Mohamed Ben Ahmed

• Bakker, Steffen J.S.; Ahmed, Mohamed Ben; Andersson, Henrik; Inngjerdingen, Christian Håkon Torsten & Møller, Simen Aksland (2026). A look-ahead policy for dynamic bike rebalancing with neighborhood interactions. Omega. The International Journal of Management Science. ISSN 0305-0483. 144. doi: 10.1016/j.omega.2026.103623. Fulltekst i vitenarkiv
• Bakker, Steffen Jaap Skotvoll; Ahmed, Mohamed Ben; Djupdal, Asbjørn; Natvig, Lasse; Andersson, Carl Henrik & Jahre, Magnus [Vis alle 7 forfattere av denne artikkelen] (2024). FOMOsim: An open-source simulator for rigorous analysis of micromobility planning problems. Expert Systems With Applications. ISSN 0957-4174. 264. doi: 10.1016/j.eswa.2024.125842. Fulltekst i vitenarkiv Vis sammendrag

  Existing simulation models for micromobility systems often face significant limitations: they are typically custom-built for specific contexts, lack generalizability, are not open-source, and undergo limited testing, which again question their reliability and applicability in broader settings. To address these challenges, this paper presents FOMOsim, an open-source simulator developed to analyze micromobility systems. The simulator’s modular design allows for better scalability and usability, facilitating detailed and realistic simulations of shared transport operations. New benchmark instances, utilizing data from bike-sharing systems (BSSs) in major American and Norwegian cities, are created and embedded within the simulator. Additionally, we introduce a new greedy heuristic for the dynamic bike rebalancing problem, integrated within FOMOsim. Rigorous testing demonstrates that the proposed heuristic, when combined with FOMOsim, outperforms state-of-the-art methods, significantly improving BSS performance by reducing bike shortages and surpluses. Furthermore, a comprehensive experimental study is designed to assess the impact of key strategic and operational decisions on BSS performance. The findings underscore the simulator’s adaptability in addressing various planning challenges and its potential to improve BSS management through informed decision-making. Consequently, FOMOsim provides the research community with a robust platform for replicating experiments, generating new instances, and exploring innovative solutions in BSS management, thereby substantially enriching the field’s body of knowledge.

• Skålnes, Jørgen; Ahmed, Mohamed Ben; Hvattum, Lars Magnus & Stålhane, Magnus (2023). New benchmark instances for the inventory routing problem. European Journal of Operational Research. ISSN 0377-2217. 313(3), s. 992–1014. doi: 10.1016/j.ejor.2023.08.010. Fulltekst i vitenarkiv Vis sammendrag

  The existing sets of benchmark instances for the inventory routing problem (IRP) have been beneficial for investigating and illustrating the properties of the problem. However, they possess certain features and design choices that are not necessarily representative of all real-world IRPs. Therefore, we propose a new collection of 270 real-world-like instances ranging from 10 to 200 customers. These instances vary in terms of the number of vehicles and their capacity, the length of the planning horizon, the demand structure, and the geographical distribution of customers. Transportation and inventory holding costs resemble costs found in practice. We present an instance space analysis showing that the new instances nicely complement the original instances. To derive lower and upper bounds for each instance, we present computational experiments with two high-quality solution methods: a matheuristic and an exact branch-and-cut method. The results confirm that the new set of instances is hard to solve with the proposed methods, and they demonstrate the need for developing new solution methods. Keywords: distribution, test instance, branch-and-cut, matheuristic, vendor-managed inventory

• Ahmed, Mohamed Ben; Molland, Even & Tomasgard, Tore (2023). Challenges and Opportunities for Adopting Green Technologies in Maritime Transportation Planning. IFIP Advances in Information and Communication Technology. ISSN 1868-4238. s. 620–633. doi: 10.1007/978-3-031-43688-8_43. Fulltekst i vitenarkiv
• Ahmed, Mohamed Ben; Hvattum, Lars Magnus & Agra, Agostinho (2023). The effect of different mathematical formulations on a matheuristic algorithm for the production routing problem. Computers & Operations Research. ISSN 0305-0548. 155(July), s. 1–19. doi: 10.1016/j.cor.2023.106232. Fulltekst i vitenarkiv Vis sammendrag

