Uncertainty Effects on Bike Spoke Wheel Modal Behaviour

In bicycles, one of the components which mostly influences the global system dynamics is the wheel-tyre subsystem. In this paper, the modal behaviour of a bike spoke wheel is numerically and experimentally investigated focusing on the characterisation of the spoke pretension effect, role of boundary conditions and parameter uncertainties. A linearised parametric finite element model (FEM) is developed with the open-source code LUPOS in Matlab® environment. A detailed description of the model which includes several components, i.e. rim, hub, spokes and hub gears, is given. The FEM model is based on a reduced set of key nodes belonging to the wheel cross section profile, material and geometrical characteristic assignment and automated meshing procedure, allowing reduced computational effort and high model accuracy. Experimental modal analysis is conducted on the wheel, and critical issues in the pole identification are highlighted, due to the high modal density given by the spokes and uncertainties. A further numerical investigation based on a variational approach is applied to investigate the role of system uncertainties on the modal parameters. The analysis shows that the identification issues are mainly related to spoke pretension, cross contact and boundary conditions. Moreover, the spoke pretension uncertainty induces a mistuning in the structure and the corresponding loss of axial symmetry. The fine model updating of the preliminary model is then achieved optimising geometrical and material properties of the components as well spoke pretension.