Engineering

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Now showing 1 - 10 of 28
  • (2009) Liu, Yue
    Thesis
    Since the rediscovery, LDPC codes attract a large amount of research efforts. In 1998, nonbinary LDPC codes were firstly investigated and the results shown that they are better than their binary counterparts in performance. Recently, there is always a requirement from the industry to design applied nonbinary LDPC codes. In this dissertation, we firstly propose a novel class of quasi-cyclic (QC) LDPC codes. This class of QC-LDPC codes embraces both linear encoding complexity and excellent compatibility in various degree distributions and nonbinary expansions. We show by simulation results that our proposed QC-LDPC codes perform as well as their comparable counterparts. However, this proposed code structure is more flexible in designing. This feature may show its power when we change the code length and rate adaptively. Further more, we present two algorithms to generate codes with short girth and better girth distribution. The two algorithms are designed based on progressive edge growth (PEG) algorithm and they are specifically designed for quasi-cyclic structure. The simulation results show the improvement they achieved. In this thesis, we also investigate the believe propagation based iterative algorithms for decoding of nonbinary LDPC codes. The algorithms include sum-product (SP) algorithm, SP algorithm using fast Fourier transform, min-sum (MS) algorithm and complexity reduced extended min-sum (EMS) algorithm. In particular, we present the proposed modified min-sum algorithm with threshold filtering which further reduces the computation complexity.

  • (2009) Cai, Zhemin
    Thesis
    In turbomachinery, extra excitation forces may result from non-idealised operation conditions and may sometime cause excessive vibrations and unsteady rotor motions. The goal of this thesis is to investigate the effects of such excitation forces. The extra excitation forces investigated here are the Thomas/Alford force due to the blade tip clearance change, the steam excitation force caused by the variation of inlet steam speed and state blade trailing wake and the dominant magnetic pull force due to dynamic eccentricity of the rotor. The main research results in this thesis include: (1) The modelling of the Jeffcott rotor and the 600MW steam-turbine generator. The used in-house ‘transient’ program can only handle the circular short bearings with the modified short bearing method while the simulated steam-turbine should be supported by tilting pad bearings. The first critical speeds of systems supported by tilting pad bearings are more approaching to the lab data for all four rotor models while that of journal bearing supported systems are normally lower than the real operating critical speed. (2) Applying three sorts of excitation forces into the single-stage rotor-bearing system. The numerical simulation shows that for the model with each single excitation force, all of these three forces need to reach some limit to force the system into the unsteady state. For all the three forces, higher limits are needed if the machine runs at lower running speeds. Furthermore, unbalance loading also can influence the system behaviours. As the unbalance increases, the system will still stay steady while the spectra become noisier, though the amplitude still low comparing to harmonics. (3) Combing three types of excitation forces into the assembled rotor-bearing system. The numerical simulation shows that the assembled system presents similar vibration responses as the single stage rotor-bearing system. Furthermore, these three forces cannot cancel each other and the combination will unstabilise the system. Meanwhile, the influence of the dominant magnetic pull force is less than other two forces.

  • (2009) Numprasanthai, Apisit
    Thesis
    Binary skeletal metal catalysts were made by starting with a ternary alloy. The precursor alloys and catalysts were characterised using Optical Microscopy, X-ray Diffractometer, Scanning Electron Microscopy, Inductively Coupled Plasma (ICP) and BET surface area in term of morphologies, phase identification, surface area and pore structure. Skeletal copper catalyst presented high surface areas and consisted primarily of CuAl2 grains, with small well-dispersed areas of the Al-CuAl2 eutectic. The CuAl2 phase, which represented a tetragonal structure, showed large cell volumes resulted in a fine skeleton structure. Binary nickel-copper catalyst composed of three majority phases including Ni2Al3, Cu4NiAl7 and Al. The Cu4NiAl7 was found to be a caustic resistant phase which led to low surface area in the nickel-copper catalyst In terms of the selective removal of aluminium from the copper-cobalt-aluminium alloy to create the binary copper-cobalt catalyst, 11 alloy samples with various compositions were produced following the ternary phase diagram. The surface area and pore size of these catalysts was dependant on the crystal structure of the phases present and the amount of remaining Al. Electrochemical glucose oxidation and carbon dioxide reduction activity have been used for testing the catalyst performance. The electrochemical oxidation of glucose experiment using 11 samples of skeletal Cu-Co catalyst as an electrode showed the results that the significant oxidation peaks were observed in sample 1, 4, 8, 9 and the small oxidation humps were observed in other sample except sample 2. These small peaks resulted from that the glucose molecule had difficulty to absorb on the surface area of the skeletal Cu-Co catalysts electrode. The difficulty may results from very fine pore volume and pore size of the catalysts. In term of assessing the skeletal Cu-Co catalyst with electrochemical reduction of carbon dioxide experiment, the skeletal Cu-Co catalyst sample 7 which presented the highest surface area was selected as an electrode to compare with Cu foil electrode. The result of using skeletal Cu-Co as an electrode indicated significantly higher current. This results from that a skeletal Cu-Co catalyst electrode presented an actual high surface area which leads to more adsorbed regions.

