This year’s QBWL workshop was hosted on 8 March 2021 by the Chair of Supply and Value Chain Management at TUM Campus Straubing. Due to the COVID-19 pandemic, the workshop was hosted in a virtual format.
116 participants from 18 universities joined the workshop which consisted of a large number of presentations and discussions. In three streams on “Last Mile Delivery, Routing & Logistics”, “ Revenue Management & Supply Planning”, and “Sequencing & Scheduling”, 20 researchers presented their current or future research projects. The presentations were complemented by vivid discussions.The agenda can be found below.
QBWL is a gathering of German research groups working on quantitative topics in business and economics. It was established about 3 decades ago and has continuously grown to a group of more than 25 chairs. The workshop is hosted once a year by one of the participating chairs, usually as a 3-day in-person workshop.
Next year’s workshop is planned for March 28-31, 2022 in Kloster Drübeck, hosted by Prof. Sven Müller from the University of Magdeburg.
30th QBWL Workshop online (2021)
von QBWL Team am 29.10.2020, 14:35
The 30. QBWL Workshop takes place March 8. - 9. 2021. The format will be online.
For further information, see the "Workshop" section.
Aus der Forschung
Study on the oil-electricity retrofit of rubber-tyred gantry cranes
Deployment and retrofit strategy for rubber-tyred gantry cranes considering carbon emissions
Driven by green port initiatives, container terminal operators have been substituting environmentally and economically inefficient diesel-powered rubber-tyred gantry cranes (RTGs) with new or retrofitted electric ones. Such an investment is closely related to operational activities, and the process of retrofitting should be carried out under the premise of satisfying the terminal yard container handling requirement. An integer programming model is proposed to help decision-makers determine the investment timing and deploy available RTGs to achieve a CO-2 emissions reduction target. Considering the distinctive characteristics of different types of RTGs, we develop a deployment plan as well as an RTGs purchase and retrofit strategy. Moreover, the decisions satisfy an operation workload requirement. A tailored Corridor Method (CM) is used to accommodate large scale real-world instances. The application is illustrated with a modestly sized container terminal yard. Results confirm that electrifying diesel-powered RTGs is effective in curbing CO-2 emissions and reducing energy costs. Our numerical experiments also highlight the importance of an appropriate emissions reduction target.
Yi Ding, Yang Yang, Leonard Heilig, Eduardo Lalla-Ruiz, Stefan Voss, Deployment and retrofit strategy for rubber-tyred gantry cranes considering carbon emissions, Computers & Industrial Engineering, Volume 161,2021,107645,ISSN 0360-8352, DOI: 10.1016/j.cie.2021.107645
Solving the time-discrete winter runway scheduling problem: A column generation and constraint programming approach
We address the runway scheduling problem under consideration of winter operations. During snowfall, runways have to be temporarily closed in order to clear them from snow, ice and slush. We propose an integrated optimization model to simultaneously plan snow removal for multiple runways and to assign runways and take-off and landing times to aircraft. For this winter runway scheduling problem, we present a time-discrete binary model formulation using clique inequalities and an equivalent constraint programming model. To solve the winter runway scheduling problem optimally, we propose an exact solution methodology. Our start heuristic based on constraint programming generates a feasible initial start solution. We use a column generation scheme, which we initialize with a heuristic solution, to identify all variables of the binary program which are required to solve it optimally. Finally, we apply a branch-and-bound procedure to our resulting binary program. Additionally, we present an enhanced time discretization method to balance model size and solution quality. We apply our algorithm to realistic instances from a large international airport. An analysis of resulting model sizes proves the ability of our approach to significantly reduce the number of required variables and constraints of the time-discrete binary program. We also show that our method computes optimal schedules in a short amount of time and often outperforms a time-continuous formulation as well as a pure constraint programming approach.
Maximilian Pohl, Christian Artigues, Rainer Kolisch, Solving the time-discrete winter runway scheduling problem: A column generation and constraint programming approach, European Journal of Operational Research, 2021,ISSN 0377-2217, DOI: 10.1016/j.ejor.2021.08.028
Performance analysis and optimisation of stochastic flow lines with limited material supply
We consider stochastic flow lines with limited buffer sizes and limited material supply. In these systems, the configuration of the flow line parameters and the configuration of the material supply determine the system output. Shortages of material supply can limit the performance of the production system. We use flexible (mixed-integer) linear programming approaches to evaluate and optimise the performance of long stochastic flow lines with limited material supply in discrete and continuous time. The approaches are used to quantify the impact of material shortages on the system output. Further, they are applied to determine the minimum material levels that are required to prevent material shortages of a given flow line configuration. The results of the numerical study reveal insights on the approximation accuracy of the linear programs as well as on the dependence of optimal material levels on flow line characteristics such as the presence of bottleneck machines and the system variability. The contribution of this paper consists of both, integrated models for stochastic flow lines with limited material supply and new insights on the optimal material supply of stochastic flow lines.
Julia Mindlina, Horst Tempelmeier Performance analysis and optimisation of stochastic flow lines with limited material supply, International Journal of Production Research (2021), DOI: 10.1080/00207543.2021.1954712
Chunking and cooperation in particle swarm optimization for feature selection
Bio-inspired optimization aims at adapting observed natural behavioral patterns and social phenomena towards efficiently solving complex optimization problems, and is nowadays gaining much attention. However, researchers recently highlighted an inconsistency between the need in the field and the actual trend. Indeed, while nowadays it is important to design innovative contributions, an actual trend in bio-inspired optimization is to re-iterate the existing knowledge in a different form. The aim of this paper is to fill this gap. More precisely, we start first by highlighting new examples for this problem by considering and describing the concepts of chunking and cooperative learning. Second, by considering particle swarm optimization (PSO), we present a novel bridge between these two notions adapted to the problem of feature selection. In the experiments, we investigate the practical importance of our approach while exploring both its strength and limitations. The results indicate that the approach is mainly suitable for large datasets, and that further research is needed to improve the computational efficiency of the approach and to ensure the independence of the sub-problems defined using chunking.
Sarhani, M., Voß, S. Chunking and cooperation in particle swarm optimization for feature selection. Ann Math Artif Intell (2021), DOI: 10.1007/s10472-021-09752-4
Strategic planning of new product introductions: Integrated planning of products and modules in the automotive industry
Timing the introduction of new products to the market is an important strategic decision in the automotive industry. For several reasons, it is also a complex decision problem. First, the use of platforms creates many interactions between different vehicles via shared modules (e.g. engines). Second, new and existing products rely on various shared resources (e.g. development resources or production capacities). Furthermore, different conflicting objectives must be considered. In this paper, we develop a mathematical linear programming model describing the decision problem based on the resource-constrained project scheduling problem. It simultaneously decides on the start of production date for vehicle models, variants, and engines as well as on the assignment of engines to the given variants. Integrating a multi-criteria approach, the model helps to analyze trade-offs between important managerial objectives related to resource utilization and fleet emission metrics. Using realistic data from a major European automotive company, we demonstrate that our model enables the efficient evaluation of various courses of action. Such capabilities are especially relevant in times of rapid technological change, such as the current transition towards electrified vehicle portfolios.
Christopher V. Bersch, Renzo Akkerman, Rainer Kolisch, Strategic planning of new product introductions: Integrated planning of products and modules in the automotive industry, Omega,Volume 105,2021,102515,ISSN 0305-0483, DOI: 10.1016/j.omega.2021.102515