Effects of Gap Resonance on the Hydrodynamics and Dynamics of a Multi-Module Floating System with Narrow Gaps

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.

Coastal Protection Using Integration of Mangroves with Floating Barges: An Innovative Concept

“…The gap between the barges is an important factor in the design, which influences whether the motion of the fluid between the barges is a piston-type or a sloshing-type. The gap width between the barges, draft of the barge and breadth of the barge also influence the resonant frequency of the fluid between the barges [56]. As the gap between the barges increases, the fluid oscillation changes from a sloshing-type to a piston-type when the water depth and the draft of the barge remain constant [57].…”

Numerical and Experimental Study of Hydrodynamic Response for a Novel Buoyancy-Distributed Floating Foundation Based on the Potential Theory

“…The singularity caused by the Green function can be eliminated by adding a damping force at the meshed free surface [42]. The AQWA codes utilize the flexible damping lid method to remove irregular frequencies [43,44]. Unreasonable overestimation values in the numerical results are suppressed to accurately and highly efficiently evaluate the hydrodynamic responses.…”

Fully Coupled Analysis of an Integrated Floating Wind-Wave Power Generation Platform in Operational Sea-States

“…1, two types of viscosity corrections are considered to tackle the numerical errors caused by the ignorance of the fluid viscosity in AQWA. The first type of viscosity correction is related to the unrealistic free surface resonance arising in the multi-body hydrodynamic interactions due to the lack of viscosity and energy dissipation terms in the potential flow theory (Chen et al, 2021a). According to Chen et al (2021a), for adjacent bodies with strong hydrodynamic interactions, ignorance of the fluid viscosity at the free surface condition may lead to unstable time-domain simulations.…”

“…The first type of viscosity correction is related to the unrealistic free surface resonance arising in the multi-body hydrodynamic interactions due to the lack of viscosity and energy dissipation terms in the potential flow theory (Chen et al, 2021a). According to Chen et al (2021a), for adjacent bodies with strong hydrodynamic interactions, ignorance of the fluid viscosity at the free surface condition may lead to unstable time-domain simulations. For the analysed FWWP, both the PAWEC and FOWT foundation structure are small in size, which may not generate strong hydrodynamic interactions as reported by Zhu et al (2021).…”

“…In addition to the aforementioned method, with certain simplifications, many researchers also applied the frequency/time-domain simulation package AQWA (Ansys, 2016) to analyse the coupled dynamics of the FWWP. This package has been widely used in analysing the dynamics of multiple floaters and WECs (Chen et al, 2021a;Chen et al, 2021b). By ignoring the aero-servo-elastic coupling effects of the upper wind turbine structure, Chen et al (2020) applied AQWA to analyse the hydrodynamic interactions solver at each time step.…”