  • (2009) Richards, Eric Wesley
    Thesis
    The past years has seen the advent of the availability of high resolution commercial satellite imagery. This study shows that whilst high resolution commercial satellite imagery is capable of producing reasonable spatial data both in quality and cost for use in an urban GIS the challenges of supplying this data commercially is not limited to simply the provision of the imagery. Since a significant amount of work has been done by others to examine and quantify the technical suitability and limitations of high resolution commercial satellite imagery, this study examines the practical limitations and opportunities presented with the arrival of this new spatial data source. In order to do this a number of areas are examined; the historical development of the satellite systems themselves, the business evolution of the owning commercial ventures, Geographical Information Systems (GIS) data and service requirements for a diverse range of spatial data applications and finally the evaluation and comparison of the imagery as a spatial data source. The study shows that high resolution commercial satellite imagery is capable of providing spatial data and imagery for a variety of uses at different levels of accuracy as well as opening up a new era in the supply and application of metric imagery. From a technical approach high resolution commercial satellite imagery provides remote access, one metre or better resolution, 11 bit imagery and a multispectral capability not previously available from space. Equally as challenging is the process or achievement in making the technical capability a reality in a commercial world requiring a financial return at all levels; from the image vendors to the spatial science professional providing a service to a paying customer. The imagery must be financially viable for all concerned.

  • (2009) Warraich, Daud Sana
    Thesis
    This thesis presents a technique used to stochastically estimate the location of hidden discontinuities in carbon fiber composite materials. Composites pose a challenge to signal processing because speckle noise, as a result of reflections from impregnated laminas, masks useful information and impedes detection of hidden discontinuities. Although digital signal processing techniques have been exploited to lessen speckle noise and help to localize discontinuities, uncertainty in ultrasonic wave propagation and broadband frequency based inspections of composites still make it a difficult task. The technique proposed in this thesis estimates the location of hidden discontinuities stochastically in one- and two-dimensions based on statistical data of A-Scans and C-Scans. Multiple experiments have been performed on carbon fiber reinforced plastics including artificial delaminations and porosity at different depths in the thickness of material. A probabilistic approach, which precisely localizes discontinuities in high and low amplitude signals, has been used to present this method. Compared to conventional techniques the proposed technique offers a more reliable package, with the ability to detect discontinuities in signals with lower intensities by utilizing the repetitive amplitudes in multiple sensor observations obtained from one-dimensional A-Scans or two-dimensional C-Scan data sets. The thesis presents the methodology encompassing the proposed technique and the implementation of a system to process real ultrasonic signals and images for effective discontinuity detection and localization.

  • (2009) Wolf, Michael
    Thesis
    Using electron beam evaporation for the production of polycrystalline silicon (pc-Si) thin-film solar cells is an attractive alternative to PECVD deposition. Due to its faster deposition rate, using evaporation technology could significantly reduce module production costs. Other advantages are lower running costs, and the fact that no toxic gases are involved. However, currently no on-shelf equipment is available, and research in this field often relies on in-house designed systems. These can have various problems with reliability, deposition uniformity, and due to their custom design require frequent maintenance. In this work, a newly purchased electron beam evaporation system was upgraded and redesigned to be capable of depositing amorphous Si diodes for the fabrication of pc-Si thin-film solar cells. The main goal of the upgrade was to provide a safe and reliable tool which allows for the deposition of high purity semiconductor material. Reliable and safe operation was accomplished by designing the entire electrical supply circuit and incorporating various safety interlocks. Source cross-contamination issues were addressed by installing a specially designed shroud (source housing). To provide uniform substrate temperatures up to 600°C, a heater was specially designed, fabricated, installed and tested. Accurate design of all mechanical system components was realised by using 3D product design software (ProEngineer). The new evaporator was commissioned, which included testing and calibration of all the system components required for depositing on substrate sizes of up to 10x10cm2. Over this area a Si film thickness uniformity of +/-2%, performed with a maximum deposition rate of 7nm/s was achieved. Initial experiments using solid phase crystallisation and rapid thermal annealing revealed a sheet resistance uniformity of +/-4% for the Phosphorus and +/-7% for the Boron dopant effusion cell. Experimentation via Raman spectrometry and X-ray diffraction has revealed good crystalline properties, of the crystallised Si films, which is comparable to those of existing evaporation systems. Although the system was upgraded to achieve deposition pressures below 3x10-7 mbar, experiments have shown that this quality of vacuum may not be necessary for the fabrication of low impurity films. The system is now ready for further research in the field of thin-film photovoltaics, and the first functioning devices have been fabricated.

