Mechanisms of Compliant Shells

Abstract

Thin shells are three dimensional curved solids with a thickness that is small compared to the two other dimensions. For structural engineers, traditional rigid thin shells are some of the most efficient structural typologies. The curvature and continuity that characterizes them are the source of their high stiffness under loading. They are also the basis for a new typology of structures: compliant shells. Used for Their ability to deform elastically under compressive buckling loads suggests that the shape of thin compliant shells can be tailored to produce mechanism-like kinematics. In this dissertation, a case is made for thin compliant shells as ideal candidates for tailored large deformation mechanisms.

Biology (and more particularly plants) is rich with compliant mechanisms. In this thesis a comprehensive categorization of the structural mechanics in plant movements demonstrates that shells are the most efficient mechanism to amplify actuation. The increase in scale of the movements of those shells for engineering purposes is shown to be limited by the influence of earth’s gravity. A non-dimensional analysis of mechanical characteristic properties of thin shells leads to the identification of a size constraint for gravity independence. A geometry-based method for the identification of compliant shell mechanisms is then presented that relies on the computation of the low frequency eigenmode. The methodology is applied to the design of a spherical motion mechanism based on the geometry of a negative Gaussian curvature toroidal shell under two degree-of-freedom compressive actuation, aimed for solar shading applications. Finally, a novel methodology for the design of dynamic external shading systems, based on compliant shell mechanisms, is presented that substantiates the use of more comprehensive comfort-centric performance-based for the reduction of energy demand in buildings.