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<p>Systematic strategies for optimal plant operation under partial shutdowns were developed. Partial shutdowns are circumscribed process unit shutdowns that permit the rest of the plant to continue operating to some degree. These strategies manipulate the degrees-of-freedom in a plant---during and after a shutdown---to restore plant production in a cost-optimal fashion, while meeting safety and operational constraints. This is accomplished through the adjustments of production rates, recycles and buffer levels.</p> <p>Our multi-tiered dynamic optimization approach allows for the prioritization of multiple objectives and the specification of trade-offs between these objectives. The solution of the optimization problem informs the formulation of inventory management policies. A Model-Predictive-Control (MPC) based partial shutdown algorithm implements these policies under feedback.</p> <p>Parsimonious discrete modeling formulations were presented for handling model discontinuities such as shutdown thresholds, induced shutdowns and minimum shutdown durations. The problem of minimizing restoration time was considered.</p> <p>We investigated the use of state/parameter estimation algorithms to moderate the effects of plant-model mismatch. The algorithms are based on novel configurations of the constrained Unscented Kalman Filter (UKF). Constraints on the estimates are enforced through a simple projection method. A dynamic feasibility tier ensures that terminal constraints and parameters are feasible for the prediction horizon in the control optimization problem.</p> <p>A modeling system (MLDO) was created for prototyping dynamic optimization models. It transforms a mathematical description of a model into code in various computer languages for the purposes of optimization, simulation, visualization and analysis of dynamic optimization problems. Facilities for problem reformulation and transformations are included.</p> / Doctor of Philosophy (PhD)

Food availability is central to humans' survival. Even though Sweden has a reasonably low self-sufficiency rate of only 50%, it has a high level of domestic wheat production and exports a lot of wheat yearly. Wheat is a good source of essential nutrients and is a cornerstone in Swedish agriculture and food production. Even though Sweden has a considerable domestic production of wheat, several risks pose a threat to domestic wheat availability in the future, which could endanger Swedish food security. Therefore, this essay evaluates three considerable risks to Swedish wheat availability: climate change, population growth, and trade disturbances. These risks have been assessed based on previous research and statistical analysis of the historical wheat production, consumption, and trade data. In addition, stochastic models have also been created to simulate the risk of a domestic shortage of wheat. Future opportunities in Swedish wheat availability are also discussed to give a nuanced picture of future wheat availability in Sweden. Among other things, ARIMA modeling has been used to predict Swedish wheat production's efficiency. The results indicate that there are positive trends in wheat production. However, wheat production is also an object of increased volatility, threatening wheat availability. This increased volatility can be linked to extreme weather caused by global warming. These extreme weather events are predicted to occur more in the future, risking volatility in wheat production to grow even further. The stochastic model implies that there is an inherent risk of wheat shortage in the future. However, when the stochastic model considers both population growth and increased efficiency in wheat production, the risk of wheat shortage decreases. The results show that population growth, trade disturbances, and especially climate change are risks that need to be considered, and resilience against these risks needs to be built up.

