## 2 Application to Flexible Structures
### Structural Vibration Control
[PERSON] proposed the pair of antagonistic SMA wires for vibration control of a flexible cantilever beam subjected to air flow (external excitation) from the wind tunnel in which the control voltage to be applied to SMA actuator was determined from a gain-scheduled H-infinity controller taking account for ambient airflow conditions [28]. [PERSON] et al. developed the compliance map variability of a flexible link structure using SMA springs and adopted the concept of driving a virtual workspace from structural deformation with a small and large displacement hypothesis [29]. [PERSON] and [PERSON] proposed an adaptive-passive beam with SMA actuator based on an underslung cable-staged girder concept in which the temperature modulation was achieved from a closed-loop control associated with the PID controller [30]. [PERSON] et al. used a restoring force generated from SMA wire to realize vibration control of flexible structure in which the resonance due to external disturbance was avoided by changing the natural frequency of the beam structure to be increased or decreased depending on the restoring force of SMA wire [31]. [PERSON] et al. investigated the aeroelastic behaviors by implementing the passive pseudo-elastic hysteresis of SMA springs in which the range of post-flutter airflow speeds with stable limit cycle oscillation was analyzed by activating SMA springs with the synchronized switching damping technique [32]. [PERSON] et al. proposed a tension-compression self-centering damper based on the energy dissipation of pre-stretched SMA wire. One of these damping groups was activated during tension and the other during compression to increase the damping capacity of the system [33]. [PERSON] and [PERSON] proposed an adaptive vibration absorber for vibration control of civil structures using the real-time temperature modulation  
Figure 2: Vibration control of flexible beam structure. © IOP Publishing. Reproduced with permission. All rights reserved. of SMA through Joule effect, which could control the elastic modulus of the structures and hence achieve a wide range of tuning the frequency for stiffness adaptation [34]. [PERSON] et al. presented an active vibration control system for the cantilever beam using SMA wires where a nonlinear controller based on the dynamic inversion and optimal control was realized after optimally installing the actuators and sensors [35]. [PERSON] et al. developed a tunable vibration absorber using SMA and applied it to suppress the vibrations of a planar structure using the interval type-2 fuzzy controller describing the nonlinear mapping between the input and the output [36]. [PERSON] et al. presented SMA-based stiffening strategy to reduce blade vibration of the large horizontal axis wind turbine where the aerodynamic loads acting on the blades were evaluated via the blade element momentum theory [37]. [PERSON] and [PERSON] applied SMA wire to a flexible needle to achieve precise tracking in medical interventional procedures where an adaptive sliding mode controller was implemented to keep the robustness against uncertainties [38]. [PERSON] and [PERSON] have embedded SMA wire into a silicone beam to achieve different natural frequencies and vibration modes of the beam structure in which the avoidance of the resonance behavior due to external excitation can be effectively achieved by activating SMA wire with different temperatures [39]. [PERSON] et al. devised a new hydraulic SMA shock absorber that uses an SMA bar as the core of a component for energy dissipation and recovery in the stress mode of pure tension and whose initial deformation is enlarged by a hydraulic system with two sizes of pistons [40]. [PERSON] et al. investigated the influence of SMA on the dynamic behaviors of flexible rotors in which a suspension composed by SMA wires was connected to the rotor-bearing test rig to achieve stiffness tuning due to the hysteretic cycle denoting energy dissipation [41]. [PERSON] et al.