Current Opportunities

Offshore Wind Turbine vibration suppression using advanced control methodologies

Supervisors: Dr Jason Zheng Jiang (z.jiang@bristol.ac.uk), Dr Tom Hill, Prof. Simon Neild

This PhD project will focus on using advanced control methods (passive, semi-active or active) for offshore wind turbine (OWT) vibration suppression. The current trends of equipping turbines with increased size, larger and slender towers and locating OWTs to deeper waters result in more vibration issues to be solved. This project will not only allow the student to build a wide range of skills including vibration control theory, mechanical and aerodynamic modelling & simulation, but also provide experience of working closely with industrial partners. 

Improving efficiency and robustness of marine energy conversion systems

Supervisors: Dr Jason Zheng Jiang (z.jiang@bristol.ac.uk), Professor Simon Neild

Renewable energy converted from marine tidal, wave is critically important for a low-carbon future. It is crucial to design marine energy conversion systems which can maximise energy conversion efficiency, and at the same time are robust to normal and extreme loading conditions. This PhD project aims at establishing a methodology to find optimum designs for both the mechanical and electrical parts.

Novel liquid-based vibration control devices

Supervisor: Dr Brano Titurus (Brano.Titurus@bristol.ac.uk)

This research aims to develop, theoretically and experimentally, a new class of controllable liquid-based devices for vibration mitigation in aerospace applications.

Damping for aeroelastic tailoring in wings and blades

Supervisor: Dr Brano Titurus (Brano.Titurus@bristol.ac.uk)

Increasing the flight stability margins and enabling higher performance lifting surfaces through embedded dynamic damping is the main focus of this project.

A combined experimental and numerical investigation on nonlinear whirl flutter

Supervisors: Dr Djamel Rezgui (Djamel.rezgui@bristol.ac.uk) and Dr Brano Titurus (brano.titurus@bristol.ac.uk)

The dynamic interaction between rotating and stationary structures in the presence of nonlinearity and uncertainty (structural, material, aerodynamic, etc.)  is a complex problem. In rotorcraft, one of the current problem is the poor prediction of the whirl flutter instabilities for tiltrotor [1] and novel multi-rotor configurations. This project aims to investigate the nonlinear dynamics of the coupled rotating-stationary system for the case of the tiltrotor aircraft, through a combined experimental and numerical (bifurcation theory) approach.

[1] Mair C, Rezgui D, Titurus B, Nonlinear stability analysis of whirl flutter in a tiltrotor rotor-nacelle system, ERF 2017 - 43rd European Rotorcraft Forum, 12-15 September 2017, Milan, Italy

Design for performance and dynamics of novel electrical Rotary Wing UAVs

Supervisors: Dr Djamel Rezgui (Djamel.Rezgui@bristol.ac.uk) and Dr Dorian Jones (Dorian.Jones@bristol.ac.uk)

Drones and Unmanned Aircraft vehicles (UAVs) are now extensively considered by major manufactures and operators in a wide range of civilian and military applications. Of a particular interest are those of multi-rotor configurations, which are considered as the future mobility vehicles as in the “Air Taxi” or “Personal Flying Car” concepts. This project aims to investigate the complex design strategies and tools of the future electric multi-rotor UAV’s, from performance and dynamics aspects using advanced efficient modelling and analysis tools.

Design and Modelling of Electromagnetic Vibration Suppression Devices

Supervisors: Professor Simon Neild (Simon.Neild@bristol.ac.uk) and Dr Jason Jiang (z.jiang@bristol.ac.uk)

This project will focus on vibration suppression via electromagnetic devices. We will use a general passive mechanical controller to replace the conventional spring/damper system and optimise it to show the potential benefits. An electromagnetic device will then be built and tested in the context of the structure it will be deployed in. This will be achieved using hybrid testing, where the structure is modelled and the device is physically tested with real-time coupling between the two to emulate the dynamics of the full system.  

Vibration suppression of nonlinear structures

Supervisors: Professor Simon Neild (Simon.Neild@bristol.ac.uk) and Dr Tom Hill (tom.hill@bristol.ac.uk)

Building on our work on nonlinear normal modes, in which the nonlinear behaviour of structures and the resulting interactions between the linear modes are analysed, this project will consider how nonlinearity in a structure can affect a vibration suppressor such as a tuned-mass-damper. Such devices can result in very favourable low amplitude response solutions, but can also exhibit isolated large amplitude response solutions. We will investigate when such large amplitude responses exist and develop tuning rules to either minimise or completely remove such solutions. 

