  In the aerospace industry the trend for light-weight structures and the
resulting complex dynamic behaviours currently challenge vibration engineers.
In many cases, these light-weight structures deviate from linear behaviour, and
complex nonlinear phenomena can be expected. We consider a cyclically symmetric
system of coupled weakly nonlinear undamped oscillators that could be
considered a minimal model for different cyclic and symmetric aerospace
structures experiencing large deformations. The focus is on localised
vibrations that arise from wave envelope modulation of travelling waves. For
the defocussing parameter range of the approximative nonlinear evolution
equation, we show the possible existence of dark solitons and discuss their
characteristics. For the focussing parameter range, we characterise modulation
instability and illustrate corresponding nonlinear breather dynamics.
Furthermore, we show that for stronger nonlinearity or randomness in initial
conditions, transient breather-type dynamics and decay into bright solitons
appear. The findings suggest that significant vibration localisation may arise
due to mechanisms of nonlinear modulation dynamics.
