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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.

Hazard identification and risk analysis of nighttime offshore helicopter operations

Coutinho Nascimento, Felipe Augusto January 2014 (has links)
Helicopters play a vital role in the movement of people and cargo to and from the installations of the oil and gas industry at sea, often in challenging environments, such as nighttime, where accidents tend to have serious impacts. The ability to remain safe is largely reliant on the processes of hazard identification and risk analysis. However, the processes currently used do not provide the offshore helicopter industry with the desired levels of safety in nighttime operations. The reasons for this include serious methodological weaknesses in current processes, especially the lack of a holistic view of the safety-critical components of the industry; biased and over-simplistic analysis of accidents; overreliance on reported incidents of doubtful statistical utility; ad hoc survey methods to elicit opinions of pilots rather than facts about hazards; and the complete absence of predictive analysis using hazard data. This thesis addresses these weaknesses by developing and implementing a new and comprehensive methodology consisting of a number of processes used in an integrated manner, with novel contributions in taxonomy development, data quality and qualitative and quantitative data analytics to enhance hazard identification and risk analysis of nighttime offshore helicopter operations. The thesis demonstrates that this new methodology is effective in describing the safety-critical components of the offshore helicopter industry, identifying systematic hazards patterns and trends from the statistical analysis of accident reports, establishing the appropriate use of incident reports for hazard identification and risk analysis and exploiting knowledge and facts elicited directly from surveys of pilots to discriminate accurately the riskiest phases of flight, identify an exhaustive and statistically representative range of hazards related to the riskiest of such phases and analyse the hazard data through quantitative predictive analysis. The methodology is easily transferable to other operations in the helicopter domain by institutions of international reach (e.g., the International Civil Aviation Organisation, ICAO) and individual helicopter operators.

Fusing knowledge and image sensor data for mission-critical control in unmanned aerial vehicles

Patterson, Timothy John January 2013 (has links)
Autonomous Unmanned Aerial Vehicles (UAVs) have the potential to significantly enhance current working practices for many applications including environmental monitoring, aerial surveillance and mountain search-and-rescue. Their ability to operate as an 'eye-in-the-sky', relaying real-time aerial imagery and other sensory data whilst removing humans 'from situations which may be considered dull dangerous or dirty ensures that the popularity and usage of such platforms will continue to increase. However, as with manned aircraft, the dependability and integrity of such platform may be influenced by the occurrence of endogenous and exogenous events ultimately resulting in safety-critical and , possibly, mission-critical situations. Such events will inevitably cause a range of errors and may ultimately result in the loss of human life, damage to property and the destruction of the UAV platform and its payload. With this in mind: the UK Civil Aviation Authority currently impose similar restrictions on small UAVs to those specified for model aircraft, thereby limiting their real-world usefulness. Before these restrictions can be relaxed and the potential of UAVs realised they must be able to demonstrate equivalent levels of safety to human pilots in safety-critical situations. As such, one objective is a forced landing scenario in which a UAV encounters an error and is required to locate and land in a Safe Landing Zone (SLZ). Within this thesis we present a programme of work aimed at researching and developing an autonomous method of UAV SLZ detection using colour aerial imagery and knowledge in the form of Ordnance Survey (OS) data. The key outputs of this thesis are as follows: 1) a method of position estimation which extends previous approaches by utilising OS data as opposed to geo-referenced aerial imagery 2) an autonomous method of SLZ detection which exploits colour aerial imagery and knowledge in the form of OS and training data 3) an approach which combines multi-resolution aerial images of the same scene with OS and training data to compute updated class parameters which are subsequently utilised to perform terrain classification 4) a method of UAV decision making within a time-constrained: safety-critical situation which is based upon constructing models of execution times. We evaluate the developed algorithms using representative aerial imagery which was captured during manned flight by piloted aircraft and present results demonstrating practicable potential in the proposed approaches.