  We perform an experimental study to evaluate the performance of a matheuristic for the production routing problem (PRP). First, we develop a basic matheuristic that prescribes starting from a partial initial solution, completing it using a sequence of constructive heuristics, and improving it using a general-purpose mixed-integer programming heuristic. Next, we investigate the effect of three state-of-the-art mathematical formulations on the proposed matheuristic convergence. The formulations are implemented and tested with and without the use of valid inequalities. In addition, by suggesting different techniques to generate a feasible starting solution for our matheuristic, we assess the contribution of an initial solution to the matheuristic’s overall performance. We conduct extensive computational experiments on benchmark data instances for the PRP. The results show that a proper choice of an embedded mathematical formulation depends on the data instances’ features, such as the number of customers and the length of the planning horizon. The comparisons undertaken in this study indicate that having a better initial solution does not necessarily lead to finding a better final solution. Keywords: lot sizing, inventory routing, mixed integer formulation, valid inequality, proximity search, experimental analysis

• Ahmed, Mohamed Ben; Okoronkwo, Onyemaechi Linda; Okoronkwo, Edwin Chimezie & Hvattum, Lars Magnus (2021). Long‐term effects of short planning horizons for inventory routing problems. International Transactions in Operational Research. ISSN 0969-6016. 29(5), s. 2995–3030. doi: 10.1111/itor.12998. Fulltekst i vitenarkiv Vis sammendrag

  This paper presents a detailed study concerning the importance of the planning horizon when solving inventory routing problems (IRPs). We evaluate the quality of decisions obtained by solving a finite-horizon IRP. We also discuss the relevance of explicitly considering profit maximization models rather than the traditional cost minimization variant. As a means to this end, we describe four classes of the IRP corresponding to different types of markets. Two of them lead to nonlinear models, which are linearized. Furthermore, we provide a deterministic simulator to evaluate the long-term effects arising from using planning horizons of varying lengths when solving the IRP. A computational study is performed on cases generated from benchmark data instances. The results confirm that the long-term performance of the IRP decisions is, in part, contingent on the length of the selected planning horizon. They also show that considering profit maximization instead of cost minimization leads to different decisions, generating considerably more revenue and profits, albeit not nearly as much as suggested by individual solutions to static IRPs with short planning horizons. Keywords: profit maximization, path flow, linearization, end effect, simulation

• Ahmed, Mohamed Ben; Hryhoryeva, Maryia; Hvattum, Lars Magnus & Haouari, Mohamed (2021). A matheuristic for the robust integrated airline fleet assignment, aircraft routing, and crew pairing problem. Computers & Operations Research. ISSN 0305-0548. 137(January), s. 1–14. doi: 10.1016/j.cor.2021.105551. Fulltekst i vitenarkiv Vis sammendrag

  We address an integrated airline scheduling problem that combines three airline planning processes: fleet assignment, aircraft routing, and crew pairing. For a given daily flight schedule, the problem requires simultaneously assigning aircraft and crews to each scheduled flight, taking into account aircraft maintenance restrictions and crew work rules. We propose to solve this complex problem of integrated flight planning while taking into account robustness considerations. In this regard, robustness is achieved by restricting tight connections in the schedule and increasing the number of connections where crews follow the aircraft. We formulate the problem using a very large-scale, yet compact, mixed-integer programming model, and we propose a matheuristic consisting of a decomposition approach and a proximity search algorithm. Computational experiments carried out on real instances from a major airline and having up to 14,014 itineraries, 646 flights, and 202 aircraft provide evidence of the proposed approach’s efficacy. In particular, we find that the average deviation from a conservative bound is at most equal to 0.6%. Keywords: mixed-integer programming, compact formulation, robustness, proximity search

• Ahmed, Mohamed Ben; Mansour, Farah Zeghal & Haouari, Mohamed (2018). Robust integrated maintenance aircraft routing and crew pairing. Journal of Air Transport Management. ISSN 0969-6997. 73(October), s. 15–31. doi: 10.1016/j.jairtraman.2018.07.007. Fulltekst i vitenarkiv Vis sammendrag

