Showing papers by "Malte Fliedner published in 2011"

Scheduling of inventory releasing jobs to satisfy time-varying demand

Abstract: This paper studies a new class of single-machine scheduling problems, that are faced by Just-in-Time-suppliers satisfying a given demand In these models the processing of jobs leads to a release of a predefined number of product units into inventory Consumption is triggered by predetermined time-varying, and product-specific demand requests While all demands have to be fulfilled, the objective is to minimize the resulting product inventory We investigate different subproblems of this general setting with regard to their computational complexity For more restricted problem versions (equal processing times and equal number of released products) strongly polynomial time algorithms are presented In contrast to this, NP-hardness in the strong sense is proven for more general problem versions (varying processing times or varying number of released products) Moreover, for the most general version, even finding a feasible solution is shown to be strongly NP-hard

On the part inventory model sequencing problem: complexity and Beam Search heuristic

Abstract: In many industries mixed-model assembly systems are increasingly supplied out of third-party consignment stock This novel trend gives rise to a new short-term sequencing problem which decides on the succession of models launched down the line and aims at minimizing the cost of in-process inventory held by the manufacturer In this work, we investigate the mathematical structure of this part oriented mixed-model sequencing problem and prove that general instances of the problem are NP-hard in the strong sense Moreover, we develop a new Beam Search heuristic, which clearly outperforms existing solution procedures

2011,02: Scheduling of inventory releasing jobs to satisfy time-varying demand

Abstract: This paper studies a new class of single-machine scheduling problems, which are faced by Just-in-Time-suppliers satisfying a given demand. In these models the processing of jobs leads to a release of a predefined number of product units into inventory. Consumption is triggered by predetermined time-varying, and product-specific demand requests. While all demands have to be fulfilled, the objective is to minimize the resulting product inventory. We investigate different subproblems of this general setting with regard to their computational complexity. For more restricted problem versions strongly polynomial time algorithms are presented. In contrast to this, NP-hardness in the strong sense is proven for more general problem versions. Moreover, for the most general version, even finding a feasible solution is shown to be strongly NP-hard.

2011,01: A survey on container processing in railway yards : decision problems, optimization procedures and research challenges

Abstract: In spite of extraordinary support programs initiated by the European Union and other national authorities, the percentage of overall freight traffic moved by train is in steady decline. This development is driven by the fact that macro-economic benefits of rail traffic, such as relief of overloaded road networks and reduced environmental impacts, are countervailed by severe disadvantages from the perspective of the shipper, e.g., low average delivery speed and general lack of reliability. Attracting a higher share of freight traffic on rail requires a more efficient freight handling in railway yards, which includes technical innovations as well as the development of suited decision support systems. This paper reviews container processing in railway yards from an operational research perspective and analyzes basic decision problems for the two most important yard types, namely conventional rail-road and modern rail-rail transshipment yards. Existing literature is reviewed and open research challenges are identified.