Tactical sugarcane harvest scheduling

[摘要] ENGLISH ABSTRACT: Computerised sugarcane harvest scheduling decision support is an active fi eld of research whichties in closely with the broader problem of automating and streamlining the various activitiesin the sugar supply chain. In this dissertation, the problem of providing decision support withrespect to sugarcane harvesting decisions is defined within a number of contexts, each representinga typical kind of organisation of sugarcane farmers into a cohesive decision making unit withits speci fic requirements and limitations that exist in practice. A number of variations relevantto these contexts of an overarching tactical sugarcane harvest scheduling problem (THSP) areconsidered and solved in this dissertation. The THSP is the problem of providing objective,responsible decision support to persons charged with the task of determining optimal harvestingdates for a set of sugarcane fields across an entire season.Sugarcane fields typically diff er in terms of the age, variety, life-cycle stage and in many otherproperties of the cane grown on them. The growth of sugarcane crops may also be a ffectedby environmental conditions such as accidentalfires, frosts or storms which have a detrimentale ffect on crop-value. Since sugarcane is a living organism, its properties change over time,an so does the potential pro t associated with it. The practicalities of farming cause furthercomplication of the problem (for example, seasonal changes alter the conditions under whichthe crop is harvested and transported). The rainy season carries with it the added cost ofdisallowing long-range vehicles to drive into thefields, forcing the unloading and reloading ofcane at so-called loading zones. Other considerations, such as the early ploughing out offields toallow them to fallow before being replanted, compounds the THSP into a multi-faceted difficultproblem requiring efficient data management, mathematical modelling expertise and efficientcomputational work.In the literature the THSP has been viewed from manydifferent standpoints and within manycontexts, and a variety of operations research methodologies have been employed in solvingthe problem in part. There is, however, no description in the literature of a solution to theTHSP that takes the negative e ffects of extreme environmental conditions on the quality ofa harvesting schedule into account in a scienti fically justifi able manner; most models in theliterature are based on optimising sucrose yield alone under normal conditions, rendering weakschedules in practice. The scope of the modelling and solution methodologies employed in thisdissertation towards solving the THSP is restricted to integer programming formulations andapproximate solution methods. The parameters associated with these models were determinedempirically using historical data, as well as previous work on deterioration of sugarcane followingenvironmental and other events.The THSP is solved in this dissertation by designing a generic architecture for a conceptualdecision support system (DSS) for the THSP in the various contexts referred to above, whichis capable of accommodating the e ects of extra-ordinary environmental conditions, as well asthe introduction of a computer-implemented version of a real DSS for the THSP conforming to the framework of this generic architecture. The DSS building blocks include predictionmodels for sugarcane yield, sugarcane recoverable value under normal circumstances, the costsassociated with a harvesting schedule and the negative e ects on sugarcane recoverable value ofextraordinary environmental conditions. The working of the DSS is based on a combinatorialoptimisation model resembling the well-known asymmetric traveling salesman problem withtime-dependent costs which is solved approximately by means of an attribute-based tabu searchin which both local and global moves have been incorporated. The DSS is also validated byexperienced sugarcane industry experts in terms of the practicality and quality of the schedulesthat it produces.

[发布机构] Stellenbosch University