Next-generation test methods for nonlinear structures

Many physical systems, whether engineered or natural, undergo sudden changes in behaviour as a physical parameter changes. Examples include the onset of wheel shimmy ("tank-slapping") in motorbikes, where the front wheel starts to oscillate violently at a critical speed, and aero-elastic flutter in aeroplanes, where an aerofoil starts to vibrate and deform at a critical wind speed. Control-based continuation (CBC) is a method for investigating these types of nonlinear dynamics and bifurcations directly in physical experiments without the need for first deriving a mathematical description of the system. This proposal seeks to advance CBC to the point where it can become a general-purpose tool for use by structural engineers (and in the longer term, wider ranging use by industrialists and applied scientists). Specifically, two aspects of CBC are addressed in this proposal. Firstly, the robustness to noise; any physical system is subject to disturbances (noise), some to higher degrees than others, and CBC must be capable of dealing with these disturbances. Secondly, the scalability to multiple degrees of freedom; physical structures and systems are not necessarily simple and may have many interacting components, CBC must scale well to large structures.

In the wider context, the direct beneficiaries of this work are likely to be engineers working in the high-value manufacturing sector (e.g., Airbus, AgustaWestland, Rolls-Royce) and other sectors where nonlinear dynamic behaviour is important (e.g., Schlumberger). Due to the increasing trend towards more lightweight and efficient structures, which in turn are more likely to demonstrate nonlinear behaviour, it is likely that the number of beneficiaries in this area will increase over time. On a longer time scale, commercial engineers working on control and system identification may also benefit from the more informative data that control-based continuation (CBC) is able to generate from physical experiments, hence allowing them to be more effective in their daily work. On a more speculative level, there are potential beneficiaries in the biotechnology industries since control-based continuation gives the possibility for new ways of investigating cell biology.