Eberhard E. Bischoff

A comparative evaluation of heuristics for container loading

Abstract This paper is concerned with the development of heuristics for determining efficient packing patterns in loading freight containers with rectangular items. A focal point is the domain-dependency of such heuristics, i.e. the effect which certain parameters of a problem may have on the performance of a heuristic. The paper draws on the result of a comparative analysis of fourteen heuristic rules which examines the impact of the number of different types of items in a load on the loading efficiency achieved. The implications for the design of composite heuristics are discussed and suggestions for a workable compound approach made.

Three-dimensional packing of items with limited load bearing strength

Abstract A new heuristic approach is put forward for tackling container loading problems where the cargo involved has varying degrees of load bearing strength. In such cases the placement rules must ensure that the weight resting on an item remains below the maximum it can withstand without suffering crushing damage. The construction heuristic proposed is embedded in a search algorithm which seeks to optimise the parameter settings of the procedure. Limiting the time required to produce a good solution and the amount of technical expertise needed by the user are key considerations. The approach is evaluated in a series of tests against benchmarks from the literature. The results demonstrate that it outperforms other approaches which have been suggested for this type of problem and that it also performs well on problems where load bearing strength is not an issue. Potentially useful extensions of the work are discussed.

Seasonality of Tourism in Wales: A Comparative Analysis

This paper examines the seasonal pattern for different types of domestic tourism demand in the UK during 1994–2000. The focus is on Wales, a region with a particularly pronounced tourism seasonality. The characteristics of the Welsh seasonal pattern are identified and compared with other UK regions, notably Scotland. An overview of various different methods for quantifying these seasonal variations is presented. Various scalar measures are used to evaluate the inequality of the distribution of tourism trips within a year. The stability of seasonal patterns between the years is also examined and more complex methodologies, such as Seasonal Decomposition, are applied in order to assess in detail the differences in the seasonal behaviour of demand among the UK home nations. On the basis of the analysis, policy implications for tackling the seasonality problem are discussed.

Allowing for weight considerations in container loading

Only very few of the existing container loading algorithms include in their logic any references to the weight or the load bearing abilities of the items to be stowed. The paper aims to make a contribution to overcoming this shortcoming. It shows how a procedure which has already been evaluated in some detail in the literature can be adapted in a fairly straightforward manner to deal with fragility considerations. The approach suggested is based on opportunity cost notions. It is demonstrated that the results obtained can be vastly superior to a procedure which considers load bearing ability merely in terms of a constraint on the packing options available at each stage. Additional refinements of the basic approach and questions related to its practical implementation are also discussed, as are possible extensions to enable ‘soft’ positioning rules to be incorporated.ZusammenfassungNur sehr wenige Containerbeladungs-Algorithmen nehmen in ihrer Logik Bezug auf das Gewicht oder die Tragfähigkeit der zu verladenden Güter. Der Artikel versucht, einen Beitrag zur Überwindung dieses Mangels zu leisten. Es wird gezeigt, wie ein Verfahren, das bereits zu einem gewissen Grad in der Literatur behandelt wurde, auf relativ einfache Weise adaptiert werden kann, um die Einbeziehung von Belastbarkeitsüberlegungen zu ermöglichen. Die vorgestellte Methode beruht auf Opportunitätskostenprinzipien. Es wird demonstriert, daß die Ergebnisse beträchtlich besser sein können als die, die man erhält wenn Tragfähigkeit nur als Restriktion bezüglich der im jeweiligen Algorithmusschritt zulässigen Alternativen behandelt wird. Zusätzliche Verfeinerungen der Methodik und Fragen hinsichtlich des praktischen Einsatzes werden ebenfalls diskutiert. Zudem werden potentielle Erweiterungen erörtert, die es ermöglichen, ‚weiche‘ Plazierungsregeln in das Verfahren einzubeziehen.

Stability aspects of pallet loading

SummaryThe algorithm-orientated literature on packing problems has concentrated on methods for achieving an efficient utilisation of the transport or storage medium concerned. Many problems arising in practice, however, also involve other objectives in addition to that of minimising unused space. The stability of the load is a prime example. The paper considers the stability objective in the context of pallet loading and examines approaches for generating stable stacking patterns that are also optimal from the viewpoint of space utilisation. A statistical performance analysis of the methods described is presented and potentially fruitful directions for further research are discussed.ZusammensetzungDie algorithmisch orientierte Literatur über Packprobleme hat sich auf Methoden zur Erzielung einer effizienten Auslastung des betreffenden Transport-oder Lagermediums konzentriert. Viele Probleme, die sich in der Praxis stellen, beinhalten jedoch auch andere, über eine Minimierung des unbenutzten Stauraums hinausgehende, Zielsetzungen. Die Stabilität der Ladung ist ein offensichtliches Beispiel. Der Beitrag betrachtet das Stabilitätserfordernis im Zusammenhang mit der Beladung von Paletten und untersucht Ansätze zur Erzeugung stabiler Stapelpläne, die gleichzeitig vom Gesichtspunkt der Raumausnutzung her optimal sind. Eine statistische Analyse der Leistungsfähigkeit der beschriebenen Methoden wird vorgestellt, ebenfalls werden potentiell ergiebige Richtungen für weitere Arbeiten auf diesem Gebiet erörtert.

