Finite Element Design and Modal Analysis of a Hexakis Icosahedron Frame for Use in a Vacuum Lighter-Than-Air Vehicle

Abstract

This research discusses the design, modal analysis, and additive manufacturing of a hexakis icosahedron frame for use in a vacuum lighter-than-air vehicle (VLTAV). A frame in the shape of a hexakis icosahedron, when encased by a thin membrane-like skin, would be able to withstand the pressure load induced by internal air evacuation and produce positive buoyancy. For a better appreciation of the force resistance within the hexakis frame, a manufactured frame was constructed. The actual frame has many varying oriented beams, making its construction complicated for standard production methods. Therefore, additive manufacturing was incorporated. A portion of this paper is directed toward the description of the method carried out. A .1778-m-diameter hexakis icosahedron frame was additively manufactured using VeroWhitePlus plastic. A modal experiment using a laser vibrometer was performed in order to determine the eigenvalues of the structure for comparison to the modal analysis results of a finite element (FE) model of the frame assuming a free-free boundary condition. This comparison allowed for the verification of the equivalent modulus of elasticity used in an analysis and the overall construction of the model. The finite element model predicted the first two frequency modes within 1% of the experimental results. Because the FE model accurately predicted the dynamic properties of the frame, the modeling technique in which the assumed member connections were verified led to confidence for future modeling.