Ismail Capar

Managing supply chains in times of crisis: a review of literature and insights

Purpose – The purpose of this paper is to review the literature to describe the current practices and research trends in managing supply chains in crisis. This paper also provides directions for future research in supply chain crisis management.Design/methodology/approach – Articles published prior to August 2008 are analyzed and classified.Findings – A unique five‐dimensional framework to classify the literature is provided. The study reveals that there has been extensive research done in this area in recent years. Much of the research is focused on proactive approaches to crisis in supply chains. Management during various internal crises such as supplier bankruptcy or loss of key clients is a new, challenging area that requires further investigation.Research limitations/implications – This paper does not include articles that are not peer‐reviewed.Practical implications – This paper will serve as a guide to supply chain managers who would like to know how crises, disasters, and disruptions in supply cha...

An arc cover–path-cover formulation and strategic analysis of alternative-fuel station locations

In this study, we present a new formulation of the generalized flow-refueling location model that takes vehicle range and trips between origin–destination pairs into account. The new formulation, based on covering the arcs that comprise each path, is more computationally efficient than previous formulations or heuristics. Next, we use the new formulation to provide managerial insights for some key concerns of the industry, such as: whether infrastructure deployment should focus on locating clusters of facilities serving independent regions or connecting these regions by network of facilities; what is the impact of uncertainty in the origin–destination demand forecast; whether station locations will remain optimal as higher-range vehicles are introduced; and whether infrastructure developers should be willing to pay more for stations at higher-cost intersections. Experiments with real and random data sets are encouraging for the industry, as optimal locations tend to be robust under various conditions.

An efficient formulation of the flow refueling location model for alternative-fuel stations

The Flow-Refueling Location Model (FRLM) locates a given number of refueling stations on a network to maximize the traffic flow among origin–destination pairs that can be refueled given the driving range of alternative-fuel vehicles. Traditionally, the FRLM has been formulated using a two-stage approach: the first stage generates combinations of locations capable of serving the round trip on each route, and then a mixed-integer programming approach is used to locate p facilities to maximize the flow refueled given the feasible combinations created in the first stage. Unfortunately, generating these combinations can be computationally burdensome and heuristics may be necessary to solve large-scale networks. This article presents a radically different mixed-binary-integer programming formulation that does not require pre-generation of feasible station combinations. Using several networks of different sizes, it is shown that the proposed model solves the FRLM to optimality as fast as or faster than currently utilized greedy and genetic heuristic algorithms. The ability to solve real-world problems in reasonable time using commercial math programming software offers flexibility for infrastructure providers to customize the FRLM to their particular fuel type and business model, which is demonstrated in the formulation of several FRLM extensions.

A decision rule for coordination of inventory and transportation in a two-stage supply chain with alternative supply sources

This paper deals with a two-stage supply chain that consists of two distribution centers and two retailers. Each member of the supply chain uses a (Q,R) inventory policy, and incurs standard inventory holding and backlog costs, as well as ordering and transportation costs. The distribution centers replenish their inventory from an outside supplier, and the retailers replenish inventory from one of the two distribution centers. When a retailer is ready to replenish its inventory that retailer must decide whether it should replenish from the first or second distribution center. We develop a decision rule that minimizes the total expected cost associated with all outstanding orders at the time of order placement; the retailers then repeatedly use this decision rule as a heuristic. A simulation study which compares the proposed policy to three traditional ordering policies illustrates how the proposed policy performs under different conditions. The numerical analysis shows that, over a large set of scenarios, the proposed policy outperforms the other three policies on average.

Efficient and equitable transnational infrastructure planning for natural gas trucking in the European Union

The European Union relies on oil for over 90% of its transportation fuels and spends one billion Euros a day on imported oil. To reduce this dependency, the EU is developing an integrated market for compressed (CNG) and liquefied (LNG) natural gas as alternatives to diesel for long-haul trucking. This paper develops a modeling approach for optimizing a subsidized European network of LNG truck stops based on the flow-refueling location model (FRLM). The FRLM locates stations to cover the maximum flow volume of origin-destination trips on their shortest paths. The FRLM explicitly accounts for the need for multiple refueling stops to serve long-distance trips given a safe driving range of vehicles. Using forecasted road freight data from the EUs TransTools model, this paper maximizes flows in terms of tkm rather than tons to prioritize longer trips that cross more borders, replace more diesel, and reduce more carbon emissions. Nevertheless, the basic maximum cover version of the FRLM achieves the most “bang for the buck” by clustering stations in Germany, which has the densest concentration of flows. For a network of subsidized stations for promoting pan-European trucking, concentrating new stations in a few countries may not be politically desirable. The authors therefore introduce and compare several new side constraints for producing a more equitable distribution of covered flows across EU members. The partial regional coverage constraint show the most promise for offering decision-makers distinct alternatives for planning an equitable and efficient network of alternative-fuel stations across several political regions.