Physical modelling of turbulent single- and multi-phase impinging jets using Particle Image Velocimetry (PIV)

McKendrick, Donna January 2015 (has links)
Two-component velocity vector maps of single- and multi-phase turbulent impinging jets were acquired using particle image velocimetry (PIV). Mean and turbulent characteristics were explored with the impingement surface located at three strategic positions; 2 (within the potential core), 6 (just outside the core) and 10 h/d (fully developed jet). Single-phase trials present the first extensive exploration of all three regions of an impinging jet. As jet height increased, the more advanced the jet expansion, and the centreline mean axial velocity decreased as the jet spread radially with increasing mean radial velocity. An increase in turbulence levels was seen from 2 to 6 h/d as the end of the potential core was exceeded where turbulence from the mixing layer penetrated to the centre, followed by a decrease at 10 h/d as the jet continued to grow before impingement. A liquid impinging jet laden with 69μm sized glass particles was explored, the particles were found to not follow the turbulent flow. Particle axial velocities were generally smaller than their single-phase counterparts. As the jet height increased the stagnation region broadened, similarly for the single-phase trials. The particles exhibited considerably lower turbulent velocities. The near-field radial wall jet saw the deflection and acceleration to a greater extent for the smallest jet height (2 h/d) than the larger two (6 and 10 h/d). Particle turbulence intensities in the near-field radial wall jet increased as the jet height increased. The particle turbulence was smaller than that of the single-phase, the greatest difference seen for the middle jet height of 6 h/d. A sensitivity study of particle size effect on a particle-laden turbulent impinging jet with jet-to-plate separation of six diameters has been completed, three particle sizes used; 20, 46 and 69μm. Within the impingement region, the particles do not decelerate as rapidly as the single-phase due to the particle inertia. Turbulent velocities of the particle phases were considerably lower than the single-phase, the turbulent velocity normal to the impingement surface larger than the radial component. And finally, a preliminary assessment of the feasibility of using fluorescent particle image velocimetry (fPIV) for the purpose of studying turbulence modulation in impinging liquid jets has been undertaken.

A computational study of helicopter coaxial rotor aerodynamics and performance

Kim, Hyo Won January 2009 (has links)
Recently, a resurgence of interest in the coaxial rotor helicopter configuration has been prompted by its potential to achieve higher thrusts and higher forward speeds than has traditionally been possible with conventional single-rotor platforms. Accurate prediction of the performance of such systems is extremely difficult because of the strong aerodynamic interaction between the upper and lower rotors. The Vorticity Transport Model (VTM) is a comprehensive rotorcraft analysis code based on the solution of the time dependent Navier-Stokes equation in vorticity-velo city form. The high resolution of the wake modelling technique used in the VTM makes it particularly well suited to capturing the complex pattern of interacting vortical structures within the wake of coaxial systems. This dissertation demonstrates that the VTM is able to capture accurately the highly interactive aerodynamic environment associated with coaxial rotor systems. The aerodynamic performance and acoustic characteristics of a coaxial rotor are contrasted with those of an equivalent single rotor. The coaxial rotor is shown to consume less induced power than the single rotor and the aerodynamic origin of the differences in the performance are highlighted. Increasing the flapwise stiffness of the coaxial system reduces its induced power consumption further. Additional savings in power can be achieved, particularly at high speeds, if the system is augmented in thrust using an auxiliary device. Aerodynamic interactions between the sub-components of a thrust- compounded helicopter with a rigid coaxial rotor are identified as the sources of acoustic focusing and unsteady loading on the aircraft. These results suggest that state-of- the-art numerical models such as the VTM may have developed to the point where they can lend useful insights into the detailed aerodynamic characteristics of modern, complex helicopter configurations.

