Paul Meehan

Control of Chaotic Flutter in a Wind Turbine Airfoil

The primary aim of this project is to develop and verify a method of control of the occurrence of chaotic flutter in a wind turbine blade section to provide more efficient insight into its occurrence and avoidance in wind energy farms.

Investigation of the problem of rail corrugation

A widespread and apparently increasing phenomenon which has persisted in the railway industry for more than a century is the problem of rail corrugation. Rail corrugation is characterised by the formation of periodic light and dark bands along the tracks and is highly undesirable as it induces severe vibrations in the bogie. Much research has been performed in this area over the past decade however a cure remains elusive. The phenomenon involves the interaction between the dynamics of the vehicle (bogie), the contact mechanics occurring in the wheel/track interface and wear mechanics.

This thesis involves the advancement and testing of existing numerical models for rail corrugation via testrig and field measurement data.

Investigation and mathematical modelling of deep brain stimulation

Deep brain stimulation DBS is surgical technique used to mitigate the symptoms of a range of neurological disorders such as Parkinsons disease. The procedure involves insertion of an electrode into the brain and then application of pulsed voltage for stimulation. The purpose of this project is to develop a mathematical understanding of deep brain under DBS and investigate optimal conditions for DBS and/or interesting nonlinear phenomena.

Investigation and modelling of nonlinear phenomena in the cardiovascular system

A relatively new cross-disciplinary field of research is the identification and modelling of dynamic phenomena in biological systems. In particular, evidence of chaotic dynamics has been identified in the heart and brain and has surprisingly been associated with normal healthy functioning. In fact recent evidence suggests that abnormalities such as heart attacks and epileptic seizure are associated with linear periodic behaviour. It is of interest that pacemakers, in general, are designed to provide periodic behaviour, however, a better performance may be achieved if they can be designed to mimic the natural chaotic behaviour of a natural heart.

This project will involve an analytical and experimental investigation of nonlinear phenomena in the human cardiovascular system. In particular, a nonlinear controller will be developed and investigated using analytical, numerical and existing experimental models of the human cardiovascular system for use as a pacemaker.

Models to demonstrate nonlinear phenomena

The purpose of this project is to design and build physical models to demonstrate nonlinear phenomena in dynamics.

In particular, it is firstly aimed to develop one or more simple but demonstration sized models for demonstrating stability and conservation concepts in 3D rigid body motion. Possible models include the tippetop (a spinning top that inverts itself), the rattleback stone (a rigid body of unidirectional spin) and Chalygin's ball (a spherical but inertially asymmetric spinning ball).

Secondly, it is aimed to develop a simple demonstration model for showing chaotic instabilities in a spacecraft, dragline or another rotating multibody system.

The design parameters will be based upon theoretical predictions of phenomena in available literature. The thesis will be expected to contain a thorough review of this literature and theoretical calculations predicting the phenomena in the physical models.

Modelling and suppression of instabilities in tethered spacecraft

A number of investigations of spacecraft stability have been performed in the recent past, motivated by the observation of abnormalities occurring in the attitude dynamics of satellites. Attitude instabilities are highly detrimental to the high pointing accuracy required by communication satellites for antennas to provide the desired coverage. These observed instabilities have usually been found to arise the inherent nonlinearity of the system dynamics.

This project will investigate the occurrence and suppression of attitude instabilities in tethered spacecraft via analytical and numerical techniques. Tethered spacecraft systems are used to reduce fuel consumption and increase mission efficiency and safety. It is expected that this project will involve a significant amount of dynamic modelling, analysis, simulation and application of novel design/control techniques.

Investigation of the problem of wheel squeal

Wheel squeal is a highly undesirable high pitched noise that is emitted as a railway vehicle traverses a corner. A similar phenomena occurs in braking. Much research has been performed in this area to determine the causes and conditions of the phenomena to find a cure. The phenomenon involves the interaction between the dynamics of the vehicle (wheel) and the contact mechanics occurring in the wheel/track interface.

This thesis involves development and or upgrade of an existing analytical, simulation and laboratory modelling of wheel squeal under dry and friction modiofied conditions. Further or alternative investigation could be focused on a control method to suppress the phenomena to higher critical angle of attacks.

Modelling the dynamics of the inner ear

The inner ear is an extremely sophisticated instrument for converting mechanical vibrational energy to neural energy that our brain interprets as sound. The operation of this system has been shown to rely on highly nonlinear dynamics. This project will investigate simple nonlinear models for the dynamics of the inner ear and identify important phenomena associated with it.

Modelling fuel slosh in spacecraft

Typical spacecraft have a lifetime determined almost solely dependent on the amount of fuel (used during attitude manoeuvres) remaining in its tanks. The existing system of estimating the fuel remaining onboard is via recording a theoretical value of the amount of fuel used in each manoeuvre and summing this over the spacecraft's lifetime. This process allows for the propagation of significant errors in the estimate of the fuel remaining at the end of life.

This project will continue previous research that has proposed that has proposed a method by which a better estimate of fuel remaining may be obtained. The aim of this project is to further develop and tune analytical and numerical models of the spacecraft fuel slosh behaviour in order to accurately predict the amount of fuel remaining. The project has major interest from Cable & Wireless Optus and the satellite communications industry in general.

Investigation of dragline bucket swing instabilities

The occurrence of nonlinear instabilities is investigated in the swing motion of a dragline bucket during normal operation cycles. A simplified representative model of the dragline is developed in the form of a fundamental rotating multibody system with energy dissipation.An analytical predictive criterion for the onset of chaotic instability has been obtained using Melnikov’s method in terms of critical system parameters. These chaotic instabilities could introduce irregularities into the motion of the dragline system rendering the system difficult to control by the operator and/or would have undesirable affects on dragline productivity and fatigue lifetime. The sufficient analytical criterion for the onset of chaotic instability is shown to be a useful predictor of the phenomenon under steady and unsteady slewing conditions via comparisons with numerical results. It is aimed to validate these preliminary results by the development of a more realistic numerical model and/or experimental model.

Predictive Modelling and Control of the Incremental Forming Process

Incremental sheet forming (ISF) is a new flexible manufacturing process in which complex 3D shapes are formed from a sheet of metal using a simple moving tool (stylus). The non-specialised tool may be used to form an infinite variety of highly complex shapes in the same manner an artist is unrestricted with a simple brush. The project aim is to investigate and develop mechanics based predictive models or controllers for the nonlinear contact mechanics, localised plastic strain dynamics and tool trajectory to facilitate product design & optimisation.

Topics in dynamics and nonlinear mechanics

Various projects on modelling, simulation and control of dynamic nonlinear phenomena in railways, spacecraft, mining and biomechanical systems (deep brain, hearing, heart) systems.

Investigation of Brake Squeal

Brake squeal is an undesirable tonal noise that results from slowing of a vehicle with disk brakes. Unfortunately it remains it remains one of the most important issues for the automotive industry causing high levels of cutomer concerns and warranty costs. The phenomenon involves an unstable interaction between the modal dynamics of the brake system and the pad contact mechanics which can be due to different feedback mechanisms. Electric and hybrid vehicles still suffer from the problem as they require friction brake disks for heavy braking which they blend with regenerative braking.

This thesis involves the numerical and experimental investigation of the occurence of the phenomenon under different mechanisms to identify conditions to avoid brake squeal with a particular focus on controlling it under brake blending in electric and hybrid vehicles.