This thesis presents the study of transonic cavity flows using CFD. The main focus of the thesis is on the turbulence modelling and simulation of cavity flows. The thesis aims to show the range of applicability of turbulence modelling for cavity flows. Aspects of cavity flow control are also addressed. The cavity models a weapons bay with a length-to-depth (L/D) ratio of 5 and length-to-width (L/W) ratio of 1. The flow is set to transonic speeds (M=0.85) and the Reynolds number based on the cavity length is in the turbulent regime (Re=6.783 million). At these flow conditions, very high noise levels are encountered inside the cavity combined with intense acoustic and turbulent interactions. Unsteady Reynolds-Averaged Navier-Stokes (URANS) was initially applied and the effectiveness of various two-equation turbulence models such as the Wilcox k - ω and the Menter's Baseline k - ω and SST turbulence models was assessed. Computations were first performed with the 2D clean cavity to minimise the computational cost, where the 2D cavity was a reasonable representation of the full 3D cavity with doors-on. Results demonstrated that linear statistical turbulence models generally gave reasonable qualitative predictions of the cavity flow-field but on coarse grids only. The amplitudes of the noise levels and frequencies were however less well predicted and the level of agreement deteriorated with grid refinement for the L/D=5 cavity. Nonetheless, out of the models employed, the SST model proved to be the most robust and provided the best agreement with experimental pressure and PIV measurements. The velocity distributions and the turbulent and acoustic spectra at the cavity floor were also analysed and compared with experiments (where possible) and in doing so the influence of turbulent processes in the cavity highlighted. With the higher acoustic frequencies and the broadband noise less well predicted with linear statistical two-equation turbulence models, attention was diverted towards simulation methods such as Large-Eddy Simulation (LES) and Detached-Eddy Simulation (DES). Numerical results for the 3D L/D=5 cavity with a width-to-depth ratio (W/D) of 1 in both doors-on and doors-off configurations were compared with experiments. Even for coarse grid simulations, better agreement was found between the LES/DES results and experimental pressure and PIV measurements for various grid levels and time-steps than URANS.

As roads become busier and automotive technology improves, there is considerable potential for driver assistance systems to improve the safety of road users. Longitudinal collision warning and collision avoidance systems are starting to appear on production cars to assist drivers when required to stop in an emergency. Many luxury cars are also equipped with stability augmentation systems that prevent the car from spinning out of control during aggressive lateral manoeuvres. Combining these concepts, there is a natural progression to systems that could assist in aiding or performing lateral collision avoidance manoeuvres. A successful automatic lateral collision avoidance system would require convergent development of many fields of technology, from sensors and instrumentation to aid environmental awareness through to improvements in driver vehicle interfaces so that a degree of control can be smoothly and safely transferred between the driver and vehicle computer. A fundamental requirement of any collision avoidance system is determination of a feasible path that avoids obstacles and a means of causing the vehicle to follow that trajectory. This research focuses on feasible trajectory generation and development of an automatic obstacle avoidance controller that integrates steering and braking action. A controller is developed to cause a specially modified car (a Mercedes `S' class with steer-by-wire and brake-by-wire capability) to perform an ISO 3888-2 emergency obstacle avoidance manoeuvre. A nonlinear two-track vehicle model is developed and used to derive optimal controller parameters using a series of simulations. Feedforward and feedback control is used to track a feasible reference trajectory. The feedforward control loops use inverse models of the vehicle dynamics. The feedback control loops are implemented as linear proportional controllers with a force allocation matrix used to apportion braking effort between redundant actuators. Two trajectory generation routines are developed: a geometric method, for steering a vehicle at its physical limits; and an optimal method, which integrates steering and braking action to make full use of available traction. The optimal trajectory is obtained using a multi-stage convex optimisation procedure. The overall controller performance is validated by simulation using a complex proprietary model of the vehicle that is reported to have been validated and calibrated against experimental data over several years of use in an industrial environment.

published_or_final_version / Transport Policy and Planning / Master / Master of Arts in Transport Policy and Planning

No description available.

