## 2 Application to Flexible Structures
### Structural Vibration Control
investigated an SMA slat-cove filler to reduce noise for the leading-edge-slat high-lift system where aero-structural experiments were conducted incorporating with the digital image correlation measurements and measured displacement from the laser sensor [56]. [PERSON] et al. investigated the use of SMA composites in a one-story frame structure subjected to earthquakes in which both linear matrix and elastoplastic matrix with isotropic and kinematic hardening were considered [57]. [PERSON] et al. assessed the concrete bridge piers subjected to the seismic loadings with different reinforcement alternatives associated with SMA where the seismic responses were evaluated by the maximum drift, residual drift, and energy dissipation [58]. [PERSON] et al. investigated the bending deformation of a flexible structure using SMA wire and SMP layer in which the SMA-SMP composite actuators were fabricated using 3D printing, and the stiffness modulation for shape retention and recovery was achieved from embedded SMP segments of different thickness whose temperature could be controlled through Joule heating [59]. [PERSON] et al. proposed an SMA-based inerter combined with electromagnetic transducer for vibration control of buildings where both the equivalent linearization for efficient input-output characterization and the ensemble surrogate analysis for the stochastic response quantification were used to validate the efficiency of vibration control capacity of a high story building as a function of wind speed [60]. [PERSON] and [PERSON] proposed a hybrid structure consisting of SMA and E-glass fiber reinforced composite to investigate the change of the stiffness and hence the natural frequencies from the free vibration response where both the fiber volume and fiber orientation were chosen as design parameters [61]. Various studies using SMA actuators have been proposed to control the vibration of single-link or two-link flexible arm structures. [PERSON] et al. implemented an optimal control of linear quadratic regulator (LQR) for vibration control of a single-link flexible arm during the rotational motion by direct current (DC) servo motor [62]. [PERSON] et al. presented design and control of two-link flexible robot arm using SMA wires to achieve precise position tracking of the end-effector in which four different controllers of proportional and derivative (PD) controller, sliding mode controller, adaptive control law, and adaptive sliding mode controller were realized, and their control performances were compared [63]. [PERSON] et al. presented an operator-based control system to control unwanted vibration of a flexible arm using SMA actuator in which the hysteresis and thermal compensator was considered to overcome the temperature change around the SMA actuator for long-term use of the system [64]. Research works using SMA actuators have been also proposed to control the vibration of flexible structures other than beams or plates. [PERSON] et al. proposed a non-contact and temperature-independent technique to suppress the vibration of rings using a light-activated SMP where the phase shift and neural network controller were implemented to enhance the actuating efficiency of SMP and hence vibration reduction capacity [65]. [PERSON] et al. proposed a thin-walled cylindrical shell with SMA driven screw-type actuators to actively control the stiffness and hence natural frequencies where the geometric parameters of the actuators were optimized based on the static and model analysis of the system, and the influence of the actuator number and actuation time on the control performance was investigated [66]. Table 1 presents a summary of vibration control methods of flexible structures using an SMA actuator. As noticed from the table, many active controllers such as sliding mode controller and fuzzy controller have been implemented in the period of 2010-2018, but there are several works on passive control methods in 2020 and 2021.