Dynamic analysis of extended bistable reeled fibre-reinforced composite booms for space applications.

Bistable Reeled Composite (BRC) booms have the potential to be used as lightweight structural elements for a number of space applications. This thesis details an approach for increasing the natural frequency and stiffness of extended BRCs. The motivation for this research is the desire to increase the scalability of a flexible “roll-up” solar array which, in its deployed state, consists of two cantilevered BRCs supporting a flexible Photo Voltaic (PV) cell-covered blanket betwee n them. A parametric study has been presented, which analysed the effects of design parameters on the vibration characteristics of a single boom using a Finite Element (FE) approach. A numerical model was combined with a nonlinear constrained optimisation to maximise the natural frequency of BRC booms with respect to the fibre orientation angles and ply discontinuity locations, under the constraints of the physically achievable braid angles and constant coiled diameters resulting from the deployment mechanism design. The results demonstrate that careful selection of the fibre orientation angles and introducing a step change in the number of plies at strategic positions along the boom length can significantly increase the natural frequency. For instance, the natural frequency of a four-carbon/epoxy-nominalbraid-ply boom (L = 5.1 m, R = 38 mm, and β = 345◦) has been improved by more than 50%. The agreement between the natural frequency values for the complete solar array and the corresponding individual BRC booms indicates that the optimised solutions for a single boom model are applicable to the complete model for the first (cantilever) mode. Experimental verification of the vibration characteristics of optimised BRC booms has also been conducted. Finally, a dynamic stability analysis of the optimised BRC booms under bending has been carried out using FE simulation, to quantify the maximum angular acceleration that they can withstand before failure. The optimised BRC booms exhibit a higher resistance to bending during a spacecraft manoeuvre.