Efficient emission reduction through dynamic supply mode selection

in European Journal of Operational Research (2023)

Optimal design of line replaceable units

in Naval Research Logistics (2023)

A restless badit approach for capacitated condition based maintenance scheduling

E-print/Working paper (2022)

Strategic Behavior in a Serial Newsvendor Setting

E-print/Working paper (2021)

Expediting in Two-Echelon Spare Parts Inventory Systems

in Manufacturing and Service Operations Management (2021), 23(6), 1431-1448

We consider a two-echelon spare parts inventory system consisting of one central warehouse and multiple local warehouses. Each warehouse keeps multiple types of repairable parts to maintain several types ... [more ▼]

We consider a two-echelon spare parts inventory system consisting of one central warehouse and multiple local warehouses. Each warehouse keeps multiple types of repairable parts to maintain several types of capital goods. The local warehouses face Poisson demand and are replenished by the central warehouse. We assume that unsatisfied demand is backordered at all warehouses. Furthermore, we assume deterministic lead times for the replenishments of the local warehouses. The repair shop at the central warehouse has two repair options for each repairable part: a regular repair option and an expedited repair option. Both repair options have stochastic lead times. Irrespective of the repair option, each repairable part uses a certain resource for its repair. Assuming a dual-index policy at the central warehouse and base stock control at the local warehouses, an exact and efficient evaluation procedure for a given control policy is formulated. To find an optimal control policy, we look at the minimization of total investment costs under constraints on both the aggregate mean number of backorders per capital good type and the aggregate mean fraction of repairs that are expedited per repair resource. For this non-linear non-convex integer programming problem, we develop a greedy heuristic and an algorithm based on decomposition and column generation. Both solution approaches perform very well with average optimality gaps of 1.56 and 0.23 percent, respectively, across a large test bed of industrial size. Based on a case study at Netherlands Railways, we show how managers can significantly reduce the investment in repairable spare parts when dynamic repair policies are leveraged to prioritize repair of parts whose inventory is critically low. [less ▲]

The stochastic maintenance location routing allocation problem for rolling stock

in International Journal of Production Economics (2020), 230

maintenance service logistics

in Operations Logistics and Supply Chain Management (2019)

Economies of scale in recoverable robust maintenance location routing for rolling stock

in Transportation Research. Part B, Methodological (2018), 117

We consider the problem of locating maintenance facilities in a railway setting. Different facility sizes can be chosen for each candidate location and for each size there is an associated annual facility ... [more ▼]

We consider the problem of locating maintenance facilities in a railway setting. Different facility sizes can be chosen for each candidate location and for each size there is an associated annual facility costs that can capture economies of scale in facility size. Because of the strategic nature of facility location, the opened facilities should be able to handle the current maintenance demand, but also the demand for any of the scenarios that can occur in the future. These scenarios capture changes such as changes to the line plan and the introduction of new rolling stock types. We allow recovery in the form of opening additional facilities, closing facilities, and increasing the facility size for each scenario. We provide a two-stage robust programming formulation. In the first-stage, we decide where to open what size of facility. In the second-stage, we solve a NP-hard maintenance location routing problem. We reformulate the problem as a mixed integer program that can be used to make an efficient column-and-constraint generation algorithm. To show that our algorithm works on practical sized instances, and to gain managerial insights, we perform a case study with instances from the Netherlands Railways. A counter intuitive insight is that economies of scale only play a limited role and that it is more important to reduce the transportation cost by building many small facilities, rather than a few large ones to profit from economies of scale. [less ▲]

A multi-item approach to repairable stocking and expediting in a fluctuating demand environment

in European Journal of Operational Research (2017), 256(1), 102-115

Repairable stocking and expediting in a fluctuating demand environment: Optimal policy and heuristics

in Operations Research (2016), 64(6), 1285-1301