I am currently involved in the development of a novel axisymmetric ultra-light deployable membrane reflector, aiming o develop 5 to 10 m diameter structures. This reflector consists of a membrane surface, supported by a series of ribs that deploy and prestress a large membrane. The ribs are long tape springs, i. e. straight, transversely curved metallic strips similar to tape measures but with a cross section that subtends a much larger angle. Flexural buckling of such ribs occurs when a large bending moment is applied, resulting in a fold which stores strain-energy. The whole reflector can be packaged with many such folds and during deployment, the strain energy is released while the ribs recover their original shape. I have investigated possible packaging methods for large membranes and related deployment aspects. I have obtained geometric constraint equations that govern the compact folding of curved surfaces and, based on these conditions, I have proposed three folding schemes for the reflector. The membrane can be folded either in the radial direction, towards the centre, or it can be wrapped around the hub. The geometric conditions underlying my approach guarantee that each folding pattern can be produced accurately, a nd repeated over and over again when the reflector is tested before launch.
I have also started to investigate the dynamic deployment of a rib with a single fold. I began by conducting some experiments and observed that the fold position travels during deployment. I then tried to reproduce the experiments with a powerful numerical finite-element package, but could not simulate this behaviour. Therefore, I developed a multi-body analytical model which is able to capture the key experimental observations and thus provide accurate simulations.
At present, I am looking into cutting patterns for membranes so that the deployed antenna reflector can be properly tensioned. To achieve high shape accuracy in the reflective surface, it is crucial that the membrane is stressed biaxially at every point, with small shear stress to avoid the formation of wrinkles. The problem can be formulated as follows. First, to find the shape which is tensioned and closest to the desired one; second, to find the cutting pattern of the flat membrane; and third to build a membrane which can produce a surface whose shape is close to the desired one. I have transformed the force density method, previously developed for cable networks to a numerical tool capable of analysing membranes.
pantographs | dynamic & | kinematic simulation | finite element method | force method | geometry | linkages | mechanisms | prestress | retractable roofs | sensitivities | single degree of freedom system | topology
This page is created by Zhong You, who is a university lecturer in the Department of Engineering Science of Oxford University. This is a link to his current address. You may e-mail firstname.lastname@example.org for further infomation.
Zhong was an EPSRC advanced fellow based at Cambridge University before moving to Oxford.