In this thesis, we have conducted a holistic capacity analysis of Scania's Gearbox and Axle finished goods inventory, as they transition toward electrified mobility and have expectations of higher production volumes. Due to an increase in the volumes, the current capacity of the inventory is expected to not be enough. The purpose of this thesis is to analyse Scania's inventory, from a current and future perspective using a simulation approach and identify ways of managing the increased new production demands. Two objectives are answered in order to get a holistic capacity analysis. The first deals with an organisational perspective and how the organisation and way of working impact the capacity of the process. The goal is to identify barriers in the way of working in order to achieve more efficient production. By conducting semi-structured interviews with co-workers and managers, we gather insight into current problems and improvement areas in the production and IT systems in the inventory. We can also understand how communication flows between customers and suppliers in the internal supply chain and what effect communication has on the FVL process. The second objective deals with how storage time policies affect the production and inventory levels. With the help of discrete event simulation and both current and future production data, we find scenarios where inventory levels are within the limits of the inventory capacity by adjusting the time policies. Our results indicate that by adjusting storage time policies and having efficient production, the capacity of the finished goods inventory is sufficient for future demand scenarios. However, there is a strong connection between organisational aspects and capacity, and in order to handle higher volumes, factors such as communication, IT systems and ways of working need to be improved. Lastly, we provide recommendations for dealing with these issues, such as reducing lay time in inventory, changing the shift schedule for operators 2 and 3, including late order handling in the warehouse management systems, and consolidating the different IT systems into one. / I denna avhandling har vi genomfört en holistisk kapacitetsanalys av Scanias färdigvarulager för växellådor. Eftersom Scania aktivt arbetar med att introducera nya eldrivna produkter samtidigt som de fortsätter produktionen av fossildrivna produkter, förväntas produktionsvolymerna öka. Vid ökade volymer uppstår förväntningar om att kapaciteten i lagret inte kommer att räcka till. Syftet med denna avhandling är att analysera Scanias lager ur både ett nuvarande och ett framtida perspektiv. För att få en holistisk analys besvarar vi två frågeställningar. Det första handlar om ett organisationsperspektiv och hur organisationen och arbetssättet påverkar kapaciteten i processen. Målet är att identifiera hinder i arbetssättet för att uppnå en effektivare produktion. Genom att genomföra semistrukturerade intervjuer med medarbetare och chefer kan vi få insikt i nuvarande problem och förbättringsområden i produktionen, samt IT-system som används i lagret. Vi kan också förstå hur kommunikationen flyter mellan kunder och leverantörer i den interna leveranskedjan och vilken effekt kommunikationen har på FVL-processen. Det andra fokuset ligger på hur liggtiden av produkter påverkar lagernivån. Genom att använda diskret händelsesimulering så kan vi med hjälp av nuvarande och framtida produktionsdata, identifiera scenarier där lagernivå ligger inom gränserna för lagerkapaciteten genom att justera liggtiden. Från våra resultat finner vi att genom att minska liggtiden är kapaciteten av lagret tillräcklig för framtida volymökningar. Det finns dock en stark koppling mellan organisatoriska aspekter och kapacitet, och för att hantera högre volymer behöver faktorer som kommunikation, IT-system och arbetssätt förbättras. Slutligen ger vi rekommendationer för att hantera dessa frågor, såsom att minska liggande tid i lagret, ändra skiftschema för operatör 2 och 3, inkludera hantering av sena order i lagerhanteringssystemen, samt konsolidera de olika IT-systemen till ett enda.

Professional nurses and their patients are directly influenced by insufficient medication, causing a decrease in the quality of care, delays in hospitalisation and it might lead to resistance. In some cases professional nurses have to leave the unit in search of medicine. Amoxicillin-clavulanic acid 1.2 gram for intravenous administration is prescribed to the majority of patients in the medical units in public South African hospitals. Yet there are intermitted insufficient stock levels and challenged inventory systems for amoxicillin-clavulanic acid 1.2 gram in some public hospitals. This fact is positioned against the background of a South African health system that has undergone major changes since the fall of Apartheid in 1994 and amidst major positive changes, is still challenged by overburdened hospital admissions and a quadruple disease burden. The aim of this research was to enhance optimal levels of amoxicillin-clavulanic acid 1.2 gram in medical units in public hospitals to ensure sufficient stock levels and timeous administration. The aim was achieved by identifying and describing the current supply chain of intravenous amoxicillin-clavulanic acid 1.2 gram in two medical