• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 215
  • 17
  • 17
  • 8
  • 3
  • 3
  • 3
  • 2
  • 2
  • 2
  • 2
  • 2
  • 2
  • 2
  • 1
  • Tagged with
  • 912
  • 912
  • 619
  • 612
  • 611
  • 217
  • 141
  • 118
  • 114
  • 59
  • 54
  • 48
  • 47
  • 45
  • 45
  • 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.
41

An assessment of the contribution of micro-scale activities to personal pollution exposure in commuting micro-environments : a thesis submitted in partial fulfilment of the requirements for the degree of Masters [i.e. Master] of Science in Geography at the University of Canterbury /

Shrestha, Kreepa. January 2009 (has links)
Thesis (M. Sc.)--University of Canterbury, 2009. / Typescript (photocopy). Includes bibliographical references (p. [192-210]).
42

Advanced modelling of helicopter nonlinear dynamics and aerodynamics

Castillo-Rivera, Salvador January 2014 (has links)
The work presented here provides a comprehensive dynamic and aerodynamic helicopter model. The possible applications of this work are wide including, control systems applications, reference and trajectory tracking methods implementation amongst others. The model configuration corresponds to a Sikorsky helicopter; a main rotor in perpendicular combination with a tail rotor. Also, a particular model of unmanned aerial vehicle has been modelled as part of collaboration with the La Laguna University (Spain). The modelling tool is VehicleSim, a program that builds rigid body systems, solves the nonlinear equations of motion and generates the time histories of the corresponding state variables of the vehicle under study. VehicleSim is able to provide the linearised equations of motion in a Matlab file and the symbolic state-space model. This is useful when control systems are to be designed. The main rotor model accounts for flap, lag and feather motions for each blade as well as for their nonlinear dynamic coupling. The tail rotor is modelled including the flap-feather coupling via delta three angle. The main and tail rotors' angular velocities are implemented by PID controllers. Main rotor linear and nonlinear equations are derived and validated by comparison with the theory. Main rotor flap and lag degrees of freedom are validated using frequency domain approaches in the absence of external forces. Also, fuselage-main rotor interaction is studied and validated by using modal analysis and root locus methodology. Vibrations originated at the main rotor are simulated and their effects on the fuselage are examined by a Short Time Fourier transformation. The aerodynamic model uses blade element theory on the main-tail rotors. Hover, climb, descent and forward flight conditions are simulated and they allow the helicopter to follow certain trajectories. Finally, the ensuing vibrations when an external perturbation is applied to the main rotor are investigated.
43

Dynamic analysis of alternative suspension systems for sport motorcycles

Ramirez, Ciro Moreno January 2015 (has links)
In this thesis, VehicleSim multi-body software is used to extend and modify an existing motorcycle model by including different non-conventional suspension systems. Girder and Hossack double wishbones front suspension systems are designed, implemented and tested. Using a synthesis of mechanism methodology, they are designed with different kinematic configurations that allow different behaviours of the motorcycle front end. By means of CAD tools and finite element analysis, realistic three dimensional models of the suspension systems designs are developed. The dynamical properties of the mechanical assemblies are obtained from the CAD models and used to build a realistic mathematical model of a sport motorcycle fitted with theses alternative suspension systems. Dynamical and stability analyses of the alternative front suspension systems are performed. For the different kinematic configurations, anti-dive properties and variation of the motorcycle's handling geometric parameters are studied by non-linear dynamical simulations. Stability analyses are performed by means of the motorcycle linear models eigenvalues. Passive interconnection of front and rear suspension systems of a sport motorcycle is also investigated. The effects of an interconnected suspensions system on the motorcycle in-plane motions are studied by means of reduced order linear models. The baseline model is modified to include passive interconnection forces between the front and rear suspension systems. The possible improvement introduced by an interconnected suspensions system in terms of suspension accuracy is investigated through non-linear simulations with delayed step tyres inputs. Appropriate values of the interconnection passive components for different possible mechanical implementation are found by means of optimization processes. Linear stability analyses are performed for each of the different optimal interconnected configurations. Nonlinear frequency analyses of the motorcycle wheels and chassis responses are also performed considering the delay between the front and rear tyre inputs. Non-linear simulations with variable frequency sinusoidal road inputs are run for this purpose. Finally, modal analyses of the motorcycle model are carried out for variable interconnection parameters in order to understand the effect of the interconnected suspensions system on the motorcycle's motion.
44

