Coastal Engineering Journal

Random wave transformations with breaking in shallow water of 2-D bathymetry are computed with the parabolic equation. A new system of gradational breaker index, the value of which gradually decreases as the level of wave height within a wave group is lowered, is introduced to simulate gradual shape variations of wave height distribution in the surf zone. Wave attenuation in the trough area of a barred beach is treated with a secondary gradational breaker index, which is applied for locations in water of constant or increasing depth. Its empirical coefficients are assigned values different from those in water of decreasing depth. The wave attenuation factor due to bottom friction is formulated by evaluating the rate of energy dissipation by shear stress along the sea bottom. Computation is made for directional spectral components with multiple levels of wave heights under the Rayleigh distribution, and the results are synthesized for the calculation of wave height distributions. The new computational scheme succeeds in reproducing the random wave breaking diagrams by Goda (1975), and shows good agreements with several experimental results on wave transformations over horizontal shelves, barred beaches, and an elliptical shoal. The scheme also yields wave height predictions in good agreement with several field measurements across the surf zone.

The reflection and transmission characteristics of regular waves by a partially immersed curtain-type breakwater have been studied by the experiment and numerical model in the paper. Non-overtopping and overtopping of the breakwater by the incident wave were considered to compare different wave dissipation efficiencies. An incompressible Smoothed Particle Hydrodynamics (SPH) theory combined with a Large Eddy Simulation (LES) model was employed as the numerical tool. The SPH method is robust for tracking free surfaces without numerical diffusion and the LES model is capable of analyzing turbulence and eddy vortices during wave-breakwater interactions. A good agreement between computational and experimental wave profiles verifies the accuracy of the SPH-LES model. The computations also disclose that the wave energy dissipation is mainly attributed to the turbulence production and vortex shedding during the wave transmission and reflection processes.

Mooring problems are still serious issues in port construction and operation. Although many studies have been carried out about moored ship motions or waves, effective countermeasures to reduce ship motions have not been accomplished in most harbours facing open seas. It is known that operators require detailed wave information near harbours when sea conditions become severe. In this study, a new numerical model is constructed for the prediction of the mooring limit condition due to typhoons. It is based on the theories of Kalman Filter, wave growth inside typhoons and wave decay in swells. The prediction model needs less input data than the meteorological models. The accuracy of the predicted model is verified for a port facing the Pacific Ocean when swells or wind waves propagate from typhoons in various situations. The prediction model is applied to other locations facing the Pacific Ocean. This new model allows us to predict the mooring limit condition 0.5–2 days before the influence of typhoons. Moreover, we propose a berth operation system to monitor the mooring limit condition using this prediction model in harbours facing open seas.

The hydrodynamic pressures due to random waves around a pipeline near a rigid bed of slope 1:10 have been measured. The tests were performed for pipelines normal and parallel to the wave direction. These tests were carried out for three gap ratios of the pipeline from the sloping bed. The pressures were resolved in the horizontal and vertical directions and integrated for the force time history in the respective directions. The effects of relative clearance of pipe from the bed and wave steepness on the probability distribution of the forces on the pipeline are reported. The average statistical force ratios as a function of scattering parameter and the variation of the force coefficients as a function of Keulegan–Carpenter number are also presented. The details of the model setup, experimental procedure, analysis of results and discussion are reported in this paper.

In this study, the reliability design method developed by Shimosako and Takahashi in 2000 for the calculation of the expected sliding distance of the caisson of a vertical breakwater is extended to take into account the variability in wave direction. The effects of directional spreading and the variation of deepwater principal wave direction about its design value were found to be minor compared with those of the obliquity of the deepwater design principal wave direction from the shore-normal direction. Reducing the significant wave height at the design site by 6% to correct the effect of wave refraction when using Goda's model was found to be appropriate when the deepwater design principal wave direction was about 20 degrees. When we used the field data in a part of the east coast of Korea, taking the variability in wave direction into account reduced the expected sliding distance to about one third of that calculated without taking the variability in wave direction into account, and the required caisson width was reduced by about 10% at the maximum.