Journal of Waterway, Port, Coastal, and Ocean Engineering

Eddies pinching off the Loop Current can have a significant impact on offshore exploration and production activities in the Gulf of Mexico. Advance knowledge of an eddy shedding event would be of considerable value to the offshore industry and coastal and ocean engineering community that serves the offshore industry. However, imperfect understanding of the dynamics of the Loop Current eddy pinch-off has made reliable forecasting of such events elusive. Two empirical, phenomenological models are presented of the Loop Current eddy detachment/separation times based on the retreat latitude of the Loop Current and its rate of intrusion prior to eddy shedding, and the volume flow rate of the outflow in the Yucatan Channel. The models do a fairly good job of hindcasting past separation and detachment events for which observational data are available. The models also showed some skill when applied to forecasting the detachment of eddy Franklin in early June 2010, which occurred not long after the Deepwater Horizon rig explosion. However, because of the inherent limitations of the observational database available and used (e.g., its less than ideal temporal coverage and interpretational errors) and the very complexity of the eddy shedding process, the author cautions that the methodology is by no means conclusively proven. However, it is one worth continuing to explore as more and more increasingly accurate data and steadily improving understanding of the underlying physics become available in the coming decades.

The no-energy and no-operation rising seawall (NEORISE) is a new type of structure for protection against tsunamis and coastal flooding. It is installed in a gap in flood defenses and usually rests on land. It can close the gap when a tsunami occurs owing to its buoyancy during inundation. It requires no additional operations or external power sources. If a high-velocity flow such as the run-up of tsunamis reaches the NEORISE, some overtopping will occur before it can close the gap. The authors evaluate overtopping quantities in NEORISE structures through numerical simulations and hydraulic experiments. The numerical model was built using a transformable overset grid method that is used to study the fluid-structure interaction and a level set method that captures the interface between two fluids. The hydraulic experiments were carried out using a $1/10\text{-scale}$ model in a wave channel. The results of the numerical simulations are found to be accurate when compared with the movements in the NEORISE and overtopping quantities observed in the experiments.

Two kinds of new tsunami protection structures have been developed: a flap-gate breakwater named FLAPGATE, and a flap-gate seawall named No Energy and no Operation Rising Seawall (NEORISE). These structures are similar to the barrier employed in the Modulo Sperimentale Elettromeccanico (MOSE) Project in Venice. FLAPGATE and NEORISE can rise up and form a continuous wall by using tsunami forces in addition to buoyancy. Using the tsunami forces allows these structures to provide real-time tsunami protection. In this study, the capability and availability of these structures for real-time protection against tsunamis was examined and verified by a series of hydraulic model experiments. It was found that FLAPGATE and NEORISE rise up rapidly against tsunami wave attacks and have the capability of providing real-time tsunami protection.

Ship-generated waves were investigated in the Göta Älv river, which is a major waterway on the Swedish west coast between the sea and Lake Vänern. Ships with a typical size of $85\times 15\times 5\hspace{0.17em}\mathrm{m}$ ($\text{length}\times \text{width}\times \text{draft}$) travel at speeds between 5 and 10 knots, generating waves that cause sediment transport and erosion along the river bed and banks. Field measurements of the wave properties and turbidity were carried out during 17 ship passages, and comparisons were made with the most commonly used formulas for predicting ship waves. The formula proposed by the Permanent International Association of Navigation Congresses yielded the overall best agreement for the divergent (secondary) waves, whereas the drawdown (primary wave) could best be estimated from the vessel sinkage. The maximum recorded turbidity was mainly a function of the drawdown, and it could be well predicted from the parameterized bed shear stress. In conclusion, ship waves often induce bed and bank erosion in restricted waterways and, although simplistic formulas involve significant uncertainties, they are still useful tools for predictions. However, more studies are needed to determine the influence of a limited river cross section on the wave generation and the relationship between ship waves and sediment transport.

This paper presents an improved incompressible smoothed particle hydrodynamics (ISPH) method for wave impact applications. In most conventional ISPH techniques the source term of the pressure Poisson equation (PPE) is usually treated by either a density invariant or a velocity divergence-free formulation. In this work, both the density invariant and velocity divergence free formulations are combined in a weighted average form to determine the source term. The model is then applied to two problems: (1) dam-breaking wave impact on a vertical wall and (2) solitary wave run-up and impact on a coastal structure. The computational results have indicated that the combined source term treatment can predict the wave impact pressure and force more accurately compared with using either formulation alone. It was further found that depending on the application case, the influence of the density invariant and divergence-free parts could be quite different. For the more violent wave impact case, the divergence-free part played a more prominent role in ensuring accurate force simulations, while in less violent wave impact cases, the density invariant part seems to be more significant. A systematic parametric study has shown that the weighting coefficient in the PPE source term is independent of particle spacing under various wave impact situations. Also, a close relationship has been found between the ratio of flow height to length scales $H/L$ and weighting coefficient $\alpha$ in the mixed pressure source term.

