687 research outputs found
Synthetic aperture guided wave imaging using a mobile sensor platform
No full textThis oral session at conference looks at synthetic aperture guided wave imaging using a mobile sensor platfor
Introducing a new method for efficient visualization of complex shape 3D ultrasonic phased-array C-scans
No full textAutomated robotic inspection systems allow the collection of large data volumes, compared to existing inspection systems. To maximize the throughput associated with the nondestructive evaluation phase, it is crucial that the reconstructed inspection data sets are generated and examined rapidly without a loss of detail. Data analysis often becomes the bottleneck of automated inspections. Therefore, new data visualization tools, suitable to screen the NDT information obtained through robotic systems, are urgently required. This paper presents a new approach, for the generation of three-dimensional ultrasonic C-scans of large and complex parts, suitable for application to high data throughput ultrasonic phased array inspection. This approach produces 3D C-scan presented as colored tessellated surfaces and the approach works efficiently on challenging geometry, with concave and convex regions. Qualitative and quantitative results show that the approach runs up to 500 times faster than other C-scan visualization techniques
Positioning for mobile NDE inspection robots
No full textAgeing infrastructure worldwide requires periodic inspection, often in-situ, in order to ensure continued safe and economic operations as well as adherence to stringent quality and performance requirements. In service automated Nondestructive Evaluation, where feasible, is highly attractive, and potentially allows inspection of operational plant. The use of such technology is very attractive in terms of safety, cost and the potential for minimal disruption to the inspection site especially if plant operations can remain online. Automated Nondestructive Evaluation in the form of remotely operated robotic vehicles is an active area of research. Knowledge of position relative to a frame of reference is a key aspect for a robotic Nondestructive Evaluation system in order to associate sensor measurements with locations on the structure being investigated. This thesis investigates relative and absolute positioning techniques for a single robot. The accuracy and repeatability of a photogrammetry system is characterised over a large volume using a high accuracy metrology instrument. It was found that the photogrammtery system was most accurate in the centre of the volume and least accurate at the edges. This photogrammetry system is then used to evaluate the performance of algorithms developed in subsequent research. An image based positioning system is implemented which extracts motion information from a camera carried onboard a robot. The system is evaluated on surfaces typically found in industrial environments. Ultrasonic ranging techniques are investigated for robot positioning. In particular a low cost, modular, ultrasonic positioning system is characterised and calibrated. Bayesian filtering in the form of an Extended Kalman and Particle Filter are implemented to fuse noisy optical encoders estimates available at 100 Hz and the ultrasonic positioning measurements available at 3 Hz. The Extended Kalman Filter, at lower computational cost, was found to produce the lowest error.Ageing infrastructure worldwide requires periodic inspection, often in-situ, in order to ensure continued safe and economic operations as well as adherence to stringent quality and performance requirements. In service automated Nondestructive Evaluation, where feasible, is highly attractive, and potentially allows inspection of operational plant. The use of such technology is very attractive in terms of safety, cost and the potential for minimal disruption to the inspection site especially if plant operations can remain online. Automated Nondestructive Evaluation in the form of remotely operated robotic vehicles is an active area of research. Knowledge of position relative to a frame of reference is a key aspect for a robotic Nondestructive Evaluation system in order to associate sensor measurements with locations on the structure being investigated. This thesis investigates relative and absolute positioning techniques for a single robot. The accuracy and repeatability of a photogrammetry system is characterised over a large volume using a high accuracy metrology instrument. It was found that the photogrammtery system was most accurate in the centre of the volume and least accurate at the edges. This photogrammetry system is then used to evaluate the performance of algorithms developed in subsequent research. An image based positioning system is implemented which extracts motion information from a camera carried onboard a robot. The system is evaluated on surfaces typically found in industrial environments. Ultrasonic ranging techniques are investigated for robot positioning. In particular a low cost, modular, ultrasonic positioning system is characterised and calibrated. Bayesian filtering in the form of an Extended Kalman and Particle Filter are implemented to fuse noisy optical encoders estimates available at 100 Hz and the ultrasonic positioning measurements available at 3 Hz. The Extended Kalman Filter, at lower computational cost, was found to produce the lowest error
Bipartite guidance, navigation and control architecture for autonomous aerial inspections under safety constraints
No full textIn this work the autonomous flight of a drone for inspection of sensitive
environments is considered. Continuous monitoring, the possibility of override and
the minimisation of the on-board computational load are prioritized. The drone
is programmed with a Lyapunov vector guidance and nonlinear control to fly a
trajectory passed, leg after leg, by a remote ground station. GPS is the main
navigation tool used. Computational duties are split between the ground station
and the drone’s on board computer, with the latter dealing with the most time
critical tasks. This bipartite autonomous system marries recent advancements in
autonomous flight with the need for safe and reliable robotic systems to be used
for tasks such as inspection or structural health monitoring in industrial environments.
