Abstract:

Large deployable space structures include requirements for reflecting surfaces for antennae, reflectors and solar arrays.  Their efficiency depends not only on surface accuracy but also on the vibration characteristics of these reflecting surfaces.  This dissertation presents a study of the vibration behaviour of various prestressed membrane structures.

A preliminary vibration analysis of arbitrary shape flat membranes is done using a finite element package, ABAQUS, and compared with analytical solutions.  The preliminary analysis shows good agreement between finite element and analytical solutions.  This gave confidence to use ABAQUS simulations for vibration analysis of other membrane structures as well.

The natural frequencies and mode shapes of a deployable membrane reflector currently under development by the European Space Agency are obtained using ABAQUS for various reflector diameters, hub dimensions, number of ribs and prestress.  The analysis results indicate that the fundamental nature frequency of the reflector decreases with the increase of diameter of the reflector and does not change greatly with the increase of hub radius. Furthermore, the fundamental natural frequency increases with the increase of membrane prestress.  A periodic nature of variation in the results is observed.

An experimental study of the vibration of a flat membrane is done.  The experimental results indicate the effect of the surrounding air on the membrane vibration.  A similar experimental study carried out at various atmospheric pressures in a vacuum chamber, published in 1983, is used to study the effect of the surrounding medium on the membrane vibration.  A new prediction method is presented to determine the natural frequencies and mode shapes of flat membranes of any shape vibrating in a fluid medium at any pressure.