In situations to do with the management of natural resources in the public domain there are often many 'interested and affected parties'. The opinions of how a given resource should be managed are as diverse as the parties themselves. Debates are frequently unproductive. We argue that in these situations the development of a decision support system (DSS) is a constructive way forward towards sound management practices. This approach enables existing knowledge to be integrated into a form that can be used immediately in decision-making. Furthermore, research can be optimally prioritised should greater accuracy or improvement in the initial DSS be required. We illustrate this approach by considering the problem of determining the freshwater requirements of estuaries. The pattern of freshwater flow into estuary of a river that has been impounded is a management decision. This inflow pattern influences the state of an estuary. This in turn affects the fish that use the estuary. In this illustration we focus on these fish in developing a DSS. The DSS is then applied in a case study of the Krom River in the Eastern Cape.
{"title":"Decision support systems for environmental management: A case study","authors":"N. Quinn, C. Green, J. Hearne, A. Whitfield","doi":"10.5784/14-0-419","DOIUrl":"https://doi.org/10.5784/14-0-419","url":null,"abstract":"In situations to do with the management of natural resources in the public domain there are often many 'interested and affected parties'. The opinions of how a given resource should be managed are as diverse as the parties themselves. Debates are frequently unproductive. We argue that in these situations the development of a decision support system (DSS) is a constructive way forward towards sound management practices. This approach enables existing knowledge to be integrated into a form that can be used immediately in decision-making. Furthermore, research can be optimally prioritised should greater accuracy or improvement in the initial DSS be required. We illustrate this approach by considering the problem of determining the freshwater requirements of estuaries. The pattern of freshwater flow into estuary of a river that has been impounded is a management decision. This inflow pattern influences the state of an estuary. This in turn affects the fish that use the estuary. In this illustration we focus on these fish in developing a DSS. The DSS is then applied in a case study of the Krom River in the Eastern Cape.","PeriodicalId":30587,"journal":{"name":"ORiON","volume":"86 13 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2014-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84008139","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this paper, we consider the problem of scheduling N jobs on a single machine to minimise total tardiness. Both the modified due date (MDD) rule and the heuristic of Wilkerson and Irwin (W-I) are very effective in reducing total tardiness. We show that in fact the MDD rule and the W-I heuristic are strongly related in the sense that both are based on the same local optimality condition for a pair of adjacent jobs, so that a sequence generated by these methods cannot be improved by any further adjacent pair-wise interchange.
{"title":"Relationship between the modified due date rule and the heuristic of Wilkerson and Irwin","authors":"J. Nyirenda","doi":"10.5784/17-0-192","DOIUrl":"https://doi.org/10.5784/17-0-192","url":null,"abstract":"In this paper, we consider the problem of scheduling N jobs on a single machine to minimise total tardiness. Both the modified due date (MDD) rule and the heuristic of Wilkerson and Irwin (W-I) are very effective in reducing total tardiness. We show that in fact the MDD rule and the W-I heuristic are strongly related in the sense that both are based on the same local optimality condition for a pair of adjacent jobs, so that a sequence generated by these methods cannot be improved by any further adjacent pair-wise interchange.","PeriodicalId":30587,"journal":{"name":"ORiON","volume":"12 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2014-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86759067","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In the industrial community it is well known that the failure rate of the manufactured units vary with time due to a variety of causes, namely, engineering design, manufacturing process, maintenance and quality inspection procedures and various assignable and non-assignable factors. Such failure rates invariably exhibit changes in both level and slope and at times exhibit periodic patterns as well. Therefore it would be quite inappropriate and erroneous to analyze such stochastic series of observations using the usual failure distribution approach. Since such data can be construed as time series, we suggest in this paper the time series techniques including the Kalman filter for their analysis. Other advantages of using the latter techniques are that the periodicities, if any, can be taken into account and short-term forecasts can be made which otherwise would not have been possible.
