Time-dependent nonlinear fluid oscillations in the gap between two side-by-side ships during transfer

Abstract

Time-dependent nonlinear fluid oscillations in the gap between two side-by-side ships during transfer process are investigated numerically based on a two-dimensional fully nonlinear potential flow solver in the time domain. The focus is on understanding the nonlinear dynamic evolution of fluid oscillations within the gap under different incident wave parameters and varying operation windows. Amplitude dynamics, phase dynamics (via Hilbert transform), and time-varying wavelet energy spectra reveal that the fluid oscillations are significantly influenced by incident wave frequency, amplitude, and operation window. The nonlinear evolutions are fundamentally governed by the relative phase between excitation and response. The significance of transfer process, especially within the resonant frequency band, is highlighted for the ship-to-ship operations. Additionally, the combined effects of free-surface nonlinearity and operation window on the relative phase, resonant frequency, and response amplitudes are examined. Two typical nonlinear behaviors of hysteresis and jump are observed in the transient fluid oscillations during the transfer process. The physical insights gained from this study provide a deeper understanding of the nonlinear transient fluid resonance involved in the ship-to-ship transfer process, offering valuable knowledge for the practical side-by-side transfer operations, and contributing new perspectives on the gap resonance problem.