Hysteresis phenomenon of the sloshing-mode resonance in a moonpool induced by rolling motion excitations

Abstract

Sloshing-mode resonance in the moonpool induced by roll motion excitations is investigated numerically using the OpenFOAM® package. Nonlinear characteristics of the sloshing-mode resonance are the main focus of the present study. When the roll motion excitation has a time-invariant amplitude, a typical softening spring behavior can be observed in the variation of free surface amplitude against the excitation frequency, including the decreased resonant amplitude and the jump frequency. Furthermore, the dimensionless jump frequency is independent of the moonpool breadth and draft in this situation. The hysteresis phenomenon is clearly observed under the roll excitation with varying amplitudes, where the phase locked-in mechanism is the essential reason for this phenomenon. The hysteresis loop is located between two jump frequencies by the accelerating and decelerating excitations that generate the lower and upper branches, respectively. With the increase in moonpool breadth, the decreased upper branch frequency and unchanged lower branch frequency are observed, leading to the increased region of the hysteresis loop. The variation of the moonpool draft has an insignificant effect on the region of the hysteresis loop.