A test case and inspection data from a test over flat lead roof structure are
presented
Arbitration and Dispute Settlement in Foreign Indirect Investment. The increasing significance and use of arbitration in international loan agreements, syndicated loans and international bond issues
No full textThis dissertation examines the suitability of arbitration for the resolution of securities regulatory claims and it adoption globally, which has resulted in international arbitration becoming the favoured dispute resolution mechanism in the securities industry. The author explains that disputes arising out of international bilateral and syndicated loan agreements are generally considered to be arbitrable, while international bond disputes are often derived from the controversies over the application of mandatory national laws and the compliance with securities regulation provisions - so the arbitrability of international bond disputes depends on the acceptance of the arbitrability of securities regulatory claims
A monolithically integrated power JFET and Junction Barrier Schottky diode in 4H silicon carbide
No full textEfficiency of power management circuits depends significantly on their constituent switches and rectifiers. The demands of technology are increasingly running up against the intrinsic properties of Si based power devices. 4H-Silicon Carbide (SiC) has superior properties that make it attractive for high power applications. SiC rectifiers are already a competitive choice and SiC switches have also been commercialized recently. Junction Barrier Schottky (JBS) diodes, which combine the advantages of PN and Schottky, have higher Figure of Merit (FOM) as rectifiers. Among switches, a robust and mature process has been developed for Silicon Carbide Vertical Junction Field Effect Transistors (VJFETs), which currently gives it the highest unipolar FOM. Switches are frequently combined with anti-parallel diodes in power circuits. This thesis describes the development of a SiC-based monolithically integrated power switch and diode. Monolithic integration increases reliability and efficiency, and reduces cost. Because of their superior properties and similarities in fabrication, we chose the SiC VJFET and JBS diode as the switch and rectifier. Detailed design, fabrication and characterization of the integrated switch to block above 800 V and conduct current beyond 100 A/cm2 is explained. In this process, the first physics-based 2-D compact model is developed for reverse leakage in a JBS diode as a function of design parameters. Since the gate-channel junctions of SiC VJFETs cannot be assumed to be abrupt, an existing analytical model for Si VJFETs is extended to account for graded gate-channel junctions. Using these analytical models, design rules are developed for the VJFET and JBS diode. Finite element simulations are used to find the best anode layout of the JBS diode and optimize electric field termination in the integrated device to ensure their capability to operate at high voltage. Finally, a spin-on glass based process is developed for filling the gate trenches of the VJFET to improve long-term robustness in extreme environments. The integrated power switch developed in this thesis points to the attractions of monolithic integration in SiC power circuits. Analytical compact design equations derived here will facilitate faster and easier design of switches and rectifiers for desired circuit operation.Ph. D.Includes bibliographical referencesIncludes vitaby Rahul Radhakrishna
Acyclic and Macrocyclic Schiff Base-Based Chelating Ligands for Uranyl Ion (Uo2 2+) Complexation
No full textA noncontact ultrasonic platform for structural inspection
No full textMiniature robotic vehicles are receiving increasing attention for use in nondestructive testing (NDE) due to their attractiveness in terms of cost, safety, and their accessibility to areas where manual inspection is not practical. Conventional ultrasonic inspection requires the provision of a suitable coupling liquid between the probe and the structure under test. This necessitates either an on board reservoir or umbilical providing a constant flow of coupling fluid, neither of which are practical for a fleet of miniature robotic inspection vehicles. Air-coupled ultrasound offers the possibility of couplant-free ultrasonic inspection. This paper describes the sensing methodology, hardware platform and algorithms used to integrate an air-coupled ultrasonic inspection payload into a miniature robotic vehicle platform. The work takes account of the robot's inherent positional uncertainty when constructing an image of the test specimen from aggregated sensor measurements. This paper concludes with the results of an automatic inspection of a aluminium sample
Acyclic and Macrocyclic Schiff Base-Based Chelating Ligands for Uranyl Ion (Uo22+) Complexation
No full textNovel algorithms for 3D surface point cloud boundary detection and edge reconstruction
No full textTessellated surfaces generated from point clouds typically show inaccurate and jagged boundaries. This can lead to tolerance errors and problems such as machine judder if the model is used for ongoing manufacturing applications. This paper introduces a novel boundary point detection algorithm and spatial FFT-based filtering approach, which together allow for direct generation of low noise tessellated surfaces from point cloud data, which are not based on pre-defined threshold values. Existing detection techniques are optimized to detect points belonging to sharp edges and creases. The new algorithm is targeted at the detection of boundary points and it is able to do this better than the existing methods. The FFT-based edge reconstruction eliminates the problem of defining a specific polynomial function order for optimum polynomial curve fitting. The algorithms were tested to analyse the results and measure the execution time for point clouds generated from laser scanned measurements on a turbofan engine turbine blade with varying numbers of member points. The reconstructed edges fit the boundary points with an improvement factor of 4.7 over a standard polynomial fitting approach. Furthermore, through adding artificial noise it has been demonstrated that the detection algorithm is very robust for out-of-plane noise lower than 25% of the cloud resolution and it can produce satisfactory results when the noise is lower than 75%
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