Engineering

Publication Search Results

Now showing 1 - 10 of 257
  • (2017) Chen, Kai
    Thesis
    Ubiquitous navigation is becoming highly demanded as Location-Based Service (LBS) becomes increasingly popular. In outdoor environments, Global Navigation Satellite System (GNSS) has been developing rapidly over the past few decades. However, indoor navigation is still in its infancy. Compared with other strategies, vision appears to be one of the most promising indoor navigation technologies. Vision sensors are cheap, self-contained and work well for both indoor and outdoor environments. However, there are several elements affecting the performance of vision-based indoor navigation. The measurements for the navigation are image coordinates of Pseudo Ground Control points (PGCPs). These measurements are processed by least squares method with two types of mathematical models. The functional model has been well documented in the literature. However, the stochastic model still presents various challenges and has not been investigated in enough detail. This research focused on dealing with randomised errors existing in navigation steps. Different stochastic models are built to estimate the covariance matrix for image coordinates of PGCPs. These stochastic models have been tested, indicating a significant improvement in the reliability of the position and orientation of the vision sensor. The major research contributions are in the following three different methods to construct a stochastic model: a. Empirical method In the commonly used stochastic model, the variances of PGCP image coordinates are assumed to be the same. However, as the images from the camera can be affected by different variables such as the light, angle, camera parameters and geometric distribution, this assumption is not always accepted. Based on this fact, the measurements should be assigned with different accuracies. Empirically, the closer to the image centre, the more accurate the PGCP image coordinates are. A realistic stochastic model based on the distance between the image features of PGCPs and image centre was constructed to achieve satisfactory positioning results. b. MINQUE method Rao (1970) developed the most commonly used method for estimating variance-covariance components, Minimum Norm Quadratic Unbiased Estimation (MINQUE). It was employed to construct the covariance matrices for PGCP image measurements with the condition that redundant measurements were available. Furthermore, a simplified MINQUE procedure was also used to evaluate the accuracy of measurements. In this research, the efficiency of the estimators was tested using simulated and real PGCP data sets in two different structures of variance component models. Group and additive models were discussed using the rigorous MINQUE method and the simplified MINQUE method. c. BQUE method The Best Quadratic Unbiased Estimator (BQUE), another method for estimating variance-covariance components, was introduced to compare the positioning results with MINQUE by the additive model. However, in MINQUE and BQUE procedure, the estimated variance components may be negative. This is not satisfactory in a real environment. The possible reasons could be a) the adjustment and/or the stochastic models are unreasonable or b) there is not enough of redundancy in the least-squares computation for vision-based navigation applications. To deal with these problems, the Best Quadratic Minimum Bias Non-Negative Estimator (BQMBNE) has been designed to obtain non-negative estimates. The six exterior orientation parameters by these methods were analysed.

  • (2019) Chen, Jessie
    Thesis
    Reservoir management is critical for petroleum production, carbon dioxide sequestration, and groundwater quality evaluation. A critical part of reservoir management involves understanding the behaviour of particles through the underground systems in which the aforementioned applications take place. By understanding the effect that particulates have on the permeability of reservoirs, we can better evaluate field performance, as well as the concentration of contaminants in aquifers. The aim of this research is to investigate the effect of rock structure and particle properties on formation damage. Pore clogging is predominantly initiated due to size exclusion for sand grains, which comprise of larger quartz particles. However, with shaly sandstone, pore clogging can also be a result of electrostatic forces between the clay fines and the porous medium. We study the phenomenon numerically in three dimensions. In order to obtain the pore structure, X-ray microtomography (micro-CT) scans are taken of rock samples. The images are then digitised into a binary format. A flow solver is used to obtain the velocity fields through the rock samples. Then fine particles are injected to the porous medium and follow a trajectory that considers hydrodynamic, body and electrostatic forces. The flow simulator updates the velocity field and determines the new permeability whenever particle retention occurs. The method simulates the particle transport directly on images without the need to simplify the geometry. The pore-scale numerical model can provide dynamic permeability prediction as particle transport occurs. Our results show that the rock structure and particle properties play an important role for determination of formation damage. Particle size can dictate the degree of electrostatic attraction and cause severe retention. Moreover, uncharged slow-moving particles, when the pressure drop is decreased by tenfold, can show a 60% reduction in permeability, in our test sample, after two pore volumes injected. Using pore scale simulation, we are able to gain insight into the extent of damage that mobilising fines or sand grains have on the near-wellbore region of reservoirs.

