Journal of Waterway, Port, Coastal, and Ocean Engineering

A numerical model is developed to analyze a flexible, floating breakwater consisting of a compliant, beam‐like structure anchored to the sea bed and kept under tension by a small buoyancy chamber at the tip. Additional stiffness is provided by mooring lines. The fluid motion is idealized as linearized, two‐dimensional potential flow and the breakwater is idealized as a one‐dimensional beam of uniform flexural rigidity and mass per unit length subjected to a constant axial force. The boundary integral equation method is applied to the fluid domain. Modifications are made to the basic formulation to account for the zero thickness of the idealized structure, and the dynamic behavior of the breakwater is described through an appropriate Green's function. Numerical results are presented illustrating the effects of the various wave and structural parameters on the efficiency of the breakwater. Small‐scale physical model tests were also carried out to validate this theory. In general, the agreement between experimental and numerical results was reasonable, but with considerable scatter.

This research demonstrates that horizontal density gradients approximated by salinity gradient represent an additional forcing term in the equations of motion, which have a significant effect in certain portions of a well‐mixed estuary. The horizontal density gradient terms have been added to a two‐dimensional depth‐averaged hydrodynamic and salinity model that is applied to Apalachicola Bay, Florida. A variable‐size finite difference cell is used in the model to allow more efficient resolution of physical details. The estuary system is assumed to be well mixed and boundary conditions are satisfied at the bottom and top of the water column but vertical components of velocity are neglected. A high‐resolution numerical model is desirable with particular emphasis on areas near passes, channels, and other critical features. This is accomplished by applying a smoothly varying grid technique. Results from the numerical model are presented and compared with prototype data. Calibration and verification of the improved numerical model is accomplished with available prototype data.

A model for the propagation of sea and swell waves in a channel bounded by rubble‐mound jetties is presented. The model combines elements of earlier work on waves normally incident on a breakwater with a modified diffraction model based on the linear mild‐slope equation. For grazing‐angle (relative to the jetty axis) wave incidence, a parabolic approximation to the governing equation is used to obtain numerical solutions for monochromatic long waves propagating down the channel. An initially plane wave evolves into a spatially complex pattern as dissipation occurs along the jetties and energy is drawn from the channel interior by diffraction. Comparisons of the model to field observations are presented in a companion paper.

Field measurements of surface gravity waves along the center line of the straight, 1 km long, 8 m deep, 250 m wide Mission Bay entrance channel (bounded by rubble‐mound jetties) are compared to a model developed in a companion paper by Melo and Guza. The observations show a rapid downchannel decay of wave energy. Additionally, the observed ratio of significant wave heights between any two stations along the channel axis is rather constant despite the different wave and current conditions encountered. The model, with all empirical coefficients determined with existing parameterizations, agrees qualitatively well with these observations. These model results are insensitive to the details of the motions and dissipation occurring within the jetties so long as an appropriate amount of energy is lost at these lateral boundaries. The wave height on the center line of a wide channel with highly absorptive jetties is controlled by diffraction. In fact, the observations and model results on the center line at Mission Bay are similar to previously published simplified models with the jetties replaced by strips of appropriate bottom dissipation and also to the decay along the center line of a breakwater gap with the gap width equal to the entrance channel width.

Measured wave force data from the Conoco test structure in hurricane Carmen have been analyzed on a wave‐by‐wave basis to determine the total hydrodynamic forces exerted on the platform. These measurements are compared with calculated total forces. The calculated forces are based on a conventional API wave‐current force determination procedure. Observations made on the basis of the Conoco test structure (CTS) data are compared with those from the Exxon ocean test structure (OTS). The comparisons indicate that the two data sets indicate similar trends if it is recognized that in contrast with the CTS data, the OTS data did not involve high storm waves; that these waves were long‐crested and unidirectional; and that there were no significant currents. The data indicate that the present API RP 2A guideline wave‐force formulation will given an unbiased estimate of maximum total hydrodynamic forces developed on small‐diameter membered structures located in deep water in intense hurricanes. Directional spreading associated with the intense, central portions of hurricanes can lead to substantial reductions in wave forces, as compared with unidirectional waves of identical heights and periods.

Laboratory tests with irregular waves to determine wave run-up characteristics and armor stability of riprap revetments are discussed. Tests include conventional, plane, 1-on-2 slope revetments and conventional revetments fronted by rubble berms. Rubble berms tested herein reduced the maximum run-up by rather modest amounts, up to about 20% but typically around 10%, but they produced substantial improvement in the armor stability. These effects are discussed and quantified. This study demonstrates the need for a reliable irregular wave run-up gauge for laboratory studies of rough, porous coastal structures.