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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Stochastic Modelling and Optimal Control of Compartment Fires

Tat, Mehmet Ali January 2002 (has links) (PDF)
Compartment fires are defined as fires in enclosed spaces. They are labeled as oxygen driven fires and are non-stationary growth phenomenon. A gap exists in the knowledge of deterministic fire growth models and stochastic fire growth models. In this thesis we develop non-stationary stochastic models in an endeavor to bridge the gap. The class of Epidemic models for infectious diseases are non-stationary growth models. In the first part of the thesis the Deterministic Simple Epidemic, Deterministic General Epidemic and the Stochastic General Epidemic models are investigated to develop equations for the growth of compartment fires by drawing analogies between the epidemic variables and the compartment fire variables. The Percolation and Contact processes are investigated for the spread of compartment fires. A mechanism for converting deterministic differential equations to stochastic differential equations based on the theory of Martingales is presented. In part two of the thesis, two deterministic models based on the risk assessment model of the National Research Council Canada (NRCC) are developed and calibrated. One of the deterministic models is a fuel driven model and the other is an oxygen driven model. The oxygen driven deterministic model is converted to a stochastic model based on the theory of Martingales, and used as an input to calculate a fire severity measure called Heat Load. Statistical tests are applied to the Heat Load data set to determine its distribution. A non-parametric statistical test, W Test, is used to calculate the upper quartiles of the heat load. A third model based on the NRCC model is built. This model is closer to the Epidemic models and its parameters do not require tedious optimisation algorithms to calculate. They are evaluated from the initial conditions of the physical process. In this model we make the assumption that the gas temperature inside the compartment is a function of the burning rate and develop a two variable model based on the burning rate and oxygen fraction. A change of variable is applied to simplify the differential equations, the equations are solved implicitly and their parameters evaluated using the initial conditions. The temperature equation is modelled using a first order differential equation with the burning rate and is solved separately. Finally part three of this thesis investigates automatic sprinkler systems and the mathematical theory of optimal control. Optimal control theory is applied to automatic sprinkler systems to model sprinklered compartment fires. To reduce water damage inside a compartment due to sprinkler activation from small fires, we model the water spray rate. Two cases are considered, the first when the water damage is proportional to the total amount of water and the second when the water damage is proportional to the integral of the square of the water flow rate. Pontryagin's principle is used to solve the integrals and obtain the water spray rate equations.
2

Improving the Structural Dynamics of Slender Beam-like Structures

Anderson, Christopher Stuart January 2003 (has links) (PDF)
This project explores a novel technique for the vibration control of slender beam-like flexible structures. For this purpose, a new method is developed based on minor structural modifications. Three applications are chosen to demonstrate the new method. The first is the sensing wire oscillations of a hot-wire probe. The second application is the problem of tool chatter due to milling tool vibration, while the third application is the bending of an arrow as it is released from a bow. Although these applications sound quite different, they are in fact similar problems dynamically. They are related to the forced transverse structural vibrations of slender beams. For all applications, the external force input is of a broadband nature in frequency, similar to a white noise excitation. This force excites the slender beams into large amplitude resonance which in the case of a hot-wire probe, causes measurement inaccuracies, for milling, causes rough surface finish and slower machining times, whereas for archery causes reduced accuracy. The choice of the particular problems to demonstrate the effectiveness of the technique is due to the current research interests and available expertise in this area in the School of the Built Environment at Victoria University. However, the methods developed through the course of this research are general methods applicable to all other slender beam-like structures with step changes in cross sectional geometry, such as flexible robotic arms or power transmission cables.
3

Opportunity Capture and Growth Strategies for Regional Ports: A Modelling Approach