Design of in-vehicle networked control system architectures through the use of new design to cost and weight processes : innovation report

Quigley, Christopher Patrick January 2011 (has links)
Over the last forty years, the use of electronic controls within the automotive industry has grown considerably. In-vehicle network technologies such as the Controller Area Network (CAN) and Local Interconnect Network (LIN) are used to connect Electronic Control Units (ECU) together, mainly to reduce the amount of wiring that would be required if hardwired integration were used. Modern passenger cars contain many networks, which means that for the architecture designer, there is an almost overwhelming number of choices on how to design/partition the system depending on factors such as cost, weight, availability of ECUs, safety, Electro-Magnetic Compatibility (EMC) etc. Despite the increasing role played by in-vehicle networks in automotive electrical architectures, its design could currently be described as a “black art”. Not only is there an almost overwhelming number of choices facing the designer, but there is currently a lack of a quantifiable process to aid decision making and there is a dearth of published literature available. NetGen is a software tool used to design CAN/J1939, LIN and FlexRay networks. For the product to remain competitive, it is desirable to have novel features over the competition. This report describes a body of work, the aim of which was to research in-vehicle network design processes, and to provide an improvement to such processes. The opportunities of customer projects and availability of customer information resulted in the scope of the research focusing on the adoption of LIN technology and whether the adoption of it could reduce the cost and weight of the target architecture. The research can therefore be seen to address two issues: firstly the general problem of network designers needing to design in-vehicle network based architectures balancing the needs of many design targets such as cost, weight etc, and secondly the commercial motivation to find novel features for the design tool, NetGen. The outcome of the research described in this report was the development of design processes that can be used for the selection of low cost and weight automotive electrical architectures using coarse information, such as that which would be easily available at the very beginning of a vehicle design programme. The key benefit of this is that a number of candidate networked architectures can be easily assessed for their ability to reduce cost and weight of the electrical architecture.
45

A vehicle-to-home simulation tool for the analysis of novel energy storage applications : innovation report

Haines, Gareth January 2013 (has links)
Vehicle-to-grid uses vehicles with on-board electricity storage as an energy storage system for the electricity grid. Vehicles not only take power from the grid when charging, but can supply power back to the grid. This storage mechanism can then be used in various applications, for example, providing balancing services and helping the introduction of renewable energy sources. Research into vehicle-to-grid suggests that it is feasible in certain applications. Indeed, the component technology required for vehicle-to-grid has been successfully demonstrated. Gaps in the analysis of vehicle-to-grid feasibility remain. Notably, the behaviour of individuals in a vehicle-to-home context is not well understood. A vehicle-to-home simulation tool was developed to address these gaps. The tool incorporates a use case methodology and a Matlab Simulink model. Application of the use case methodology identifies the inputs and constraints determined by users in a vehicle-to-home system. Feeding these inputs into the model facilitates the sensitivity analysis of vehicle-to-home operation to these user dependent variables. The use of the simulation tool is demonstrated in two case studies: Using an electric vehicle as back-up power supply; and using an electric vehicle to support small-scale distributed generation. The operation of a vehicle-to-home system in these case studies is presented, along with the sensitivity of operation to input parameters including: battery storage capacity, vehicle usage and vehicle charging. Both case studies demonstrated that, given the correct conditions|notably cooperation of the vehicle user|vehicle-to-home can operate successfully in storage applications. It was shown that an electric vehicle could provide back-up storage to households for a useful amount of time|between 20 hours and several days. It was shown that an electric vehicle can be used to store energy from a small-scale wind turbine such that the generation is better utilised than if no storage is available. The developed simulation tool enables analysis of novel vehicle-to-home applications not possible with previous models of vehicle-to-grid. The use of the tool highlighted the importance of including individual variation in behaviour when studying vehicle-to-home systems.
46

