Journal of Waterway, Port, Coastal, and Ocean Engineering

A method is suggested for finding the dynamic displacement response of a four legged offshore tower under the action of waves. The structure is idealized as a single degree of freedom vibrator and generalized co‐ordinate system is chosen for assessing the tower properties for which a suitable sinusoidal shape function is assumed. Morison's equation is used to represent the forcing function arid Airy's linear theory to describe the flow‐characteristics. A Fourier analysis of the generalized load is made and the response of the system computed as the linear combination of its responses to the individual Fourier components. An experimental investigation has been conducted and the results obtained have been compared with the predictions of the present theory and another theory suggested by Harleman and others. The present theory is seen to yield results that compare better with the experimental ones.

Laboratory experiments were conducted to investigate the influence of wind waves on ponding level, surf beat, transmitted wave characteristics, and beach runup of an idealized reef‐lagoon system. Independent variables included the incident wave conditions, depth of water at the reef crest, and width of the lagoon separating the reef from the shore. Narrow banded incident wave spectra representative of typhoon generated waves were employed in irregular wave tests and emphasis was placed on high wave conditions. Monochromatic wave tests were also performed. Deepwater wave characteristics and processes associated with wave groups were found to have important influence on the ponding water level and surf beat in the lagoon.

A previously developed Great Lakes ice forecasting model for winter navigation aid has been calibrated using observed data from specific Lake Erie ice transport events. The model is based on the macroscopic continuum hypothesis for the fragmented ice field and the internal ice stress is represented by a viscous‐plastic type constitutive law. The external driving force includes the time‐dependent wind and water current fields as well as the thermodynamic source/sink terms for the ice mass conservation. By adjusting the model coefficients employed in the constitutive equations and the thermodynamic factors, the computed results are in reasonable agreement with the short‐term observations for the 1978–79 ice season in Lake Erie. Major findings include the profound effects of the wind‐driven water currents and the ice melt at the icewater interface on the ice regime of Lake Erie during the late stage of the ice season.

Definitions are presented for transit time, age, flushing time and residence time. Using a continuous exchange model, analytical expressions for the transit time distribution function and the age distribution function are derived for a basin having a constant volume. The residence time for instantaneous as well as continuous dye injections equals the volume of the basin divided by the rate at which new water is added to the basin. Using the tidal prism model it is shown that the normalized residence time for an instantaneous dye injection is a function of three dimensionless parameters. These parameters are: (1) The average basin volume divided by the volume of new water returning on the flood; (2) the fraction of the flood volume $(=\mathrm{tidal}\mathrm{prism})$ that is new water; and (3) the phase of the tide at which the dye is injected. For a continuous dye injection, the normalized residence time is a function of the first two parameters only. Numerical computations show that, to a first approximation, the residence times equal the average basin volume divided by the volume of new water entering during flood with secondary effects introduced by the other parameters.

Gravel islands in the southern Beaufort Sea are subjected to wave activity during the short open water season. Occasional, severe storms may cause a significant amount of wave overtopping, resulting in flooding and erosion on the top of the gravel island. The statistical distributions of wave steepness, surf similarity parameter, and runup height are derived analytically using a wave‐by‐wave method. A unidirectional, irregular sea state is expressed in terms of the joint distribution of wave heights and periods proposed by a group C.N.E.X.O. The figures required for calculating the probability that runup height will exceed a selected berm height in a given sea state are presented. The expected quantity of water overtopping the berm is expressed in the form of a single integral which can be integrated numerically. Computation for a typical gravel island indicates that the probability of occurrence of wave overtopping and the expected quantity of overtopped water will increase with the spectral bandwidth and the correlation coefficient between individual wave heights and periods for the practical range of the berm height.

Steady potential motion induced by a tidal jet in an ebbing ocean is analyzed by representing the jet as a distribution of sink singularities and relating the sink strength to jet solutions for steady bottom‐frictional turbulent jets over constant bathymetry. Circulation patterns are determined for various inlet configurations of practical interest and for different values of the bottom friction parameter. Particular attention is given to the jet induced alongshore current which is shown to be sensitive to the presence of jetties and also to the bottom friction experienced by the jet. The present theory is applied to Fort Pierce Inlet, Florida, where severe erosion is known to exist on both sides of the inlet. It is suggested that the alongshore current, albeit small in magnitude, is a potential contributor to the movement of suspended beach material toward the inlet due to its continual occurrence during every ebb tide.

A theoretical expression for the change of the spreading rate of momentum surface jets due to opposing surface gravity waves is obtained. A scale analysis performed on the depth averaged Eulerian momentum equation of the jet wave flow has revealed that wave momentum flux, induced by wave refraction, is the dominant force to cause the increase of the jet spreading rate. An estimate of this increase is derived from the transverse momentum equation. The theory predicts a linear increase in the rate of spreading of the jet, within the jet zone of established flow. The increase in the rate is expressed by the ratio of the wave momentum action, on the jet, to the jet initial momentum density. Deductions made from the experimental results, using flow visualization techniques, agree quite well with theoretical predictions. The agreement is excellent within a longitudinal distance equal to 64 times the jet nozzle half‐width.

Secondary pressures resulting from the waves breaking on a vertical wall are studied experimentally with beaches having four different slopes. Pressure history of the wave impact consists of two distinct parts: The first peak and the second peak. The magnitudes of the second peak pressure are found to be much lower than those of the first peak pressures. The duration of the second peak pressure is considerably longer than the first peak pressure. The vertical distribution of simultaneous second peak pressure is almost linear vertically and this pressure is somewhat similar to a hydrostatic pressure. The major parameter affecting the second peak is the initial wave steepness. The effective pressure head is about the wave crest for low waves and moves below it for steep waves.

Improved understanding of beach erosion and accretion has been attained by reanalyzing large-scale, two-dimensional monochromatic laboratory data, using the data to develop an empirical beach volume change model, and systematically studying the influence of each parameter on predicted beach volume changes. The sediment fall velocity is predicted to be especially important in determining the amount and direction of beach volume change.