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Wave radiation stress is the main driving force of wave-induced near-shore currents. It is directly related to the hydrodynamic characteristics of near-shore current whether the calculation of wave radiation stress is accurate or not. Irregular waves are more capable of reacting wave motion in the ocean compared to regular waves. Therefore, the calculation of the radiation stress under irregular waves will be more able to reflect the wave driving force in the actual near-shore current. Exact solution and approximate solution of the irregular wave radiation stress are derived in this paper and the two kinds of calculation methods are compared. On the basis of this, the experimental results are used to further verify the calculation of wave energy in the approximate calculation method. The results show that the approximate calculation method of irregular wave radiation stress has a good accuracy under the condition of narrow-band spectrum, which can save a lot of computing time, and thus improve the efficiency of calculation. However, the exact calculation method can more accurately reflect the fluctuation of radiation stress at each moment and each location.

The hydrodynamic response of closed and semi-closed (open-bottom) rigid cylindrical aquaculture platforms was examined through combined model tests and numerical simulations. Free decay tests in calm water quantified natural periods and damping ratios for heave and pitch motions. Subsequent regular wave testing characterized response amplitude operators (RAOs) and wave elevations at interior and exterior wave gauges. Finally, the motion and wave elevation characteristics of the two types of aquaculture platforms under irregular waves were analyzed under extreme sea conditions. Results demonstrated that bottom openings significantly altered hydrodynamic responses of aquaculture platforms, with a 59% enhancement in heave damping ratio and a 47% reduction in heave natural period. Semi-closed cages exhibited asymmetric internal sloshing profiles along the mid-transverse axis, with lateral sloshing amplitudes increasing by 200–300% at lateral wave gauges. Under irregular wave conditions, compared to closed aquaculture platform, semi-closed aquaculture platform increased the heave, pitch motion, and internal sloshing response but reduced run-up on the outer wave-facing side.

Hong, S.; Dodaran, A.A.; Kim, T.; Kim, J.; Huynh, V.M.; Lee, J., and Kwon, S., 2021. Variation of irregular waves passing over an Artificial Coral Reef (ACR). In: Lee, J.L.; Suh, K.-S.; Lee, B.; Shin, S., and Lee, J. (eds.), Crisis and Integrated Management for Coastal and Marine Safety. Journal of Coastal Research, Special Issue No. 114, pp. 524–528. Coconut Creek (Florida), ISSN 0749-0208. To investigate the variation of irregular waves due to an Artificial Coral Reef (ACR), two-dimensional experiments on the wave steepness, wave period, and relative submergence were conducted. The results for the wave transmission coefficient under ACR installation indicated that the wave steepness and period conditions are closely related to wave attenuation, which has similar trends for general coastal structures, even under irregular wave conditions. Additionally, the total spectral energy decreased gradually, whereas an inconsistent peak-energy decrement occurred with a wave steepness of 0.032, which was expected because of spectral energy redistribution due to ACR. The correlation between the relative submergence and spectral energy was investigated via a spectral analysis. In high frequency domain (1.25∼2.25f/fp), the composition ratio of spectral energy increased with larger relative submergence, whereas opposite trend was observed in low frequency domain (0.25∼0.75f/fp). The main findings of this study can provide basic knowledge for understanding irregular wave variation over the ACR.

Accurate resistance performance evaluation is essential to predict the minimum propulsion horsepower required for ships in real sea. Therefore, in this paper, the added resistance performance of K-Supramax in various wave conditions was calculated using CFD (Computational Fluid Dynamics). First, to compare the resistance performance according to the DOF (Degree of Freedom), the added resistance performance in the head regular wave was investigated and compared with the experiment. The 2DOF and 6DOF results in the head regular wave had no significant differences. Second, to compare the resistance performance among various wave conditions, the effect of the heading angle was analyzed by comparing resistance and motion RAOs (Response Amplitude Operators) in bow quartering sea conditions using 6DOF. The added resistance showed the highest value near the resonance frequency of 170°. As the heading angle increased, the added resistance tended to decrease, regardless of the wavelength ratio. Also, the added resistance performance in irregular waves was investigated with reference to the adverse conditions. The spectral method, which linearly superimposes regular wave results, and the added resistance generated during irregular waves directly through CFD were compared. The resistance in irregular waves increased by approximately 92% for the spectral method and by approximately 72% for the direct irregular wave calculation compared to the resistance in calm water. In addition, the PSD (Power Spectral Density) of resistance and the distribution of motion RAOs obtained from direct irregular wave calculations were investigated.

Wave attenuation performance is the prime consideration when designing any floating breakwater. For a 2D hydrodynamic analysis of a floating breakwater, the wave attenuation performance is evaluated by the transmission coefficient, which is defined as the ratio between the transmitted wave height and the incident wave height. For a 3D breakwater, some researchers still adopted this evaluation approach with the transmitted wave height taken at a surface point, while others used the mean transmission coefficient within a surface area. This paper aims to first examine the rationality of these two evaluation approaches via verified numerical simulations of 3D heave-only floating breakwaters in regular and irregular waves. A new index—a representative transmission coefficient—is then presented for one to easily compare the wave attenuation performances of different 3D floating breakwater designs.

