Wave slamming is an important phenomenon due to its destructive power, and with the rapid development of offshore wind turbines, wave slamming on vertical cylinders has garnered lots of attention. However, the phenomenon of wave slamming on vertical cylinders is very complicated due to both the intrinsic complexity of breaking waves and that of slamming forces. The objective of this paper is to provide a general review of research related to this problem, including theoretical methods, experimental studies, numerical simulations, and full-scale measurements. Based on these approaches, the momentum theory/pressure impulse theory, spatial distribution characteristics of impacts to various breaking waves, wave generation methods, analysis methods for measured forces under structure response, scale effects in experiments, and in-situ measurements have been introduced and discussed. Results show that simplifications in existing models for wave impacting such as wave characteristics and structural response reduce its applicability and should be studied further both in theoretical, experimental and numerical researches.

With the advancement of the global economy, the coastal region has become heavily developed and densely populated and suffers significant damage potential considering various natural disasters, including tsunamis, as indicated by several catastrophic tsunami disasters in the 21st century. This study reviews the up-to-date tsunami research from two different viewpoints: tsunamis caused by different generation mechanisms and tsunami research applying different research approaches. For the first issue, earthquake-induced, landslide-induced, volcano eruption-induced, and meteorological tsunamis are individually reviewed, and the characteristics of each tsunami research are specified. Regarding the second issue, tsunami research using post-tsunami field surveys, numerical simulations, and laboratory experiments are discussed individually. Research outcomes from each approach are then summarized. With the extending and deepening of the understanding of tsunamis and their inherent physical insights, highly effective and precise tsunami early warning systems and countermeasures are expected for the relevant disaster protection and mitigation efforts in the coastal region.

An experimental study is presented on the non-Gaussian statistics of random unidirectional laboratory wave fields described by JONSWAP spectra. Relationships between statistical parameters indicative of the occurrence of largeamplitude waves are discussed in the context of the initial steepness of the waves combined with the effect of spectral peakedness. The spatial evolution of the relevant statistical and spectral parameters and features is also considered. It is demonstrated that over the distance the spectra exhibit features typical for developing nonlinear instabilities, such as spectral broadening and downshift of the peak, along with lowering of the high-frequency tail and decrease of the peak magnitude. The wave fields clearly show an increase of third-order nonlinearity with the distance, which can be significant, depending on the input wave environment. The steeper initial conditions, however, while favouring the occurrence of extremely large waves, also increase the chances of wave breaking and loss of energy due to dissipation, which results in lower extreme crests and wave heights. The applied Miche-Stokes-type criteria do confirm that some of the wave extremes exceed the limiting individual steepness. Eventually, this result agrees with the observation that the largest number of abnormal waves is recorded in sea states with moderate steepness.

“Green–Naghdi Theory, Part A: Green–Naghdi (GN) Equations for Shallow Water Waves” have investigated the linear dispersion relations of high-level GN equations in shallow water. In this study, the GN equations for deep water waves are investigated. In the traditional GN equations for deep water waves, the velocity distribution assumption involves only one representative wave number. Herein, a new velocity distribution shape function with multiple representative wave numbers is employed. Further, we have derived the three-dimensional GN equations and analyzed the linear dispersion relations of the GN-3 and GN-5 equations. In this study, the finite difference method is used to simulate focus waves in the time domain. Additionally, the GN-5 equations are used to validate the wave profile and horizontal velocity distribution along water depth for different focused waves.

This paper presents a comprehensive experimental study on the effect of extreme waves on a LNG carrier. The LNG carrier model was equipped with a variety of sensors to measure motions, green water height on deck as well as local and global loads. Experiments in transient wave packets provided the general performance in waves in terms of response amplitude operators and were accompanied by tests in regular waves with two different wave steepness. These tests allowed detailed insights into the nonlinear behavior of the vertical wave bending moment in steep waves showing that green water on deck can contribute to a decrease of vertical wave bending moment. Afterwards, systematic model tests in irregular waves were performed to provide the basis for statistical analysis. It is shown that the generalized extreme value distribution model is suitable for the estimation of the extreme peak values of motions and loads. Finally, model tests in tailored extreme wave sequences were conducted comparing the results with the statistical analysis. For this purpose, analytical breather solutions of the nonlinear Schr?dinger equation were applied to generate tailored extreme waves of certain critical wave lengths in terms of ship response. Besides these design extreme waves, the LGN carrier was also investigated in the model scale reproduction of the real-world Draupner wave. By comparing the motions, vertical wave bending moment, green water column and slamming pressures it is concluded that the breather solutions are a powerful and efficient tool for the generation of design extreme waves of certain critical wave lengths for wave/structure investigations on different subjects.