The objectives of the current study are to develop a two-phase flow solver and to investigate the two-dimensional regular wave overtopping flow field over a sea dike. The solver is based on the Navier-Stokes equations and the classical Smagorinsky eddy-viscosity model. A coupled approach of wave generation and absorption is accomplished in the numerical wave flume, and the wave reflection from the work zone can be eliminated efficiently. Simulations of the wave run-up and breaking were performed to validate the effectiveness of the numerical wave flume. The influences of turbulent eddy viscosity and grid refinement on the simulations of the breaking waves are discussed. The flow features of wave overtopping over a sea dike are investigated systematically for both nonbreaking and breaking waves. The numerical results show that the layer thicknesses along the dike crest decay following an exponential rule, whereas the maximum velocities along the dike crest exhibit a mild increasing trend. Furthermore, a relationship between the overtopping discharges and the maximum velocities on the dike crest is obtained by regression analysis. With this correlation, the maximum overtopping velocity can be estimated from the overtopping discharge, which provides a practical approach for the risk assessment of a sea dike.

In the current study, the effect of mooring line typology and layout upon the structural behavior of a floating breakwater (FB) is studied. Different elastic anchor stiffness levels and initial pretensions were analyzed to improve knowledge of mooring lines and module connectors as well as of the structural performance of FBs as a whole. For this purpose, mooring line forces together with the stress and momentum between modules have been measured using one-dimensional and three-dimensional strain gauges. Furthermore, three-dimensional tests with different incident wave angles were carried out. The results were applied to the design of the installation of a FB at Aguete Port (Pontevedra, Spain).

The hydrodynamic character of a wall-free and near-wall circular cylinder oscillating in the transverse direction in a steady current was experimentally investigated at a Reynolds number of $2\times {10}^5$. Forces in both the in-line and cross-flow directions were measured by three-dimensional force transducers. The effects of the near wall on the hydrodynamic coefficients of the cylinder at high Reynolds number are studied. Experimental results indicate that: (1) the first-order oscillating drag coefficient obtained in the near-wall cases is larger than the second-order oscillating drag coefficient and is almost one-third of the mean drag coefficient; (2) compared with the wall-free cases, the Strouhal number is bigger, and the lock-in phenomenon occurs at a higher nondimensional frequency in the near-wall cases; (3) the near wall has a significant effect on the power transfer and therefore leads to a larger lift coefficient in phase with the velocity than in the wall-free cases, indicating that hydrodynamic coefficients based on wall-free cylinders may not be suitable for predicting the vortex-induced vibration of pipelines; and (4) as the gap ratio decreases to 0.1, the vortex shedding can be totally suppressed by the near wall.

Wave scattering of a solitary wave traveling over a submerged horizontal plate was studied. Experiments for normal incidence were conducted in a wave flume, with a horizontal plate suspended at two different depths in the middle of the flume. Gauge pressures above and underneath the plate, surface elevations on and near the plate, and flow velocities at three representative fields of view were measured. The flow underneath the plate was found to behave almost like a plug flow, driven by the time-dependent, spatially uniform pressure gradient between the two openings. Complex vortices formed near the two edges of the plate as the plate acted like a flow divider. A numerical model based on two-dimensional Navier-Stokes equations was used to confirm the main features captured by the experimental measurements. Analytical solutions based on the linear long wave theory, which admits a soliton-like impulse wave solution, were also derived. The linear theory was applicable for obliquely incident impulse waves. When the analytical solutions were applied to the wave conditions used in the experiments, it was found that the theory described pressure and surface elevation satisfactorily when the nonlinearity was insignificant. Based on the pressure distribution above and beneath the plate, the total vertical force and moment exerted on the plate were calculated. As the wave passed over the plate, the plate first experienced a lift, followed by a force in the downward direction, and then a lift again. As a result, a nonzero time-varying moment existed. The analytical solution was also utilized to examine the effects of relative plate width on the transmitted and reflected waves. The effects of the angle of incidence are also discussed briefly.

This study presents an application of a two-dimensional beach evolution model to a shoreline change problem at the Kızılırmak River mouth, which has been facing severe coastal erosion problems for more than 20 years. The shoreline changes at the Kızılırmak River mouth have been thus far investigated by satellite images, physical model tests, and one-dimensional numerical models. The current study uses a two-dimensional depth-averaged numerical beach evolution model, developed based on existing methodologies. This model is mainly composed of four main submodels: a phase-averaged spectral wave transformation model, a two-dimensional depth-averaged numerical wave-induced circulation model, a sediment transport model, and a bottom evolution model. To validate and verify the numerical model, it is applied to several cases of laboratory experiments. Later, the model is applied to a shoreline change problem at the groin field to the east of the Kızılırmak River mouth at the Bafra alluvial plain. The results of the numerical model agree with the existing laboratory and field measurements.