A set-based approach to passenger aircraft family design

Riaz, Atif January 2015 (has links)
In today's highly competitive civil aviation market, aircraft manufacturers develop aircraft families in order to satisfy a wide range of requirements from multiple airlines, with reduced costs of ownership and shorter lead time. Traditional methods for designing passenger aircraft families employ a sequential, optimisation-based approach, where a single configuration and systems architecture is selected fairly early which is then iteratively analysed and modified until all the requirements are met. The problem with such an approach is the tendency of the optimisers to exploit assumptions already 'hard-wired' in the computational models. Subsequently the design is driven towards a solution which, while promising to the optimiser, may be infeasible due to the factors not considered by the models, e.g. integration and installation of promising novel technological solutions, which result in costly design rework later in the design process. Within this context, the aim is to develop a methodology for designing passenger aircraft families, which provides an environment for designers to interactively explore wider design space and foster innovation. To achieve this aim, a novel methodology for passenger aircraft family design is proposed where multiple aircraft family solutions are synthesised from the outset by integrating major components sets and systems architectures set. This is facilitated by integrating set theory principles and model-based design exploration methods. As more design knowledge is gained through analysis, the set of aircraft family solutions is gradually narrowed-down by discarding infeasible and inferior solutions. This is achieved through constraint analysis using iso-contours. The evaluation has been carried out through an application case-study (of a three-member passenger aircraft family design) which was executed with both the proposed methodology and the traditional approach for comparison. The proposed methodology and the case-study (along with the comparison results) were presented to a panel of industrial experts who were asked to comment on the merits and potential challenges of the proposed methodology. The conclusion is that the proposed methodology is expected to reduce the number of costly design changes, enabling designers to consider novel systems technologies and gain knowledge through interactive design space exploration. It was pointed out, however, that while the computational enablers behind the proposed approach are reaching a stage of maturity, allowing a multitude of concepts to be analysed rapidly and simultaneously, this still is expected to present a challenge from organisational process and resource point of view. It was agreed that by considering a set of aircraft family solutions, the proposed approach would enable the designers to delay critical decisions until more knowledge is available, which helps to mitigate risks associated with innovative systems architectures and technologies.

Automatic pipeline surveillance air-vehicle

Alqaan, Hani January 2016 (has links)
This thesis presents the developments of a vision-based system for aerial pipeline Right-of-Way surveillance using optical/Infrared sensors mounted on Unmanned Aerial Vehicles (UAV). The aim of research is to develop a highly automated, on-board system for detecting and following the pipelines; while simultaneously detecting any third-party interference. The proposed approach of using a UAV platform could potentially reduce the cost of monitoring and surveying pipelines when compared to manned aircraft. The main contributions of this thesis are the development of the image-analysis algorithms, the overall system architecture and validation of in hardware based on scaled down Test environment. To evaluate the performance of the system, the algorithms were coded using Python programming language. A small-scale test-rig of the pipeline structure, as well as expected third-party interference, was setup to simulate the operational environment and capture/record data for the algorithm testing and validation. The pipeline endpoints are identified by transforming the 16-bits depth data of the explored environment into 3D point clouds world coordinates. Then, using the Random Sample Consensus (RANSAC) approach, the foreground and background are separated based on the transformed 3D point cloud to extract the plane that corresponds to the ground. Simultaneously, the boundaries of the explored environment are detected based on the 16-bit depth data using a canny detector. Following that, these boundaries were filtered out, after being transformed into a 3D point cloud, based on the real height of the pipeline for fast and accurate measurements using a Euclidean distance of each boundary point, relative to the plane of the ground extracted previously. The filtered boundaries were used to detect the straight lines of the object boundary (Hough lines), once transformed into 16-bit depth data, using a Hough transform method. The pipeline is verified by estimating a centre line segment, using a 3D point cloud of each pair of the Hough line segments, (transformed into 3D). Then, the corresponding linearity of the pipeline points cloud is filtered within the width of the pipeline using Euclidean distance in the foreground point cloud. Then, the segment length of the detected centre line is enhanced to match the exact pipeline segment by extending it along the filtered point cloud of the pipeline. The third-party interference is detected based on four parameters, namely: foreground depth data; pipeline depth data; pipeline endpoints location in the 3D point cloud; and Right-of-Way distance. The techniques include detection, classification, and localization algorithms. Finally, a waypoints-based navigation system was implemented for the air- vehicle to fly over the course waypoints that were generated online by a heading angle demand to follow the pipeline structure in real-time based on the online identification of the pipeline endpoints relative to a camera frame.

Application of improved Lagrangian techniques for helicopter crashworthiness on water

