Vasiliki Katsardi

This work aims to highlight the effects of nonlinearity on the crest shape of large directional water wave events. To simulate such events, we chose to focus frequencies on a pre-determined time step over a wavefield with randomised phases, running the simulations with HOS-ocean, a fully nonlinear potential flow solver. By also applying a phase separation scheme, we were able to identify the contributions of the various orders of nonlinearity to the formation of these large wave events. The findings show a significant change in the shape of these large water waves compared to linear theory, particularly in shallower water depth. In addition, the phase separation reveals the increased significance of high-order harmonics in finite water depths compared to deep water.

This work highlights the effects of nonlinearity on the crest shape of extreme directional water wave events in infinite and finite water depths. HOS-ocean, a High-Order Spectral code developed for solving the deterministic propagation of nonlinear wavefields in open ocean [Ducrozet et al., “HOS-ocean: Open-source solver for nonlinear waves in open ocean based on High-Order Spectral method,” Comput. Phys. Commun. 203, 245–254 (2016)], is used for comparisons with linear simulations. Nonlinear wave harmonics were extracted combining and extending previous methods [Fitzgerald et al., “Phase manipulation and the harmonic components of ringing forces on a surface-piercing column,” Proc. R. Soc. A 470, 20130847 (2014) and Hann et al., “A new set of focused wave linear combinations to extract non-linear wave harmonics,” in Proceedings of 29th International Workshop on Water Waves and Floating Bodies, 2014], showing the contribution of various orders of nonlinearity. The work shows that “walls of water,” [Adcock et al., “Nonlinear dynamics of wave-groups in random seas: Unexpected walls of water in the open ocean,” Proc. R. Soc. A 471, 20150660 (2015) and Adcock et al., “On the shape of large wave-groups on deep water—The influence of bandwidth and spreading,” Phys. Fluids 28, 106601 (2016)], a significant increase in the crest width, are also formulated in finite water depths. Mainly responsible for this is the first order harmonic, with significant energy transfers away from components propagating at an angle, which are more pronounced in finite water depths. As nonlinearity increases, higher order harmonics (>second) become, as expected, more significant. In deep water, rapid energy transfers lead to a broadening of the spectrum which is reflected in the increase in the first order amplitude sum and hence increased crest elevations at the point of the large event. However, in finite water depths, energy transfers are gradually leading to a narrowing of the spectrum around the spectral peak and to a general broadening of the spectrum at the higher harmonics; reflected in the significant decrease in the first order amplitude sum and hence a decrease in crest elevations at the point of the large event, also aided by the larger increase in the out-of-phase difference terms (zeroth harmonic).

This study explores the geomorphological evolution and shoreline dynamics of Chorefto Beach in Zagora, Pelion, Greece over the period 1945–2023. Combining historical data analysis, field observations, and advanced numerical simulations, the research evaluates natural and anthropogenic influences on sediment transport, erosion, and shoreline stability. Using sediment transport models like the Revised Universal Soil Loss Equation (RUSLE) and the Erosion Potential Method (EPM), the study identifies increased rainfall as a primary driver of sediment deposition. Key findings reveal that sediment contributions from nearby streams, coupled with wave dynamics and wind action, sustain a state of dynamic equilibrium that mitigates erosion risks. Numerical modelling via the MIKE 21/3 coupled system further validates these findings, indicating that even under extreme wind and wave scenarios, erosion remains negligible in critical areas. The results highlight a consistent long-term trend of shoreline accretion, supported by sediment influx from streams and a stable balance of natural forces. The study underscores the importance of integrated coastal zone management strategies to preserve the environmental integrity of Chorefto Beach and promote sustainable coastal development in the face of evolving climatic and anthropogenic pressures. These findings provide critical insights for managing similar vulnerable coastal zones effectively.

In the present paper a Coupled-Mode System Model is used for the numerical simulation of wave transmission through flushing culverts. Numerical results are presented for waves propagating over regions with submerged breakwaters, simulating flushing culverts that are never perfectly filled with water. These are compared with a series of 64 experiments, for different wave conditions and/or geometrical characteristics of the openings. The present numerical approach has given good comparisons with more than the 50% of the experimental data. Deviations were observed when simulating steeper waves and/or narrower culverts, enabling the identification of the cases where the increased effects of nonlinearity, the generation of higher harmonics and 3D effects are important and should be taken into account. Nevertheless, the present model can be used as a useful starting tool in calculating efficiently the effectiveness of a flushing culvert in terms of maintaining water quality in a harbor basin.

Standard openings in coastal structures are the flushing culverts at breakwaters, allowing periodic exchange of the harbor basin water leading to improved water quality. These openings involve sudden water depth changes occurring when the incident waves meet these openings and transmitted into the harbour. The wave transformations during wave propagation through flushing culverts are dominated by 3D diffraction effects due to sudden water depth changes, along with the finite width of the culvert. A new coupled-mode model, based on eigenfunctions expansions of the Laplace equation, is developed and applied to the numerical solution of the local 3D wave flow problem at the opening. The harmonic wave field is excited by incident parallel waves. The numerical solution converges rapidly, permitting the series truncation at its first terms. The proposed method fully accounts for the 3D diffraction effects and produces information to couple with mild-slope models describing efficiently wave propagation and transformation in coastal regions.