The thesis introduces a new version of an elliptic-blending low-Reynolds-number eddy-viscosity Reynolds-averaged Navier Stokes model. It is a model intended to be implemented in an industrial solver. It will be argued that there is still room for such a simple model, though eddy-viscosity models must rely on developments specificallymade for higher order formulations. It is the aim of the v2-f model to integrate elements of Reynolds-stress modelling developments into a simpler formulation, but the former paradoxically suffers from numerical stiffness, which kept it out of reachof industry researchers everyday simulations. The v2-f formulation endeavours to reproduce the near-wall asymptotic behaviour of the turbulent quantities, as sounder alternative to empirical damping functions, and the required near-wall balance of small terms represents a numerical challenge. The present work first provides a comprehensive review of v2-f developments proposed over the past twenty years, and the different remedies for the numericalstiffness linked to the original formulation. The review focuses on ten v2-f variants, proposed between 1991 and 2006, whose behaviour is compared in some fundamental flows: the channel flow for five different Reynolds numbers, the asymptotic case of the logarithmic layer at infinite Reynolds number and the case of a flow with homogeneous sheared turbulence. Based on the conclusions of the review, the thesis proposes new developments. Firstly, the derivation of a new model, namely the φ - α model, is introduced. It relies on the resolution of two non-dimensional variables: φ represents the wall-normal anisotropy and α is a wall-proximity sensor. It is argued that only this formulation can address the numerical problems already mentioned without altering the predictions. Secondly, additional upgrades of the φ - α model are proposed to correct the dissipation rate equation. The aim is to improve the model behaviour in some specific regions of a boundary layer, by isolating some viscous terms and by improving the representation of turbulent transport at the edge of a boundary layer. Final developments are combined in a new model, the BL-v2/k model. The φ - α and BL-v2/k models are then validated for a set of two pressure induced separated flows and two buoyant flows, and beneficial effects of the proposed developments on the predictions are demonstrated. The numerical properties of the convergency of the BL-v2/k model are also reported at the end of this work.

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.

Thesis (Ph.D. (Physics)) -- University of Limpopo, 2016 / Refer to the document / National Research Foundation

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.

The aim of this research project is to investigate, experimentally and analytically, the effects of reinforcement corrosion on the flexural, shear and blast behaviours of reinforced concrete beams. As part of the experimental study, twenty-four beams reinforced were tested under quasi-static and simulated blast loads using the University of Ottawa Shock tube. All beams had dimensions of 125 mm x 250 mm x 2400 mm and were tested under four-point bending. Tension reinforcement consisted of either 2 – 10M (ρ= 1%) or 2 – 15M bars (ρ= 1.6%) for the flexure dominant specimens, and 2 – 25 M bars (ρ= 4%) for the shear-dominant specimens. In all cases, transverse reinforcement consisted of 6 mm stirrups spaced at s = 100 mm (d/2) throughout the beam span. Eighteen of the specimens were subjected to an accelerated corrosion process to induce different amount of mass loss in the longitudinal and transverse steel reinforcement. The test variables included: the type of corrosion (i.e. on the longitudinal or transverse reinforcement), the amount of corrosion (i.e. % mass loss in the steel reinforcement) and the extent / location of corrosion on the tension steel reinforcement (i.e. over the full length, middle span or end spans). The results from the experimental tests showed that corrosion of the tension and transverse steel reinforcement decreased the strength and ductility of the reinforced concrete beams under static loading, ultimately changing the failure mode. Similarly, the results from the blast tests showed that corrosion of the longitudinal and transverse reinforcement affected maximum displacements and support rotations, reduced blast capacity, increased damage and fragmentation, and ultimately changed the failure process from ductile to brittle. Results under both static and blast loads were sensitive to the amount and extent/location of the corrosion. As part of the analytical study, the static results were predicted using 2D finite nonlinear element (FE) modelling. The effects of corrosion were considered using several modeling features including: reduction in steel bar cross-sectional area, modification of the steel stress-strain response, and introducing corrosion-induced cracking using applied pre-strains. The predicted results from the FE simulations were to provide acceptable predictions in terms of load capacity and failure mode when compared to the experimental static test results. The blast results were predicted using two approaches, including: 1) single-degree of freedom (SDOF) analysis (with the resistance functions developed using FE modelling); and 2) the blast analysis capabilities of FE software VecTor2. Overall both approaches led to acceptable predictions of maximum mid-span displacements when compared to the experiments.

This diploma thesis deals with analysis of current state of the paint shops M11A and M11B in Mladá Boleslav and following creation of the universal simulation model of the paint shop M11A in the company Škoda Auto a.s. by which availability of daily production in different input parameters will be verify. The model of the paint shop M11A will be created in system SimPro which comes under the programs working with discreet simulation. The model input parameters will be defined in the program Excel. According to these experiments will be possible realized a detailed analysis of results of the simulation.

Snow avalanches a natural phenomenon typical for snowy winter mountains consist of snow and sometimes of other material (debris, rocks, truncated trees and soil). On first sight they seem to be harmless mass of snow sliding down on a slope. But not they can be disastrous. Despite the snow avalanches event lasts for couple of seconds, they can take human lives, and destroy infrastructure. Until they occur in far and remote places they are not concern. The avalanche run- out has been always an issue. How far avalanches can travel? Is there avalanche activity out there? How large is the avalanche hazard on certain places? Will the avalanche airbag will influence the probability of not being critically buried by an avalanche. These are the question the thesis attempt to solve with the use of GIS, remote sensing and statistical analysis. The aim of the thesis was to find reasonable answers to these questions. The effectiveness of avalanche airbags was first tested by pilot study when the artificial avalanche was triggered and motion of the dummies with different types was recorded. Additional estimation of impact forces, speed and final position of dummies was investigated and modelled (publication 6). The mechanism behind the avalanche airbags - inverse segregation was proofed to work in field test, but how is...

