Figure 2. (a–c) The steady-state interwell motion of the conventional BEH when the base acceleration is 4 m/s 2 and the excitation frequency is 20 Hz. (d–f) The steady-state interwell motion of the 2-DOF MCBEH when the base acceleration is 7 m/s 2 and the excitation frequency is 13.5 Hz. The values of Case A and Case C (Table 1) are used to (a–f) , respectively. (a,d) Show the phase portraits and the stroboscopic points. The time-domain responses are plotted in (b,e) , and their corresponding fast Fourier transform (FFT) results are depicted in (c,f)