Advancing the development of hybrid electric vehicles in motorsport : innovation report

Lambert, Stephen January 2013 (has links)
Club motorsport, a low cost, amateur form of motorsport, forms a significant part of the motorsport industry in the United Kingdom. If efforts are not made to move towards more environmentally friendly technologies, then this form of motorsport is at risk of becoming irrelevant. One approach taken by other motorsport sectors has been to implement hybrid electric vehicle technology, which can result in improved vehicle performance on the race track. However, the companies that operate in the club motorsport sector do not typically have the resources and experience necessary to develop these technologies. An innovative process was used to guide the design of a new hybrid electric vehicle drivetrain for use in club motorsport. This process made use of the ability for vehicle manufacturers to set the vehicle specifications in club motorsport. A conjoint analysis of customer requirements was carried out, a first for the industry, and led to the development of a market simulation tool. A vehicle simulation tool was then developed to assist in the evaluation of the hybrid electric drivetrain design options. The result of following this process was a new and innovative hybrid electric drivetrain installed in a Westfield Sportscars Sport Turbo, reducing 0-60mph acceleration time from 5.4 seconds to 3.8 seconds. An innovative type of system control was implemented, by where the driver is given a finite amount of boost energy for use throughout the race. The drivetrain can also be easily transferred to other vehicle platforms, as the first shelf engineered hybrid drivetrain for motorsport, allowing its use by multiple manufacturers across the club motorsport and niche vehicle sectors. This project has shown that it is possible to implement environmentally friendly technologies, such as hybrid electric vehicle technology, into club motorsport and be able to meet customer, technical and cost requirements. The process that has been developed enables innovation in hybrid electric race car design. This has been shown in the development of a hybrid electric vehicle suitable for use, and sale, in the club motorsport industry.
47

Investigation of the performance of a slotted aerofoil at low Reynolds numbers

Obiga, Otuami January 2018 (has links)
Slotted aerofoils have been suggested by numerous researchers as an effective means of controlling boundary layer flow separation, and improving aerodynamic performance. Numerous slot designs have been studied at high Reynolds number, but there is scarcity of study of such slots effect on aerofoil performance in low Reynolds number scenarios. In the present work, wind tunnel and numerical investigation of the effect of a unique slot configuration and its geometric parameters on the aerodynamic performance of a NACA0018 aerofoil at low Reynolds number was executed. The aim of this work is to ascertain if the unique slot configuration on the NACA0018 can improve the aerodynamic performance compared to a plain NACA0018, and if the slotted NACA0018 could be applied as rotors on a Darrieus-style vertical axis micro wind turbine for small scale energy conversion at low wind speeds. Four aerofoils were initially fabricated for the wind tunnel tests, each conforming to the NACA0018 profile; a plain aerofoil and three other slotted aerofoils, each with a span–length slot positioned at X=15%, X=45% and X=70% from the leading edge. The, chord length (c), span, slot slope (ψ) and slot width of the slotted aerofoils were 0.25m, 0.3m, 55° and 0.02c respectively. A 2D wind tunnel set up was used in testing the four aerofoils at Reynolds numbers of 92x103 138x103, 184x103 and 230x103, within 0° to 20° range of incidence. Comparing the slotted and plain aerofoils, the aerodynamic force data shows that the presence of the slots was detrimental to aerodynamic performance especially when the slot location is closer to the leading edge. Therefore, a 2D numerical parametric study of slot width and slope was carried out using ANSYS FLUENT 16.0 with the intention of improving the lift–to–drag (L/D) ratio of the span–length slotted aerofoils. Furthermore, a final slot configuration consisting of segmented slot pattern which incorporated the results of the parametric study was fabricated and tested in a wind tunnel. The aerodynamic force analysis shows a 50% increase in L/D ratio of the slotted aerofoil with slot position at X=70%, but its aerodynamic performance was still less than the Plain NACA0018. Thus this work proves that the suggested slot layout did not improve the aerodynamic performance of the NACA0018 aerofoil and as a result, it cannot be recommended to be used as a vertical axis wind turbine rotor. Finally, in order to improve the NACA0018 aerofoil performance, it was suggested that a new slot layout with slot slope on the pressure side inclined towards the leading edge should be designed and studied.
48