  Given a daily flight schedule and a set of aircraft fleets, the integrated aircraft routing and crew scheduling problem requires finding a maintenance feasible set of aircraft routes and crew pairings such that each individual flight is covered by exactly one aircraft route and one crew pairing. Although these problems are interdependent, they have been traditionally solved sequentially, where the aircraft routing problem, which is solved first, defines a set of periodic aircraft rotations that impose some restrictions on short connections that are subsequently accommodated by the crew pairing problem. A major drawback of this sequential approach is that it ignores most of the interdependencies between the two problems. In particular, it fails to build robust solutions that are resilient to unpredictable disruptions (like adverse weather, aircraft breakdowns, etc.) that translate into delayed and canceled flights. In this paper, we propose an integrated robust model that incorporates the aircraft routing and crew pairing problems within a single framework that aims at generating aircraft routes that are both robust and cost-effective while accommodating technical constraints. A peculiar feature of the proposed model is that it includes a polynomial number of variables and constraints. We solve the resulting integrated model by using a general-purpose solver. Computational results obtained by using data from major airlines demonstrate the benefits of the proposed robust model. Keywords: aircraft routing, crew pairing, robust airline planning

• Ahmed, Mohamed Ben; Mansour, Farah Zeghal & Haouari, Mohamed (2017). A two-level optimization approach for robust aircraft routing and retiming. Computers & industrial engineering. ISSN 0360-8352. 112, s. 586–594. doi: 10.1016/j.cie.2016.09.021. Fulltekst i vitenarkiv
• Ahmed, Mohamed Ben; Ghroubi, Wissal; Haouari, Mohamed & Sherali, Hanif D. (2017). A hybrid optimization-simulation approach for robust weekly aircraft routing and retiming. Transportation Research Part C: Emerging Technologies. ISSN 0968-090X. 84, s. 1–20. doi: 10.1016/j.trc.2017.07.010. Fulltekst i vitenarkiv
• Al-Thani, Nayla Ahmad; Ahmed, Mohamed Ben & Haouari, Mohamed (2016). A model and optimization-based heuristic for the operational aircraft maintenance routing problem. Transportation Research Part C: Emerging Technologies. ISSN 0968-090X. 72, s. 29–44. doi: 10.1016/j.trc.2016.09.004. Fulltekst i vitenarkiv
• Ahmed, Mohamed Ben; Mansour, Farah Zeghal & Haouari, Mohamed (2016). A simulation-optimization approach for robust aircraft routing. I Kacem, Imed (Red.), 45th International Conference on Computers & Industrial Engineering 2015 (CIE45). Curran Associates, Inc.. ISSN 9781510817456. s. 17–24. Fulltekst i vitenarkiv
• Ahmed, Mohamed Ben; Mansour, Farah Zeghal & Haouari, Mohamed (2015). A PSO approach for robust aircraft routing. I Xplore, Digital Library IEEE (Red.), Industrial Engineering and Engineering Management (IEEM), 2015 IEEE International Conference. IEEE Press. ISSN 9781467380669. s. 219–223. doi: 10.1109/IEEM.2015.7385640. Fulltekst i vitenarkiv

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• Ahmed, Mohamed Ben; Gullbekk, Henning Lied G; Wian, Trym & Stålhane, Magnus (2025). Strategic Crew Pairing in Long-Haul Airline Operations. Fulltekst i vitenarkiv
• Ahmed, Mohamed Ben; Fagerholt, Kjetil & Bakker, Steffen Jaap Skotvoll (2025). Enhancing operational efficiency in automated container terminals: a matheuristic for AGV routing and scheduling. Fulltekst i vitenarkiv
• Ahmed, Mohamed Ben (2024). Incorporating neighborhood interactions in bike sharing rebalancing. Fulltekst i vitenarkiv
• Ahmed, Mohamed Ben; Bakker, Steffen Jaap Skotvoll & Fagerholt, Kjetil (2024). Scheduling and conflict-free routing of automated guided vehicles in container terminals. Fulltekst i vitenarkiv
• Ahmed, Mohamed Ben (2023). Challenges and opportunities for adopting green technologies in maritime transportation planning. Fulltekst i vitenarkiv
• Ahmed, Mohamed Ben; Hvattum, Lars Magnus & Haouari, Mohamed (2021). A matheuristic for the robust integrated airline scheduling problem. Fulltekst i vitenarkiv
• Ahmed, Mohamed Ben (2019). Testing the importance of the planning horizon when solving inventory routing problems. Fulltekst i vitenarkiv
• Ahmed, Mohamed Ben (2023). Analysis of integrated planning models in logistics. Molde University College - Specialized University in Logistics. ISSN 9788279623397. Fulltekst i vitenarkiv

Se alle arbeider i NVA