Traditional concrete revetments can destroy the ecological environment and the water landscape. An increasing number of ecological revetment structures have been applied in coastal, lake, and river regulation projects. It has been found that honeycomb-type revetments display a better performance in the attenuation of wave overtopping when compared to experimental data collected using the Eurotop and Muttray’s formula; recording a 40% decrease in the wave run-up in comparison to the latter. To further investigate the wave run-up and overtopping of the ecologically vegetated honeycomb-type revetment, based on OpenFOAM, an open source computational fluid dynamics software, a three-dimensional numerical wave tank was established. The Discrete Particle Method (DPM) was used to simulate gravel movement, and the flexible plant move boundary model was developed to simulate vegetation. The results of wave run-up calculated by the numerical model and those obtained by the experiments were in good agreement, with errors less than 20%. The modeled results of wave overtopping were within the same order of magnitude as those from the experiments; however, critical limitations were noticed due to effects of plant generalization and grid restrictions imposed by DPM methods. The results showed that wave overtopping increased with increasing wave period and wave height. However, with an increase in the wave overtopping, the influence of the wave period on wave overtopping decreased. The increase in vegetation density effectively reduced wave overtopping. Furthermore, an empirical formula for wave overtopping, considering the effects of vegetation density, was proposed.

A joint distribution of significant wave heights ($H_s$) and peak wave periods ($T_p$) in the northwestern South China Sea is created using a conditional distribution model in this work. An unstructured triangular mesh wave model covering the northwestern South China Sea is established based on the third-generation spectral wave model SWAN. This wave model has been extensively validated against field data and was run from 1979 to 2020 to generate long enough one-hourly $H_s$ and $T_p$. Four probability density functions including Normal, Lognormal, Gamma and 3P Weibull distributions are adopted to construct the marginal independent distribution of $H_s$. The results show that the 3P Weibull distribution is more suitable in fitting the marginal distribution of $H_s$ compared to the other three distributions. Three combinations of dependence functions ($\mu \mathrm{and} \sigma$), namely, power3 and exp3, insquare2 and asymdecrease3, and logistics4 and alpha3, are used to create the Normal and Lognormal distributions for $T_p$. The estimations of dependence functions and corresponding fitted $T_p$ demonstrate that the $\mu \mathrm{and} \sigma$ using power3 and exp3 perform best in producing the conditional distribution of $T_p$. In addition, the environmental contours derived by an IFORM are used to generate the extreme sea states with return periods of 1, 5, 10, 25, 50 and 100 years.

The Beibu Gulf’s ocean circulation system regulates regional marine ecosystems, sediment transport, and coastal geomorphology while also supporting vital economic activities. This study integrates one-year current observations from four in-situ current observation stations (B1−B4) with simulations using the Regional Ocean Modeling System (ROMS) to characterize circulation dynamics in the gulf. Observations show persistent northward subtidal currents west of Hainan Island year-round, primarily sustained by tidal-induced residual currents. These currents briefly reverse southward during strong northerly wind events, whereas subtidal currents in the northern Beibu Gulf are more wind-dependent, showing pronounced seasonal variations. Numerical results confirm that winter circulation is dominated by a basin-wide cyclonic gyre driven by northeasterly monsoons. In summer, circulation in the northern gulf is cyclonic under southeasterly winds, but turns anticyclonic when southwesterly winds prevail, indicating strong sensitivity to summer monsoon wind direction. By combining multi-station observations and numerical simulations, this study provides a systematic characterization of the seasonal circulation of the oceanic system in the Beibu Gulf, offering new insights into its dynamic mechanisms.

The composite cylindrical wind turbine foundation is characterized by its large-diameter cylindrical base, which offers superior anti-overturning capability, and it is widely used in the soft soil seabed of Jiangsu, China. Due to its complex structural form, the local scour under combined waves and current significantly differs from that of monopile foundations. However, research on the scour characteristics specific to composite cylindrical wind turbine foundations remains scarce. A numerical model for local scour of wind turbine foundations was established in this study, which was verified with the field-measured scour data. A series of numerical simulations of local scour depths for composite cylindrical wind turbine foundations under various water depths and wave-current combinations were conducted. The simulation results indicate that the wake vortex shedding caused by the complex structural form leads to the local scour around the composite cylindrical wind turbine foundation; the normalized scour depth increases with the Keulegan-Carpenter number and the relative current strength; when the relative current strength is greater than 0.6, the influence of the Keulegan-Carpenter number on scour depth tends to be weakened; similarly, as the Keulegan-Carpenter number increases, the effect of the relative current strength on scour depth gradually diminishes. A scour equation of the composite cylindrical wind turbine foundation is suggested to predict the local scour in fine sand bed under waves and current.

Offshore pipeline landfall sections in tropical coastal zones are often exposed to dynamic hydrodynamic forcing, which may induce seabed erosion and wave-driven liquefaction and thereby affect burial stability. This study presents an integrated assessment of seabed stability for an offshore gas pipeline along the Sarawak coast of the South China Sea, aiming to support burial-depth design in the nearshore surf zone. A multi-model framework was applied to simulate regional hydrodynamics, sediment transport, storm-induced seabed morphodynamics, and wave-induced liquefaction. Model performance was evaluated using field observations, bathymetric survey data, and laboratory experimental results. The results indicate that the seabed remains generally stable under normal environmental conditions, whereas extreme storm-wave forcing may induce localized surf-zone erosion and shallow seabed weakening. Under the 100-year storm-wave scenarios, the maximum simulated erosion depth reaches approximately 0.82 m, and the potential liquefaction response is mainly confined to the upper approximately 1.0 m of the seabed. These results suggest that storm-induced morphodynamic cover loss and wave-induced degradation of near-surface soil support should be evaluated jointly. Based on this integrated process envelope, a minimum burial depth of 2 m is recommended as a conservative engineering requirement for the examined landfall conditions. This process-integrated assessment workflow offers an applicable reference for the design and risk mitigation of analogous offshore pipeline projects in tropical coastal zones.