A numerical model for simulating a dry forward in-situ combustion process in two dimensions, was developed. The primary focus is on the simulation of the compositional changes that take place inside the porous medium during the running of the process. The model allows any number of hydrocarbon components and six others, namely, liquid water, water vapour. oxygen, nitrogen, carbon dioxide, and carbon monoxide. It describes the flow of water. oil, and gas, and includes the gravity and capillary effects. The vapourisation and condensation effects of both hydrocarbons and water enhanced the heat transfer, primarily by conduction and convection, ahead of the combustion front. Equilibrium calculations are performed on the components in both the liquid and vapour phases. The changes in pressure, temperature, and flUid compositions govern the direction of the interphase mass transfer. Heat is generated by two types of reaction, namely, low temperature oxidation and burning of the crude oil. The model allows the movement of a thin burning front inside the burning cell. It is found to give a better temperature profIle. representative of the combustion process. Oxygen mole fraction is calculated throughout the porous medium according to the reaction kinetics. thus no assumption is made regarding the degree of oxygen consumption. The effects of oxygen bypassing caused by the kinetic-limited combustion is therefore represented. A total of 18 components were used in the computer runs. Results show the preferential vapourisation of the lighter components in the vicinity of the high temperature burning front. The lighter components then move towards the producer. faster than do the heavier ones. This segregation produce fuel that is heavier than the original oil. High temperature in the upstream cells causes a reduction in the oil viscosity. which in turn increases its mobility, thus transporting more heat downstream. The rise in temperature in the condensation cell results in a decrease in the rate of water vapour condensation; extending the condensation zone downstream. In the high pf(>ssure run. all the hydrocarbon in the downstream cells condenses. In the burning cell however. both the vapour and the liquid phases are present due to the high front temperature. The vapour phase is richer in the light components while the liqUid is richer in the heavy components.

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Software processes relate to the sequence of steps that must be carried out by humans to pursue the goals of software engineering. In order to have an accurate representation of what these steps actually are, software processes can be modelled using a process modeling language (PML). Some PMLs simply support the specification of the steps, while others enable the process to be executed (or enacted). When enacted, software processes can provide guidance, automation and enforcement of the software engineering practices that are embodied in the model. Although there has been much fruitful research into PMLs, their adoption by industry has not been widespread. While the reasons for this lack of success may be many and varied, this thesis identified two areas in which PMLs may have been deficient: human dimension issues in terms of support for awareness and visualisation; and support for addressing management and resource issues that might arise dynamically when a process model is being enacted. In order to address some of these issues, a new visual PML called Virtual Reality Process Modelling Language (VRPML) has been developed and evaluated. Novel features have been introduced in VRPML to include support for the integration of a virtual environment, and dynamic creation and assignment of tasks and resources at the PML enactment level. VRPML serves as a research vehicle for addressing our main research hypothesis that a PML, which exploits a virtual environment, is useful to support software processes for distributed software engineering teams.

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Due to the penetration of variable renewable energy (VRE) sources, conventional coal fired power plants need to operate with greater flexibility via two-shifting or low load operation whilst remaining reliable and conserving the lifetime of components. Thick sectioned components are prone to thermal fatigue cracking as a result of through-wall temperature gradients during start up and shutdown. These temperature gradients can be significantly amplified during quenching when components at high temperature are unintentionally exposed to colder liquid or steam. Such quench events are known to occur during two-shift operation of a large once-through coal fired tower type boiler, which is the subject of this study. The purpose of this study is to develop and demonstrate a methodology to determine the root cause of quenching in a once-through tower type boiler and provide information that can be used to predict the impact on thick-walled components by estimating the through-wall temperature gradients. The first modelling element in the methodology is a simplified transient heat transfer model for investigating condensation of steam in the superheater. The model is presented and verified by comparison with real plant data. The second element is a liquid tracking model that approximates the liquid level in the superheater as a function of time to predict the location and magnitude of through-wall temperature gradients. The complex geometry of the superheater was divided into a number of control volumes and a dynamic thermo-fluid process model was developed to solve the transient conservation of mass and energy equations for each volume using a semi-implicit time wise integration scheme. The liquid tracking model was verified by comparison with a similar model constructed in Flownex and also by comparison with plant data. Varying levels of discretisation were applied to a particular quench event and the results are presented. The third modelling element is a two-dimensional transient pipe wall conduction model that is used at selected localities to evaluate the temperature gradients within the pipe wall. The temperature gradients and internal heat flux were verified by temperature measurements from the outer surface of a main steam pipe undergoing quenching. The stresses associated with the temperature gradients were also briefly considered. The real plant quenching problem is analysed in detail and found to be caused by liquid overflow from the separators. A particular plant configuration creates a previously unidentified siphon of water from the separating and collecting vessel system into the superheater. This situation is not recognised by plant operators and thus persists for some time and causes flooding of the superheater. Analysis of the resultant through-wall temperature gradients show that quenching causes significant stresses which can be avoided. By understanding the causes and preventing the occurrence of quenching, the life of thick-walled high temperature components can be conserved.

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Made available in DSpace on 2016-08-29T15:33:10Z (GMT). No. of bitstreams: 1 tese_3334_.pdf: 6590453 bytes, checksum: 5654758329fe7af83bec07339d8a3ffb (MD5) Previous issue date: 2009-12-16 / Business process modelling basically comprises an activity whose main goal is to provide a formalization of business processes in an organization or a set of cooperating organizations (Recker, et al., 2006) (van der Aalst, et al., 2003). By modelling an organizations business processes, it is possible to capture how the organization coordinates the work and resources with the aim of achieving its goals and strategies (Sharp, et al., 2001). Since business processes and goals are intrinsically interdependent, establishing an alignment between the process and the goal domains arises as a natural approach. This thesis reports on a real-life exploratory case study in which we investigated the relationship between the elements of the enterprise (modeled in the ARIS framework) and the goals (modeled in the Tropos framework and modeling language) which are attained by these elements. The case study has been conducted in the Rheumatology Department of a University Hospital in Brazil. In the course of the case study, we have identified the need of splitting this effort into three phases: the elicitation phase (in which goal models and business process models are captured from the organizational domain), the harmonization phase (in which the goal domain is structured for alignment according to the business processes structures that will support it) and the alignment phase (in which the relationships between the goal domain and the elements of the organizational domain are established). In order to investigate the relation between goals and enterprise elements, we propose an ontological account for both architectural domains. We recognize the importance in considering the business process as the means for implementing an enterprises strategy, but we do not exclude the remaining enterprise elements. Furthermore, we are concerned with both the identification of the relationships and with a classification for their nature.