The effects of wave height and forward speed on the seakeeping performance of a small fishing vessel in irregular waves are evaluated using computational fluid dynamics (CFD). The wave height effect changed linearly for a forward speed in the head sea and beam sea. In the stationary state, the heave and roll motions attributed to the wave height appear nonlinearly. The effect of the speed showed a non-linear shape wherein the heave motion became larger with an increase in the forward speed in beam sea. The seakeeping performance of pitch motion is greatly improved at forward speed rather than in a stationary state. The seakeeping performance of the roll motion is more dangerous than the pitch motion, regardless of wave height and vessel speed. The mean roll period in irregular waves is obtained through this study, and it is longer than the natural roll period in still water. It is necessary to be careful as the probability of exceeding the limit is high and GM is decreased in transverse waves.

Liu, C.; Liang, Y.; Liu, X., and Zhang, X., 2020. Numerical investigation of irregular waves and induced currents in the Modaomen, Pearl River Estuary. In: Zheng, C.W.; Wang, Q.; Zhan, C., and Yang, S.B. (eds.), Air-Sea Interaction and Coastal Environments of the Maritime and Polar Silk Roads. Journal of Coastal Research, Special Issue No. 99, pp. 181–188. Coconut Creek (Florida), ISSN 0749-0208. The Modaomen Estuary has evolved from a runoff-dominated to runoff-and-wave-dominated estuary; thus, waves have become an important dynamic force. However, the nearshore irregular waves and wave-induced currents in the Modaomen Estuary have not been well studied. For the first time, a coupled wave-current model was developed in which the wave properties were calculated by the hyperbolic mild-slope equation, and the flow motion was simulated using a depth-averaged shallow water equation that was modified by introducing wave radiation stresses. The computational capability of this model was well calibrated by laboratory data from published references. Subsequently, the validated model was employed to analyze the wave height distributions, flow field characteristics and residual current under irregular waves, as well as to determine the differences in the above results with the scenarios under pure wave or pure tide. The results showed that the irregular wave heights reach 0.75 m near the sand bar and its surrounding shoals, reach 0.7 m in the main channel, and are approximately 0.3 m in the wave shadow area behind the Sisha shoal, which is more powerful than that under regular waves. The effect of waves on the current at the maximum ebb tide is greater than that at the maximum flood tide, especially in the estuarine shoal zone. Compared with the current velocity under pure tide, the residual current velocity is larger, and the vortex scale and the sediment transport route are all prominent under the combined wave and tide.

Numerical studies were performed to investigate bow flare slamming loads under irregular waves. To estimate the slamming forces in the simulations, two time windows were selected based on existing experimental data. This study examined horizontal and vertical slamming phenomena by analyzing the relationship between the motions and the resulting slamming forces. The horizontal and vertical slamming forces from the simulations were directly compared with the experimental data. Furthermore, the experiment and simulation results were compared against a representative classification code for additional validation. The findings provide insights into the physical phenomena of horizontal and vertical slamming and confirm that the formulation suggested by classification societies provides a reasonable estimation of slamming loads. Finally, the results emphasize that both horizontal and vertical slamming forces are significant design parameters.

Floating caissons may oscillate primarily due to ocean waves during towing operations. Reducing the oscillation based on the extension part (footing) of the bottom slab of the caissons can efficiently increase the safety of towing maneuvers. However, the influence of the footing length on the motion of floating caissons has not been adequately studied. This study investigates this topic through hydraulic model experiments and numerical simulations. Experimental results for regular waves show that the rotational motion (pitch) of the caisson around the wave crest direction increases owing to resonance. This suggests that the pitch could be reduced by designing caissons, such that resonance may be prevented along the footing length. In the numerical simulations of irregular waves, the Fourier amplitudes of the heave and pitch show that the footings amplify their low-frequency components and reduce their high-frequency components. Furthermore, the significant total amplitudes of the heave and pitch show a different trend from that of the regular waves observed in the hydraulic model experiments. This suggests that it is essential to examine the motion of a caisson under irregular waves when assessing the effect of footings in an actual marine environment.

This article derives the time scale of pipeline scour caused by 2D (long-crested) and 3D (short-crested) nonlinear irregular waves and current for wave-dominant flow. The motivation is to provide a simple engineering tool suitable to use when assessing the time scale of equilibrium pipeline scour for these flow conditions. The method assumes the random wave process to be stationary and narrow banded adopting a distribution of the wave crest height representing 2D and 3D nonlinear irregular waves and a time scale formula for regular waves plus current. The presented results cover a range of random waves plus current flow conditions for which the method is valid. Results for typical field conditions are also presented. A possible application of the outcome of this study is that, e.g., consulting engineers can use it as part of assessing the on-bottom stability of seabed pipelines.