Floating wind technology represents a critical advancement for the wind energy sector, enabling development in deep-water regions beyond the reach of fixed-bottom structures. Its primary benefits are twofold: it significantly mitigates seabed disturbance, thereby reducing ecological impact, and it taps into the superior and more powerful wind resources available in the open ocean. While numerical modeling is integral to the design and control systems of floating platforms, a clear need persists for models that achieve an optimal compromise between computational demand and predictive accuracy. This investigation conducts a comparative analysis of various numerical methodologies—including Navier–Stokes solvers, potential flow theory, and boundary element methods (BEM)—in simulating the hydrodynamics of a floating offshore wind turbine platform. Using the standard VolturnUS-S platform as a case study, the findings indicate that the low-fidelity analytical potential flow model, based on matched eigenfunction expansions and strip theory with geometric simplifications, exhibits notable inaccuracies when benchmarked against high-fidelity Computational Fluid Dynamics (CFD). In contrast, the mid-fidelity numerical BEM solvers, which apply potential flow theory through full numerical discretization of the wetted surface, demonstrate a strong correlation with CFD results, with deviations specifically on the heave hydrodynamic coefficients. Furthermore, the study reveals consistent results across different CFD models themselves. The research concludes that mid-fidelity models, particularly those based on the boundary element method, can deliver both computationally efficient and sufficiently accurate predictions of hydrodynamic behavior for floating wind turbines, offering a viable alternative to the more time-intensive CFD simulations.
The Stokes drift generated by surface gravity waves has been widely investigated in both laboratory and field studies. However, key uncertainties remain, particularly regarding the modulating role possibly played by long-term oscillations induced by infragravity-like waves locally varying the mean depth. This study addresses these gaps by evaluating Eulerian and Lagrangian mean motions under weakly nonlinear monochromatic and bichromatic surface waves in controlled laboratory experiments. Particle tracking velocimetry (ptv) is used to infer fluid and particle flows underneath the waves. Short-wave-related Stokes drifts are then extrapolated and compared with theory. Results show that the inferred Stokes drift dynamics for the periodic monochromatic wave align well with the theoretical profile. Moreover, albeit long wave flow components are dominant on both short-wave Eulerian and Lagrangian dynamics as they are capable of shifting mean flow profiles onwards and backwards according to long-wave phase, the structure of the ensuing Stokes drift is relatively unaltered and still follows the theoretical law. The experimental findings suggest that the theoretical Stokes profile for a monochromatic wave may still be valid when short-wave motions are modulated by long period fluctuations in water surface and velocity, as long as a weakly nonlinear regime is attained.
Undertow beneath breaking waves controls nearshore mass balance and sediment transport, yet the transition between the lower wave–bottom-influenced region and the overlying flow affected by breaking-generated turbulence lacks a clear dynamical definition. This study investigates the vertical structure of undertow and turbulence beneath two regular laboratory plunging waves propagating over a sloping bottom, based on detailed velocity measurements. Time-averaged and phase-resolved fields, together with turbulent statistics, reveal a vertically differentiated flow, with a lower region more directly influenced by wave–bottom interaction and an upper region increasingly affected by breaking-generated turbulence. To formalize this structure, a classical undertow model is used as a diagnostic framework linking the lower and upper flow regions, allowing the identification of an effective matching level directly from the measurements. This level is not interpreted as a geometric thickness, but as a data-driven interface linking lower-layer wave-induced dynamics to the overlying flow. An independent stress-ratio analysis shows that this level is generally located near a transition in the measured partition between wave-coherent and turbulent shear stresses, supporting its interpretation as a stress-partitioning elevation rather than a purely fitted parameter. The present data exhibit a regime-conditioned relationship between the wave-induced stress evaluated at this level and the forcing acting in the overlying region when combined with wave non-linearity. The organization of the present dataset, together with departures observed for additional data, suggest that undertow dynamics in the surf zone are governed by regime-dependent balances rather than by a single universal law.
Belharra, a wave-energy hotspot located on the French Basque coast, is renowned for occasionally presenting world-class big-wave surfing conditions. This study investigates the underlying processes leading to exceptionally large waves breaking at this site, treated here as a natural case study for bathymetry-driven wave-energy focusing. A combination of spectral and phase-resolving numerical modeling is used to examine a range of incident swell conditions and tide levels, revealing the key processes that shape the wave field at both coastal and local scales. A wave-by-wave analysis of high-energy scenarios is complemented by qualitative comparisons with surfer trajectory data recorded during a large swell event, while coastal hindcasting is used to study historical large swell events. The findings show that extreme conditions at Belharra result from multi-scale bathymetric focusing, in which coastal-scale refraction over offshore features preconditions the incoming swell, while local shoaling over the seamount triggers depth-induced breaking. The most energetic conditions occur for long-period swells approaching from a narrow directional window. Within this window, maximum wave-height amplification and maximum breaking intensity occur for different incident directions, near 295^∘ and 315^∘ , respectively. In addition, higher tide levels lead to larger wave heights but reduced breaking intensity. These findings improve our understanding of the wave dynamics at Belharra and provide broader insight into bathymetry-driven wave-energy concentration and extreme breaking in coastal environments.
This paper presents a feasibility study of an ultra-low-cost wave buoy for measuring water waves, built from a 3D-printed hull and an off-the-shelf data logger with an integrated MEMS inertial measurement unit. The buoy records continuously and carries no telemetry, which reduces the average power consumption to 4.7 mA, so that two D-cell batteries sustain more than 6 months of sampling at 100 Hz. A custom firmware stores the raw sensor data in binary form with a GPS-disciplined UTC time base, and the surface elevation is reconstructed in postprocessing through orientation estimation, removal of the gravity component, adaptive band selection, and double integration. The validation is organized so that each stage isolates a single source of error. Under pure translation, where the orientation of the sensor is constant, the measured acceleration amplitude equals the target on average and three sensors agree with one another to within 1–2
