing in concentration from 1.6 particles/L to 0.16 particles/L. Based on subsampling at 50- and 150-mm intervals in soil cores from two areas of the unit, PCBs, Hg, and MeHg were all present at the highest concentrations in the upper 100 mm in the surface media layers. Based on residential screening concentrations, the surface media layer near the inlet would need to be removed and replaced annually, whereas the rest of the unit would need replacement every 8 years. The results of this study support the use of bioretention in the San Francisco Bay Area as one management option for meeting load reductions required by San Francisco Bay total maximum daily loads, and provide useful data for supporting decisions about media replacement and overall maintenance schedules.

The stochastic opportunistic replacement problem, part\xa0III: improved bounding procedures

We consider the problem to find a schedule for component replacement in a multi-component system, whose components possess stochastic lives and economic dependencies, such that the expected costs for maintenance during a pre-defined time period are minimized. The problem was considered in Patriksson et al. (Ann Oper Res 224:51–75, 2015b), in which a two-stage approximation of the problem was optimized through decomposition (denoted the optimization policy). The current paper improves the effectiveness of the decomposition approach by establishing a tighter bound on the value of the recourse function (i.e., the second stage in the approximation). A general lower bound on the expected maintenance cost is also established. Numerical experiments with 100 simulation scenarios for each of four test instances show that the tighter bound yields a decomposition generating fewer optimality cuts. They also illustrate the quality of the lower bound. Contrary to results presented earlier, an age-based policy performs on par with the optimization policy, although most simple policies perform worse than the optimization policy.

PROTOTIPE PEMBERI PAKAN IKAN DAN PENGGANTIAN AIR PADA AKUARIUM BERBASIS MIKROKONTROLER ATMEGA328P

Technological developments have encouraged many human lives in automatic matters. One of the uses of the rapidly developing electronics field is the application of household appliances. This study will be made a prototype of fish feed and water replacement in the aquarium of ATmega328P microcontroller based. This prototype aims to facilitate feeding of fish and replacing water in the aquarium. The sensor reading is using an ultrasonic sensor to control the amount of fish feed which when the feed runs out will be marked with a buzzer that lights up. The system for regulating fish feeding and replacement of water is regulated by the DS1307 Real Time Clock IC with a display in a 20x4 cm LCD. A valve opening for fish feed containers uses a servo motor. The program used in designing this prototype is to use the C Programming Language. The results achieved in this study are fish feed schedules and water changes can be arranged with a switch button with a twice daily feeding schedule and water replacement every three days. Another condition that is achieved is the servo motor and the water drain pump can work according to the schedule of the time that has been arranged. The conclusion of this research is that the prototype of fish feed and water replacement can already be implemented using the ATmega328P microcontroller. The fish feeder prototype can realize wave reflections from the ultrasonic sensor when the feed has run out, and it will automatically move the servo motor to open the valve, and the buzzer will sound if the fish feed is below 20%.