Abstract
Multi-module floating system has attracted much attention in recent years as ocean space utilization becomes more demanding. This type of structural system has potential applications in the design and construction of floating piers, floating airports and Mobile Offshore Bases (MOBs) generally consists of multiple modules with narrow gaps in which hydrodynamic interactions play a non-neglected role. This study considers a numerical model consisting of several rectangular modules to study the hydrodynamics and dynamics of the multi-module floating system subjected to the waves. Based on ANSYS-AQWA, both frequency-domain and time-domain simulations are performed to analyze the complex multi-body hydrodynamic interactions by introducing artificial damping on the gap surfaces. Parametric studies are carried out to investigate the effects of the gap width, shielding effects of the multi-body system, artificial damping ratio on the gap surface, and the dependency of the hydrodynamic interaction effect on wave headings is clarified. Based on the results, it is found that the numerical analysis based on the potential flow theory with artificial damping introduced can produce accurate results for the normal wave period range. In addition, the effects of artificial damping on the dynamics and connector loads are investigated by using a simplified RMFC model. For the case of adding an artificial damping ratio of 0.2, the relative heave and pitch motions are found to be reduced by 33% and 50%, respectively. In addition, the maximum cable and fender forces are found to be reduced by 50%, compared with the case without viscosity correction.
Highlights
With the size and weight of offshore floating structures being continually increased to meet the needs for exploiting various resources from the ocean, the multi-module floating system has become increasingly popular due to its advantages such as the ease of fabrication, transportation, and installation as well as the reduction of the overall waveinduced longitudinal loads
Wang et al [15] adopted the linear potential flow theory to study the hydrodynamic interaction between two semi-submersible types of VLFS modules in the frequency domain
Effectiveness of introduction the introduction of artifidamping is validated with the frequency-domain results and is further cross-verified cial damping is validated with the frequency-domain results and is further cross-verified with withthe thetime-domain time-domainsimulations simulationsby byusing usingthe thestandard standardcode codeANSYS-AQWA
Summary
With the size and weight of offshore floating structures being continually increased to meet the needs for exploiting various resources from the ocean, the multi-module floating system has become increasingly popular due to its advantages such as the ease of fabrication, transportation, and installation as well as the reduction of the overall waveinduced longitudinal loads. Li et al [16] built a numerical wave tank based on the fully nonlinear potential flow theory to investigate the fluid resonant phenomenon at the gap in-between the adjacent floating bodies. Koo et al [29] investigated the hydrodynamic interaction and mechanical coupling effects of two floating platforms by using a time-domain coupled dynamics analysis method Their results show that the cross-coupling terms in the offdiagonal region of the full hydrodynamic coefficient matrix play an important role in the case of multi-floaters in close proximity. The aforementioned numerical studies are all based on the potential flow theory, which has been widely used to analyze the wave-structure interaction problems in offshore engineering This method ignores the fluid viscosity and cannot accurately predict the gap resonant behaviour arising from the interactions between the waves and the multi-body system. The resonant frequency prediction in the frequency domain and the effect of artificial damping on the impulse response function and connector load in the time domain are both investigated
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