Design of Structures That Adapt to Loads through Large Shape Changes

Abstract

Adaptive structures can modify their geometry and internal forces through sensing and mechanical actuation in order to maintain optimal performance under changing actions. Previous work has shown that well-conceived adaptive design strategies achieve substantial whole-life energy savings compared with traditional passive designs. The whole-life energy comprises an embodied part in the material and an operational part for structural adaptation. Structural adaptation through controlled large shape changes allows a significant stress redistribution so that the design is not governed by extreme loads with long return periods. This way, material utilization is maximized, and thus embodied energy is reduced. This paper presents a new design process for adaptive structures based on geometry and member sizing optimization in combination with actuator placement optimization. This method consists of two parts: (1) geometry and sizing optimization through sequential quadratic programming is carried out to obtain shapes that are optimal for each load case; and (2) a formulation based on stochastic search and the nonlinear force method (NFM) is employed to obtain an optimal actuator layout and commands to control the structure into the target shapes obtained from Part 1. A case study of a planar statically indeterminate truss is presented. Numerical results show that 17% and 37% embodied energy savings are achieved with respect to an identical active structure designed to adapt through small shape changes and to a weight-optimized passive structure, respectively. The combinatorial task of optimal actuator placement is carried out efficiently. The method formulated in this work produces actuator layouts that enable accurate geometric nonlinear shape control under quasi-static loading through a low number of actuators compared to the number of members of the structure.