Journal of Waterway, Port, Coastal, and Ocean Engineering

On the basis of a time-domain higher-order boundary element method, a two-dimensional fully nonlinear numerical wave flume is developed to investigate the nonlinear interactions between a regular wave and a submerged horizontal plate in the presence of uniform currents. A two-point method is used to discriminate bound (i.e., nonlinearly forced by and coupled to free waves) and free harmonic waves propagating upstream and downstream from the structure. The proposed model is verified against experimental and other numerical data for wave-current interaction without obstacles and nonlinear wave scattering by a submerged plate in the absence of currents. A first-order analysis shows that the reflection coefficient increases in the following current (i.e., current in the same direction as the incident wave) and decreases in the opposing current (i.e., current in the opposite direction to the incident wave). Moreover, the plate length for the maximum reflection to occur is not sensitive to the current. A second-order analysis indicates that downstream from the plate, the current has a stronger influence on the secondary free mode than on the first free mode. The energy transfer between the fundamental wave and the higher harmonics is intensified by a following current but weakened by an opposing current. The second free harmonic wave amplitude is affected more by the opposing current than it is by the following current.

Although little attention is usually given to the armor porosity and armor randomness of randomly placed concrete armor units in mound breakwaters, significant model effects may occur if armor porosity and randomness are different for prototype and small-scale models. Armor randomness and porosity are easier to control in small-scale models because they are generally constructed by hand in dry and perfect viewing conditions; equipment and environmental constraints make control at prototype scale more difficult. Results from three-dimensional small-scale placement tests are analyzed when cube and Cubipod units are placed with a small-scale crawler crane and pressure clamps. Armor porosity was not workable below 37% for cubes and 35% for Cubipods; placement grids were obtained for feasible armor porosities, considering row settlements during construction as well. A methodology to measure armor randomness using high-precision laser scanning, similar to terrestrial LIDAR, was tested with small-scale cube and Cubipod armor. Three armor randomness indexes (ARIs) measured the randomness of cube and Cubipod armor; the values for ARIs were higher for Cubipod armor than for cube armor.

Data for approximately 20,000 small marine vessels damaged by the 2011 Great East Japan tsunami, including information on motor types and tonnage, were collected and used to develop loss functions. The observed maximum tsunami heights from the field survey were used, and the maximum tsunami flow velocities from numerical simulation were obtained. Damage ratios were calculated, and loss functions were fit using linear regression analysis and log-normal distributions. The damage probability was significantly increased when the tsunami height was more than 2 m or when the flow velocity was more than $1\hspace{0.17em}\text{m}/\text{s}$. The results show that small vessels (weighing less than 5 t) with outboard motors were the most vulnerable. In addition, vessels at locations farther from the tsunami source had less damage because they were hit by smaller tsunamis with slower arrival times, which most likely gave them a chance to evacuate to deep sea. The results of this study, including the loss functions, will be useful for macroscale tsunami hazard and loss predictions involving small marine vessels.

Wetland vegetation can attenuate storm surge and waves and thus play an important role in coastal protection. In this study, laboratory experiments were used to quantify wave attenuation as a function of vegetation type, density, and height, as well as wave conditions. Wave attenuation characteristics were investigated under regular and irregular waves for rigid and flexible model vegetation in addition to live Spartina alterniflora and Juncus roemerianus, two common coastal species. Vegetation densities were $156–623\hspace{0.17em}\text{stems}/{\text{m}}^2$ for model vegetation, $405–545\hspace{0.17em}\text{stems}/{\text{m}}^2$ for S. alterniflora, and $\mathrm{2,857}\hspace{0.17em}\text{stems}/{\text{m}}^2$ for J. roemerianus. Bulk drag coefficients ($C_D$) of the vegetation species were calibrated based on wave gauge data and video images, and regression equations were derived for the drag coefficient as a function of Keulegan-Carpenter number ($\mathit{KC}$). $C_D$ did not depend significantly on the relative vegetation height with respect to water depth for rigid vegetation models in the emergent and submerged conditions tested here. In general, drag coefficients were higher for live vegetation species than for rigid and flexible vegetation models. The results also showed that vertical variation of plant density strongly influenced the drag coefficient.

In this study, a simple air-bubble model was developed for unidirectional, homogeneous, plunging-wave propagation over a sloping beach to calculate wave height and wave setup in the surf zone. Two parameters used in the model, the reference void fraction and the decay factor, were determined by comparing model results with experimental results, and they are functions of the local wave height and the relative distance from the breaking point, respectively. Moreover, a free parameter of the model was calculated using the best fit of a curve based on experimental data from different flow regimes of plunging wave breaking. The results of the air-bubble model were compared with laboratory data and the computed results showed good agreement, except for some discrepancies in the vicinity of the breaking point and near the shoreline.

The evolution of a toe-protected nourished beach, located at Belvedere Marittimo (Italy), was investigated by means of both a physical model and a numerical morphological approach. Several surveys, including bottom profiles, sedimentology, and wave climate, were available after the nourishment for this site. Results showed that the physical model is in a fairly good agreement with the field surveys regarding localized phenomena such as the scour around the barrier, whereas it lacks in predicting the slope of the beach profile. The results of the morphological model, carried out on the basis of the field data, well reproduce the beach slope. On the other hand, when it is applied with the same parameters of the physical model, it lacks accuracy in predicting the experimental beach profile.