No description available.

This thesis investigates the relationship between discrete event and system dynamics simulation modelling. Each modelling technique has its own strengths and limitations. The choice of using one particular modelling technique often depends on the preference and the knowledge of the modeller rather than on the nature of the problem. The basis of this research has been to address the problem from a different perspective. This has been to look at the nature of the problem first, and then determine the most appropriate modelling technique to apply. The basic method adopted was to compare, contrast and experiment with these two modelling techniques in order to determine a number of common and unrelated concepts between them. This investigation discovered that a system dynamics flow diagram could be used to represent an activity cycle diagram of a discrete event model. The converted flow diagram can provide a different viewpoint from the discrete event model due to the feedback characteristic of system dynamics. This research went on to develop a set of guidelines to convert an activity cycle diagram into a system dynamics flow diagram. Experimentation with many examples demonstrates that these conversion guidelines provide a consistent and systematic method for obtaining a system dynamics flow diagram. The final stage of this research was to develop a prototype computer system (SMCP) to demonstrate these guidelines. SMCP consists of two modules, the ACD module which allows the user to specify a discrete event model through textual descriptions, and the SD module which allows the user to build a system dynamics model by drawing symbols and using text inputs. In addition, SMCP allows users to convert an ACD to a system dynamics flow diagram quickly and easy, and also demonstrates the concept of data sharing.

This work compares the procedures used in the Emergency Departments in the University of Benin Teaching Hospital (UBTH) in Nigeria and in Manchester Royal Infirmary (MRI) in the UK. It goes on to develop a discrete event model of the latter in Rockwell Arena®.Raw data from UBTH were obtained over a number of visits by interviewing senior administrators, clinicians and nursing staff and by tracking patients over a period of 2 months between 1 July and 29 August, 2011. Information from MRI was supplied through an approved ethical protocol to the National Research Ethics committee (REC Reference 13/NN/0175, IRAS ID 124168, dated March 4, 2013). This embraced patient journeys, locations, investigations and tests for the 98236 patients who attended the ED between April 2012 and March 2013. These (anonymised) data were obtained as spreadsheets from the original Symphony® records, which were then manipulated and analysed using the computer language, R. Anecdotal information on ED operations, patient flow and procedure duration times were also obtained from ED staff. All of this information identified similarities and differences between patient journeys in the two hospitals and were used to generate appropriate process maps. Proposals were made to improve the recoding and maintenance of patients’ records in UBTH. In the case of MRI, each patient’s journey was expressed as a journey-string, which was an ordered list of locations and milestones derived from the time-stamps recorded in the original spreadsheets. A large transition matrix (168 by 168) was generated from the set of journey strings and established the probability of a patient going from one location to any another. This reflects all the decisions which were made at each step of the patient’s journey. The number of destinations from a particular source reflects the options available at a particular instant in time, while the size of each probability reflects the preferred destination. The transition matrix together with the duration and resource requirement of the process associated with the destination is the key to the generation of a process map for each journey through the system. This methodology is original and can be applied generally. This was used as a basis for the journey-path model. In the final MRI model the 4h deadline was not included since the mechanism for its actual implementation was somewhat vague. Instead some isolated models based on patients’ priorities and resource re-allocation were described. From these it was inferred that changing the priority of a patient may not in itself be sufficient to alter the journey profile and in order to do so resources must be re-allocated. The only alternative would appear to be the fast-tracking of patients.

No description available.

Business processes and information technology are two areas that are very closely related to the sustained competitive advantage in organisations. However, investment in information technology often leads to disappointment, which may in part be due to the non-alignment of the information system domain with the business process domain. Simulation modelling is an established technique often used in business process change projects, as it allows a comparison of different possible scenarios without the expense of physically implementing the system. However business process simulation fails to effectively capture the information systems perspective in the model. This thesis contends that by combining information systems modelling techniques with business process simulation the model will be able to capture all the four perspectives (functional, behavioural, organisational and informational) of an organisation, and the design of the business processes and the information system will be better aligned. Initially, attempts were made to integrate business process simulation with computer network simulation in a simple two- or three-layered simulation model, but this gave rise to significant problems the most significant being the underlying assumptions of the original hypothesis. This led to a refined hypothesis in which the layered models were discarded along with the network domain. The revised hypothesis aimed to capture the informational changes that occur in the information system and therefore combines prototyping with business process simulation. This overcomes the unsafe assumptions of the initial hypothesis about whether the system is 'correct' and provides a method of validating the design of the information system within the context of the business processes. The integrated model allows concurrent design of the information system domain and the business process domain and therefore ensures that the domains are better aligned. The framework is tested on a case study and the results indicate that it is an effective tool in the combined design of business processes and information systems.

No description available.

The Climatic Wind Tunnel (CWT) is a facility used by the motor industry to test vehicles under climatic extremes without the need for expensive overseas test programs. This work focuses on the application of computer simulation to the Heating Ventilation and Air Conditioning (HVAC) plant that makes up a CWT facility. The objective being to reduce its operational costs through the identification of energy saving operational strategies. When in operation the CWT has a peak power consumption of 3MW. The implementation of any measures that would reduce this peak load would give rise to considerable savings in the operating costs of the facility. Computer simulation is an accepted technique for the study of systems operating under varying load conditions. Simulation allows rapid analysis of different strategies for operating plant and the effectiveness of achieving the desired effect without compromising the buildings performance. Models for the components of the CWT have been developed and coded in Neutral Model Format. These models have then been linked together in a modular simulation environment to give a model of the complete plant. The CWT plant naturally decomposesin to four major subsystems these being the test chamber, the soakroom, air make-up and refrigeration system. Models of all the primary and secondary HVAC plant are described as is how they constitute the systems that make up the CWT. Validation tests for individual components as well as for the systems have been carried out. To illustrate the potential of the application of computer simulation into finding improved modes of operation that would reduce the energy consumption of the facility, four studies have been carried out. The studies involve the possibility of scheduling the operation of condenser fans as a function of refrigeration load and outside ambient temperature, methods for the pre-test conditioning of a vehicle, a reduction in the secondary refrigerant flow temperature and an increase in the thickness of the insulated panels from which the facility is constructed. The studies carried out showed that there was potential for moderate energy savings to be made in the operation of the facility and that extended simulation runs would allow for the in-depth assessment of a large range of possible modes of plant operation in order to identify the areas where the greatest savings are possible.