  • (2019) Liang, Jiaxing
    Thesis
    Due to the severe environment pollution and critical energy issues around the world, fossil fuel is being replaced by new energy sources, e.g. solar power, wind power, etc. To enhance the efficiency of those new energies, electrochemical energy systems (EESs), including lithium-ion battery (LIB), supercapacitor (SC) and lithium-ion capacitor (LIC) are widely used in our daily life. Combining the advantages of LIB and SC, LIC seems to be the most competitive candidate for the next generation EESs. The similarities and differences between three of them are discussed in chapter 1. Also, evaluation methods, device design principles, together with configurations are summarized. By reviewing the development status of LIC, it’s worth to pointing out that pre-lithiation step is necessary in almost all the device design. Moreover, to further enhance the energy density of the device, there is also the call for new cathode material with wide operational voltage and large capacity. Lastly, symmetric LIC design is not popular because the lack of suitable active materials. Aiming to build up a high performance symmetric LIC, 2-dimensional tungstate acid-link polyaniline (TALP), which has a wide working potential range from 0.01V to 4.5V versus Li/ Li+, is used as active material in this thesis. Solvent exchange effect in TALP is observed and confirmed. Water, NMP and electrolyte could diffuse in the interlayer to form the nanoconfined fluid and replace the former existed solution. Plus, as spotted by XPS, not just Li+, but also PF6- is able to intercalate/ de-intercalate into/ from TALP interlayer, thanks to the large interlayer spacing, resulting in a high areal capacity of 39 mAh cm-3 under a large current of 2000 mA g-1. As anode, getting use of the solvent exchange effect and layered structure, interlayer SEI is formed for pre-lithiaiton. The modified sample (5FEC-SEI-TALP) exhibits 4 times higher initial columbic efficiency than the fresh sample. Later, symmetric LIC is produced with TALP as cathode and 5FEC-SEI TALP as anode, which demonstrates a high energy density of 102.63 Wh kg-1 under a power density of 224.5 W kg-1, which is superior to the AC-based symmetric LIC.

  • (2019) Fu, Yunhao
    Thesis
    Substrate integrated waveguide (SIW) technology has attracted significant attention in recent decades. Substrate integrated waveguides combine the high-power capability of the rectangular waveguides (RWG) with the low profile of the planar technology. In this thesis, two SIW components are designed, fabricated, and measured. The first design is an in-line transition between SIW and RWG. Most in-line transitions are metallic with steps of different heights. In this thesis, an SIW transition in K-band is proposed, where the transition part is made of printed circuit board (PCB) panels and the steps are identical. To provide the height of the steps equal to the thickness of the panel, a novel 1:2 E-plane step is designed, by profiling the widths along the midline. Based on the proposed 1:2 E-plane step, a cascaded network is developed to reach the height of waveguide. This cascaded network is then connected to an air-filled SIW taper. The proposed transition in the back-to-back form is fabricated for the measurement, and the results show 15 dB return loss for the frequency range from 20.14 to 25.84 GHz. Such SIW transition with identical steps allows the fabrication on PCB panels, achieving reduced complexity, lighter weight and lower cost. The second design is about a bandwidth enlargement method of the SIW Y-type power divider. In most Y-type dividers, the TE30 mode either degenerates in-band reflection or limits the frequency band of operation due to a transmission zero. The transmission zero is analysed and the mode coupling is utilized to reduce its impact. In the presented configuration, the co-existence of the TE10 and TE30 modes combines the two non-contiguous bands which were separated by the transmission zero. A broadband balun based on the proposed method is designed and fabricated. The measurement shows 15 dB return loss for the frequency range from 8.23 to 12.89 GHz. The measured amplitude and phase imbalance are below 0.7 dB and ± 3 degrees, respectively. The fabricated balun reveals performance, consistent with the simulation, and demonstrates the validity of the applied broadband enlargement method.

