References of "Minner, Stefan"
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See detailSimulation optimization for the stochastic economic lot scheduling problem with sequence-dependent setup times
Löhndorf, Nils UL; Riel, Manuel; Minner, Stefan

in International Journal of Production Economics (2014), 157

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See detailStrategic Safety Stock Placement in Supply Networks with Static Dual Supply
Klosterhalfen, Steffen UL; Minner, Stefan; Willems, Sean

in Manufacturing and Service Operations Management (2014), 16(2), 204-219

Many real-world supply networks source required materials from multiple suppliers. Existing multiechelon inventory optimization approaches either restrict their scope to multiple supply sources in two ... [more ▼]

Many real-world supply networks source required materials from multiple suppliers. Existing multiechelon inventory optimization approaches either restrict their scope to multiple supply sources in two-echelon systems or single suppliers in multiechelon systems. We develop an exact mathematical model for static dual supply in a general acyclic N-echelon network structure, which builds on the guaranteed-service framework for safety stock optimization. It is assumed that the suppliers are allocated static fractions of demand. We prove that for normally distributed demand an extreme point property holds. We present a real example from the industrial electronics industry consisting of five echelons and three dual-sourced materials. This example forms the basis for a numerical analysis. Compared with the only previously published approximate solution, our exact approach results in considerable cost savings because the exact model captures inventory pooling in a way that the approximation is unable to do. For a set of test problems, total safety stock cost savings are 9.1%, on average. [less ▲]

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See detailSimulation optimization for the stochastic economic lot scheduling problem
Löhndorf, Nils UL; Minner, Stefan

in IIE Transactions (2013), 45(7), 796--810

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See detailOptimizing Trading Decisions for Hydro Storage Systems using Approximate Dual Dynamic Programming
Löhndorf, Nils UL; Wozabal, David; Minner, Stefan

in Operations Research (2013)

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See detailAn Integrated Guaranteed- and Stochastic-Service Approach to Inventory Optimization in Supply Chains
Klosterhalfen, Steffen UL; Dittmar, Daniel; Minner, Stefan

in European Journal of Operational Research (2013), 231

Multi-echelon inventory optimization literature distinguishes stochastic- (SS) and guaranteed-service (GS) approaches as mutually exclusive frameworks. While the GS approach considers flexibility measures ... [more ▼]

Multi-echelon inventory optimization literature distinguishes stochastic- (SS) and guaranteed-service (GS) approaches as mutually exclusive frameworks. While the GS approach considers flexibility measures at the stages to deal with stockouts, the SS approach only relies on safety stock. Within a supply chain, flexibility levels might differ between stages rendering them appropriate candidates for one approach or the other. The existing approaches, however, require the selection of a single framework for the entire supply chain instead of a stage-wise choice. We develop an integrated hybrid-service (HS) approach which endogenously determines the overall cost-optimal approach for each stage and computes the required inventory levels. We present a dynamic programming optimization algorithm for serial supply chains that partitions the entire system into subchains of different types. From a numerical study we find that, besides implicitly choosing the better of the two pure frameworks, whose cost differences can be considerable, the HS approach enables additional pipeline and on-hand stock cost savings. We further identify drivers for the preferability of the HS approach. [less ▲]

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See detailA hybrid general lot-sizing and scheduling formulation for a production process with a two-stage product structure
Transchel, Sandra; Minner, Stefan; Kallrath, Josef et al

in International Journal of Production Research (2011), 49(9), 2463--2480

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See detailA Comparison of the Constant-Order and Dual-Index Policy for Dual Sourcing
Klosterhalfen, Steffen UL; Kiesmüller, Gudrun; Minner, Stefan

in International Journal of Production Economics (2011), 133(1), 302-311

We analyze a single-product, periodic-review, stochastic demand inventory model with backorders and two supply options, a regular and a more expensive expedited one, with deterministic, offsetting lead ... [more ▼]

We analyze a single-product, periodic-review, stochastic demand inventory model with backorders and two supply options, a regular and a more expensive expedited one, with deterministic, offsetting lead times. Since the optimal policy for such a problem is generally unknown, several simpler policies have been proposed in the literature, e.g., the single-index (SIP), dual-index (DIP), or constant-order policy (COP). In previous research the DIP has been found to perform closely to the optimal policy in specific numerical settings. The COP, on the other hand, is very appealing from a practical point of view. We explore the relative cost performance of these two policies in a numerical study to gain insights into appropriate policy choices. We find that in settings, where dual sourcing is most valuable, the simpler COP delivers satisfactory results, sometimes even better ones than the DIP, and therefore represents a legitimate policy alternative for practical situations. [less ▲]

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See detailMachine and labor flexibility in manufacturing networks
Francas, David; Löhndorf, Nils UL; Minner, Stefan

in International Journal of Production Economics (2011), 131(1), 165--174

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See detailOptimal day-ahead trading and storage of renewable energies—an approximate dynamic programming approach
Löhndorf, Nils UL; Minner, Stefan

in Energy Systems (2010), 1(1), 61--77

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See detailSafety Stock Optimisation in Distribution Systems: A Comparison of Two Competing Approaches
Klosterhalfen, Steffen UL; Minner, Stefan

in International Journal of Logistics Research and Applications (2010), 13(2), 99-120

Contributions to multi-echelon safety stock optimisation can broadly be divided into models following either a stochastic- or guaranteed-service approach. These approaches form the basis of several ... [more ▼]

Contributions to multi-echelon safety stock optimisation can broadly be divided into models following either a stochastic- or guaranteed-service approach. These approaches form the basis of several commercial inventory optimisation software tools. To date, there is still a lack of a detailed comparison between the two approaches. This paper presents a cost comparison for two-stage distribution systems by means of a simulation study. The results indicate that the cost difference between the two approaches is quite small amounting to 4 at most. We observe that in most cases, the resulting (lower) internal warehouse service level is a good indicator for the superiority of an approach. The guaranteed-service approach shows a better performance for moderate flexibility costs, large warehouse processing times and high retailer service levels. [less ▲]

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