Effect of recess position on fluid resonance in a recessed moonpool

This study numerically investigates the effect of recess position on internal fluid resonance in recessed moonpools using a two-dimensional multiphase viscous flow solver. This is motivated by the fact that the horizontal placement of the recess relative to the incident wave direction alters geometric asymmetry, thereby modulating nonlinear free-surface dynamics and intermodal energy coupling. A systematic analysis is conducted to clarify how recess location affects frequency- and spatial-dependent amplitude operators, as well as transient phase adjustment processes. Results indicate that the right recess promotes faster phase stabilization and more effective energy synchronization with incident waves, yielding stronger resonant oscillations. Time-resolved wavelet spectrogram and Fourier harmonic decomposition reveal that the right configuration intensifies nonlinear harmonic generation and broadens the spatial and spectral energy distribution. Spatial modal decomposition further shows enhanced excitation of higher-order sloshing modes and stronger multimodal interactions over a wider frequency range. The influence of recess position on piston-mode radiation damping is also elucidated, highlighting its impact on frequency-dependent wave reflection and transmission. Additionally, viscous energy dissipation is evaluated via vorticity field analysis. The findings of this study provide new physical insights into the geometric sensitivity of moonpool resonance and offer practical guidance for recess placement in engineering applications.