Dynamic Design Tools For Understanding and Exploiting Nonlinearity in Structures

The dynamic behaviour of mechanical systems and structures is often critical to their performance. Examples where unpredicted dynamic behaviour has resulted in poor performance include the London Millennium Footbridge prior to retrofitting with dampers and wheel shimmy experienced in aircraft landing gear and motorbikes.

When structures remain in their linear operating region, where the response is proportional to the size of the force causing it, there are well-established modelling and experimental validation tools for analysing their dynamic behaviour. If the structure exceeds the linear operating region and starts to exhibit nonlinear behaviour, for example due to large deflections, the effectiveness of these tools rapidly reduces leading to high degrees of design uncertainty. This uncertainty leads to multiple design iterations and increased costly experimental validation and even the discovery of undesirable behaviour late in the design process resulting in significant delay and additional expense.

This presents a problem when trying to innovate to improve performance, for example by reducing weight or using new materials, as this tends to add nonlinear effects. Currently the consequence of the limitations in existing tools is that the resulting uncertainty is compensated for by conservative design. What are urgently needed are design tools that can cope with complex nonlinear behaviour. The new nonlinear design tools this research will provide will greatly reduced the costs associated with designing new high performance products. Such step changes to the UK's capability for advanced design will assist high-end manufacturing industry to maintain its competitive edge.

The design tools proposed here will provide a means of analysing and validating the response of structures with nonlinearities. Currently it is normal practice to design structures such that they operate in their linear response regime. However this often leads to over-restrictive design resulting in, for example, stiffer and hence heavier structures that in an aerospace context would lead to reduced fuel efficiency. The tools that will be developed during this fellowship will remove the conservative linear design constraint. This will allow, for example, more efficient light-weight structures resulting in better energy efficiency and reductions in material used so reducing pressures on resources and benefiting the environment.

The new tools will make a major step toward reducing the high levels of uncertainty associated with the presence of nonlinear effects. The current uncertainty leads to multiple design iterations and increased costly experimental validation and even the discovery of undesirable dynamic behaviour late in the design process resulting in delay and additional expense. For example, full-scale testing of an aircraft engine can cost in the order of £1million a day at the end of a design cycle whereas tests much earlier in the process cost two or even three orders of magnitude less. The reduced uncertainty the new tools will provide will greatly reduce the costs associated with designing new high performance products. Such step changes to the UK's capability for advanced design will assist the UK high-end manufacturing industry to maintain its competitive edge in the face of increasing competition from around the world.

The key outcomes from the fellowship will be the software-implemented tools for nonlinear dynamic design of structures. To maximise its impact every effort will be made to ensure that these tools can be used for industrial applications without requiring expert knowledge of the fundamental research and so providing an out-of-the-box analysis method.