Structural Modeling of a Five-Meter Thin-Film Inflatable Antenna/Concentrator
Inflatable structures have been the subject of renewed interest in recent years for space applications such as communications antennas, solar thermal propulsion, and space solar power. A major advantage of using inflatable structures in space is their extremely light weight. An obvious second advantage is on-orbit deployability and related space savings in the launch configuration. A recent technology demonstrator flight for inflatable structures was the Inflatable Antenna Experiment (IAE) that was deployed on orbit from the Shuttle Orbiter. Although difficulty was encountered in the inflation/deployment phase, the flight was successful overall and provided valuable experience in the use of such structures. Several papers on static structural analysis of inflated cylinders have been written, describing different techniques such as linear shell theory, and nonlinear and variational methods, but very little work had been done in dynamics of inflatable structures until recent years. In 1988 Leonard indicated that elastic beam bending modes could be utilized in approximating lower-order frequencies of inflatable beams. Main, et al. wrote a very significant 1995 paper describing results of modal tests of inflated cantilever beams and the determination of effective material properties. Changes in material properties for different pressures were also discussed, and the beam model was used in a more complex structure. The paper demonstrated that conventional finite element analysis packages could be very useful in the analysis of complex inflatable structures. The purposes of this paper are to discuss the methodology for dynamically characterizing a large 5-meter thin film inflatable reflector, and to discuss the test arrangement and results. Nonlinear finite element modal results are compared to modal test data. The work is significant and of considerable interest to researchers because of 1) the large size of the structure, making it useful for scaling studies, and 2) application of commercially available finite element software for modeling pressurized thin-film structures.
Importance of geometric non-linearity and follower pressure load in the dynamic analysis of a gossamer structure
Abstract Vibration analysis of a gossamer or inflated structure poses special problems, usually not encountered in a conventional metallic or composite structure. In an inflated structure, internal pressure is a major source of strength and rigidity. In the past, most of the studies conducted on the vibration analysis of gossamer structures used inaccurate or approximate theories in modelling the internal pressure. The inexactness in these theories arises due to (1) exclusion of the follower pressure loads, and (2) approximations in the geometric non-linearity. Taking cues from the earlier work done in this area and using line-of-curvature co-ordinates, we re-derive the governing equations for vibration analysis of a shell under pressure, and point out the shortcomings of the previous approximate theories. The same governing equations were derived earlier by Budiansky using tensors. Thereafter, a free-vibration analysis of an inflated torus with free boundary condition is performed using the accurate and the approximate shell theories. It can be seen that the natural frequencies and the mode shapes obtained from the approximate theories are significantly different from those obtained from the accurate shell theory. Since the boundary condition of the torus is free, the vibration analysis should yield six zero frequencies corresponding to the six rigid-body modes. It is shown here that while the accurate theory does give six zero frequencies, the approximate theories do not.
New approach to vision-based BGA package inspection
Ball grid array (BGA) techniques have developed very fast due to the advantages of more I/O ports, small size, and so on. In this paper, a vision-based algorithm for BGA package inspection is proposed to accurately estimate center and diameters of solder-balls of BGA packages, so that defects of BGA packages, such as missing or extra balls, oversize or undersize balls, over-height or under-height balls, and pitch can be detected for ensuring the quality of BGA packages.