Numerical modelling of impact and friction

Supervisors: Dr Robert Szalai (r.szalai@bristol.ac.uk) and Professor Alan Champneys

This project is part of a research theme investigating dynamic behaviour of frictional contact. The project will focus on numerical simulation of frictional contact. Simulation of frictional contact is problematic, because most methods predict non-unique solutions. These numerical methods are also badly conditioned due to the multiple time and length-scales present in the problem. In contrast, theory tells us that the continuum contact problem has unique solutions. This means that there is room for improvement. A recent result [1] addresses this issue in an analytical setting and for point contact only. There is now a rigorous model reduction technique that retains uniqueness and other essential qualitative features of continuum contact problems. The task is therefore to extend this new method so that it can be implemented in numerical schemes. 

The main task is to adapt a finite element, boundary element or collocation method using the rigorous model reduction technique [1]. The project does not aim to implement the method in a full-featured finite element software, instead we will take a semi-analytical approach and focus on simple examples, initially. We will start with a classical problem, when an elastic rod hits a rigid surface so that impact and friction needs to be considered simultaneously. (This is one representation of Painleve's paradox.) Further tasks involve extending the method to surface-surface contact to study how frictional contact ruptures. 

[1] R. Szalai, Model reduction of infinite dimensional piecewise-smooth systems, https://arxiv.org/abs/1509.08040 [2] O. Ben-David, G. Cohen, J. Fineberg The Dynamics of the Onset of Frictional Slip, Science, 330(6001), pp. 211-214, (2010)

Identification of reduced models of mechanical systems from vibration data

Supervisor: Dr Robert Szalai (r.szalai@bristol.ac.uk)

In order to gain understanding of the dynamics of a mechanical system it is useful to have a reduced order model. The best reduced models are exact: they describe the motion exactly for a specific set of initial conditions. For other initial conditions the dynamics will exponentially tend to the solution described by the reduced model. Finding such reduced models is equivalent to finding invariant manifolds with certain properties. In a recent paper [1] we have shown that it is possible to find such unique reduced models from experimental data. We have used the most general model that was constructed using a least squares method. This model then was analysed using analytical techniques. It is however desirable that the model being identified has low number of parameters, which is possible to achieve if the fitting and analysis of the model is carried out in one step. The task in the PhD project is to develop this method with the minimum number of parameters required to obtain a reduced model. In order to test the method, we will use various experimental data and data from finite element simulations to test the method.

 [1] R. Szalai, D Ehrhardt, G. Haller. Nonlinear model identification and spectral submanifolds for multi-degree-of-freedom mechanical vibrations. Proc. R. Soc. A 2017 473 20160759   

Computational fight mechanics - analysis of control law sensitivity for aircraft control and active load alleviation

Supervisors: Professor Mark Lowenberg (M.Lowenberg@bristol.ac.uk) and Professor Simon Neild (Simon.Neild@bristol.ac.uk)

Aircraft controllers are typically designed using linear techniques at a number of operating points, and combined into a gain-scheduled (nonlinear) controller.  The design requirements are usually based on linear design techniques and include frequency response criteria: the assumptions involved in applying these in the presence of significant nonlinearity and uncertainty (such as aircraft flying near their envelope limits) may be questionable.  This project aims to exploit numerical continuation techniques to explore this problem, including periodically-forcing the system to extract nonlinear frequency responses.  The study will consider sensitivity of the periodically-forced system stability to perturbation/uncertainty and aims to provide a new perspective on the stability and robustness of control law design where the dynamics is especially nonlinear.

The initial focus will be on rigid aircraft models under nominal and off-nominal design conditions (such as in the vicinity of upset, loss-of-control), with an extension to incorporate aeroelastic influences and active load control if feasible.

Funding restrictions: none (note: studentship funding needs to be sought for this project).

Experimental fight dynamics – multi-DOF dynamic wind tunnel testing of aeroelastic models

Supervisors: Professor Mark Lowenberg (M.Lowenberg@bristol.ac.uk), Professor Simon Neild (Simon.Neild@bristol.ac.uk) and Dr Djamel Rezgui (Djamel.Rezgui@bristol.ac.uk)

The 5-DOF ‘manoeuvre rig’ has been developed at the University of Bristol to investigate the aerodynamics and flight mechanics of model aircraft motions, driven by on-board control surfaces or externally via the rig, that involve nonlinear and unsteady flow phenomena.  To date, only rigid models have been tested.  This PhD will extend the use of the rig to complement previous work on modelling, analysis and testing of flexible wings that exhibit nonlinear behaviour.  The objective is to develop a new experimental approach to the study of dynamics of coupled wing-plus-airframe aeroelastics in the presence of nonlinearity.  It will incorporate multi-degree-of-freedom dynamic testing with compensation of rig effects to allow physical simulation of highly flexible air vehicles in flight, and will also involve modelling and numerical analysis of the coupled systems.

Funding restrictions: none (note: studentship funding needs to be sought for this project).

 

 

 

 

How to apply

If you are interested in applying, please contact the named supervisor(s) for the relevant project on this page. For further information on the application process, please see our postgraduate pages.

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