Improved autogyro flying qualities using automatic control methods

Ahmad Shah, Shahrul January 2018 (has links)
An autogyro or Autogiro is a unique type of rotary-wing aircraft that was successfully flown in the 1920s, many years before the first helicopter came to service. As far as the rotorcraft technology is concerned, the technical issues addressed by autogyros were eventually rectified and paved the way for the success of helicopter development. When helicopter became more popular and accepted in the civil aviation industry in the 1940s, autogyros were nearly forgotten and the popularity slowly diminished. The re-emergence of autogyros in the last two decades in hobby and sports flight activities, however, coincides with bad safety records due to stability issues. At the time of this writing, there are no specific flying qualities standards to be em- ployed as guidelines to design a light autogyro with good stability attributes. The only requirements available are addressed in the BCAR Section T airworthiness standard for light autogyros which only prescribes some basic dynamic stability requirements for the vehicle. For existing conventional light autogyros which mostly of 'home-built' type, complying with the airworthiness standards would be an issue as most of them were built beforehand. From these concerns, this Thesis aims to improve the flying qualities performance of existing light autogyros through automatic flight control methods, as one of the ways to practically achieve the required performance. Consequently, specific flying qualities requirements for light autogyros must first be proposed as preliminary guidelines for design and flying qualities improvement. A generic mathematical model of light autogyros named ARDiS is developed based on the 'multiblade' simulation ap- proach which is computationally cost-effective. This model was successfully validated against real autogyro flight data and later implemented in the control enhancement of the vehicle. The control enhancement was developed using classical approaches with limitation in size and simplicity of the vehicle as a light aircraft. Proper actuation control hard- ware was separately modelled and deployed into the autogyro to demonstrate a higher dynamics in the control mechanism so that a more realistic attitude behaviour of the vehicle is presented. This control enhancement was successfully evaluated with both, linear and nonlinear simulations according to the proposed autogyro flying qualities attributes. All presented results signify a higher possibility of improving the flying qualities of currently used and future built light autogyros through control enhance- ment.
49

Assessment of the accuracy and the contribution of multi-GNSS in structural monitoring