units in a district (level 2) public hospital in the North West Province (from here referred only as North West) by identifying inefficiencies in the current supply chain and to formulate recommendations for management to enhance the supply chain of intravenous amoxicillin-clavulanic acid 1.2 gram to medical units in public hospitals. An exploratory case study approach was followed to explain the supply chain of amoxicillin-clavulanic acid 1.2 gram by utilising a qualitative, descriptive, explorative and contextual design. A case study approach was chosen as it examined single units within the context of real life as environment, which in this case were medical units in a level two public hospital, North West. The case selection was motivated and described, followed by case records of policies and standard operational procedures. Field participants included all levels of nurses (professional, enrolled and auxiliary) in medical male and female units on day and night duty, and the head of pharmacy [n=8]. Non-probable, purposive sampling was conducted according to inclusion criteria after all levels of ethical clearance and consent were granted. Three semi-structured individual interviews followed, after which two focus groups were conducted. Thematic analysis of transcriptions was done, followed by an analysis of case records regarding where after all results were integrated. Results indicated complex organisational, unit-specific and behavioural challenges that impact on the supply chain management of amoxicillin-clavulanic acid 1.2 gram and insufficient stock levels are predominantly positioned within retailer and customer aspects of the supply chain. Despite well-formulated standard operational procedures, the realisation thereof lacks, implicating a greater need for managerial control. Recommendations were formulated for management to enhance the supply chain of amoxicillin-clavulanic acid 1.2 gram in medical units in public South African hospitals integrated with good pharmacy practices. The close collaboration, mutual respect and effective communication between health professionals in the multi-professional team are reiterated. / MCur, North-West University, Potchefstroom Campus, 2015

Professional nurses and their patients are directly influenced by insufficient medication, causing a decrease in the quality of care, delays in hospitalisation and it might lead to resistance. In some cases professional nurses have to leave the unit in search of medicine. Amoxicillin-clavulanic acid 1.2 gram for intravenous administration is prescribed to the majority of patients in the medical units in public South African hospitals. Yet there are intermitted insufficient stock levels and challenged inventory systems for amoxicillin-clavulanic acid 1.2 gram in some public hospitals. This fact is positioned against the background of a South African health system that has undergone major changes since the fall of Apartheid in 1994 and amidst major positive changes, is still challenged by overburdened hospital admissions and a quadruple disease burden. The aim of this research was to enhance optimal levels of amoxicillin-clavulanic acid 1.2 gram in medical units in public hospitals to ensure sufficient stock levels and timeous administration. The aim was achieved by identifying and describing the current supply chain of intravenous amoxicillin-clavulanic acid 1.2 gram in two medical units in a district (level 2) public hospital in the North West Province (from here referred only as North West) by identifying inefficiencies in the current supply chain and to formulate recommendations for management to enhance the supply chain of intravenous amoxicillin-clavulanic acid 1.2 gram to medical units in public hospitals. An exploratory case study approach was followed to explain the supply chain of amoxicillin-clavulanic acid 1.2 gram by utilising a qualitative, descriptive, explorative and contextual design. A case study approach was chosen as it examined single units within the context of real life as environment, which in this case were medical units in a level two public hospital, North West. The case selection was motivated and described, followed by case records of policies and standard operational procedures. Field participants included all levels of nurses (professional, enrolled and auxiliary) in medical male and female units on day and night duty, and the head of pharmacy [n=8]. Non-probable, purposive sampling was conducted according to inclusion criteria after all levels of ethical clearance and consent were granted. Three semi-structured individual interviews followed, after which two focus groups were conducted. Thematic analysis of transcriptions was done, followed by an analysis of case records regarding where after all results were integrated. Results indicated complex organisational, unit-specific and behavioural challenges that impact on the supply chain management of amoxicillin-clavulanic acid 1.2 gram and insufficient stock levels are predominantly positioned within retailer and customer aspects of the supply chain. Despite well-formulated standard operational procedures, the realisation thereof lacks, implicating a greater need for managerial control. Recommendations were formulated for management to enhance the supply chain of amoxicillin-clavulanic acid 1.2 gram in medical units in public South African hospitals integrated with good pharmacy practices. The close collaboration, mutual respect and effective communication between health professionals in the multi-professional team are reiterated. / MCur, North-West University, Potchefstroom Campus, 2015

