Journal of Waterway, Port, Coastal, and Ocean Engineering

Longshore sediment transport rates were estimated on a microtidal estuarine beach in Great South Bay, N.Y., during two dyed sand tracer experiments using a temporal sampling method. Mean onshore wind speeds of 5.8 and 9.9 m/s resulted in root-mean-square wave heights of 0.07 and 0.08 m and wave angles of 3.0 and 10.1, causing transport rates of 0.468 and 0.972 m³/h. Rates were 3.1 to 6.5 times greater than predicted by existing equations using standard coefficients. Greater rates are attributed to the concentration of sediment transport in the energetic swash zone under plunging breakers.

A 3D numerical solution was derived to determine the wave field in a physical wave tank equipped with a porous wave absorber of variable width and draft. The solution was achieved by applying the boundary element method. The model was applied to analyze the effect of the geometry and material of wave absorbers on wave reflection to eventually equip a wave tank with a proper wave absorber. The results show that absorber geometry has a complex, often surprising and nonintuitive effect on wave reflection. A more pronounced effect on wave reflection possesses physical and hydraulic properties of the material used to build a wave absorber. A reduction of wave reflection can usually be achieved by increasing absorber length and simultaneously decreasing its slope, and often a reduction of wave reflection can be achieved by increasing absorber draft or width. Moreover, a reduction of wave reflection, often substantial, can be achieved by increasing porosity and the damping coefficient. The results and additional analysis show that a reasonable wave reflection level can already be achieved for fairly short absorbers, and the model can be applied to select an optimal wave absorber for any prespecified conditions. Theoretical results are in reasonable agreement with experimental data.

In the design of oil and gas terminals, six degrees of freedom (SDF) models are often used to calculate the motions of the moored ship and forces in mooring lines and fenders. Although the SDF simulation programs have been used for more than 20 years, there is still little verification of the results with prototype measurements. This paper includes the results of a verification of one of these SDF models using prototype measurements as reference data. The prototype measurements consisted of mooring line loads of liquefied natural gas (LNG) carriers at berth for periods during which environmental conditions were recorded. A study was carried out to simulate these conditions in the model and to compare the model results with the measurements. In addition to mooring line loads, the computed vessel motions have been analyzed. For the studied berth situation, the yaw motion resulting from swell waves is quite dominant and is causing large breast line forces. An empirical expression has been derived to calculate the yaw motions of the moored LNG carrier in swell waves. This expression is a first step in defining a general expression to estimate maximum yaw motions and mooring forces to be used in preliminary harbor design.

The hydrodynamic performance characteristics of a quadrant front-face pile-supported breakwater are investigated through a comprehensive experimental program. The breakwater model consists of a quadrant front face resting on piles. The variation of the reflection and transmission coefficients due to both regular and random waves as a function of a scattering parameter ka are reported. The effect of the gap ratio (spacing between the piles/pile diameter) and relative water depth (water depth/pile height) on the above coefficients are brought out. In addition, the variation of dynamic pressures exerted on the quadrant front face as well as the total forces exerted on the entire model are measured and presented in a dimensionless form. The details of the experimental facility, setup, and analysis of results are presented and discussed in this paper.

This paper summarizes a part of the work carried out in the framework of the European research program MAST III-PROVERBS. It deals with the evaluation of pressure distribution and forces acting on the different faces of a perforated caisson breakwater. Various 2D model tests were performed at LeHavre and Caen Universities, and field measurements were made on the Dieppe breakwater. The aim of the study was to improve common knowledge and design of this type of dissipative monolithic breakwater. A new method for the calculation of maximum horizontal wave forces is proposed. The method is tested for more than 120 force estimates derived from various experimental sources, and it proves to be fairly good and reliable for engineering applications.

Beach-profile evolution, along with measurements of waves, currents, and sediment concentration, under spilling and plunging breakers of similar height were studied in the three-dimensional Large-Scale Sediment Transport Facility at the U.S. Army Engineer Research and Development Center. Unidirectional irregular waves were generated over a fine-sand beach. Beach-profile shape reached equilibrium after 1,330 and 280 min of spilling and plunging wave actions, respectively. Near the main breaker line, the profile evolved differently under plunging and spilling breakers. Across most of the midsurf zone dominated by surf bores, the equilibrium profile shapes were similar. Uniform energy dissipation per unit volume at equilibrium, as assumed in the Dean 1977 model and often used in cross-shore sediment-transport modeling, was measured for both cases across most of the surf zone except at the main breaker line, where a much greater rate of dissipation occurred. The bar/trough formation and maintenance were closely related to the local patterns of sediment suspension and bed scour at the plunging point.