As the turbine blade size becomes larger for economic power production, the coupling effect between wind turbine and floating substructure becomes important in structural assessment. Due to unsteady turbulent wind environment and corresponding coupled substructure response, time-domain analysis is required by international electrotechnical commission and class societies. Even though there are a few numerical tools available for the time domain structural analysis based on conventional coupled motion analysis with wind turbine, the application of conventional time domain analysis is impractical and inefficient for structural engineers and hull designers to perform structural strength and fatigue assessment for the required large number of design load cases since it takes huge simulation time and computational resources. Present paper introduces an efficient time-domain structural analysis practically applicable to buckling and ultimate strength assessment. Present method is based on ‘lodal’ response analysis and pseudo-spectral stress synthesizing technique, which makes timedomain structural analysis efficient and practical enough to be performed even in personal computing system. Practical buckling assessment methodology is also introduced applicable to the time-domain structural analyses. For application of present method, a 15-MW floating offshore wind turbine platform designed for Korean offshore wind farm projects is applied. Based on full-blown time domain structural analysis for governing design load cases, buckling and ultimate strength assessments are performed for the extreme design environments, and the class rule provided by Korean Register is checked.

A moving submarine can generate internal waves, as well as extremely small free surface waves, in a fluid with density stratification. In this study, the internal and free surface wave wakes caused by a moving submarine in two layers of constant density fluid were studied numerically using the commercial software STAR-CCM+. The realizable k–ε turbulence model was used to solve the Reynolds-averaged Navier–Stokes equation, and the volume of the fluid method was used to monitor the fluctuations of the internal interface and free surface. Different cases of a moving submarine with different cruising speeds and relative diving depths were studied. Results showed that the maximum fluctuation amplitude of the free surface increased as the speed of the submarine increased; however, the maximum fluctuation amplitude of the internal interface first decreased and then increased. When the submarine moved at the maximum cruising speed, the maximum fluctuation amplitude of the free surface decreased as the diving depth increased, while the wavelength of the free surface wave was basically the same. If the submarine moved at the minimum cruising speed, then the wave elevation in the free surface was extremely small, but the internal surface had obviously large-amplitude internal waves, and the relative diving depth had a great influence on internal waves.

Spectral bandwidth is a relevant parameter of water wave evolution and is commonly used to represent the number of wave components involved in wave–wave interactions. However, whether these two parameters are equivalent is an open question. Following the high-order spectral method and taking the weakly modulated Stokes wave train as the initial condition, the relationship between the spectral bandwidth and the number of wave components is investigated in this work. The results showed that the number of wave components can vary with the same spectral bandwidth and that distinct wave profiles emerge from different numbers of wave components. With a new definition of significant wave components, the characteristics of this parameter in the long-time wave evolution are discussed, along with its relationship with common parameters, including the wave surface maximum and the wave height. The results reveal that the wave surface evolution trend of different numbers of significant wave components (N_s) is the same from a holistic perspective, while the difference between them also exists, mainly in locations where extreme waves occur. Furthermore, there is a negative correlation between r (a_j/a₀) and wave surface maximum (η_max/a₀) and wave height (H_max and H_s). The evolution trends of the relative errors (RE) of η_max/a₀, H_max, and H_s of different N_s show the periodic recurrence of modulation and demodulation in the early stage when the Benjamin–Feir instability is dominated. The difference is that in the later stage, the RE of η_max/a₀ and H_max is chaotic and irregular, while those of H_s gradually stabilize near an equilibrium value. Furthermore, we discuss the relationship between the mean relative error (MRE) and r. For η_max/a₀, MRE and r show a logarithmic relationship, while for H_max and H_s, a quadratic relationship exists between them. Therefore, the choice of N_s is also important for extreme waves and is particularly meaningful for wave generation experiments in the wave flume.

Owing to the large amplitude and nonlinearity of extreme sea waves, sailing ships exhibit obvious large-amplitude motion and green water. For a tumblehome vessel, a low-tumblehome freeboard and wave-piercing bow make green water more likely. To study the green water of a wave-facing sailing tumblehome vessel in strong nonlinear regular waves, the computational fluid dynamics software STAR-CCM+ was used. The Reynolds-averaged Navier–Stokes method was used for the numerical simulation, and the k-epsilon model was adopted to deal with viscous turbulence. The volume of the fluid method was used to capture the free surface, and overset grids were utilized to simulate the large-amplitude ship motion. This study delves into the influence of wave height on the ship motion response and a tumblehome vessel green water under a large wave steepness (0.033 ≤ H/λ ≤ 0.067) at Fr = 0.22. In addition, the dynamic process of green water and the “wave run-up” phenomenon were evaluated. The results suggest that when the wavelength is equal to the ship length and the wave steepness increases to 0.056, the increase in the water height on the deck is obvious. However, the wave height had little effect on the green water duration. The wave steepness and “backwater” have a great impact on the value and number of the peak of the water height on the deck. When the wave steepness exceeded 0.056, the water climbed up, and the plunging-type water body was formed at the top of the wave baffle, resulting in a large water area on the deck.