{"title":"Distribution-free approach to the evaluation of reliability of complex systems","authors":"V. Yadavalli, N. Signh, H. Boraine","doi":"10.5784/18-0-185","DOIUrl":"https://doi.org/10.5784/18-0-185","url":null,"abstract":"In the industrial community it is well known that the failure rate of the manufactured units vary with time due to a variety of causes, namely, engineering design, manufacturing process, maintenance and quality inspection procedures and various assignable and non-assignable factors. Such failure rates invariably exhibit changes in both level and slope and at times exhibit periodic patterns as well. Therefore it would be quite inappropriate and erroneous to analyze such stochastic series of observations using the usual failure distribution approach. Since such data can be construed as time series, we suggest in this paper the time series techniques including the Kalman filter for their analysis. Other advantages of using the latter techniques are that the periodicities, if any, can be taken into account and short-term forecasts can be made which otherwise would not have been possible.","PeriodicalId":30587,"journal":{"name":"ORiON","volume":"56 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2014-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83924261","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this article, we survey the developments in the generalised models of repairable systems reliability during 1990s, particularly the last five years. In this field, we notice the sharp fundamental problem that voluminous complex models were developed but there is an absence of sufficient data of interest for justifying the success in tackling the real engineering problems. Instead of following the myth of using simple models to face the complex reality, we select and review some practical models, particularly the stochastic processes behind them. The Models in three quick growth areas: age models, condition monitoring technique related models, say, proportional intensity and their extensions, and shock and wearing models, including the delay-time models are reviewed. With the belief that only those stochastic processes reflecting the instinct nature of the actual physical processes of repairable systems, without excessive assumptions, may have a better chance to meet the demands of engineers and managers.
{"title":"Generalized models of repairable systems: A survey via stochastic processes formalism","authors":"R. Guo, H. Asher, E. Love","doi":"10.5784/16-2-406","DOIUrl":"https://doi.org/10.5784/16-2-406","url":null,"abstract":"In this article, we survey the developments in the generalised models of repairable systems reliability during 1990s, particularly the last five years. In this field, we notice the sharp fundamental problem that voluminous complex models were developed but there is an absence of sufficient data of interest for justifying the success in tackling the real engineering problems. Instead of following the myth of using simple models to face the complex reality, we select and review some practical models, particularly the stochastic processes behind them. The Models in three quick growth areas: age models, condition monitoring technique related models, say, proportional intensity and their extensions, and shock and wearing models, including the delay-time models are reviewed. With the belief that only those stochastic processes reflecting the instinct nature of the actual physical processes of repairable systems, without excessive assumptions, may have a better chance to meet the demands of engineers and managers.","PeriodicalId":30587,"journal":{"name":"ORiON","volume":"43 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2014-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82685889","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The need to construct optimal drape surfaces arises in airborne geophysical surveys where it is necessary to fly a safe distance above the ground and within the performance of the aircraft used, but as close as possible to the surface. The problem is formulated as an LP with constraints at every point of a grid covering the area concerned, yielding a huge problem. The lifting algorithm is suggested. This is a surprisingly simple algorithm which starts with the drape surface at ground level and lifts it one point at a time. Only points which are too low relative to one or more of their neighbours are considered and they are lifted just enough to bring them into kilter with their neighbours. It is shown that the lifting algorithm is both exact and has great speed advantages. Some numerical results confirming exactness and speed are presented. An enhanced method with better complexity is proposed and tested numerically.
