Research Seminars


Raik STOLLETZ - University of Mannheim, Germany

June 3rd 2013

Designing Lean Manufacturing Systems: Stationary and Dynamic Buffer Allocation in Flow Lines

Abstract: KANBAN-controlled production systems are often installed if the effective processing times of machines in production systems are stochastic. These stochastic influences are due to machine breakdowns, uncertain times of repair, and random processing times. The optimal allocation of KANBAN-cards (buffer spaces) throughout a line guarantees a certain average throughput while minimizing the required buffer space. Besides the uncertainty, such flow lines often operate under time-dependent influences. They are caused by learning effects during the ramp up phase, changing station capacities, or time-dependent demand patterns. We discuss different decision models for the static and dynamic buffer allocation in stochastic flow lines. Sampling approaches for the analytical performance evaluation are proposed. They are based on huge mixed integer decision models in discrete and continuous time. Efficient solution approaches for the respective optimization models of the buffer allocation are presented. The numerical study demonstrates the accuracy of the proposed approaches.

Dominique DE WERRA - EPFL Lausanne, Switzerland

April 22th 2013

Grouping Processors in Open Shop Scheduling

Abstract: In the basic classical open shop model we have processors and jobs to be processed on the processors according to some requirements. We shall concentrate on the case in which some processors have to be grouped (becoming so multiprocessors) in order to perform some of the tasks required by the jobs. Such a model is motivated by applications in timetabling as well as in testing of electronic systems in particular. We shall describe these applications and review the basic results related to the simple cases of ordinary open shop. We will examine the implications of processor grouping on the form of optimal schedules. Complexity issues will be discussed for the situations with some grouping of processors. Joint work with W. Kubiak and T. Kis.

Laurent ALFANDARI - ESSEC Business School, France

March 18th 2013

A Column-Generation Based Method for Optimal Electricity Production and Maintenance Planning

Abstract: This talk presents a heuristic method based on column generation for the EDF (Electricité De France) long term electricity production planning problem proposed as subject of the ROADEF/EURO 2010 Challenge. This is to our knowledge the first-ranked method among those methods based on mathematical programming, and was ranked fourth overall. The problem consists in determining a production plan over the time horizon for each thermal power plant of the French electricity company, and for nuclear plants, a schedule of plant outages which are necessary for refueling and maintenance operations. The average cost of the overall outage and production planning, computed over a set of demand scenarios, is to be minimized, so as to find a robust solution. The method proceeds in two stages. In the first stage, dates for outages are fixed once for all for each nuclear plant. Data are aggregated with a single average scenario and reduced time steps, and a set-partitioning reformulation is solved for fixing outage dates with a heuristic based on column generation. The pricing problem associated with each nuclear plant is a shortest path problem in a specific graph. In the second stage, the reload level is determined at each date of an outage, considering all scenarios. Finally, the production quantities between two outages are optimized for each plant and each scenario by solving independent linear programs. The efficiency of the approach is demonstrated by numerical results.

Matthew MYERS - University of Tennessee at Knoxville, USA

February 25th 2013

The Value of Collaborative Knowledge Sharing in Global Supply Chains

Abstract: Research in collaborative inter-organizational relationships has typically focused on the value of these relationships to a specific supply chain partner. Furthermore, the literature has largely ignored the potential benefits of knowledge sharing between independent buyers and suppliers in a global setting. In this study, we investigate the influence of inter-firm knowledge sharing on the performance of both the buyer and the supplier within global dyads, testing the contention that both members benefit from knowledge sharing efforts, and both enjoy equal pieces of the benefits pie. Using primary data from 132 cross national dyads representing relationships in Asia-Pacific, Europe, Latin America, and the United States, we investigate three specific types of knowledge sharing and their influence on firm performance.

Workshop on G-GRAPHS defined from groups, organized by ESSEC Business School

Feburary 12th 2013

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