Efficient generation of an accurate numerical wave is an essential part of the Numerical Wave Basin that simulates the interaction of floating structures with extreme waves. computational fluid dynamics (CFD) is used to model the complex free-surface flow around the floating structure. To minimize CFD domain that requires intensive computing resources, fully developed nonlinear waves are simulated in a large domain that covers far field by more efficient potential flow model and then coupled with the CFD solution nearfield. Several numerical models have been proposed for the potential flow model. the higher-level spectral (HLS) method presented in this paper is the extended version of HLS model for deep water recently been derived by combining efficiency and robustness of the two existing numerical models–Higher-Order Spectral method and Irrotational Green-Naghdi model (Kim et al. 2022). The HLS model is extended for the application of finite-depth of water considering interaction with background current. The verification of the HLS model for finite depth is made by checking the qualification criteria of the generated random waves for a wind-farm application in the Dong-Hae Sea of Korea. A selected wave event that represents P90 crest height is coupled to a CFD-based numerical wave tank for the future air-gap analysis of a floating wind turbine.

Extreme value analysis is an indispensable method to predict the probability of marine disasters and calculate the design conditions of marine engineering. The rationality of extreme value analysis can be easily affected by the lack of sample data. The peaks over threshold (POT) method and compound extreme value distribution (CEVD) theory are effective methods to expand samples, but they still rely on long-term sea state data. To construct a probabilistic model using shortterm sea state data instead of the traditional annual maximum series (AMS), the binomial-bivariate log-normal CEVD (BBLCED) model is established in this thesis. The model not only considers the frequency of the extreme sea state, but it also reflects the correlation between different sea state elements (wave height and wave period) and reduces the requirement for the length of the data series. The model is applied to the calculation of design wave elements in a certain area of the Yellow Sea. The results indicate that the BBLCED model has good stability and fitting effect, which is close to the probability prediction results obtained from the long-term data, and reasonably reflects the probability distribution characteristics of the extreme sea state. The model can provide a reliable basis for coastal engineering design under the condition of a lack of marine data. Hence, it is suitable for extreme value prediction and calculation in the field of disaster prevention and reduction.

Al-Nakheel beach is located northwest of Alexandria city, Egypt, along the Mediterranean coast. During the period from 1998 to 2003, seven detached breakwaters were constructed along Al-Nakheel beach to create a sheltered area for swimming. Unfortunately, the structures amplify rip currents, shoreline accretions, and erosions. The aim of this research is to track the variations of the rip currents within the study area and show the effects of the breakwaters on the shoreline. The research is based on the hydrodynamic and morphological data of the study area and uses the Delft3D hydrodynamical model combined with other data analysis tools to serve the model input. The data include measured sea-level observations in 2013, the ERA-interim wave datasets from 2015 to 2018 and wind data in 2018, bed morphologies, and Google Earth satellite images from 2010 to 2020. The model is calibrated on the basis of the available current measurements within the nearshore zone. Results show that the shoreline eroded at an average rate of about 0.9 m/yr. Moreover, pairs of vortices are formed behind the breakwaters with an average current velocity of 0.6 m/s. The predominant northwest waves induce rip currents on the leeside of the structures with velocities reaching 1.2 m/s, associated with the rip pulsation that extends offshore. The problem solution decision recommends the removal of the sand deposition on the leeside of the breakwaters by an average amount of 100 000 m³/yr and the fencing of the safe area for swimming by a floating fence of 1 000 m length and 65 m average width.

At present, studies on large-amplitude internal solitary waves mostly adopt strong stratification models, such as the twoand three-layer Miyata–Choi–Camassa (MCC) internal wave models, which omit the pycnocline or treat it as another fluid layer with a constant density. Because the pycnocline exists in real oceans and cannot be omitted sometimes, the computational error of a large-amplitude internal solitary wave within the pycnocline introduced by the strong stratification approximation is unclear. In this study, the two- and three-layer MCC internal wave models are used to calculate the wave profile and wave speed of large-amplitude internal solitary waves. By comparing these results with the results provided by the Dubreil–Jacotin–Long (DJL) equation, which accurately describes large-amplitude internal solitary waves in a continuous density stratification, the computational errors of large-amplitude internal solitary waves at different pycnocline depths introduced by the strong stratification approximation are assessed. Although the pycnocline thicknesses are relatively large (accounting for 8%–10% of the total water depth), the error is much smaller under the three-layer approximation than under the two-layer approximation.