  • (2018) Chapre, Yogita Gunwant
    Thesis
    Indoor localization traditionally uses fingerprinting approaches based on Received Signal Strength (RSS), where RSS plays a crucial role in determining the nature and characteristics of location fingerprints stored in a radio-map. The RSS is a function of the distance between transmitter and receiver, which can vary due to in-path interference. This thesis identifies the factors affecting the RSS in indoor localization, discusses the effect of identified factors such as spatial, temporal, environmental, hardware and human presence on the RSS through extensive measurements in a typical IEEE 802.11 a/g/n network, and demonstrates the reliability of RSS-based location fingerprints using statistical analysis of the measured data for indoor localization. This thesis presents a novel Wi-Fi fingerprinting system CSI-MIMO, which uses fine-grained information known as Channel State Information (CSI). CSI-MIMO exploits frequency diversity and spatial diversity in an Orthogonal Frequency Division Multiplexing (OFDM) system using a Multiple Inputs Multiple Outputs (MIMO) system. CSI-MIMO uses either magnitude of CSI or a complex CSI location signature, depending on mobility in indoor environments. The performance of CSI-MIMO is compared to Fine-grained Indoor Fingerprinting System (FIFS), CSI with Single Input Single Output (SISO), and a simple CSI with MIMO. The experimental results show significant improvement with accuracy of 0.98 meter in a static environment and 0.31 meter in a dynamic environment, with optimal war-driving over existing CSI-based fingerprinting systems.

  • (2019) Zhou, Weiwei
    Thesis
    The penetration of renewable energy, e.g. solar and wind, contributes to the creation of – prosumer, who consumes electrical energy and can produce the energy as well. The bidirectional energy flow goes up the challenge for the grid and consequently delay the process of smart electrification, especially in the regional area, where conventional architecture is still in operation. However, the evolvement of grid infrastructure cannot keep up with the development, especially for the regional microgrids, e.g. single-wire-earth-return lines. There is in need a wireless sensor network in place to monitor the power quality transmission line. It’s an engineering challenge to be able to manage the needs from different stakeholders for this research. What’s more, it involves three independent research teams, who are responsible for three different modules of the system. To manage the requirements and streamline the research process, System Engineering is adopted to manage the complexity with requirements as the capstone, which is named Requirement Based System Engineering (RBSE). With the help of RBSE, a novel architecture “LoRa-Hybrid” is created to tackle the obstructions in wireless network penetration in buildings and hills. It also gained much wider signal coverage. In our field test in suburban areas, the new architecture achieved almost full coverage of a building, which could not manage with conventional star-of-stars topology. Additionally, the distance test proves that single node hopping network can reach as twice as the former distance without sacrificing latency. The RBSE contributes to the decomposition of requirements in the way that all the top-level requirements, such as business requirements, are derived in the systematic manner. So that the integrity of the prototype is guaranteed, and research results satisfy the expectation. The new architecture, LoRa-Hybrid, can deliver the requirements from different stakeholders, e.g. grid operator.

  • (2019) Chen, Ming
    Thesis
    Radio frequency electric field treatment (RFEF) is a non-thermal method of food preservation that utilizes high intensity oscillating electric field to inactivate bacteria. Past studies reported that RFEF operated at lower frequencies resulted in a higher inactivation rate of bacteria. However, the electrode may corrode at lower frequencies, especially at frequencies lower than 20 kHz, which could potentially degrade the quality of the processed liquid food. This research studied on the electrode corrosion occurred during the high intensity RFEF operated under 20 kHz, also called the audio frequency electric field treatment (AFEF), and it proposed a novel method to reduce the corrosion rate of electrodes. Inspired by the electrical double layer (EDL) and its equivalent electrical circuit, applying a high permittivity coating on the surface of electrodes was proposed to reduce the corrosion rate. Three coatings composed of titanium dioxide, barium titanate, and CCTO, having low, moderate, and high permittivities, respectively, were selected as the coatings applied on the surface of electrodes to explore how the permittivity of the coatings affect the corrosion rate. Mathematical modeling and experiments were conducted to test whether the three coatings could mitigate the electrode corrosion. In mathematical modeling, an equivalent electrical circuit of the coating-solution system was employed to calculate the phase angle and voltage drop across the three coatings and the solution (saline water). After that, the experiment of the electrode corrosion, with/without applying the three coatings on electrodes during the high intensity AFEF treatment, was conducted. Furthermore, the electrical impedance, atomic and molecular structures, surface morphology, and elemental analysis of the three coatings were conducted. Finally, the concentration of the metallic ions in the AFEF-processed saline water was measured. In conclusion, the corrosion rate generally increased with the increase of the electric field strength and the conductivity and the reduction in frequency, respectively. The CCTO coating performed the best on the reduction of the electrode corrosion among the three proactive coatings, while the titanium dioxide coating marginally reduced the electrode corrosion. However, calcium ions were detected in the processed saline water when the CCTO coating was applied, although the concentration was deficient. As a novel study in this area, this research contributes to the effective mitigation of electrode corrosion, during the electric field treatment, thereby increasing the Industrial applicability of the electric field treatments.

