Numerical study of fluid resonance of a two-dimensional heaving-free moonpool in a wide range of incident waves

The fluid resonance of a moonpool freely heaving in a beam sea is studied by an in-house constrained interpolation profile (CIP) code. Generally, the moonpool behaves as in the piston mode with a narrow opening. The numerical studies are carried out for a wide range of the incident waves, and a new secondary resonant region is identified in the low frequency region of the incident waves, besides the ordinary main resonant region. Numerical results demonstrate that the horizontal wave forces are significant in the secondary resonant region, although the resonant wave elevations are less remarkable than those of the main resonant region. It is concluded that the fluid resonance of the low frequency is excited mainly by the heave motion of the moonpool. Parameter studies of the moonpool draft and the gap width of the moonpool based on the fluid resonance are also performed.