Journal of Waterway, Port, Coastal, and Ocean Engineering

In this work, the influence of the geometry of lightweight perforated breakwaters on its performance against green water impact loads is investigated systematically through a series of numerical simulations. For this purpose, a fully Lagrangian meshfree particle-based method is adopted to model transient and impulsive hydrodynamic phenomenon with free surface and complex geometry. The green water flow is represented by a dam-break problem; the breakwater is modeled as a perforated plate and the protected installation as a vertical wall. Computed impact force, moment, and impulse on the breakwater and protected wall show nonlinear effects, and the main geometric parameter is the open-area ratio. In addition, the increase in the breakwater height is effective only for low open-area ratios. The influence of the arrangement of the holes are also investigated. Different flow patterns are obtained for small and large gaps between the breakwater and the wall. The relation between the loads on the breakwater and the wall also provides the basis for the optimal design of the breakwater, considering the tolerant hydrodynamic loads of protected structures.

Carrying out a hazard assessment for offshore structures can entail the consideration of a number of different factors. Scour hazard assessments are routinely undertaken, and scour development at offshore structures should be considered a time-varying process. However, scour may take place within a morphologically dynamic environment, the combination of which will impact on the soil–structure–fluid response. This paper presents the analysis of an unique data set that shows the partial collapse of a scour hole at a large monopile foundation within a morphologically active site. The collapse suggests a slope failure mechanism, resulting in the movement of around 450 m³ of material within a period of about 75 min. The paper analyzes the processes involved regarding formation and development of the collapse.

A hydraulic physical model study was conducted to quantify horizontal forces and pressure distributions on an elevated structure under nonbreaking, impulsive breaking, and broken wave conditions. Regular wave trials with varying wave heights and periods were used to estimate phase-averaged horizontal pressure distributions at the time of the maximum horizontal force for a range of air-gap conditions, defined as the distance between the still-water level and the base of the elevated structure. Measured pressures for all wave conditions were compared to the Goda equations, originally developed for wave pressures on a vertical caisson breakwater and modified for elevated structures. For breaking waves, the pressure distribution predicted by both the modified Goda equations and equations in ASCE 7-16 were compared to measured pressures. The modified Goda equations showed good agreement with measured pressures and the total horizontal force per unit width and were generally conservative for all wave conditions over a range of structural elevations, including cases in which the structure was elevated above the still-water level. The ASCE 7-16 equations for breaking wave–induced pressures and forces were conservative by factors of 3–20. Results suggest that the modified Goda equations may be used to improve design guidance for at-grade and elevated coastal structures under wave loads with constant storm surge.

We investigated, from two laboratory experiments, the kinematic behavior and the three-dimensional turbulence that is generated due to a breaking solitary wave propagating over irregular shallow water bathymetry. The bathymetry was composed of a deep water region followed by a shallow shelf via a relatively steep slope. The offshore boundary of the shelf break varied in the longshore direction. The shelf had a triangular shape in plan view, with the widest part of the shelf located along the center of the basin. The first experiment used a planar shelf, while an obstacle in the shape of a conical island was placed near the shelf apex for the second experiment. Measurements of fluid velocities and free surface elevations were collected using three-dimensional acoustic Doppler velocimeters (ADVs) and wave gauges, respectively. In the first experiment, the inundating flow varied weakly in the alongshore direction, but demonstrated strong variations in the second experiment. A refraction-generated jetting mechanism caused by the convergence of water mass near the basin centerline characterized the run-up. The greatest cross-shore velocities were located near the basin's centerline and were triggered by the jetting mechanism. The greatest turbulent events were well correlated with four identified bore fronts. The bore fronts were generated by a combination of waves including the leading wave, beach reflections, and shelf oscillations. A primary conclusion of this study is that nonlinear long-wave transformation over irregular bathymetry can lead to a highly complex nearshore wave field with little apparent correlation to the offshore wave.

In this study, the effect of water depth on vertical motion responses and added resistance of ships in waves was numerically examined. The applied numerical method corresponded to the time domain B-spline three-dimensional Rankine panel method. The effect of water depth was considered by placing panels on the floor and applying the bottom boundary condition. The added resistance at a finite water depth was analyzed via a pressure integration method that integrated the second-order pressure on a body surface. The experimental and numerical results for a restrained vertical cylinder were compared under a zero-speed condition. Under a forward-speed condition, a similar comparison was performed for a blunt-modified Wigley model at an infinite water depth. When the water depth decreased, the motion response and added resistance tended to decrease. Finally, to identify the water depth effect on an actual ship, the presented method was applied to a lifelike ship, namely, the KVLCC2 tanker, under full and ballast loading conditions.