Rip currents are fast offshore currents generated during the breaking process of waves propagating nearshore, posing a potential life safety threat to coastal bathers. This study utilizes a Boussinesq phase-resolving model to investigate the formation mechanism of rip currents at Dadonghai Beach, based on its actual topography, and explores the characteristics of rip current formation under various wave conditions, with an emphasis on analyzing vortices, the mean water level and the spatial distribution of average velocity. The results indicate that rip current formation is significantly influenced by wave height and period. The increase in wave height and period results in more intense rip currents and higher water level fluctuations on arc-shaped beaches and on both sides of the bay, leading to complex vortex distributions. An increase in the angle of wave incidence hinders rip current formation in arc-shaped beach areas but is favorable to the generation of deflection rips on both sides of the bay. Furthermore, an increase in bottom friction inhibits rip current formation. When the water depth decreases in the channels, rip currents transition into longshore currents. The findings of this research offer valuable scientific insights into the formation mechanisms of rip currents and contribute to their prediction and prevention.

In this study, systematic experiments are conducted on a vertical rigid cylinder with two degrees of freedom in the subcritical Reynolds-number regime. The selected flow conditions cover the excitation stage, the lock-in stage, and the post-lock-in stage of vortex-induced vibration. Structural displacements, hydrodynamic forces, and wake vorticity fields are measured simultaneously using laser displacement sensors, force transducers, and particle image velocimetry. The results show that the cross-flow motion remains dominant throughout the investigated range, while the in-line motion is activated through phase coupling within the lock-in region. A stage-dependent redistribution of hydrodynamic loading is identified. The loading first concentrates in the cross-flow direction during synchronization, then partially shifts toward the in-line direction under coupled motion, and finally becomes spatially dispersed as desynchronization develops. This directional redistribution moderates the peak cross-flow amplitude, broadens the lock-in region, and alters the sequence of force-coefficient peaks. The synchronized wake measurements reveal that the flow evolves from incoherent structures to organized vortex streets and then to fragmented and irregular patterns, directly reflecting the formation and collapse of directional load concentration. These findings establish a consistent linkage between hydrodynamic loading, structural response, and wake evolution, and provide experimental evidence for the coupled dynamics of two-degree-of-freedom vortex-induced vibration, offering physical insight for the design and assessment of realistic marine cylindrical structures.

The Peregrine breather (PB), a classical localized solution of the nonlinear Schrödinger equation (NLSE), is widely used to describe the evolution of deep-water rogue waves. However, the influence of variable bathymetry on PB focusing remains insufficiently understood. A two-dimensional RANS–VOF numerical wave tank is therefore established using computational fluid dynamics (CFD) to investigate deterministic PB propagation over variable bathymetry. The model is validated through mesh- and time-step-sensitivity analyses and comparison with the analytical PB solution. Relative water depth, bathymetric interaction length, and bathymetric position are systematically examined. The results reveal for the first time a bathymetry-induced delayed-focusing phenomenon: the PB undergoes local defocusing over elevated topography and refocuses farther downstream after re-entering deeper water. The delay increases as water depth decreases. For k₀h_shelf > 1.363, increasing the interaction length mainly enhances the focusing delay, while self-focusing recovers in deeper water. In contrast, for k₀h_shelf < 1.363, an interaction length of approximately two carrier wavelengths disrupts the coherent PB structure and splits it into two wave packets. The onset position of bathymetric forcing has only a minor effect on the final delay. These results clarify how variable bathymetry modulates PB focusing and structural stability and provide a theoretical reference for nearshore extreme-wave risk assessment.