Icebergs calved from high-latitude glaciers and ice shelves pose a threat to vessels and offshore infrastructure at a time when Arctic shipping and resource exploration are increasing. Knowledge of the location of potential ice hazards is therefore critical to ensure safe and efficient operations in this remote region. The Canadian Ice Service (CIS; Environment and Climate Change Canada) provides information to stakeholders on the observed and predicted distribution of icebergs in Canadian waters by combining iceberg observations with forecasts from the North American Ice Service (NAIS) iceberg drift model. The NAIS model estimates the forces acting on an iceberg to predict its future position and velocity. It is widely used for the east coast of Canada but largely unproven in the Arctic and suffers from insufficient validation due to a paucity of reliable in-situ observations of iceberg drift. This study represents the first comprehensive validation of the NAIS iceberg drift model for the Canadian Arctic. A total of 133 hindcast simulations for the period 2009-2019 were performed against in-situ drift observations of 44 icebergs. These data, collated in an iceberg beacon database (compiled by Carleton University and CIS), includes observations collected by Cryologgers; novel iceberg tracking beacons designed as part of this study. Quantified comparisons of the distance error between observed and modelled drift tracks indicate that the NAIS model produces realistic simulations of iceberg drift in Baffin Bay. Root mean square error after 24-hours of simulated drift ranged from 18-22 km and increased at a daily rate of 11-13 km, which is typical of previous model verification and validation studies. Improved model performance was observed for longer (>250 m) and deeper-keeled (>100 m) icebergs, which appears to counteract the model’s tendency to overestimate drift by reducing the influence of stronger surface ocean currents acting on the iceberg. Ocean current direction, wind direction, and iceberg keel geometry were identified by a sensitivity analysis as the model parameters and environmental driving forces that have the greatest influence on modelled iceberg drift. These results emphasize the need for accurate environmental information and underscore the importance of properly representing the physical characteristics of icebergs in drift models.

Due to its impact on human health and the nature surrounding us, diesel engine emissions have been significantly reduced over the last two decades. This reduction has been enforced by the legislating organs around the world that gradually have made the manufacturers transform their engines to today’s complex high-tech products. One of the most challenging areas to meet the legislations is transient operation where the inertia in gas-exchange system makes transition from one load to another problematic.   Modern engines have great potential to minimize the problems associated with transient operation. However, their complexity also imposes a great challenge regarding optimization and systematical testing of transient control strategies in an engine test bed could be both expensive and time consuming.   The objective of this project is to facilitate optimization of transient control strategies. This should be done by identifying appropriate measurement methods for evaluation of transients and by providing models that can be used to optimize strategies off-line.   Measurement methods for evaluation of transients have been tested in several experiments, mainly focusing on emission but also regarding e.g. EGR flow. Applicable instruments for transient emission measurements have been identified and used. However, no method to measure soot emissions cycle resolved has yet been found. Other measurements such as EGR flow and temperatures are believed to have significantly decreased accuracy during transients.   A model for prediction of NOx emissions have been used and complemented with a new approach for soot emission predictions that has been developed in this project. The emission models have been shown to be applicable over a wide range of operating conditions with exception for highly premixed combustion. It has also been shown that models developed for steady state conditions can be used for transients operation.

Eskom produces approximately 90% of the electricity used in South Africa of which approximately 90.8% is from fossil fuel power plants. The process of electricity generation requires a significant quantity of raw water; therefore, Eskom is considered a strategic water user in South Africa. Water management is a growing focus area due to the increase in water usage and requires continuous improvement. Water management has been identified as an area lagging behind on the advanced analytics initiatives in Eskom. Excel based tools were used for the development of water balance models and water performance calculations in Eskom. This was attributed to the user-friendly functionality and availability to all users. However, the Excel tool posed challenges in allowing for standardisation and validation of calculations, tracking of model changes, continuous trending and storage of data as well as structured graphical user interfaces for screens and dashboard developments. There was therefore a need to develop a methodology on how to structure a water balance model for coal-fired power plants with standard calculation templates that allowed for customisation by each power plant within Eskom. It was required that the water balance model be implemented on a performance and monitoring tool allowing for comparison of power plant targets to actual online data in real time, enhancing the monitoring capabilities. It should have the ability to generate real time water performance data creating an opportunity for improved water management across the generation fleet. The approach adopted in this dissertation was to learn from existing Eskom Excel water balance tools and develop a standard mathematical model in the form of EtaPRO calculation templates. These templates are be structured such that they function as process components to develop water balances at power plants. The mathematical verification of the Excel calculations were to be conducted using Mathcad. The access to real time data, performance monitoring capabilities and availability at all Eskom Power plants, led to the selection of EtaPRO as the modelling platform. The research conducted led to the development of a methodology for setting up a water balance model for a wet-cooled coal-fired power plant. Calculation templates developed into EtaPRO were validated against the Mathcad mathematical model. The results included a well-documented mathematical model of a water balance in Mathcad and the development of 19 calculation templates that perform the function of standard process components. In addition to calculation templates, multiple Non Volatile (NV) records were created to allow the power plants to capture and track permanent data inputs. NV records also allow for creation of case studies, improving the process monitoring capabilities. A water balance model for a selected power plant was simulated in EtaPRO using the developed calculation templates and user defined formulae. Test screens and dashboards were created to illustrate how the calculation templates and water balance framework would be used to develop a typical water balance model and monitoring system. In conclusion, it is possible to develop process models within the EtaPRO software from well-defined mathematical models to address the performance monitoring concerns on water systems within Eskom.