Abstract
Water wave resonance between two side-by-side vessels is a multimode resonant hydrodynamic phenomenon with low damping. The potential flow damping and viscous damping inside the gap play a significant role, influencing the amplitudes of the gap resonances. The frequencies of the gap modes can be well predicted by linear potential flow theory, while much effort has been made to explore the nature of the viscous damping. A series of experiments is conducted to explore the temporal (Zhao et al., Journal of Fluid Mechanics, vol. 812, 2017, 905–939) and spatial structure (Zhao et al., Journal of Fluid Mechanics, vol. 883, 2020, A22) of the resonant responses along the gap. Ultimately, it is of practical interest to understand the response statistics along the gap in random seas, to facilitate decision making for safe offshore operations. Following our previous studies which focused on new physics, here we identify the design waves that produce the most probable maximum responses under unidirectional random linear wave excitation. This is achieved through an efficient prediction model within linear theory. Combining the experimental data and linear potential flow calculations, we provide the lower and upper bounds of gap responses, bracketing possible responses at field scale. The statistical model is expected to be of practical importance for offshore operations.
Highlights
Gap resonance is a wave–structure interaction phenomenon, where the potential flow damping is small due to the difficulty for waves ‘escaping’ from the gap and the viscous damping becomes important
It is understood that the experimental results cover both radiation damping and viscous damping, limiting the gap resonance amplitudes; while linear potential flow calculations, where viscous damping is ignored which otherwise needs to be identified by experiments, produce much larger resonant responses
Focusing on the statistics of gap resonances driven by linear wave excitation, analysis is performed on the extreme surface elevation motions within the gap
Summary
Gap resonance is a wave–structure interaction phenomenon, where the potential flow damping is small due to the difficulty for waves ‘escaping’ from the gap and the viscous damping becomes important. To examine the temporal (Zhao et al, 2017) and spatial structure (Zhao, Taylor, Wolgamot, Molin, & Eatock Taylor, 2020) along the gap, we conducted a series of experiments for two fixed vessel models in side-by-side configuration It is found in Zhao et al (2017) that the viscous damping inside the gap behaves in a linear form at the large laboratory scale. According to the definition of Blondeux & Vittori, the maximum Reynolds number in our experiment is Rδ = u 2/(ωv) ≈ 180, where u, ω and v denote the velocity amplitude, oscillatory frequency and kinematic viscosity of the fluid, respectively It remains unclear how the damping will behave at full scale.
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