Msaewe, Hussein Alwan Mahdi January 2018 (has links)
Structural health monitoring requires precise techniques with high accuracy, due to the relatively small deformations that can be found in many structures. It has been proved that GPS is capable of detecting the characteristics of the response of flexible structures. Although GPS can be applied for displacement monitoring, some existing constraints may limit the accuracy of the monitoring application. Some sources of these limitations are the multipath error, random noise, cycle slips and the geometry of the satellite constellation. Studies have been conducted to overcome these limitations using a combination of the GPS and other sensors: geodetic (e.g. Robotic Total Stations) or non-geodetic (e.g. accelerometer). Although these studies succeeded generally to reduce the effects of these limitations, they are still restricted on specific cases of monitoring, due to difficulties of using the accelerometer for monitoring static or quasi-static displacements and RTS due its limited range. The introduction of the Global Navigation Satellite Systems (GNSSs), apart from GPS, such as GLONASS, BeiDou, and Galileo provides an alternative solution by combined GPS data with additional observations from other GNSS constellations to overcome GPS-only limitations. Therefore, the current study aims to develop a multi-GNSS method for structural health monitoring. The integration of different constellations contributes to improving the accuracy and availability of the solution, which allows the structural response and its characteristics effectively. The positioning performance in this study is investigated and achieved in three conducted stages: Firstly, a series of GNSS zero baseline measurements are conducted simultaneously for 12 consecutive days in the UK and China sites to investigate the noise level of different GNSS solutions. The main aim is to investigate the correlation between the geometry of satellite constellation and the performance of the GPS-only and multi-GNSS solution. It is proved that for periods of a poor GPS-only solution, due to the satellite constellation or problematic satellites, the multi-GNSS solution leads to more accurate and of higher availability solution. Secondly, short baselines of GNSS measurements of static (1 Hz) and kinematic (10 Hz and 20 Hz) observations are collected to evaluate the precision and accuracy of different GNSS solutions. Following the same analysis approach and using the 3D best fitting of non-linear least squares adjustment models, it is proved that the multi-GNSS solution is significantly improved in comparison with the GPS-only solution for periods of weak geometry or problematic satellites. This can be attributed to the geometry improvement of the combined solution, which can reach 30% for GDOP values. Finally, the GNSS measurements are investigated at the Severn Bridge and the Forth Road Bridge in the UK for real structural monitoring of long-span suspension bridges. The analysis was based on an assessment of workflow methodology applied in this study. The noise level of GNSS data was assessed by zero baseline at the base station of the Severn Bridge. It was approved that the combined GPS/GLONASS solution reduced the noise level and led to more accurate results with less discontinuous time intervals. Regarding the spectral analysis, the GPS-only solution led to a higher noise level of the spectrum and less easy to be detected peaks for some intervals relatively to the spectra of the multi-GNSS solution. It was inferred from the results presented in the current study that the noise errors and discontinuity problems, as well as other limitations of the GPS-only solution, were significantly reduced and improved by combined GNSS solution. These findings are promising for many real structural monitoring applications.
50

An adaptive data filtering model for remaining useful life estimation

Bektas, Oguz January 2018 (has links)
The field of Prognostics and Health Management is becoming ever more important in the modern maintenance era, with advanced techniques of automation and mechanisation becoming increasingly prevalent. Prognostic technology has promising abilities to forecast remaining useful life and likely future circumstances of complex systems. However, the evolution of data processing and its critical impact on remaining useful life predictions continually demand increasing development so as to meet higher performance levels. There is often a gap between the adequacy of prognostic pre-processing and the prediction methods. One way to reduce this gap would be to design an adaptive data processing method that can filter multidimensional condition monitoring data by incorporating useful information from multiple data sources. Due to the incomplete understanding on the multi-dimensional failure mechanisms and the collaboration between data sources, current prognostic methods lack the ability to deal effectively with complicated interdependency, multidimensional condition monitoring information and noisy data. Further conventional methods are unable to deal with these efficiently. The methodology proposed in this research handles these deficiencies by introducing a prognostic framework that allows the effective use of monitoring data from different resources to predict the lifetime of systems. The methodology presents a feed-forward neural network filtering approach for trajectory similarity based remaining useful life predictions. The extraction of health indicators is applied as a type of dynamic filtering, in which the time series having full operational conditions are used to train a neural network mapping between raw training inputs and a health indicator output. This trained network function is evaluated by repeating condition monitoring information from multiple data subsets. After the network filtering, the training trajectories are used as baselines to predict the future behaviours of test trajectories. The similarity between these data subsets compares the relationship between the historical performance deterioration of a system's prior operating period with a similar system's degradation behaviour. The proposed prognostic technique, together with dynamic data filtering and remaining useful estimation, holds the promise of increased prediction performance levels. The presented methodology was tested using the PHM08 data challenge provided by the Prognostics Centre of Excellence at NASA Ames Research Centre, and it achieved the overall leading score in the published literature.

Page generated in 0.0489 seconds