  • (2009) Chiu, Tekkie Tak-Kei
    Thesis
    This thesis presents an indoor obstacle avoidance system for car-like mobile robot. The system consists of stereo vision, map building, and path planning. Stereo vision is performed on stereo images to create a geometric map of the environment. A fast sparse stereo approach is employed. For different areas of the image there are different optimal values of disparity range. A multi-pass method to combine results at different disparity range is proposed. To reduce computational complexity the matching is limited to areas that are likely to generate useful data. The stereo vision system outputs a more complete disparity map. Abstract Map building involves converting the disparity map into map coordinates using triangulation and generating a list of obstacles. Occupancy grids are built to aid a hierarchical collision detection. The fast collision detection method is used by the path planner. Abstract A steering set path planner calculates a path that can be directly used by a car-like mobile robot. An adaptive approach using occupancy grid information is proposed to improve efficiency. Using a non-fixed steering set the path planner spends less computation time in areas away from obstacles. The path planner populates a discrete tree to generate a smooth path. Two tree population methods were trialled to execute the path planner. The methods are implemented and experimented on a real car-like mobile robot.

  • (2009) Yang, Shuxiang
    Thesis
    Uncertainty is inherent in many novel and important applications such as market surveillance, information extraction sensor data analysis, etc. In the recent a few decades, uncertain data has attracted considerable research attention. There are various factors that cause the uncertainty, for instance randomness or incompleteness of data, limitations of equipment and delay or loss in data transfer. A probabilistic threshold range aggregate (PRTA) query retrieves summarized information about the uncertain objects in the database satisfying a range query, with respect to a given probability threshold. This thesis is trying to address and handle this important type of query which there is no previous work studying on. We formulate the problem in both discrete and continuous uncertain data model and develop a novel index structure, asU-tree (aggregate-based sampling-auxiliary U-tree) which not only supports exact query answering but also provides approximate results with accuracy guarantee if efficiency is more concerned. The new asU-tree structure is totally dynamic. Query processing algorithms for both exact answer and approximate answer based on this new index structure are also proposed. An extensive experimental study shows that asU-tree is very efficient and effective over real and synthetic datasets.

  • (2009) Hou, Wanwan
    Thesis
    The international oil and gas industry views China as a key country in its search for petroleum exploration and development investment opportunities. China offers a range of opportunities from mature, producing areas to frontier exploration areas. When Oil and gas companies make investment decisions to explore for and develop petroleum resources in a particular country, they need to examine many aspects of that country. The decision to invest focuses on assessments of the likely economic rewards and the risks involved. In this thesis, I attempt to provide a detailed assessment of various factors affecting the economics of petroleum exploration and development in China from an oil and gas investors point of view. The thesis is aimed at assisting international oil and gas companies to make investment decisions and assisting their understanding of the petroleum prospects in China. Based on detailed economic modelling, the thesis aims to demonstrate the profitability of exploration and development of a range of hypothetical but representative oil and gas prospects and discoveries in different areas in onshore and offshore China. The thesis also reviews the key fiscal terms in China and shows the economic impact of individual components of Chinese fiscal terms on field developments in China. The thesis quantifies and analyses the impact of Chinese fiscal terms by measuring the Government Take for a range of hypothetical oil field developments. It includes an analysis of the flexibility of the Chinese fiscal terms by quantifying the effect of Government Take on marginal field developments. In addition, the thesis intends to assess the competitiveness of Chinese fiscal regime in terms of its severity and flexibility as compared to other fiscal regimes in the Asia Pacific Region.

  • (2009) Luo, Cheng
    Thesis
    Robust object tracking plays a central role in many applications of image processing, computer vision and automatic control. In this thesis, robust object tracking under complex environments, including heavy clutters in the background, low resolution of the image sequences and non-stationary camera, has been studied. The interest of this study stems from the improvement of the performance of visual tracking using particle filtering. A Geometric Active contour-based Tracking Estimator, namely GATE, has been developed in order to tackle the problems in robust object tracking where the existence of multiple features or good object detection is not guaranteed. GATE combines particle filtering and the level set-based active contour method. The particle filtering method is able to deal with nonlinear and non-Gaussian recursive estimation problems, and the level set-based active contour method is capable of classifying state space of particle filtering under the methodology of one class classification. By integrating this classifier into the particle filtering, geometric information introduced by the shape prior and pose invariance of the tracked object in the level set-based active contour method can be utilised to prevent the particles corresponding to outlier measurements from being heavily reweighted. Hence, this procedure reshapes and refines the posterior distribution of the particle filtering. To verify the performance of GATE, the performance of the standard particle filter is compared with that of GATE. Since video sequences in different applications are usually captured by diverse devices, GATE and the standard particle filters with the identical initialisation are studied on image sequences captured by the handhold, stationary and PTZ camera, respectively. According to experimental results, even though a simple color observation model based on the Hue-Saturation-Value (HSV) color histogram is adopted, the newly developed. GATE significantly improves the performance of the particle filtering for object tracking in complex environments. Meanwhile, GATE initialises a novel approach to tackle the impoverishment problem for recursive Bayesian estimation using sampling method.