{"title":"The construction of drape surfaces with constrained first derivatives","authors":"R. Fossati, J. Wolvaardt","doi":"10.5784/17-0-190","DOIUrl":"https://doi.org/10.5784/17-0-190","url":null,"abstract":"The need to construct optimal drape surfaces arises in airborne geophysical surveys where it is necessary to fly a safe distance above the ground and within the performance of the aircraft used, but as close as possible to the surface. The problem is formulated as an LP with constraints at every point of a grid covering the area concerned, yielding a huge problem. The lifting algorithm is suggested. This is a surprisingly simple algorithm which starts with the drape surface at ground level and lifts it one point at a time. Only points which are too low relative to one or more of their neighbours are considered and they are lifted just enough to bring them into kilter with their neighbours. It is shown that the lifting algorithm is both exact and has great speed advantages. Some numerical results confirming exactness and speed are presented. An enhanced method with better complexity is proposed and tested numerically.","PeriodicalId":30587,"journal":{"name":"ORiON","volume":"12 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2014-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87463327","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The process of scheduling fruit pulping for the production of fruit juices is of great importance in the beverage industry. Decisions have to be made regarding available processing time, the disposal of fruit that will not be pulped before stock loss due to spoilage, the fulfilment of customer demand and an optimal financial position. Sheduling depends on the capacity of the work force, pulping machine limitations and delivery deadlines. However, the situation is often encountered where the plant manager has to decide which fruit batches (usually from stock piles of overwhelming proportions during the harvesting season) are to be pulped in order to minimize losses due to fruit deterioration. Such decisions are usually done manually, based on intuition and experience. A mathematical model is presented here which constructs a pulping strategy while minimising cascading financial losses associated with fruit grade drops within the stock pile. It is shown in particular that a minimisation of fruit losses is not a good criterion for optimality, and that substantial financial gains may be accomplished when minimising financial losses in stead of fruit losses, which is currently standard practice at most fruit pulping plants.
{"title":"Seeking optimality in fruit pulping schedules: A case study*","authors":"Jh van Vuuren, G. E. Huddlestone","doi":"10.5784/15-0-415","DOIUrl":"https://doi.org/10.5784/15-0-415","url":null,"abstract":"The process of scheduling fruit pulping for the production of fruit juices is of great importance in the beverage industry. Decisions have to be made regarding available processing time, the disposal of fruit that will not be pulped before stock loss due to spoilage, the fulfilment of customer demand and an optimal financial position. Sheduling depends on the capacity of the work force, pulping machine limitations and delivery deadlines. However, the situation is often encountered where the plant manager has to decide which fruit batches (usually from stock piles of overwhelming proportions during the harvesting season) are to be pulped in order to minimize losses due to fruit deterioration. Such decisions are usually done manually, based on intuition and experience. A mathematical model is presented here which constructs a pulping strategy while minimising cascading financial losses associated with fruit grade drops within the stock pile. It is shown in particular that a minimisation of fruit losses is not a good criterion for optimality, and that substantial financial gains may be accomplished when minimising financial losses in stead of fruit losses, which is currently standard practice at most fruit pulping plants.","PeriodicalId":30587,"journal":{"name":"ORiON","volume":"39 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2014-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82609005","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We describe an approach towards forecasting the manpower requirements in each of the branches of a bank, based on regression models fitted to the sets of efficient branches. DEA is employed to identify the efficient branches within a category, using the numbers of employees in the different grades at each branch as input variables, and the average volumes of different types of work performed by them during a month as output variables. Forecasts of future volumes of work are obtained by fitting a model which takes into account branch and seasonal effects, as well as separate trend effects for each of the branches. The models have been tested on data from a large bank, with very encouraging results. The approach holds great promise for use towards a decision support system for managing the bank's total branch manpower requirements.
{"title":"Use of data envelopment analysis and regression for establishing manpower requirements in a bank","authors":"L. Fatti","doi":"10.5784/14-0-421","DOIUrl":"https://doi.org/10.5784/14-0-421","url":null,"abstract":"We describe an approach towards forecasting the manpower requirements in each of the branches of a bank, based on regression models fitted to the sets of efficient branches. DEA is employed to identify the efficient branches within a category, using the numbers of employees in the different grades at each branch as input variables, and the average volumes of different types of work performed by them during a month as output variables. Forecasts of future volumes of work are obtained by fitting a model which takes into account branch and seasonal effects, as well as separate trend effects for each of the branches. The models have been tested on data from a large bank, with very encouraging results. The approach holds great promise for use towards a decision support system for managing the bank's total branch manpower requirements.","PeriodicalId":30587,"journal":{"name":"ORiON","volume":"69 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2014-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90283383","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A zero-one mixed integer linear programming model is developed for the scheduling of projects under the condition of inflation and under penalty and reward arrangements. The effects of inflation on time-cost trade-off curves are illustrated and a modified approach to time-cost trade-off analysis presented. Numerical examples are given to illustrate the model and its properties. The examples show that misleading schedules and inaccurate project-cost estimates will be produced if the inflation factor is neglected in an environment of high inflation. They also show that award of penalty or bonus is a catalyst for early completion of a project, just as it can be expected.