Thesis (MComm)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: PEP is a devision of Pepkor Retail Limited and is the biggest single brand store network in Southern Africa and also owns and runs the largest clothing factory in Southern Africa. It was founded in 1965 and has since grown to more than 1 400 stores in 9 African countries (there is a PEP store in almost every town and village in South Africa). Currently the warehouse management system (WMS) implemented by PEP only allows for a stock keeping unit (SKU) to be placed on one picking line in one location when the distribution list (DBN) is released. Because pickers are only allowed to walk clockwise around the conveyor belt, they are forced to pass a location at least the same number of times as the number of branches to which the SKU is to be distributed to. Therefore if the SKUs with the highest pick frequency can be assigned to 2 locations (it is duplicating the SKU), the number of times each of these locations must be passed may be reduced. In this study 4 questions are considered when 15 algorithms are constructed that will determine how an algorithm assign the SKUs to picking lines. Question 1 determines whether the original picking lines are to be treated separately (PS) or to combine them rst (PC). The second question is to decide if the SKUs are rst to be duplicated and then assigned to picking lines (DA) or if they are rst assigned to picking lines and then duplicated (AD). Question 3 determines whether the non-duplicate and duplicate SKUs are treated separately (ND) or simultaneously (S) when they are assigned to the picking lines. The nal question is to specify how the SKUs are assigned to the picking lines. Three assignment methods (cyclical, set length subset sequential assignment, remaining high, low cyclical assignment) and 6 clustering algorithms are introduced. The conclusion is made that the SKUs with the highest pick frequency is duplicated rst to yield the biggest saving in the number of cycles. Between 40{70% of the SKUs should be duplicated, dependant on the algorithm used. The only decision that has a major in uence on the number of cycles is the assignment method used. Algorithm 5 and 8 yielded the greatest saving in the number of cycles (40.7% and 39.8% respectively), both implementing set length subset sequential assignment, followed by the clustering algorithms. / AFRIKAANSE OPSOMMING: PEP is 'n afdeling van Pepkor Retail Limited en is die grootste enkel-handelsmerk winkelnetwerk in Suidelike Afrika. PEP besit en bestuur ook die grootste klerefabriek in Suidelike Afrika. PEP is gestig in 1965 en het sedertien gegroei tot meer as 1 400 winkels in 9 Afrika lande (daar is 'n PEP winkel in amper elke dorp in Suid-Afrika). Op die oomblik laat die pakhuisbestuurstelsel, wat deur PEP in sy distribusie sentrum ge mplementeer word, slegs toe dat voorraadeenhede (VEs) in 'n enkele vakkie langs 'n enkele uitsoeklyn geplaas word. Aangesien werkers slegs toegelaat word om kloksgewys om die vervoerband te beweeg, word hulle gedwing om ten minste soveel keer verby elke vakkie in die uitsoeklyn te loop as wat die aantal winkels is waarna die VEs in daardie vakkie versprei moet word. Dus indien die vakkies wat die VEs bevat wat na die meeste winkels versprei moet word, tussen 2 vakkies verdeel word (die VE word gedupliseer), verminder die aantal kere wat beide vakkies besoek moet word. In hierdie studie word 4 vrae beskou wat geantwoord moet word wanneer die 15 algoritmes opgestel word, wat sal bepaal hoe die algoritme die VEs hanteer. Vraag 1 bepaal of die oorspronklike uitsoeklyne wat deur PEP verskaf is apart hanteer word en of hulle eers gekombineer moet word. Die tweede vraag bepaal of die VEs eers gedupliseer word en dan aan die onderskeie uitsoeklyne toegedeel word en of die VEs eers aan die uitsoeklyne toegedeel word en dan gedupliseer word. Vraag 3 is slegs van toepassing wanneer die VEs eers gedupliseer word en dan toegedeel word aan die uitsoeklyne, en bepaal of die nie-gedupliseerde en gedupliseerde VEs apart of gelyktydig hanteer word. Die laaste vraag spesi seer met behulp van watter metode die VEs toegedeel word aan die onderskeie uitsoeklyne. Drie toedelingsmetodes (sikliese toedeling, vaste lengte subversameling opeenvolgende toedeling, oorblywende hoogste/laagste sikliese toedeling) en 6 bondelalgoritmes word voorgestel. Die gevolgtrekking word gemaak dat die VEs met die hoogste uitsoek frekwensie eerste gedupliseer moet word om die grootste besparing mee te bring in die aantal siklusse om al die VEs uit te soek. Tussen 40{70% van die VEs moet gedupliseer word afhangende van die algoritme wat gebruik word. Die enigste besluit wat 'n noemenswaardige invloed op die aantal siklusse het is die toedelingsmetode. Algoritme 5 en 8 lewer die grootste besparing in die aantal siklusse (40.7% en 39.8% onderskeidelik), beide implementeer die vaste lengte subversameling opeenvolgende toedeling, gevolg deur die bondelalgoritmes.

