Coupling Actions Between Motion Response and Gap Resonance in a Roll-Fixed Two-Box System

The coupling actions between the sway and roll motion responses of a ship with sloshing inside are investigated according to experimental measurements and numerical simulations. The increased coupling actions between sway and sway motion responses can be observed after considering the internal sloshing flow actions. When the ship is empty, only the sway motion response around the roll resonant periods can be affected by the roll motion coupling actions, while the sway motion coupling actions cannot affect the roll motion response. After considering the internal sloshing flow, the discrepancy between the sway-roll system and individual roll or sway system can be observed not only around the sloshing natural periods but also around the resonant sway and roll resonant periods and sloshing natural periods. It includes both the sway and roll motion responses. Finally, the influence of incident wave amplitudes and filling conditions are also discussed in this study.

The hydrodynamic characteristics of a free-floating moonpool encountering the gap resonances are investigated based on the constrained interpolation profile method in numerical wave tank. This paper mainly concentrates on the influences of the moonpool's motion responses and the incident-wave height on the gap resonances in the free-floating moonpool. Numerical results demonstrated that the heave response significantly changes the frequency and the magnitude of the linear gap resonance, while the roll motion influences more on the vertical wave loads and the wave responses in the fluid field. The heave and roll response of the free-floating moonpool are generally independent. Moreover, the magnitudes of the nonlinear gap resonances have the tendency of catching up and exceeding the linear gap resonance as the incident-wave height increasing for the free-floating moonpool, which is the consequence of the higher-order harmonics driven by the nonlinear processes and the linear secondary resonant region induced by the heave response. Based on the wavelet transform, it could be observed that the amplified harmonic component usually takes more time to be fully developed than other harmonic components during the development of its corresponding nonlinear gap resonance.

Analytical study on an oscillating buoy integrated with a perforated structure with a quadratic pressure drop condition: A case study on a WEC-perforated breakwater integration system

Berthing is a common marine operation frequently occuring in harbors and at open sea. It involves a moving vessel closely approaching a moored offshore structure or a pier from a far distance. During the berthing operation, the distance between the stationary structure and berthing vessel decreses continuously, resulting in increasing hydrodynamic interaction. In this study, the berthing problem between a FSRU and a LNGC was investigated by using three different numerical methods including dynamic simulation. At first, frequency-domain diffraction computations were carried out to study hydrodynamic interaction between two floaters in the berthing operation. With various relative positions, the effect of gap resonance and sheltering effect were discussed based on the frequency-domain solution. As the second numerical method, time-domain simulation using convolution integrals was used to simulate the berthing problem. The simulation results were directly compared with the model test data. The third numerical approach is dynamic simulation combined with direct fluid solver. In head sea condition, focus is made on the effect of the gap resonance on the wave forces and related motion responses during berthing operation. As for the quartering sea, the sheltering effect is mainly discussed with different berthing routes based on the dynamic simulation results.

The growth of global energy transportation has promoted the rapid increase of large-scale LNG (liquefied natural gas) carriers, and concerns around the safety of LNG ships has attracted significant attention. Such a floating structure is affected by the external wave excitation and internal liquid sloshing. The interaction between the structure’s motion and the internal sloshing under wave actions may lead to the ship experiencing an unexpected accident. In this research, a hydrodynamic experiment is conducted to investigate the motion responses of a floating tank mooring, both close to and away from a dock. The resonance coupling effect of the internal sloshing and gap flow on the tank’s motion is considered. Based on the measured motion trajectory of the floating tank, the stability and safety of the floating tank are estimated. The results show that the sloshing resonance and narrow gap resonance are beneficial to the stability of the ship. This is helpful for controlling the motion of a berthed ship under wave action with a reasonable selection of the gap distance and the liquid level.

Fluid resonance may occur in a narrow gap between two side-by-side vessels under wave actions, which can cause significant wave height amplification inside the gap and further induce large wave loads and motion responses of the vessel. Based on an open-sourced computational fluid dynamics (CFD) package, OpenFOAM, the steady-state gap resonance phenomenon formed in between two side-by-side boxes and triggered by the incident regular waves is simulated, where the upriver box keeps fixed and the downriver one heaves freely under wave actions. This article comprehensively investigates the influence of the vertical degree of freedom of the downriver box on the wave loads exerting on both boxes and further reveals how the relative position of the heaving box with respect to the incident wave direction affects the characteristics of wave loads during the steady-state gap resonance. The results show that both the normalized largest wave loads and the dimensionless wavenumber where the normalized largest wave loads occur are significantly affected by both the incident wave heights and the relative position of the heaving box to the incident wave direction.