Evaluation of Double-Layer Suspension Cable-Network Design For Vibration Isolation in Membrane Structures
- Paper number
IAC-05-C2.2.02
- Author
Dr. Hiraku Sakamoto, University of Colorado, United States
- Coauthor
Prof. K.C. Park, University of Colorado, United States
- Year
2005
- Abstract
The present study discusses design aspects of a proposed membrane design, so-called doubly web-cable girded design. The motivation to introduce the double layers of cable-networks around a membrane is that these web-cables passively isolate the membrane from the vibration that emanates at the cable-supporting points. The present study shows that the passive vibration-isolation effect can be significantly enhanced by the proposed design when the cable thickness is appropriately tuned based on a vibration analysis. As a result, the proposed design reduces the requirement for active controllers applied along the web-cables. As observed in conventional structures, increasing the passive vibration-suppression effect reduces the active control requirements, yet increases the structural mass; whereas, increasing the active controllers results in increasing the complexity. The significance of the proposed design is that we can address this classical passive/active vibration-suppression dilemma only in the suspension cable-network design, without considering a membrane control. This is possible because the proposed design localizes the vibration in the web-cables. The vibration-isolation effect of the proposed design is corroborated with a series of transient analyses using a geometrically nonlinear finite element method, which allows for membrane wrinkling and cable slackening.
Membrane space structures have been intensively studied to construct solar sails or large reflectors. There are three design issues for membrane structures: (i) Minimization of mass, (ii) preservation of a wrinkle-free taut condition in membranes during an operation, and (iii) vibration suppression in membranes. A wrinkle-free condition in a membrane is usually desired, not only because wrinkles in the membrane degrade the surface reflectivity, but also because they modify the dynamic characteristics of the membrane, making its response less predictable. Accordingly, the introduction of a single catenary cable along each membrane edge has been discussed to provide a uniform pre-stress throughout the membrane (e.g. [1,2]); however, these conventional catenary design requires very thick and heavy cables to satisfy the cable/membrane strain compatibility. By contrast, the proposed web-cable design substantially reduces the required cable mass to achieve a uniform pre-stress state; additionally, the web-cable design facilitates the introduction of vibration suppression strategies along the web-cables. Active control methods are attractive, yet we also need to enhance the passive vibration suppression in the web-cables. The present study offers a basic guideline to achieve an optimal balance between active and passive vibration suppression schemes in membrane structures by presenting the doubly web-cable girded design.
The proposed doubly web-cable girded design only requires thin and light-weight cables, since the applied tension in each cable can be distributed in the web-networks. Furthermore, the cross-sectional area of the outer perimeter cables can be independently determined without considering the strain compatibility with the membrane, thus enabling a dynamic tailoring of the cable-networks. The present study tunes these cables based on a classical concept of a dynamic vibration absorber.
References
- [Gresc02]
-
Greschik, G. and Mikulas, M. M., “Design Study of a Square Solar Sail Architecture,” Journal of Spacecraft and Rockets, Vol. 39, No. 5, Sept.-Oct. 2002, pp. 653–661.
- [Mikul03]
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Mikulas, M. M. and Adler, A. L., “Rapid Structural Assessment Approach For Square Solar Sails Including Edge Support Cords,” AIAA Paper 2003–1447, 2003.
- Abstract document