Yes / Fluid Catalytic Cracking (FCC) unit is an important unit of modern refineries and any improvement in the unit’s operations and design to increase yield and meet the ever increasing demand for fuel brings about the overall profitability of the FCC. In this work, simulation of an FCC riser of varied diameter was carried out to improve the unit’s operations and design, and the results are compared with risers of different diameters. The riser with varied diameter produces 53.4 wt%, a 3.18% increased yield of gasoline at low catalyst to oil (C/O) ratio of 1.27 compared to 51.7 wt% from a 1 m diameter riser. At increased C/O ratio, more gases and coke are produced in the varied diameter riser. Larger diameter demands more catalyst but yields more gases. Process variables can be directly correlated with yield of gasoline, which can aid process design.

Healthcare problems are complex; they exhibit both detail and dynamic complexity. It has been argued that Discrete Event Simulation (DES), with its ability to capture detail, is ideal for problems exhibiting this type of complexity. On the other hand, System Dynamics (SD) with its focus on feedback and nonlinear relationships lends itself naturally to comprehend dynamic complexity. Although these modelling paradigms provide valuable insights, neither of them are proficient in capturing both detail and dynamic complexity to the same extent. It has been argued in literature that a hybrid approach, wherein SD and DES are integrated symbiotically, will provide more realistic picture of complex systems with fewer assumptions and less complexity. In spite of wide recognition of healthcare as a complex multi- dimensional system, there has not been any reported study which utilises hybrid simulation. This could be attributed to the fact that due to fundamental differences, the mixing of methodologies is quite challenging. In order to overcome these challenges a generic theoretical framework for hybrid simulation is required. However, there is presently no such generic framework which provides guidance about integration of SD and DES to form hybrid models. This research has attempted to provide such a framework for hybrid simulation which can be utilised in healthcare domain. On the basis of knowledge induced from literature, three requirements for the generic framework have been established. It is argued that the framework for hybrid simulation should be able to provide answers to Why (why hybrid simulation is required), What (what information is exchanged between SD and DES models) and How (how SD and DES models are going to interact with each other over the time to exchange information) within the context of implementation of hybrid simulation to different problem scenarios. In order to meet these requirements, a three-phase generic framework for hybrid simulation has been proposed. Each phase of the framework is mapped to an established requirement and provides guidelines for addressing that requirement. The proposed framework is then evaluated theoretically based on its ability to meet these requirements by using multiple cases, and accordingly modified. It is further evaluated empirically with a single case study comprising of Accident and Emergency department of a London district general hospital. The purpose of this empirical evaluation is to identify the limitations of the framework with regard to the implementation of hybrid models. It is realised during implementation that the modified framework has certain limitations pertaining to the exchange of information between SD and DES models. These limitations are reflected upon and addressed in the final framework. The main contribution of this thesis is the generic framework for hybrid simulation which has been applied within healthcare context. Through an extensive review of existing literature in hybrid simulation, the thesis has also contributed to knowledge in multi-method approaches. A further contribution is that this research has attempted to quantify the impact of intangible benefits of information systems into tangible business process improvements. It is expected that this work will encourage those engaged in simulation (e.g., researchers, practitioners, decision makers) to realise the potential of cross-fertilisation of the two simulation paradigms.

Mine cooling system components are an integral part of a mine‟s ventilation system. A mine‟s reliance on these capital intensive components are set to increase as mines deepen. Mine cooling systems consume up to a quarter of the electricity used on mines. Component efficiency should be monitored to ensure optimum utilisation. Downtime should be minimised so that production is not negatively influenced. Replacing expensive components in an age of severe economic pressure should be avoided altogether. In this study, the performance of mine cooling system components was monitored. The effects of various operational and maintenance interventions on component performance have been quantified. Quantifying the effects of management decisions led to the refining of operational procedures, the optimisation of future maintenance, and the subsequent identification of electrical energy savings potential without the need for expensive modifications. Investigations show that a mine could realise a saving of up to nine hundred thousand rand annually by optimising the maintenance schedule of chillers. Extrapolated results estimate an electrical energy saving of 52 127 MWh per year if the strategy were implemented on twenty of South Africa‟s biggest mines. In addition, a monetary saving in excess of five hundred thousand rand could be saved through refining operational procedures. These strategies will be possible without the need for expensive installations or complicated modifications. Monitoring cooling system performance allows management to identify trends in performance, to understand component inter-dependence, and to allow for informed decision-making. In addition, performance monitoring allows for the identification of component and instrumentation faults. Statistical control charts and simulation modelling are some of the tools that have been employed in this study. These tools assist management formulate strategies and decisions with a higher degree of confidence. / MIng (Mechanical Engineering), North-West University, Potchefstroom Campus, 2014