This thesis is focused on a simulation modelling approach to address the inventory inaccuracy problems in a warehouse operation. The main motivation which led to this research was a desire to investigate the inventory inaccuracy issues that have been highlighted by a logistics company. Previous and current research into inventory inaccuracy issues is largely related to the development of RFID technology as a possible solution to inventory problems. Since the inventory inaccuracy related to RFID technology is focused on the overall measurement of inventory management and retail business, there are differences between this existing research and the research presented in this thesis which is focused on issues of inventory inaccuracy in a warehouse operation. In this thesis, warehouse operation is studied as a detailed sequence of processes that are involved in the flow of items physically in parallel with related information being stored in the computer system. In these processes there are many places where errors can occur in counting or recording details of inventory, or in physically moving, storing or picking items incorrectly. These details of a warehouse operation are used to develop a conceptual model of inventory inaccuracy in warehouse operations. The study also found that typically a product needs to be considered differently at different stages of its progress through a warehouse (and therefore within different sections of the conceptual model). This is because initially batches of a product are likely to be delivered from a supplier, therefore if errors occur soon after the product is delivered to the warehouse, the error might involve the whole batch (for example the batch may be misplaced and put in an incorrect storage location), or the error might involve just part of the batch (for example poor transportation by forklift truck may damage the packaging carton and some of the items within the carton). When the product is stored ready for meeting customer orders, it needs to be considered as individual items (and errors can occur in counting of individual items or individual items may be misplaced or stolen). Finally, when a customer order is received, the product will be picked and grouped to meet the requirements of the order (for example, one order may require 10 of the product whilst another order may require 20 of the product). Errors might again occur to the whole group or to just part of the group. (Continued ...)

Poor quality of information and forecasting create a number of problems for manufacturing companies, such as poor planning of products and insufficient service levels, which leads to increased inventory and stock holding or stockouts and increased total costs. Cussons (UK) Limited is experiencing precisely these problems. Apart from these problems normally associated with forecasting demand for fast moving consumer goods there is an additional problem of reconciling the Western calendar with the Muslim calendar, and a recognition of the effects that Muslim religious holidays, as opposed to Christian religious holidays, have on demand. Muslim religious holidays rotate backwards with regard to the Western calendar, but in fact they occur at known dates and therefore the effect they have on demand for products can be taken into consideration when attempting to forecast demand. An additional problem that influences Cussons' sales in the market is the seasonal pattern of demand. Due to this, there is an increase in demand for Cussons' products during summer months. From the analysis of both data sets it was identified that the warehouse movement data is less variable and more reliable for business forecasting than order data. In this thesis, these forecasting problems are examined as a case study, focusing on these particular problems. To overcome these problems and to improve business forecasting of Cussons' products in the Middle East market, a forecasting strategy has been suggested which will enable Cusson's to reduce the inventories throughout the supply chain and to improve their customer's service.

This study identifies the concepts of reliability, cost of downtime, cost of spare parts, and procurement lead time as the four key moderators of spare parts availability. These concepts are used to establish a model to manage spare parts inventories. Reliability was assessed in terms of developing failure predictions for major component categories. Cost of downtime was evaluated by identifying various methods for determining costs associated with downtime. Cost of spare parts was examined to find correlations with economic indicators. These correlations were used to predict future price movements. Yearly changes in lead time were identified and correlated with economic indexes to develop movement predictability.