Convoys to combat Somali piracy

As the world becomes increasingly globalized, interruptions to international trade cannot be permitted. Piracy off the coast of Somalia has hampered international trade in the region and poses significant risks to the sailors required to navigate those waters. Over the past three years the global community has attempted, through a number of different naval tactics, to stop these acts of piracy; however, these tactics have proven ineffective. This article looks at historical precedence and military theory to support the concept of using convoys to protect the thousands of cargo vessels traveling round the Horn of Africa every year. This tactic will greatly decrease the number of successful pirate attacks and save countless lives in the process.     

Trajectory predictions of new lift separation sabots

This paper presents a modified analytical model to evaluate the trajectories of various lift separation sabot configurations. The aerodynamic forces acting on the sabot surfaces during a supersonic flight are modeled in the present analytical model by incorporating the pressures on the windward side of the sabot due to the detached/attached shock and its reflections and then integrated using the 3-DoF dynamical equations. The trajectory and the aerodynamic coefficients were obtained for these config-urations at a projectile Mach number of 3. The sabot configurations, which include two new designs, are compared with each other and with the conventional free flight trajectory data of the conventional sabots. The mechanical interaction between the sabot and projectile is also addressed in the present work. The comparison shows that the new designs with the aerodynamic surfaces close to the center of gravity, lift-off from the projectile with minimal mechanical interaction compared to a conventional sabot.     

Outsourcing warranty repairs: Dynamic allocation

In this paper we consider the problem of minimizing the costs of outsourcing warranty repairs when failed items are dynamically routed to one of several service vendors. In our model, the manufacturer incurs a repair cost each time an item needs repair and also incurs a goodwill cost while an item is awaiting and undergoing repair. For a large manufacturer with annual warranty costs in the tens of millions of dollars, even a small relative cost reduction from the use of dynamic (rather than static) allocation may be practically significant. However, due to the size of the state space, the resulting dynamic programming problem is not exactly solvable in practice. Furthermore, standard routing heuristics, such as join‐the‐shortest‐queue, are simply not good enough to identify potential cost savings of any significance. We use two different approaches to develop effective, simply structured index policies for the dynamic allocation problem. The first uses dynamic programming policy improvement while the second deploys Whittle's proposal for restless bandits. The closed form indices concerned are new and the policies sufficiently close to optimal to provide cost savings over static allocation. All results of this paper are demonstrated using a simulation study. © 2005 Wiley Periodicals, Inc. Naval Research Logistics, 2005     

Rhetoric versus reality: Canadian defence planning in a time of austerity

As Canada's military mission in Afghanistan winds down and the country faces several years of fiscal austerity, all of Canada's major political parties are agreed that Canadian defence budgets must stay level or be cut. This comes at a time when the defence department is slated to replace the Canadian Forces’ (CF) major equipment fleets. Canada's defence establishment thus faces some critical decisions. One option is to try to maintain its expeditionary capabilities across all three services: army, navy and air force. Absent substantial new infusions of funds, however, this approach is likely to lead to an overall and largely chaotic reduction of capabilities. Another option is to make some difficult choices as to which expeditionary capabilities to maintain as part of a strategic review of Canada's future military needs. Such an option would ensure that Canada has at least some military capacities which can reliably be devoted to the most demanding international operations, while maintaining those capabilities required for domestic duties and North American defence. Pursuing this option would accord with the new North Atlantic Treaty Organization Strategic Concept and the call for “Smart Defense” within the Alliance. This article assesses the arguments for and against the option of specialising Canada's future defence capabilities and explores scenarios as to what a future CF may look like.     

Economic lot scheduling of fully loaded processes with external setups

Without restricting the class of permissible schedules, we derive optimal schedules for economic lot scheduling problems that are fully loaded, have external setups, and have only two products. The fully loaded condition accurately represents certain types of bottlenecks. We show that the optimal schedule must have the Wagner-Whitin property. We also develop a measure of aggregate inventory, derive an optimal steady-state aggregate inventory policy, and provide conditions under which the aggregate inventory level of an optimal schedule must approach a steady state. By restricting the class of permissible schedules to rotation cycle schedules, we extend these results to more than two products.     

Parallel machine replacement

We consider the parallel replacement problem in which there are both fixed and variable costs associated with replacing machines. Increasing maintenance costs motivate replacements, and the fixed replacement cost provides incentive for replacing machines of different ages together in “clusters.” We prove two intuitive results for this problem. First, it is never optimal to split a cluster of like-aged machines, and second, it is never optimal to replace newer clusters before older clusters. By incorporating these two results into an algorithmic approach, we vastly reduce the amount of computation required to identify an optimal replacement policy.     

Two heuristics for the economic lot scheduling problem: An experimental study

In this article we present and test two heuristics for the economic lot scheduling problem. The first heuristic was developed by one of us (P.C. Geng) during Ph.D. research, while the other is a convergent implementation of an algorithm due to Doll and Whybark. We study the performance of these heuristics on a large set of test problems constructed using a new form of problem generation that yields random problems within an experimental design.     

Finite Markov chain models skip-free in one direction

Finite Markov processes are considered, with bidimensional state space, such that transitions from state (n, i) to state (m, j) are possible only if m ≤ n + 1. The analysis leads to efficient computational algorithms, to determine the stationary probability distribution, and moments of first passage times.