Journal of Waterway, Port, Coastal, and Ocean Engineering

The cost‐effective optimization of rubble‐mound breakwater cross sections requires a summation of all the life cycle costs for each alternative design, including construction costs, maintenance costs and associated economic losses due to wave attack. A systematic procedure is proposed for estimating the economic losses with and without breakwater protection along with the first and maintenance costs for a set of alternatives with varying functional performance and structural integrity design criteria.

One numerical and two physical models are combined to study shoreline erosion problems at Buhne Point (Humboldt Bay), California. Flood and ebb tide levels and currents are computed with a vertically integrated hydrodynamic model of Humboldt Bay, and are verified against prototype measurements. This tidal information provides boundary conditions for the two physical models. A 1:100‐scale model is used to determine local wave climates near Buhne Point from hindcast data. The tidal and wave information from these models are used in a 1:50‐scale model, to simulate shoreline changes at Buhne Point from 1966–1980, and to develop a shoreline stabilization plan for the site. An optimum plan is tested in the model with a wide range of tides and waves to insure that the plan would not erode. The plan was constructed at Buhne Point in 1984 and now functions successfully, as predicted by the model study.

The mean wave drift force on a vertical axisymmetric ice floe in regular waves is computed using available computation methods for linear wave diffraction and radiation by a floating rigid body. The computed results for a fixed vertical cylinder are shown to be in good agreement with the corresponding analytical solution. The computed wave drift force on a rigid cylindrical ice floe, with a 20‐m diameter, is compared with the previous two‐dimensional result obtained, assuming that the ice is a thin elastic raft with a 20‐m width. The comparison indicates that the normalized wave drift force is dependent on the size of the floe relative to the wavelength and rather insensitive to the different assumptions made in these two analyses. Furthermore, the computed wave drift forces on the ice floes investigated during previous field studies suggest that the wave drift force will be important in the ice floe force balance associated with the horizontal floe movement if the surface waves in partially ice‐covered water are not negligible.

Measurements are presented here of the onset of breaking of deep water waves. The results of recent experiments conducted at NRL to study the growth of steep waves to breaking in a convergent channel are in good agreement with a variety of other recent measurements. For both spilling and plunging breakers, the steepness at breaking Was less than 90% of the computed value for the steepest symmetric wave in deep water. The measured steepness at breaking can be used to estimate the frequency of occurrence of breaking waves in deep water. A discussion also is given of the measured rates of potential energy density and momentum flux losses for spilling and plunging breakers in deep water. The energy density and momentum flux loss rates for a plunging breaker are about twice those measured for a spilling breaker.

The common analysis technique for field records of wind waves is the variance spectrum. The phase spectrum, half of the information available from the record, is routinely ignored on the assumption that the Gaussian random wave model is a sufficiently complete description of the record. Procedures are developed for unwrapping and detrending the phase spectrum. Evaluation of these algorithms provide insight into the potential identification of ordered structures, possibly wave groups, in the phase spectrum without sacrificing the convenience of linear analysis.

Added mass and damping for ice floes are important parameters in determining floe collision forces with arctic structures. They are measures of the hydrodynamic resistance to the change of the floe motion. An analytical approach is presented based on long water wave theory to determine: (1) The added mass and damping for a circular ice floe for a wide frequency range and with general floe movements including two translations (surge and heave) and one rotation (pitch); and (2) the hydrodynamic impulse function on a circular ice floe resulting from its impact with a rigid structure. The governing equations are solved by: (1) The Fourier transformation; or (2) the Laplace transformation method, depending on the problem. Closed‐form solutions and plots are provided for estimating the added mass, damping, and the hydrodynamic impulse function for a circular ice floe.