Analysing trade-offs in container loading: combining load plan construction heuristics with agent-based simulation

In this paper we describe two operations research techniques, cutting and packing optimisation (CPO) and simulation, and present a multi-methodology approach for analysing the trade-offs between loading efficiency and various important practical considerations in relation to the cargo, such as its stability, fragility or possible cross-contamination between different types of items over time. The feasibility of this approach is demonstrated by considering a situation where the items to be loaded have differing degrees of perishability and where badly deteriorated items can affect those in their immediate vicinity (e.g. through the spread of mould). Our approach uses the output of the CPO algorithms to create agents that simulate the spread of mould through proximity-based interactions between the agents. The results show the trade-offs involved in container utilisation and the propagation of mould, without evidence of any correlation between them. The contribution of this research is the methodology and the feasibility study.

Developing Effective Strategies for Tackling Seasonality in the Tourism Industry

Seasonality is a key aspect for the performance of the majority of tourism enterprises and a central theme for policy makers. The usual practice of strategy formulation in this area, whilst often involving a sound analysis of objective performance data, largely ignores the perceptions which the businesses concerned have of the seasonality issue. This paper demonstrates that the heterogeneity of attitudes and perceptions in the sector need to be recognised when developing effective strategies for tackling seasonality. An empirical quantitative approach is applied using occupancy data of the serviced accommodation sector in addition to a survey of owner/managers. The findings indicate that an insufficiently detailed level of segmentation of the business sector concerned may lead to ill-focused broad-brush strategies and consequent misallocations of resources. The paper contends that policy makers in this area need information beyond what can be obtained from the usual performance measurement systems.

A multi-methodology agent-based approach for container loading

The paper deals with container loading and contends that combining Container Loading Algorithms (CLAs) with Agent-Based Simulation (ABS) is a feasible and useful way of analyzing trade-offs between loading efficiency and various practical considerations in relation to the cargo - such as its stability, fragility, or possible cross-contamination between items over time. The latter perspective is used to demonstrate the merits of the approach. More specifically, the paper considers a situation where the items involved have differing degrees of perishability and badly deteriorated items can affect others (e.g., through mold spreading). The output of the CLAs is used to create agents that simulate the spread of mold through proximity-based interactions. The results show the trade-offs between container utilization and the propagation of mold and demonstrate that there is not necessarily any correlation between these two factors. The key contribution of the research is the multi-methodology agent-based approach to container loading.

Proximity-based modelling of cross-contamination through agent-based simulation: a feasibility study

Proximity-based modelling methodology enables mathematical representation of a real system that is characterised by the existence of entities that come into physical contact. Healthcare systems can benefit from this methodology since physical proximity between entities (e.g., patients, clinical items like surgical equipment and blood units) can result in the spread of infectious diseases and cross-contamination. The existing analytical techniques, which are mainly based on differential equations, are unsuitable for representing the fine-grained, micro-world view of the entity interactions that we intend to model. We therefore extend Agent-Based Simulation (ABS) by enabling individual agents to be aware of the physical location of the other agents being modelled in a 3-dimensional space – this is a perquisite for our proximity-based modelling methodology. To demonstrate the feasibility of our approach, we experiment with a scenario wherein boxes of degradable clinical items, modelled as agents, are stored in close proximity. We use Cutting and Packing Optimisation (CPO) algorithms from literature to define the arrangement of these agents in the 3-D space and to make the individual agents ‘location-aware’. An ABS model then simulates cross-contamination by modelling the spread of contaminants among the agents confined in the well-defined space. Our approach can be used to model analogous situations wherein physical proximity between entities in the underlying system is a necessary condition for entity interactions.

Palletisation efficiency as a criterion for product design

The paper is concerned with the question of how implications for palletisation efficiency may be taken into account in the product/packaging design process. The perspective from which this topic is approached is the reverse of that usually adopted: rather than dealing with an evaluation of pre-determined design alternatives, the paper considers the problem of identifying the options open to the designer if a given palletisation efficiency target is to be achieved. In addition to a number of algorithmic issues various practical aspects of the problem are also discussed. The results of two case studies provide a concrete frame of reference throughout the paper.ZusammenfassungDer Artikel befaßt sich mit der Frage, wie bei der Gestaltung eines Produkts oder seiner Verpackung die Auswirkungen auf den Nutzungsgrad von Paletten berücksichtigt werden können. Die dabei eingenommene Perspektive ist die umgekehrte der üblichen: an Stelle einer Bewertung vorab bestimmter Alternativen betrachtet der Artikel das Problem, die Wahlmöglichkeiten zu identifizieren, die dem Designer zur Verfügung stehen, wenn ein bestimmter Nutzungsgrad der Palette erreicht werden soll. Zusätzlich zu mehreren algorithmischen Problemstellungen werden verschiedene praktische Aspekte des Problems erörtert. Die Ergebnisse zweier Fallstudien dienen als konkrete Bezugspunkte für alle Teile des Artikels.