Magala, Mateus January 2004 (has links) (PDF)
Regional ports adjacent to capital city ports have often developed as bulk ports (Hilling and Hoyle 1984), but for most there is a recognition that they may be no longer able to rely solely on the benefits of exploiting bulk commodities and trades to sustain competitive advantage and growth. To attain growth and survival there is the perception and often the reality that they need to diversify their trade base or/and enter new markets - most of which are likely to be dominated by their capital city ports. But challenging the market dominance of established capital city ports is likely to be very difficult, especially given the rationalisation of shipping networks and the restructuring of supply chains at few suitable ports - most of which in Australia are likely to be capital city ports. How will regional ports which are in the shadow of capital city ports and constantly face significant economic and competitive penalty manage to compete for growth and survival? How will regional ports manage to grow if the nature and scale of trades in their markets are severely restricted as commercial activities, mainly high-value container trades, are concentrated in the larger established capital city ports - even when there is a recognition that some container trades could be handled economically and cost-effectively in regional ports? Simple observation of the economic health of many regional ports, often ill-devised and/or poorly implemented strategies set in place by regional port managers, and of unclear and less-than-adequate conceptual frameworks for the mechanisms of port growth as set out in the literature all suggest that there is 'strategy decay' (Hamel 2002) and the need for a clear understanding of port growth, and particularly of the dynamics and mechanisms of port growth for regional ports in the shadow of their capital city ports. This study seeks to define the basis of and the mechanisms for regional port growth. The study identifies opportunity capture as the basis for defining effective growth strategies for a regional port; and argues that competition for opportunity share rather than competition for market share is the key for regional port growth. The study offers a theoretical framework which regional port managers can use to effectively capture and increase the share of valuable opportunities in the quest for growth; and empirically investigates the perceptions of regional port managers about effective growth strategies for regional ports. A detailed review of the relevant literature revealed a considerable range of factors and conditions underlying port growth; but to our knowledge, there has been no analytical testing of the proposition that opportunity capture is the appropriate mechanism for regional port growth nor has there been any rigorous attempt to define growth strategies for regional ports that are in the shadow of capital city ports. It was, therefore, necessary to collect data from port specialists in order to gain useful insights into regional port growth strategies and opportunity capture. The qualitative data collected were categorized in relevant dimensions - using content analysis - and then used to develop a more structured and formal Internet-based survey which sought to collect data from a much broader sample of regional port managers with the objective of testing their perceptions about effective regional port growth strategies; and to model opportunity choice - a critical process of opportunity capture. The determinants of opportunity choice were identified with discrete choice modelling which called for a stated choice experiment in order to investigate how regional port managers actually make opportunity selection decisions. Discrete choice modelling as used in this study to model executive judgment at strategic level is novel and constitutes an important departure from more traditional approaches. A major conclusion of the study is that regional ports that have developed in the shadow of their capital city ports have the opportunity for growth if they can capture valuable opportunities over time; and that critical to opportunity capture is entrepreneurship and market-driven strategies that regional port managers can implement and orient to provide shippers and other regional port customers with superior access to markets in which they compete for competitive advantage and market dominance. Superior access to markets is provided through supply chains that are value driven; that is, supply chains that are integrated and focus on the end-to-end, cost-effective movement of freight. Such supply chains seek to deliver competitive advantage or value to shippers and to capture value for the port.
4

