Øyvind Halskau

General solutions to the single vehicle routing problem with pickups and deliveries

The single vehicle routing problem with pickups and deliveries (SVRPPD) is defined on a graph in which pickup and delivery demands are associated with the customer vertices. The problem consists of designing a least cost route for a vehicle of capacity Q. Each customer is allowed to be visited once for a combined pickup and delivery, or twice if these two operations are performed separately. This article proposes a mixed integer linear programming model for the SVRPPD. It introduces the concept of general solution which encompasses known solution shapes such as Hamiltonian, double-path and lasso. Classical construction and improvement heuristics, as well as a tabu search heuristic, are developed and tested over several instances. Computational results show that the best solutions generated by the heuristics are frequently non-Hamiltonian and may contain up to two customers visited twice.

Routing of supply vessels to petroleum installations

Purpose – In the Norwegian oil and gas industry the upstream logistics includes providing the offshore installations with needed supplies and return flow of used materials and equipment. This paper considers a real‐life routing problem for supply vessels serving offshore installations at Haltenbanken off the northwest coast of Norway from its onshore supply base. The purpose of the paper is to explore how the offshore installations limited storage capacity affects the routing of the supply vessels aiming towards creating efficient routes.Design/methodology/approach – A simplified version of the real‐life routing problem for one supply vessel is formulated as a mixed integer linear programming model that contains constraints reflecting the storage requirements problem. These constraints ensure that there is enough capacity at the platform decks and that it is possible to perform both pickup and delivery services.Findings – The model has been tested on real‐life‐sized instances based on data provided by th...

Relationship duration and buyer influence in just-in-time relationships

Abstract Heavy investments tailored to a specific JIT-relationship highlight the trade-off between improved value-added and inter-firm dependence in industrial purchasing relationships. The main reason for dedicating specific investments in a JIT-relationship is to enhance production efficiency and logistics performance. On the other hand, such investments induce substantial inter-firm dependence and high switching costs, which must be offset by stronger inter-firm co-ordination. Using transaction costs analysis (TCA) and relational contracting theory (RCT), the authors have examined whether the buyers influence on a JIT-relationship is contingent upon the length of that relationship. Data from a survey of 165 industrial purchasing relationships demonstrate that as a JIT-relationship evolves over time, inter-firm co-ordination tends to increase reliance on relational governance. When the level of the JIT-investment is substantial, hierarchical buyer control relaxes significantly as the length of the relationship increases.

Helicopter routing in the Norwegian oil industry

Purpose – In the Norwegian offshore oil industry, helicopters have been used as a major mode of transporting personnel to and from offshore installations for decades. Helicopter transportation represents one of the major risks for offshore employees. The purpose of this paper is to study the safety of helicopter transportation in terms of the expected number of fatalities on an operational planning level. Design/methodology/approach – Based on an analysis of helicopter accidents, this paper proposes a mathematical model that can aid in the planning of routes for the fleet in order to minimize the expected number of fatalities. Findings – A theorem proven in this paper tells that hub-and-spoke configuration is the best way of routing helicopters in terms of minimizing expected number of fatalities. Computational results indicate that the expected number of fatalities may be reduced at the expense of longer travel time by implementing the proposed method into planning of routes for helicopter fleet. Researc...

EOQ models for postponed payment of stored commodities

In inventory theory the inventory holding cost per unit plays an important part. In most transactions concerning selling and buying a certain postponement of payment is offered or accepted by the seller. This should have some consequences for the order size and can be regarded as a kind of discount. Traditionally, when average costs (AC) are used, these kinds of effects are not explicitly incorporated in the classical formulas for economic order quantities (EOQs). On the other hand, such effects have been treated to a certain degree in the literature when a present value criterion (PVC) is used to estimate the inventory holding costs over a certain time interval. However, in these models one does not differentiate between the holding costs incurred by the capital tied up in the inventory and other costs incurred by storing an item. Approaches this problem in an AC manner, but, opposed to the PVC, splits the inventory holding costs into two parts. Offers an EOQ formula for the simple case of a single item stored; enhances this formula for a situation where a family of items are ordered in a co‐ordinated way, and into a situation with stochastic demand for a single item. Finally, interprets the postponed payment in terms of an all unit discount.

Offshore Helicopter Routing in a Hub and Spoke Fashion: Minimizing Expected Number of Fatalities☆

Abstract Helicopters are often used for transportation of workers to and from offshore installations. Flying helicopter is a risky business and is often considered as one of the main risk factors in this industry. The present paper is dealing with different routing policies for minimizing the expected number of fatalities where the transportation is performed in a hub and spoke fashion from a land based heliport to a set of offshore installations either using the heliport as a hub or using one or more offshore installations as hubs. Some theoretical results are offered as well as an exact model when one operates with more than one offshore hub.

The effect of buyer specific-monitoring procedures on buyer control in dynamic supply chain links

Based on transaction cost analysis (TCA), resource dependency theory (RDT), and supply chain management literature, this study explores the effect of buyer-specific monitoring procedures on buyer control in industrial buyer-seller transactions, particularly in relation to how environmental uncertainty affects the buying firms ability to exercise control over the supplier firm. The research design is based on primary data from a survey of 168 industrial buyer-seller relationships which map a broad set of dimensions of the economic transactions and structures in these business-to-business relationships. The empirical findings provide support for the hypotheses, and demonstrate that the effect of the buyer-specific monitoring procedures is positively associated with buyer control arrangements under conditions with rather modest external disturbances. This governance pattern is completely changed when business relationships face substantial environmental uncertainty. Under such conditions, the effect of buyer specific monitoring procedures on buyer control is significantly attenuated.