M.Ing. / In the highly competitive environment in which all companies have to operate, it is becoming more and more important to optimise the amount of time a piece of equipment is down for scheduled repairs and the scheduling of these repairs. In this dissertation the equipment that is considered are the seventeen Babcock Borsig designed boilers situated on the Sasol Secunda site. A schematic drawing of these boilers is shown in figure 1. This drawing does not include the Electrostatic Precipitator that is located at the outlet of the boiler. The main function of the seventeen boilers on the Secunda site is to supply process steam to the rest of the factory. With each of the plants that are supplied with process steam having its own needs at any point in time, ensuring that enough steam is available in the system becomes an extremely important issue. The reason for this is that the plants that are supplied with process steam form a train and if one of the plants can not produce to full capacity, the down stream plants are also affected. The secondary function of the boilers is to supply steam to ten turbines for the generation of electricity. This means that any steam that the factory is not using is used for the generation of electricity. The ten generators can not supply the full need of the factory and the rest is drawn in from the national electricity supplier. It is thus best to generate as much electricity as possible. With the price of electricity varying during the year, winter being more expensive, the time when a boiler is off becomes critical. To ensure that the necessary process steam is available the long term plan of the factory is used to calculate the year budget for steam required by the factory. But as with everything plans do change and a short term plan is used to ensure that enough process steam is available for the factory.

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Aiming at aggregating numerous distributed resources to provide immense computing power, Grid computing has emerged as a promising paradigm to run complex composite applications such as workflows. However, the inherent uncertainties of grid systems as well as the structural complexity of workflow applications make it extremely challenging to schedule workflows in an efficient way, regardless of whether the objective is to minimize execution time or meet specific user and/or system Quality of Service (QoS) requirements. For both these cases, this thesis considers scheduling problems motivated by grid uncertainties and advances the state-of-the-art by developing new techniques to address these problems.First, based on existing scheduling heuristics, a Monte-Carlo approach is developed to minimize the average makespan (i.e., the overall execution time) in the presence of task estimates exhibiting limited uncertainty in the form of (controlled) random behaviour. Next, a scenario where performance prediction is difficult to obtain and resource availability may vary over time, is considered. A low-cost efficient just-in-time heuristic is proposed to cope with grid uncertainties.After addressing these performance-driven scheduling problems, a QoS-driven problem, which considers not only the aforementioned uncertainties but also the uncertainty caused by queue-based scheduling, is examined. In order to tackle all these uncertainties, an integrated scheduling model consisting of three supportive techniques is developed. Extensive evaluation using simulation shows that the proposed techniques can achieve substantial improvements towards the ultimate goal of providing a good solution for QoS-driven workflow scheduling on the Grid.

This research is focused on project scheduling with the aim to capture the monetary objectives of the project in the form of the maximisation of Net Present Value (NPV). In addition, this research is also highlighted key project management practices and scheduling methods. Project scheduling is very attractive for researchers and it has recently been drawn considerable attention because of the high cost of capital and the significant effect of the time value of money. This is the principal motivating factor behind this study. Project-scheduling problem is solved by priority rule-based heuristic methods in this study. The idea behind heuristic algorithms is to rank the activities by some rules. This research proposes a new rule called m-CCF with improved performance from the existing one. The m-CCF is also embedded in serial and parallel schedule generation schemes and is extended by implementing in a forward and backward strategy. The experiments are conducted to evaluate the performance of the proposed technique measuring the NPV generated for a particular project. This research also presents a framework summarising the previous research on project scheduling techniques. It is found that the m-CCF results in higher NPVs than any other heuristics. A series of different projects are examined to validate the potential of the m-CCF technique. The main findings of the research discover that the m-CCF is worthwhile to be employed in priority rule-based scheduling technique. Furthermore, the main findings suggest that it is beneficial to utilise forward-backward solution for scheduling improvement and selecting the schedule with the largest NPV among those available. In conclusion, this research contributes to existing knowledge by developing the combination of m-CCF priority rule methods and backward–forward scheduling. This can be considered as a good direction to develop further heuristics that can be exploited as a powerful tool in project planning and control systems.

In this thesis, we address a multi-objective personnel scheduling problem where personnel’s workload is uncertain and propose a two-stage robust modelling approach with demand uncertainty. In the first stage, we model a multi-objective personnel scheduling problem without incorporating demand coverage and, in the second stage, we minimize over or under-staffing after the realization of the demand and the assignments from the first stage. Two solution approaches are introduced for this model. The first approach solves the proposed model through a cutting plane strategy known as Benders dual cutting plane method, and the second approach reformulates the problem based on the strong duality theory. As a case study, the proposed model and the first solution approach are applied to an existing scheduling problem in the pathology department at The Ottawa Hospital. It is shown that the proposed model is successful at reducing the unmet demand while maintaining the performance with respect to other metrics when compared against the deterministic alternative.

The call for reform to raise student achievement has required educators, school leaders, and researchers to look for new methods to improve the learning process. One method used increasingly is block scheduling. Block scheduling is the restructuring of the school day into classes much longer than the traditional 50-55 minute class period. The purpose of this study was to determine high school principals’ and teachers’ perceptions of block scheduling in Mississippi high schools in three areas: achievement, attendance, and discipline. Many theorists believe that a person’s perceptions form the basis of reality for that person. If a teacher believes that block scheduling is effective, then for them, it is effective. Because some theorists believe that there is little to be gained from general studies that compare the objective results of block scheduling with the objective results of traditional scheduling since these comparisons have shown mixed results, this study addressed the social validity of block scheduling which is the extent to which participants perceive the worthiness of block scheduling. The research design used in this study was a cross sectional survey design. A researcher-developed survey instrument was used to collect data from teachers and principals in Mississippi high schools that had implemented block scheduling in the last 5 years. A total of 22 schools were used for the study. A 5 point Likert-type scale was used to measure respondents’ perceptions of the effectiveness of block scheduling on the three areas. While both principals and teachers appeared to have positive perceptions of the impact block scheduling has on student achievement, discipline, and attendance, principals had a more positive perception than teachers in all three areas. Both groups appeared to believe that student discipline was the most positively affected area, while attendance was the least positively affected. Recommendations based upon the findings of this study included conducting: (a) studies that include a larger sample of principals, (b) studies that identify student perceptions of block scheduling, and (c) studies to determine how important staff development is when implementing block scheduling.

Yes / The classical generation scheduling problem defines on/off decisions (commitment) and dispatch level of all available generators in a power system for each scheduling period. In recent years researchers have focused on developing new approaches to solve nonclassical generation scheduling problems in the newly deregulated and decentralized electricity market place. In this paper a GA-based approach has been developed for a system operator to schedule generation in a market akin to that operating in England and Wales. A generation scheduling problem has been formulated and solved using available trading information at the time of dispatch. The solution is updated after information is obtained in a rolling fashion. The approach is tested for two IEEE network-based problems, and achieves comparable results with a branch and bound technique in reasonable CPU time.

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