  • (2011) Dong, Xu
    Thesis
    A comprehensive literature review on the AWJ cutting technology and associated sciences has been carried out and reported. It has been found that little research effort has been made to the AWJ cutting process for AMM laminations. As a result, the first comprehensive study on AWJ cutting of AMM laminations using various cutting techniques is presented in this thesis, with a view to understanding and improving the cutting performance, i.e. the depth of cut, the top kerf width and the kerf taper angle. An experimental study in the traditional way of AWJ operation (i.e. placing the nozzle perpendicularly to the work surface without nozzle oscillation) was carried out first to gain the basic understanding of the cutting process and cutting performance. Studies with cutting performance enhancement techniques, i.e. the nozzle oscillation and kerf taper compensation techniques, were then undertaken. The experimental studies included about 200 test runs to provide sufficient data for statistical analysis. Plausible trends of the cutting performance measures with respect to the process parameters have been found from the statistical analyses of the experimental data. In general, an increase in the water pressure and a decrease in the nozzle traverse speed and abrasive mass flow rate within the tested ranges increase the depth of cut. An increase in the kerf taper compensation angle decreases the kerf taper angle almost linearly. Nozzle oscillation cutting can reduce the kerf taper angle to less than 1o, and the kerf taper compensation cutting technique can eliminate the kerf taper if the process parameters are properly selected. Recommendations have been made on the selection of the most appropriate process parameters to be used in practice for each cutting technique. Predictive models for the various cutting performance measures have finally been developed. The depth of cut models were developed using the energy conservation approach, while those for the top kerf width and kerf taper angle were developed empirically. The models were then assessed both qualitatively and quantitatively. It has been found that the model predictions are in good agreement with the experimental data and can give adequate predictions of the cutting performance measures.

  • (2017) Wu, Xiaowei
    Thesis
    Machine-to-Machine (M2M) communications are expected to play an essential role in the upcoming fifth generation (5G) cellular networks. It is going to support various emerging services with new types of requirements including support of massive numbers of connected devices, high link reliability, and low latency real-time operations. To fulfill these requirements, the frame length of each individual transmission tends to be very small. This gives rise to new challenges of designing channel codes for short information length. On the basis of nested convolutional codes, we propose a new method of constructing rate-compatible tail-biting convolutional codes (RC-TBCC). This method allows us to search for a class of rate 1/n TBCC codes, which have a tradeoff between implementation flexibility and error performance for different information length. The numerical results show that the RC-TBCC codes constructed by our proposed method not only have near optimal error performance for long information length, but also have consistent error performance for short information length. Furthermore, our proposed codes outperform the TBCC codes used in the LTE standards. We also investigate the error performance of polar codes for short information length. Polar codes are designed for approaching channel capacity for long information length. Hence, they have performance degradation for short information length. Our simulation results show that the error performance of polar codes for short information length is not as good as TBCC codes. But with the aid of CRC, the error performance of polar codes for short information length can be greatly improved.

  • (2017) Lim, Johnny
    Thesis
    Pancreatic cancer is an aggressive and debilitating human cancer. Due to lack of symptoms and limited diagnostic methods, once diagnosed, the chance for survival is ominous. Gemcitabine has been studied extensively in a variety of tumours and has been found to be effective as a single agent in the treatment of pancreatic cancer. Gemcitabine is a nucleoside analogue of deoxycytidine. Nucleoside antimetabolites have long been the most successful class of anticancer drugs, due to their optimised structures. They are engineered and designed specifically to target DNA synthesis. Nucleosides are known to form complementary hydrogen bonds between base pairs, in this case guanosine. The interaction with guanosine was identified as a potential method of encapsulating gemcitabine. A biocompatible, thermo-responsive polymer was successfully synthesised by using a copolymer with NiPAAm. RAFT, a controlled living radical polymerisation technique pioneered in Australia, was used to produce moderately narrow polydispersed polymers. The polymer properties were subsequently investigated. Solution properties demonstrated self-assembly at near physiological temperature 33°C. Cytotoxicity testing revealed the polymer to be biocompatible and the gemcitabine loaded polymer had improved toxicity than the current administered form. The loading capacity for the micelle was low however, this has set an impetus to improve.