Experimental investigation into the diffraction of propagating L1-type crescent waves by a circular cylinder

Crescent waves are an abnormal wave pattern caused by the instability of Stokes wave. In academic research, crescent waves are classified into symmetric and asymmetric types based on their surface profile symmetry. This study focuses on the diffraction effects of the asymmetric crescent waves (specifically, the propagating L₁-type crescent waves) on a vertical cylinder, examining the spectral differences between the asymmetric crescent and Stokes wave fields, as well as the amplitude distribution and evolution across various orders around the cylinder. The findings indicate that, due to the resonant effect of the disturbance waves, energy is transferred from integer orders to non-integer orders. This transfer results in distinct non-integer order energy at 1.32ω₀ and 1.68ω₀ (ω₀ is the Stokes wave frequency) in the amplitude spectrum, which may induce high-frequency resonance in marine structures. Additionally, the amplitude distribution of integer-order crescent waves around the cylinder aligns with that of corresponding Stokes waves. In contrast, the non-integer order amplitudes can be symmetric to the propagation direction of their disturbance waves, leading to significant contributions to high-frequency transverse forces. What's more, the non-integer order amplitudes can enhance the formation of sharp crests of crescent waves, promoting wave breaking and energy dissipation around the cylinder. It also can increase the pounding effect on the marine structure and raise the risk of overtopping.