Force and Shape Control Strategies for Minimum Energy Adaptive Structures

Abstract

This work presents force and shape control strategies for adaptive structures subjected to quasi-static loading. The adaptive structures are designed using an integrated structure-control optimization method developed in previous work, which produces minimum "whole-life energy" configurations through element sizing and actuator placement optimization. The whole-life energy consists of an embodied part in the material and an operational part for structural adaptation during service. Depending on the layout, actuators are placed in series with the structural elements (internal) and/or at the supports (external). The effect of actuation is to modify the element forces and node positions through length changes of the internal actuators and/or displacements of the active supports. Through active control, the stress is homogenized and the displacements are kept within required limits so that the design is not governed by peak demands. Actuation has been modeled as a controlled non-elastic strain distribution, here referred to as eigenstrain. Any eigenstrain can be decomposed into two parts: an impotent eigenstrain only causes a change of geometry without altering element forces while a nilpotent eigenstrain modify element forces without causing displacements. Four control strategies are formulated: (C1) force and shape control to obtain prescribed changes of forces and node positions; (C2) shape control through impotent eigenstrain when only displacement compensation is required without affecting the forces; (C3) force control through nilpotent eigenstrain when displacement compensation is not required; and (C4) force and shape control through operational energy minimization. Closed-form solutions to decouple force and shape control through nilpotent and impotent eigenstrain are given. Simulations on a slender high-rise structure and an arch bridge are carried out to benchmark accuracy and energy requirements for each control strategy and for different actuator configurations that include active elements, active supports and a combination of both.

Motion Design with Efficient Actuator Placement for Adaptive Structures that Perform Large Deformations

“…If energy harvesting is not possible, this formulation might lead to an underestimation of the actuation energy that is required to control the structure through the optimal deformation path. To avoid energy gains during motion, the objective function should become a discontinuous function as formulated in Senatore and Reksowardojo (2020), which, in this case, since large deformations are considered, would make the optimization formulation significantly more complex.…”

Seismic control performance of a three‐story frame prototype equipped with semi‐active variable stiffness and damping structural joints

“…Whole‐life energy minimization is a design criterion that accounts for the energy embodied (or embodied carbon equivalent) in the material and the operational share for active control. Numerical and experimental studies have shown that well‐designed adaptive structures achieve significant whole‐life energy savings (up to 70%) compared to weight‐optimized passive structures thus minimizing adverse environmental impacts 23–26 …”

Shape and force control of cable structures with minimal actuators and actuation

“…The technique of controlling shape and internal force has been applied practically on cable arch stayed bridges, 9,10 cable-stayed bridges, 11 and adaptive structures. 12 Furthermore, the optimization for actuation has been applied to double-layer domes. 13,14 In terms of cable net structures, which is highlighted as a reference in this study, You 1 proposed a method.…”