Optimal maintenance of multi-component systems: a review

In this article we give an overview of the literature on multi-component maintenance optimization. We focus on work appearing since the 1991 survey "A survey of maintenance models for multi-unit systems" by Cho and Parlar. This paper builds forth on the review article by Dekker et al. (1996), which focusses on economic dependence, and the survey of maintenance policies by Wang (2002), in which some group maintenance and some opportunistic maintenance policies are considered. Our classification scheme is primarily based on the dependence between components (stochastic, structural or economic). Next, we also classify the papers on the basis of the planning aspect (short-term vs long-term), the grouping of maintenance activities (either grouping preventive or corrective maintenance, or opportunistic grouping) and the optimization approach used (heuristic, policy classes or exact algorithms). Finally, we pay attention to the applications of the models.literature review;economic dependence;failure interaction;maintenance policies;grouping maintenance;multi-component systems;opportunistic maintenance;maintencance optimization;structural dependence

Selective maintenance optimisation for series-parallel systems alternating missions and scheduled breaks with stochastic durations

This paper deals with the selective maintenance problem for a multi-component system performing consecutive missions separated by scheduled breaks. To increase the probability of successfully completing its next mission, the system components are maintained during the break. A list of potential imperfect maintenance actions on each component, ranging from minimal repair to replacement is available. The general hybrid hazard rate approach is used to model the reliability improvement of the system components. Durations of the maintenance actions, the mission and the breaks are stochastic with known probability distributions. The resulting optimisation problem is modelled as a non-linear stochastic programme. Its objective is to determine a cost-optimal subset of maintenance actions to be performed on the components given the limited stochastic duration of the break and the minimum system reliability level required to complete the next mission. The fundamental concepts and relevant parameters of this decision-making problem are developed and discussed. Numerical experiments are provided to demonstrate the added value of solving this selective maintenance problem as a stochastic optimisation programme

Development and implementation of preventive-maintenance practices in Nigerian industries.

A methodology for the development of PM using the modern approaches of FMEA, root-cause analysis, and fault-tree analysis is presented. Applying PM leads to a cost reduction in maintenance and less overall energy expenditure. Implementation of PM is preferable to the present reactive maintenance procedures (still prevalent in Nigeria

THE COLUMBUS GROUND SEGMENT – A PRECURSOR FOR FUTURE MANNED MISSIONS

In the beginning the space programs were self standing national activities, often in competition to other nations. Today space flight becomes more and more an international task. Complex space mission and deep space explorations are not longer to be stemmed by one agency or nation alone but are joint activities of several nations. The best example for such a joint (ad-) venture at the moment is the International Space Station ISS. Such international activities define complete new requirements for the supporting ground segments. The world-wide distribution of a ground segment is not any longer limited to a network of ground stations with the aim to provide a good coverage of the space craft. The coverage is sometimes – like for the ISSanyway ensured by using a relay satellite system instead. In addition to the enhanced down- and uplink methods a ground segment is aimed to connect the different centres of competence of all participating agencies/nations. From the space craft operations point of view such transnational ground segments are required to support distributed and shared operations in a predefined decision/commanding hierarchy. This has to be taken into account in the technical topology as well as for the operational set-up and teaming. Last not least increases the duration of missions, which requires a certain flexibility of the ground segment and long-term maintenance strategies for the ground segment with a special emphasis on nonintrusive replacements. The Russian space station MIR has been in the orbit for about 15 years, the ISS is currently targeted for 2020, to be for over 20 years in space

Maintenance optimization of a production system with buffercapacity

Marketing;Optimization;produktieleer/ produktieplanning

Housing, management and health in Swedish dairy calves

This thesis discusses the results of an observational study conducted in dairy herds in the south-western Sweden and a questionnaire survey of dairy herds done throughout Sweden. In the observational study the health of 3 081 heifer calves in 122 dairy herds was monitored from birth until 90 days of age. Disease incidence was recorded by farmers and by project veterinarians. The calves’ heart girth was measured at birth and at weaning. The average growth of the calves was 600 g per day. We investigated the effects of calf-level, herd-related and dam-related factors on growth and the incidence risk of infectious diseases. The total morbidity found was 23%; enteritis and respiratory disease were the most common diagnoses. The placing of calf pens along an outer wall, ingestion of first colostrum by suckling, receiving colostrum from a younger cow, being of Swedish Red and White breed (SRB) and birth during the summer were significantly associated with an increased risk for enteritis. A low ammonia concentration, draught, bovine viral diarrhoea virus infection in the herd, a poor capacity of the farmer to keep accurate records, being a cross-breed, housing in large group pens, and birth during the winter season, during the night, in a cubicle, a group calving pen or at pasture, as well as unsupervised calving, and factors related to the health of the dam were significantly associated with an increased risk of respiratory morbidity. Receiving colostrum from a young cow, absence of draught, being housed in a calf pen placed along an outer wall and being born during the night were found to be significantly associated with an increased risk of other infectious diseases. Growth was negatively affected by being of SRB breed, housing in large group pens, disease, difficult calving, first parity of the dam and retained placenta. The questionnaire was sent to 1 500 dairy farmers in Sweden and asked for routines from birth to first calving for replacement heifers. It identifies several areas in which advisory input is urgently needed, such as the colostrum routines, the heating of whole milk and the housing of calves and heifers