Journal of Waterway, Port, Coastal, and Ocean Engineering

Experimental investigations were undertaken to develop a generalized hydraulic conductivity equation for rubble mounds. The generalized equation takes into account the inertial force due to the unsteadiness of the flow and the effect of entrained air. Two‐phase flow models are used to analyze the air/water flow. A modified Morrison‐type equation for the unsteady flow forces is presented. The generalized hydraulic conductivity equation is developed for a wide range of Reynolds numbers. The objective of this study was to provide a generalized equation for modeling wave motion in rubble‐mound structures, and an outline of the computations required is given.

A mixed numerical model is developed to simulate wave motion in rubble‐mound structures. The mixed model utilizes a combined finite difference method of characteristics scheme to integrate the unsteady continuity and momentum equations in the $x-t$ plane to obtain the internal water levels while the two‐dimensional properties of the flow are found from a finite element solution for the internal flow domain, $x-y$ plane, at any time t. The two‐dimensional solution is used to update pressure distribution coefficient and hydraulic conductivity values in the $x-t$ plane. The model is applied to the Sines breakwater in order to check the dynamic stability of the seaward slope under severe wave attack. The predicted values for the internal water surface are found to be in fair agreement with a physical model measurement. Furthermore, the model indicates a lower factor of safety than the traditional analysis. Special provisions are included in the model to account for added mass and to detect and correct for internal wave breaking and the entrainment of air near the interface.

After a storm on December 31, 1979 and January 1, 1980, with a maximum $H_s$ of 23.3 ft (7.1 m) a large number of broken Dolosse of 15 metric tonnes (15,000 kg) was observed on the west breakwater of Gioia Tauro, Italy. The present paper describes a study in which the storm was reproduced in a model at a scale of 1 to 45.5 and with which a stable modified design was determined. A model technique using single frame film exposures was applied in order to detect rocking of Dolosse. The main conclusion is that the number of rocking plus the number of displaced Dolosse observed in the model corresponds well to the number of broken Dolosse in nature. This conclusion is only valid for the slope above still‐water level.

Wave height parameters used in coastal and ocean engineering are grouped into three classes according to their definition bases: height statistics, energy, and monochromatic. Parameters within each class are easily interrelated lor most engineering purposes. However, parameters from different classes are difficult to interrelate, particularly for shallow water applications where waves are near breaking. The often‐used parameter “significant wave height” has traditionally been based on height statistics but many modern estimates are based on wave energy. A simple empirical method is developed to relate statistical and energy based significant height estimates. The method is developed with CERC laboratory flume data from a 1:30 plane slope, two samples of field data, and stream function wave theory. Since the two significant height estimates differ by over 40% in some laboratory cases, engineers should clearly recognize the distinction between them.

A numerical model based on the parabolic approximation method is developed to calculate the wave characteristics in the nearshore region. The model is developed for monochromatic linear waves and considers refraction, diffraction, and energy dissipation caused by the bottom turbulent boundary layer. A numerical algorithm is also proposed to treat digitized bathymetry data. The accuracy of the present model is verified by comparing numerical results with two sets of field measurements collected by the Coastal Engineering Research Center along its research pier at Duck, North Carolina.

The vertical force on a horizontal cylinder partially submerged in random seas shows large secondary peaks in its power spectrum. An equation is derived which predicts these peaks taking account of buoyancy, inertia and drag forces. It is also shown that at critical depths, the mean force on the cylinder is large and negative and components of the force near the mean frequency of the sea spectrum are very small.

Riprap and sandbag model tests are conducted in a wave flume to investigate the effects of berm‐type slopes on the stability of armor units and wave runup as compared to uniform slopes. Measurements of wave runup, rundown, wave height, breaker type and the response of armor units under regular wave action are made for each test run. The uniform and composite slope test results are analyzed using a modified Saville's method which accounts for the overall effects of the slope configuration on the stability of armor units and wave runup. A simple analysis procedure based on the proposed method is developed for a preliminary design of a berm configuration. An example computation is made for a composite slope protected with riprap. The berm width, the berm slope and the water depth at the shallowest point of the berm are varied so as to determine the optimal berm configuration for increasing the stability of riprap under the assumed wave conditions.

An analytical model is developed to examine the response and efficiency of a rigid, hinged floating breakwater. The theoretical model is verified experimentally and is used to develop design curves which may be employed to estimate necessary physical breakwater characteristics to satisfy specified wave attenuation criteria. The utility of these curves is demonstrated in a design problem. It is shown that a structure of reasonable size is an effective dynamic barrier for high frequency waves and an effective kinematic barrier for low frequency waves.

The integral equation method is utilized to calculate the wave‐induced loading on a surface‐piercing cylinder of circular cross‐section inclined at an arbitrary angle to the sea bed. Numerical values of the various force and moment components are presented for a range of wave and cylinder parameters. The computed estimates of the force coefficients show good agreement in the inertial limit with published experimental results. In addition, the estimates confirm that the inertia force on an inclined cylinder may be severely underestimated by using the vectorial form of the Morison equation with a mass coefficient appropriate to the corresponding vertical cylinder case.

A method is developed in which an optimum design of breakwaters s achieved by taking into account wave climatological uncertainties and he potential maintenance risk as function of these uncertainties. Wave climatological ncertainties result from small sampling and errors of measurement f hindcast calculations. The economic impact which results from these uncertainties on the cost of breakwaters clearly evidenced the need for long‐term ccurate measurement programs. However, because of the required duration, these programs can only be conceived as an investment for future generations.