Atle Nordli

European Journal of Operational Research 263(3) s. 838-863 Doi: https://doi.org/10.1016/j.ejor.2017.05.008

Following our previous paper (Brahimi, Dauzère-Pérès, Najid, & Nordli, 2006), we present an updated and extended survey of Single-Item Lot-Sizing Problems with focus on publications from 2004 to 2016. Exact and heuristic solution procedures are surveyed. A concise and comprehensive summary of different extensions of the problem is given. The classification of the extensions is based on different characteristics such as resource limitations, assumptions on demand and cost structure. The large number of surveyed papers shows the increased interest of researchers in lot-sizing problems in general and in single-item problems in particular. The survey and the proposed classification should help researchers to identify new research topics, to propose relevant problems and/or novel solution approaches.

Interfaces 37(1) s. 39-51 Doi: https://doi.org/10.1287/inte.1060.0276

The Norwegian company Omya Hustadmarmor supplies calcium carbonate slurry to European paper manufacturers from a single processing plant, using chemical tank ships of various sizes to transport its products. Transportation costs are lower for large ships than for small ships, but their use increases planning complexity and creates problems in production. In 2001, the company faced overwhelming operational challenges and sought operations-research-based planning support. The CEO, Sturla Steinsvik, contacted More Research Molde, which conducted a project that led to the development of a decision-support system (DSS) for maritime inventory routing. The core of the DSS is an optimization model that is solved through a metaheuristic-based algorithm. The system helps planners to make stronger, faster decisions and has increased predictability and flexibility throughout the supply chain. It has saved production and transportation costs close to US$7 million a year. We project additional direct savings of nearly US$4 million a year as the company adds even larger ships to the fleet as a result of the project. In addition, the company has avoided investments of US$35 million by increasing capacity utilization. Finally, the project has had a positive environmental effect by reducing overall oil consumption by more than 10 percent

European Journal of Operational Research 168(1) s. 1-16

A state-of-the-art of a particular planning problem, the Single Item Lot Sizing Problem (SILSP), is given for its uncapacitated and capacitated versions. First classes of lot sizing problems are briefly surveyed. Various solution methods for the Uncapacitated Single Item Lot Sizing Problem (USILSP) are reviewed. Four different mathematical programming formulations of the classical problem are presented. Different extensions for real-world applications of this problem are discussed. Complexity results of the Capacitated Single Item Lot Sizing Problem (CSILSP) are given together with its different formulations and solution techniques. (c) 2004 Published by Elsevier B.V.

Proceedings of the annual conference for nordic researchers in logistics (NOFOMA)

Using sea transportation with increasing capacity usually leads to a smaller transportation cost per unit. In this paper we introduce such economies of scale in the classical Harris- Wilson cost function. We show that the classical EOQ formulas will take different shapes depending on the new cost function, indicating that the classical formulas are specialisations of more general settings. Our new formulation uses a common power function to model the economies of scale. It is well known that the deviations from the classical Harris-Wilson order quantity are fairly insensitive as far as the total logistic costs are concerned. We show that this insensitivity becomes even more noticeable if economies of scale are increased. Finally, we offer real-life examples of the above-mentioned economies of scale.