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- Flow-shop-Problem (2)
- Scheduling (2)
- clearing functions (2)
- Ablaufplanung (1)
- Bestandsmanagement (1)
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- Energieverbrauch (1)
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This research paper has evaluated the potential of reducing energy consumption by scheduling jobshop production systems with machines using standby modes in free times. The initial introduction of the planning issue is followed by a description of the approach to assess the available potential. Subsequently, the research procedure by means of simulation, a detailed discussion of the results and a perspective on future research is given. Moreover, the notion that scheduling influences the energy consumption in jobshop production systems is supported. The presented simulation research also documents that there is no direct correlation between energy consumption and total lead time, although this was presumed usually. Finally, this paper provides a forecast for a possible optimisation model as well as an exemplary model with an energy-optimised schedule plan.
Beitrag zur Abfallreduktion mittels mathematischer Optimierung und simulationsbasierter Validierung
(2015)
Perishable goods with a shelf life of 3-5 days require frequent inventory controls in the food retail trade. Maintaining a high service level for these products in stores is difficult due to demand uncertainty. A high service level often leads to a lot of stock in stores. In case it is not sold, it is waste. As an approach towards waste volume reduction, the economic order quantity (EOQ) problem is optimised in combination with the delivery frequency problem on the basis of the microperiods, i.e. morning, midday, afternoon, and evening. The presented model is designed for multiple stores with one regional warehouse. The simulation model measures the waste volume in stores. Experiments show that the combined optimisation of both problems leads to a reduction of total costs and waste volume.
Local search is an established meta heuristic for scheduling problems. To avoid of getting stucked in a local optimum, the achieved solution is destroyed. Usually, this is done randomly. Here, two problem specific procedures are suggested. One focuses on jobs with the highest difference between the actual processing time and the net processing time of the job and the other one tries to remove jobs which causes the highest idle time for themselves or other jobs. Comprehensive simulations of test scheduling problems as well as a real world application show that both problem specific procedures outperform a random procedure.
Companies use special designed flow shops, in order to satisfy specific demands. Products need to be transported (from one station to the next station) by a crane and the way of working of this crane excludes the intermediate storage (of a work piece). In addition, the way of working restricts the set of feasible schedules even more than the no-buffer restriction discussed in the literature in the case of limited storage. Since this scheduling problem is integrated in the usual hierarchical planning, the tardiness is minimised. A linear optimisation model is presented to provide a formal description of this NP-hard problem. It is also used to explain the performance of priority rule based heuristic solutions on small test problems. In detail, priority rules as well as a priority rule based branch and bound procedure are analysed; priority rules are regarded, because a priority rule is still the standard procedure for on-line scheduling in industrial practise. Out of successful priority rules in the literature the best one is identified by an extensive simulative investigation. An improved look-ahead is realised by a restricted search over all possible schedules.