Hughes, Kevin January 2005 (has links)
This thesis concerns the crashworthiness of helicopters onto water and presents a comparison between test and simulation for the impact of a typical helicopter sub floor section onto both hard and water surfaces. The experimental campaign was extended to incorporate a fully instrumented WG30 helicopter drop test onto water, which allowed a comprehensive assessment of the predictive capabilities of the non-linear code LS- DYNA3D to be performed. Validation data was supplied from specific drop tests, which permitted a complete frarne-by-frame analysis to be performed and compared both quantitively and qualitatively with the numerical results. The conclusions from this work enabled a assessment of the validity of the component and full-scale simulations with respect to one another, together with the design changes that could potentially improve the level of crashworthiness currently offered with the current design. Modelling the compressive behaviour of a fluid using a Lagrangian approach is difficult, due to the inherent mesh problems associated with large definitions. Sensitivity studies were performed, which led to the development of a tuned water model that was capable of recreating the impact of various rigid shapes onto water. Alternative techniques to water modelling are also presented in a attempt to minimise the stability problems that arise between fluid and structure boundary, where the definite elements attempt to form a splash. To complete this review of the capabilities of the code, a assessment with respect to capturing joint failure was also performed, through comparison with joint coupon tests. As no methodology concerning the simulation of fluid-structure interaction problems exists within the literature, this thesis addresses this issue by discussing the contributions made to the SAFESA approach (SAFE Structural Analysis), in identifying potential sources of error that are relevant when performing these types of analysis. A discussion of the sources of idealisation, procedural and formulation errors will be performed, along with techniques and recommended practices that have been developed to minimise their affects. The methodology has been extensively tested to be a robust and reliable approach that will greatly assist engineers working in this field. The culmination of this research is the application of the validated simulation tools in developing a potential solution for improving the water crashworthiness response. The concept of maximising skin defection through the purposeful collapse of the interconnecting frames is presented. This would allow the skin to form a continuous curve, as opposed to several inter frame defections. The numerical results verify that this hypothesis could be of benefit in reducing the magnitudes of the accelerations and raises the question of whether next generation designs should concentrate on developing energy absorbing characteristics for each individual cell, or whether a coupled, multiple cell configuration is more preferable.

Investigating drivers of phytoplankton blooms in the North Atlantic Ocean using high-resolution in situ glider data

Rumyantseva, Anna Sergeevna January 2016 (has links)
Autonomous buoyancy-driven underwater gliders represent a powerful tool for studying marine phytoplankton dynamics due to their ability to obtain frequent depth-resolved profiles of bio-optical and physical properties over inter-seasonal time scales, even under challenging weather conditions and low light. This thesis is based on a unique year-long deployment of pairs of gliders at the Porcupine Abyssal Plain Sustained Observatory located in the Northeast Atlantic Ocean, complemented by remotely sensed chlorophyll and photosynthetically active radiation (Aqua MODIS products), surface net heat (NCEP/NOAA reanalysis), surface wind stress (ASCAT products) and in situ measurements of nutrients, chlorophyll, microscale turbulence and meteorological parameters. The data were used to study drivers of autumn and spring phytoplankton blooms. In the beginning of the deployment, the gliders captured the upper ocean dynamics during an autumnal storm. The onset of an autumn phytoplankton bloom due to nutrient intrusion was detected. Additional data collected during a simultaneous sampling campaign allowed quantification of the nutrient supply by two physical mechanisms associated with a storm event: entrainment of nutrients during a period of high wind forcing and subsequent shear-spiking at the pycnocline due to interactions of storm generated inertial currents with wind. The importance of the two mechanisms is discussed, and I conclude that storms play an important role in fuelling ocean primary production during periods of nutrient depletion. The glider data from winter and spring captured the onset and development of the phytoplankton spring bloom. Mechanisms controlling the bloom onset were studied in light of the main competing hypotheses: the critical depth, the critical turbulence, and the dilution-recoupling hypotheses. The bloom onset was consistent with the critical depth hypothesis, if the decoupling between the actively mixing layer and the mixed layer is considered. However, the observed bloom developed slowly and was relatively low in magnitude. The frequent passage of storms and periods of convective mixing can significantly decrease mean growth rate for phytoplankton populations affecting the rate of bloom development. Finally, the impact of biotic factors, such as zooplankton grazing, on spring bloom dynamics is discussed. In order to address potential zooplankton variability that underlies the observations, the glider data was coupled with a simple phytoplankton-zooplankton model. The model was forced with the phytoplankton growth rate evaluated based on the observational data. It is shown that gradual phytoplankton growth in winter results in tight coupling between phytoplankton and zooplankton that can hamper the formation of high-magnitude spring blooms in the North Atlantic Ocean.

Cold expansion of large holes in thick 7010 light alloy aircraft material : strains in the time domain

O'Brien, Edwin William January 1997 (has links)
No description available.

Fly-away tooling : the kinematics of planar assembly

O'Reilly, Nicholas January 2001 (has links)
No description available.

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