Experimental study of primary- and higher-mode resonant sloshing in a horizontally excited square-base tank

This study experimentally investigates primary- and higher-mode resonant sloshing induced by horizontal excitations in a square-base tank with finite depth. Due to the equal length and width of the three-dimensional rectangular tank, two predominant sloshing modes (the transverse mode and longitudinal mode) emerge simultaneously, even when the tank is subjected to unidirectional external excitation. Consequently, direct excitation of one mode leads to indirect excitation of the other through nonlinear coupling, a complex phenomenon known as autoparametric interaction. This phenomenon is widely observed in (i, j) sloshing modes, where i ≠ j. However, the coupling of autoparametric interaction is stable only in the lowest mode, higher modes are found to be unstable. The experiment also reveals that when the natural frequencies of two modes are very close, applying external excitation at one natural frequency causes a shift in the dominant frequency towards the natural frequency of the other mode. In summary, the findings of this study highlight that liquid sloshing in a square-base tank involves more complex physics compared to sloshing in a two-dimensional rectangular tank.