5.3.1. Sinusoidal Excitation

RTHS under sinusoidal excitation was first carried out by employing the *H*∞ controller. The frequency of the excitation was 2 Hz, and the amplitude was increased slowly from 0 to 344.492 N. The period and damping ratios of the simulated structure were 1 s and 0.02, respectively. The stiffness of the NS was the same as that of the PS, which was 34 kN/m. The tracking performance of the actuator with the *H*∞ controller was examined first, and the commanded and measured displacements are shown in Figure 22. It is seen in the figure that at the end of each time integration step, the displacement measurement was almost identical to that of the command. Moreover, the reference solution is also given in Figure 22. It is seen that the measured displacements were in good agreemen<sup>t</sup> with the reference ones.

**Figure 22.** Steady-state response under sinusoidal excitation. (**a**) Overall view; (**b**) enlarged view.