Congestion severely affects air traffic in the US and Europe. To protect air traffic controllers from overloads a planning activity, Air Traffic Flow Management (ATFM), emerged during the 1970s. ATFM control actions range from departure delays to the re-routing of flights. This research explores how models can be used to support decision-making in European ATFM. To date, most research into this subject has been directed at ATFM in the US, which differs from European ATFM both in terms of decision-making and time scales. Fieldwork was carried out at the EUROCONTROL Central Flow Management Unit, the organisation that manages traffic flows in most of the European airspace. The fieldwork was an OR intervention aimed at identifying suitable decision support models for re-routing flights. The research described here contributes by: 1) describing the European ATFM field and identifying decision support needs; 2) structuring the problems involved in re-routing flights in Europe; 3) providing a framework for the development of re-routing decision support systems (DSS) and 4) assessing the usefulness of optimisation approaches to re-routing flights. A demonstrator is developed to illustrate different re-routing decision support possibilities to the users. This leads to conclusions on the feasibility of various decision support functions including an identification of models and algorithms which can be used for each of the functions. Conclusions on levels of automation and complexity for re-routing DSS are also taken. Three integer models for re-routing flows are presented. They differ in the way congestion is represented. The models are tested on data of traffic crossing the whole French upper airspace. The test reveals that the models can be of use in re-routing flows and can provide significant savings in delays. It also shows that an 'intelligent' component to define the scope of the optimisation problem and a component to process all the data for the models, are needed in a re-routing DSS. The models are compared in terms of impact on congestion, size and execution time and conclusions on their feasibility taken. Extensions to the models are suggested.

MEMS actuators and their effect on boundary layers is investigated using numerical simulation. The thesis is specifically focussed on jet actuators and their application to the targeted control of turbulent boundary layers. A complete numerical model of jet-type actuators, including the popular synthetic-jet actuator, is developed. The assumed input is the voltage signal to the piezocermic driver and the calculated output is the exit jet velocity. Thorough validation of the numerical code is presented and simulations performed to highlight the key issues in MEMS-actuator design. The three-dimensional boundary-layer disturbance created by the MEMS actuator is modelled using a velocity-vorticity formulation of the Navier-Stokes equations. The parallel code is rigorously validated against results from linear stability theory and transitional-streak measurements. The boundary-layer code is used to determine a performance criterion for MEMS jets; it is shown that the net mass flow from a jet best determines its effectiveness. The code is also used to demonstrate the macro-scale capabilities of MEMS-scale actuators; a grid-scaling method is described and employed to facilitate this calculation. A method is presented that enables high- and low-speed streaks to be modelled economically in otherwise undisturbed mean flows. Using this model, the fundamental principles of targeted control using MEMS actuation are explored. The MEMS-actuator and boundary-layer models are coupled, and an investigation into the interactive effects of the two systems is described. Using the coupled code, disturbances in the boundary layer are shown to induce velocities in inactive devices. One special case occurs when an oscillating pressure field creates Helmhotz resonance within the cavity of a MEMS actuator, thus causing large mass flow rates in and out of the device. It is also suggested that the MEMS device could strongly interact with the random fluctuations of a turbulent boundary layer, leading to highly unpredictable actuator responses.

The development of modern sailing boats has been based almost entirely on the cooperative efforts of enthusiastic skippers, designers and sail-makers, with very little contribution from scientists and technologists and using just basic scientific principles. In recent times, urgent and strong requests for improved performance, mostly for racing yachts, have guided the interest and the attention of the scientific community in the optimisation of sail performance and design approach. Sailing performance depends on the sailboat velocity, aerodynamic and hydrodynamic characteristics. This thesis focuses on the importance of the quantitative evaluation of the sail loads and how this contributes to the improvement of the performance of a sailboat through the development of a system for aiding sail design and assisting mast design. The objective of this study is to provide an integrated design system, which supplies analysis method and design features via a user-friendly graphical interface of a single-sail configuration. The major achievement is the development of an integrating numerical method, which evaluates loads and their distribution and the consequent deformed sail-shape. It improves sail performance analyses and design of new sails. Summarising, the major achievements are: • efficacy of accurate performance analysis for each sail, for any given shape over all the possible sailing courses; • critical investigation of the sail behaviour in the above-mentioned cases; improved approach to an integrated sail design; improvements in mast design from the structural and aerodynamic point of view; limited design costs, in terms of time consumed and computational power employed; efficacy of the visualisation of novel designed sail and predicted performance, which reduces the number of possible design flaws. hi conclusion, the integrated sail analysis and design system presented has important margins of improvements and diversification: extensions to non-homogeneous and anisotropic sailcloth, to two-sail configuration, windsurfs and integration of the mast.