Use of Stormwater as an Alternative Supply Source

Goonrey, Carolyn Michelle January 2005 (has links) (PDF)
Changing climate, increasing demand for potable water supplies and increased community interest for sustainable use of fresh water sources have resulted in a new focus on water use and sourcing. New sources are being sought, in conjunction with water demand minimisation strategies, to decrease the pressure on existing urban water resources. At the same time, the management of stormwater is being re-examined with the focus changing from the traditional practice of rapid disposal of stormwater (to reduce the risks of flooding) to utilisation of stormwater as an alternative water supply source. The focus of this thesis is the use of stormwater as an alternative supply source in urban areas at a cluster (or neighbourhood) scale. A decision making framework was developed to assist the adoption of a holistic approach to determining the most appropriate stormwater use scheme option. It was developed as an integrated planning tool to be used in the initial stages of investigating water sourcing and stormwater management ideas. Due to the time constraints of this project, the focus of the decision making framework was on the technical components (with associated issues) and financial costs. Since additional issues such as environmental, social and economic issues, are crucial to ensure a balanced view is taken in the decision making process, they are included in the process through additional information sources. Development of the decision making framework considered the following steps: • Development of stormwater use scheme options based on the technical components and associated issues of collection, storage, treatment, distribution and end use; • Development of screening tools to screen out infeasible or clearly inferior stormwater use scheme options; • Development of steps in the decision making framework; and • Demonstration of the decision making framework through the use of a case study. The decision making framework consists of eleven steps. The initial six steps of the decision making framework relates to collection and end use issues and are based around matching stormwater runoff to demand and matching stormwater quality to required quality. Steps 7 to 9 of the decision making framework consist of examining and determining feasible storage, treatment and distribution options. Step 10 of the decision making framework focuses on the integration of the feasible technical options identified in the previous steps, in order to develop stormwater use scheme options. The final step of the decision making framework is to determine costs of the stormwater use scheme options and compare the scheme options on the basis of cost, reliability of supply, quantity of stormwater utilised and end use demands met. The decision making framework was demonstrated as an easy and practical tool for determining the most appropriate stormwater use scheme through the use of a case study. An existing urban area was chosen as the case study due to the potential for the greater impact in terms of minimising potable water use for non-potable end uses. Feasible collection, storage, distribution, treatment and end use options were determined and integrated into 19 stormwater use schemes. Comparison of all the stormwater use scheme options, as well as the base case with no stormwater use, determined four options as being superior in terms of financial costs, reliability, quantity of stormwater used and end uses met. The decision making framework was developed based on existing constraints (such as the lack of guidelines directly examining stormwater use) and knowledge, while being flexible enough to include future scientific and practical knowledge, as it becomes available. Recommendations for future development of the decision making framework include expanding this decision making framework to identify the optimum scales of stormwater use schemes. Additionally, an effective yet simple to use costing tool needs to be developed so that all environmental, social and economic costs are determined and actual benefits of stormwater use schemes can be determined.
5

Liquid sloshing in containers with flexibility

Gradinscak, Marija January 2009 (has links) (PDF)
Sloshing is the low frequency oscillations of the free surface of a liquid in a partially filled container. The dynamic response of structures holding the liquid can be significantly influenced by these oscillations, and their interaction with the sloshing liquid could lead to instabilities. It is critical to predict and to control sloshing in order to maintain safe operations in many engineering applications, such as in-ground storage and marine transport of liquid cargo, aerospace vehicles and earthquake-safe structures. Contributions to the state of knowledge in predicting and controlling sloshing are the main objectives of the proposed research. To this end, a numerical model has been developed to enable reliable predictions of liquid sloshing. The numerical results are compared with experimental results to determine the accuracy of the numerical model. Further, the research addresses the employment of intentionally induced sloshing to control structural oscillations. The novelty of this research is in its use of a flexible container. Results indicate that intentionally introduced flexibility of the container is capable of producing effective control. The practical application of the proposed research is in the early design stages of engineering systems for which liquid sloshing plays a significant part in structural loading.
6

A study of air flow in a network of pipes used in aspirated smoke detectors

Singh, Rohitendra K January 2009 (has links) (PDF)
A Very Early–warning Smoke Detection Apparatus (VESDATM) detects the earliest traces of smoke by continuously sampling the air from a designated area. Air sampling is achieved by use of a system of long pipes containing numerous small inlet orifices termed as sampling holes. The air samples are drawn to the detector by means of an aspirator. In spite of the high sensitivity of the detector, much of this advantage can be lost if the smoke transport time within the pipe network is excessive. Consequently there has been a legislation introduced by Standards such as AS 1670 and BS 5839 stating the maximum transport time to be within 60 seconds of entering that extremity of a pipe system of 200 meters aggregate length, and the suction pressure was to be no less than 25 Pascals. Once the pipe network is installed, it is impractical and often impossible to test the transport time and suction pressure drop of every sampling hole in a complex network of pipes. Therefore, a software modelling tool is required to accurately predict these parameters to 90% of measured value with high accuracy. The flow regimes within the sampling pipes proved complex, involving frequent transitions between laminar and turbulent flows due to disturbances caused to the main flow by jet flows from the sampling holes. Consequently, the published equations to determine friction factors does not predict pressure loss and transport time results to an acceptable accuracy for this thesis. Computational Fluid Dynamics simulations were carried out at various magnitudes of disturbances similar to the effects in VESDA pipe network. The data from the CFD were analysed and the results were used as a guide to develop mathematical models to calculate the friction factor in flow regimes where jet disturbances are present. The local loss coefficients of fittings such as bends and couplings were experimentally determined for all types of fittings used in VESDA pipe networks. The local loss coefficients that were determined made significant improvements in calculating pressure losses compared to the results obtained when commonly used loss coefficient values were used. The characteristics of the VESDA aspirators of all models were determined. The experiments were carefully set up to ensure the apparatus did not have any influence on the aspirator performance. Mathematical models were developed for each VESDA model. A relationship between the magnitude of disturbance and the delay it caused for the smoke to travel from one segment to the next was established. From this relationship, a new transport time mathematical model was developed. Validations of all mathematical models were carried out in different pipe configurations. In all cases the results calculated were within 90% or better compared to the measured results.
7