{"title":"A model for scheduling projects under the condition of inflation and under penalty and reward arrangements","authors":"J. Jolayemi","doi":"10.5784/17-0-191","DOIUrl":"https://doi.org/10.5784/17-0-191","url":null,"abstract":"A zero-one mixed integer linear programming model is developed for the scheduling of projects under the condition of inflation and under penalty and reward arrangements. The effects of inflation on time-cost trade-off curves are illustrated and a modified approach to time-cost trade-off analysis presented. Numerical examples are given to illustrate the model and its properties. The examples show that misleading schedules and inaccurate project-cost estimates will be produced if the inflation factor is neglected in an environment of high inflation. They also show that award of penalty or bonus is a catalyst for early completion of a project, just as it can be expected.","PeriodicalId":30587,"journal":{"name":"ORiON","volume":"50 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2014-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79463900","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This study focuses on developing an agricultural investment model based upon proven financial investment portfolio techniques. The model can be used as a tool to diversify agricultural risk over the long-term by optimising the proportion of land allocated to each of the agricultural products, resulting in increased value of the agricultural enterprise. Sensitivity analysis allows the strategist to understand the impact that future prices, gross margins and land availability may have on the long-term sustainability of the farming enterprise.
{"title":"A mathematical approach to increasing the long-term wealth of an agricultural enterprise","authors":"P. Théron, R. Honert","doi":"10.5784/19-0-180","DOIUrl":"https://doi.org/10.5784/19-0-180","url":null,"abstract":"This study focuses on developing an agricultural investment model based upon proven financial investment portfolio techniques. The model can be used as a tool to diversify agricultural risk over the long-term by optimising the proportion of land allocated to each of the agricultural products, resulting in increased value of the agricultural enterprise. Sensitivity analysis allows the strategist to understand the impact that future prices, gross margins and land availability may have on the long-term sustainability of the farming enterprise.","PeriodicalId":30587,"journal":{"name":"ORiON","volume":"25 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2014-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74645143","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Availability of a binary repairable system is generalised on the case when the quality of the system’s operation is characterised by some decreasing in time (since the latest renewal) function of performance. The corresponding equation for the time-dependent availability is derived and the stationary characteristic is considered as well. The probability of exceeding the fixed level of performance for an arbitrary instant of time is also obtained. A further generalisation is performed by assuming the possibility of a gradual repair. This means that the system can be partly available (with the decreased level of performance) during the process of repair. Finally, the specific case of imperfect repair is treated. Possible generalisations of the last approach are discussed.
{"title":"A note on parametric availability","authors":"M. Finkelstein","doi":"10.5784/16-2-407","DOIUrl":"https://doi.org/10.5784/16-2-407","url":null,"abstract":"Availability of a binary repairable system is generalised on the case when the quality of the system’s operation is characterised by some decreasing in time (since the latest renewal) function of performance. The corresponding equation for the time-dependent availability is derived and the stationary characteristic is considered as well. The probability of exceeding the fixed level of performance for an arbitrary instant of time is also obtained. A further generalisation is performed by assuming the possibility of a gradual repair. This means that the system can be partly available (with the decreased level of performance) during the process of repair. Finally, the specific case of imperfect repair is treated. Possible generalisations of the last approach are discussed.","PeriodicalId":30587,"journal":{"name":"ORiON","volume":"7 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2014-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82771215","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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