Journal of the Operational Research Society

Amos, F; Rönnqvist, M; Gill, G

doi: 10.1057/palgrave.jors.2600436pmid: N/A

AbstractPooling is usually present throughout an oil refinery right from the processing of raw crudes through to the blending of petroleum products. Pooling occurs when two or more crudes, each with specific properties such as cost, sulphur content and unique distillation yields, are processed through distilling units simultaneously to yield downstream fractions. The decisions required in this problem are to select the quantities of each crude to be processed in each crude distiller and to select the best cut points which produce the desired fractions while minimising total cost of crude. Cut points are temperatures in the distillers at which different output streams are separated. In the proposed model, we introduce the use of cumulative functions for the distillation yields which enables a detailed description of the process in a mathematical model. Preliminary numerical results at the New Zealand Refining Company show that the non-linear model accurately describes the pooling problem and simultaneously is efficiently solvable.

Brown, G G; Ronen, D

doi: 10.1057/palgrave.jors.2600430pmid: N/A

AbstractWe describe the development and operation of an interactive system based on a mathematical optimisation model which is used by a major US manufacturer to consolidate customer orders into truckloads. Dozens of users employ the system daily for planning delivery of orders from manufacturing plants to customers by truckload carriers, saving numerous hours of the users' time and reducing transportation costs.

Basnet, C; Foulds, L R; Wilson, J M

doi: 10.1057/palgrave.jors.2600433pmid: N/A

AbstractThis paper reports on a decision aid that recommends solutions to a particular vehicle allocation problem occurring in the New Zealand dairy industry. The decision aid has been developed for use by New Zealand milk tanker schedulers. It is designed to aid them in the allocation of tankers to milk collection routes in order to alleviate pumping bay congestion, which occurs when the tankers return to unload milk at a processing plant. It enables its users to remain in control of the tanker allocation process, while using their own experience and preferences. The paper describes the issues involved and the type of help that the schedulers need. It introduces a typical allocation problem and describes some heuristics for its solution, which are incorporated in the decision aid.

Powell, J H; Coyle, R G

doi: 10.1057/palgrave.jors.2600437pmid: N/A

AbstractMany strategic decisions in business are made in a context which the decision makers perceive as uncertain, complex and opaque. A method, based on Rhyne's field anomaly relaxation technique, is described of generating a network of states which characterise the environment or context in which strategic decisions are to be made. These states represent possible future conditions for the business, and knowledge of them allows improved strategic understanding and decision making to be achieved. This paper describes the method, using a representative real-life application to illustrate the process.

Wilson, J M

doi: 10.1057/palgrave.jors.2600431pmid: N/A

AbstractA new algorithm for the generalised assignment problem is described in this paper. The algorithm is adapted from a genetic algorithm which has been successfully used on set covering problems, but instead of genetically improving a set of feasible solutions it tries to genetically restore feasibility to a set of near-optimal ones. Thus it may be regarded as operating in a dual sense to the more familiar genetic approach. The algorithm has been tested on generalised assignment problems of substantial size and compared to an exact integer programming approach and a well-established heuristic approach.

Wang, K-H; Wang, C-H; Bai, S X

doi: 10.1057/palgrave.jors.2600429pmid: N/A

AbstractThis paper deals with an unloader queueing model in which N identical trailers are unloaded by one or more unloaders. Theoretical solutions are obtained with the assumption of negative exponential distributions for trip times, unloading times, and finishing times. A cost model is developed to determine the optimal number of trailers. In order to evaluate the model robustness, simulation models are developed for three different distributions, exponential, second-order Erlang, and triangular. We demonstrate, through simulation results, that the unloader queueing model is sufficiently robust to the variations of probability distributions.

Armstrong, R; Gu, S; Lei, L

doi: 10.1057/palgrave.jors.2600387pmid: N/A

AbstractWe present an efficient algorithm for solving a class of two-resource allocation problem defined on a series-parallel graph, where nodes represent tasks of a given project and arcs represent precedence relationships. Two separate workloads are associated with each task and the time to complete a workload is inversely proportional to the amount of resource allocated. The time to complete a task is the maximum of the times taken to complete the two workloads. The problem is to allocate the two resources across the project so as to minimize the project duration. The proposed algorithm is derived based on the Equivalent Load Method by Monma, Schrijver, Todd, and Wei for the single-resource allocation problem.

Jamal, A M M; Sarker, B R; Wang, S

doi: 10.1057/palgrave.jors.2600428pmid: N/A

AbstractIn many inventory situations, the purchaser is allowed a permissible period to pay back the cost of goods bought without paying any interest. Depending on the length of that payment period, the purchaser can earn interest on the sales of the inventory. This paper develops a model to determine an optimal ordering policy for deteriorating items under permissible delay of payment and allowable shortage. Different facets of the permissible delays in payment are discussed, and this generalized model exhibits a set of solutions that reduces to an existing model. Results are discussed and demonstrated with an illustrative example.

Sundararaghavan, P S; Kunnathur, A S; Viswanathan, I

doi: 10.1057/palgrave.jors.2600408pmid: N/A

AbstractIn this study, a new class of proportional parallel flow shop problems with the objective of minimizing the makespan has been addressed. A special case for this problem in which jobs are processed on only one machine as opposed to two or more machines in a flow shop, is the well-known multiple processor problem which is NP-complete. The parallel processor problem is a restricted version of the problems addressed in this paper and hence are NP-complete. We develop and test heuristic and simulation approaches to solve large scale problems, while using exact procedures for smaller problems. The performance of the heuristics relative to the LP lower bound as well as a comparison with the truncated integer programming solution are reported. The performance of the heuristics and the simulation results were encouraging.

Kim, T S; Chae, K C

doi: 10.1057/palgrave.jors.2600423pmid: N/A

AbstractWe present a method for finding the age distribution of the absorbing semi-Markov process, age being the total time elapsed since the beginning of the process. Several examples are given.