A description of the experimental investigation of the aerodynamic characteristics of variable geometry of an aircraft model is presented. Aerodynamically, the model is tested-for a sweep range of 0°,12.5° 32.5°, and 52.5° and incidence range of 0° to 200° in 4° intervals. All the pressure distributions on the wing, glove, and body are recorded for each wind tunnel test. Aerodynamic forces and moments were also taken through a balance mechanism system which is attached to the model. This is connected to an independent computer terminal and a Teletype printer. Initially, a flow visualization to test the flow separation on the wing model was carried out. A three-dimensional subsonic program, which was already developed by Hawker Siddeley Aviation Limited, was modified for our purposes in order to carry out numerical calculation of the aerodynamic characteristics and investigate the interference of wing and body. This programme has also been developed to include the compressibility effects and compare these results with those for incompressible flow. The three-dimensional numerical solution was a Panel method for the subsonic case. This investigates the three-dimensional flow-field using a distribution of quadrilateral vortex panels, the effects of which are summed to calculate the aerodynamic characteristics of the model. This subsonic theory was applied to calculate the characteristics of the wind tunnel model over a similar range of sweep and incidence to those tested, for Mach numbers of 0 and 0.5. As the only input data required is the configuration geometry and the flight condition, however, the program can be used to calculate the aerodynamics of any wing-body arrangement specified by the user. The program includes the capability of analysing both fixed-wing and variable sweep-wing configurations. This computational method is capable of being applied to general arbitrary subsonic three-dimensional potential flows, including inlet flow fields. In panel methods, the velocity potential at any point in a flow field is expressed in terms of the induced effects of source and doublet (or vortex) sheet distributed on the boundary surfaces. The configuration surfaces are divided into panels, and essentially, this is a general three-dimensional boundary value problem solver that is capable of being applied to most problems that can be modelled within the limitations of potential flow. Compressibility effects are approximated by the Göthert rule. Comparisons were made between the subsonic calculations and the experimental results and some other theoretical results. Hence, an indication of agreement and accuracy among them is seen, which is good up to a certain degree of incidence (about 10°). Owing to viscous effects, the experimental results for lift coefficient show a significant decline in size with respect to subsonic calculated results. Wing-body interference was calculated for subsonic flows and found to be favourable. Similarly, a general supersonic program was developed for numerical analysis of the aerodynamic characteristics of a thin wing. The theory was extended to include wing-body interferences. This extended treatment consists of slender body theory combined with a thin wing solution using a "characteristic box" method for supersonic analysis. Streamwise pressure-distributions on an aircraft wing are presented, and also-some aerodynamic force and moment coefficients of this wing are-presented. Finally, for wing body interaction analysis, the Nielsen method was used. All the relevant computations including centre of pressure position and interferences of wing and body for a combined model are presented. Comparisons of the supersonic results with some theoretical and experimental results shows good agreement. The interference calculations in this case showed favourable effects, which very broadly tend to be lower than those calculated for subsonic flow.

In autonomous navigation of mobile robots the dynamic environment is a source of problems. Because it is not possible to model all the possible conditions, the key point in the robot control is to design a system that is adaptable to different conditions and robust in dynamic environments. This study presents a reactive control system for a Khepera robot with the ability to navigate in a dynamic environment for reaching goal objects. The main motivation of this research is to design a robot control, which is robust to sensor errors and sudden changes and adaptable to different environments and conditions. Behavior based approach is used with taking the advantage of fuzzy reasoning in design. Experiments are made on Webots, which is a simulation environment for Khepera robot.

CD-ROM containing source codes of the numerical scheme (appendix A) is attached to back cover. / Includes bibliographical references (leaves 459-472). / System requirements for accompanying CD-ROM: Macintosh or IBM compatible computer. Other requirements: Adobe Acrobat Reader. / xxxvi, 473 leaves ; ill. ; 30 cm. + 1 computer optical disk (4 3/4 in.) / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / A numerical scheme, based on discrete-vortex and surface-vorticity boundary-integral methods, has been developed for stimulating time dependent, two-dimensional, viscous flow over arbitary arrays of solid bodies of arbitary cross-section / Thesis (Ph.D.)--Adelaide University, Dept. of Mechanical Engineering, 2001