Development of Multi-layer Films Containing Natural Antimicrobial Agents

Rardniyom, Chanun January 2009 (has links) (PDF)
In this research, multi-layer packaging films comprising an inner coating layer containing natural antimicrobial (AM) agents were developed. Volatile essential oils obtained from plant extracts including carvacrol, linalool and methylchavicol were used as the active AM agents in the coating layer. The amount of natural AM agents and the composition of the coating system required to provide the optimum AM effect in food media and on Cheddar cheese was explored. The stability of the AM coatings in various food simulants was also explored. In the film preparation, the AM coatings were embedded between low-density polyethylene (LDPE) layers to construct multilayer AM films. Investigation of the retention and subsequent release of the AM agent from multi-layer films suggested that a coating layer consisting of ethylacrylatemethylmethacrylate performs satisfactorily as the carrier for the AM agent. Furthermore, LDPE is able to successfully control the release of the AM agent into food simulants. The controlling layer thickness, AM layer thickness and the solubility of AM agent are critical factors affecting the overall effectiveness of the multi-layer AM film. At subambient temperatures, the multi-layer AM films successfully inhibited the growth of E. coli in liquid food media and on Cheddar cheese.
8

Computational and experimental investigations of biologically interesting molecules

Stewart, Matthew Blair January 2009 (has links) (PDF)
The reconciliation of experimental and computational data is an on-going challenge in many fields of scientific enquiry. This is particularly true in chemistry, especially with respect to biologically interesting molecules, given the myriad of problems that now lend themselves to theoretical investigation. This work sampled several areas of this greater landscape using various computational methods, and compared these results to relevant, experimentally derived data.
9

A reconfigurable low noise amplifier for a multi-standard receiver

Mustaffa, Mohd Tafir January 2009 (has links) (PDF)
Mobile devices are widely used for a vast range of applications such as mobile phones,personal digital assistant, personal computers, video games console, etc. However, the performance of these devices is restricted by the support of the network and the mobile functionality and efficiency. Current applications require high data rates and global mobility which can be satisfied with the co-existence and handover between newly developed third generation (3G) or Universal Mobile Telecommunication System (UMTS) standard and current second generation (2G) standards including: Global Standards for Mobile (GSM), Digital Cellular System (DCS), and Personal Communication Systems (PCS). Therefore, recent research in wireless communication has shifted towards achieving a multi-standard terminal, which can support efficiently multiple standards including GSM/DCS/PCS/3G. In this research, the aim is to design and implement a new LNA for a multi-standard mobile receiver based on reconfigurability concept. This research was carried out in two major parts. The first part is to design and implement wide band multi-standard multiband LNAs for two bands of interest (lower frequency band – 800 to 1000 MHz and upper frequency band – 1800 to 2200 MHz). These two bands should cover most of the 2G and 3G standards currently in use worldwide. In this work, the design of LNA based on IDCS topology using wide band approach has been investigated, designed, implemented and approved by means of simulations, and measurement of fabricated ICs. The second part of this research, to develop a single reconfigurable multi-standard multi-band LNA is based on the design of the multi-standard multi-band LNAs. This LNA has the capability to function in two modes of operation, either at lower band or upper band of the 2G or 3G standards.

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