Journal of Waterway, Port, Coastal, and Ocean Engineering

A fully implicit finite‐difference, N‐line numerical model is developed to predict bathymetric changes in the vicinity of coastal structures. The wave field transformation includes refraction, shoaling, and diffraction. The model simulates the changes in N‐contour lines due to both longshore and onshoreoffshore sediment transport. A new equation for the distribution of sediment transport across the littoral zone is applied. The model is capable of simulating one or more shore‐perpendicular structures, movement of offshore disposal mounds and beach fill evolution. The structure length and location, sediment properties, equilibrium beach profile, etc., are user‐specified along with the wave climate. Results are presented for two example cases, sediment transport of dredge disposal in the vicinity of Oregon Inlet, and simulation of the Longshore Sand Transport Study at Channel Islands Harbor, California. These examples demonstrate the model's ability to simulate various physical situations and that the model predicts realistic shoreline changes.

A description of major features and patterns of motion in water waves just after breaking is presented. Previous literature is synthesized and new observations utilized to develop a new qualitative picture of the breaking process. Both classic spilling and plunging‐type breakers are found to have similar initial breaking motions, but at vastly different scales. Two primary vortex motions are identified. A plunger vortex is initially created by the overturning jet, which in turn causes a splash‐up of trough fluid and subsequent formation of a surface vortex similar to the roller in a hydraulic jump. Introduced for the first time is the hypothesis that the plunger vortex translates laterally to push up a new surface wave with vastly different wave kinematics that continues propagating into the inner surf zone. Of primary interest is the outer or transition region where momentum is being exchanged between mean, periodic and random flow processes along with some energy loss. Evidence is presented from the literature to support the new, second wave hypothesis and all other concepts introduced.

The Eulerian water particle velocities under paddle‐generated regular waves in a closed channel are not always accurately predicted by a conventional application of Stokes' first, second or fifth order wave theory. Phenomena, which give rise to errqrs, include mass‐transport, the partial clapotis formed by reflection from the spending beach and the free second harmonic wave produced by the sinusoidal motion of the paddle. Measurements taken with a Laser Doppler Anemometer indicate that the amplitudes predicted for the second harmonics of the velocity components can be over 100% in error. Furthermore, there is a mean horizontal velocity which is often greater than the amplitude of the second harmonic and can be 20% of the amplitude of the first harmonic. The observed mean velocities are compared with predictions based on Longuet‐Higgins' conduction solution. Because the design of a wave facility influences the particle kinematics, it is concluded that local empirical data will generally be required to achieve accurate predictions.

Inertia coefficients for use in Morison's equation in conditions of orbital flow are significantly lower than those appropriate to planar oscillatory flow. Circulation around the cylinder resulting from asymmetrical shedding of vorticity generates a lift which opposes the conventional inertia force. The magnitude of the lift and the effect of Reynolds number are discussed on theoretical grounds and with reference to force and velocity measurements in orbital flow. Consideration of the lift leads to the formulation of a modified Morison equation, which is appropriate to all circumstances of wave loading on a cylinder when the incident velocity vector is not collinear with the incident acceleration vector.

An alternative Stokes theory for steady waves in water of constant depth is presented where the expansion parameter is the wave steepness itself. The first step in application requires the solution of one nonlinear equation, rather than two or three simultaneously as has been previously necessary. In addition to the usually specified design parameters of wave height, period and water depth, it is also necessary to specify the current or mass flux to apply any steady wave theory. The reason being that the waves almost always travel on some finite current and the apparent wave period is actually a Dopplershifted period. Most previous theories have ignored this, and their application has been indefinite, if not wrong, at first order. A numerical method for testing theoretical results is proposed, which shows that two existing theories are wrong at fifth order, while the present theory and that of Chappelear are correct. Comparisons with experiments and accurate numerical results show that the present theory is accurate for wavelengths shorter than ten times the water depth.

Recent models for nearshore sediment transport suggest the importance of various moments of the fluid velocity field in determining transport rates. Using two days of field data from a low slope beach with moderate wave heights $(H\sim 70\mathrm{cm})\text{,}$ some low order, normalized moments are compared to results from simple monochromatic and linear random wave models. Not surprisingly, the random wave model is substantially more accurate than the monochromatic model. However, wave breaking and other nonlinearities introduce effects not explained by either formalism. The observed cross‐shore velocity variance is decomposed into wind wave and surf beat components. The surf beat contribution is maximum at the shoreline, while the wind wave component is maximum offshore. The total variance is nearly constant across the surf zone. This observation contradicts assumptions that are fundamental to many models of surf zone dynamics and sediment transport. Analysis of a wider range of wave conditions is needed to assess the generality of these preliminary results. Using field data in the sediment transport model of Bailard (1981) suggests that both bed and suspended load are significant cross‐shore transporting mechanisms on this low slope beach with moderate wave energy. Asymmetries in the oscillatory wave field tend to transport sediment shoreward, while the interaction of the offshore mean flow with waves produces an offshore sediment flux.

The effect of an increased discharge on the tide progressing into a river is evaluated quantitatively by gaging the signal recorded at upstream stations against a reference station, during intervals of effectively constant discharge; this process is repeated for progressively larger values of the discharge. Upstream, the tidal range is reduced by an increased discharge; the time of arrival of low water is accelerated, while high water is retarded. The changes in range and in time may be represented by simple regression relations. Downstream an increased discharge causes a decrease in the effective friction during flood and an increase in it during ebb. Low water is retarded and high water is accelerated; some tidal components may actually be amplified over a segment of the river.

The effects of steady, uniform currents on random waves, and the associated water‐particle kinematics, are investigated. The basic equations describing the interactions between waves and currents are reviewed, with special reference to the changes in the variance spectra of free‐surface displacement and of horizontal water‐particle velocity. Theoretical predictions are compared with laboratory measurements of random waves propagating onto an opposing current. The theoretical model is shown to be in reasonable agreement with observations.

An analytical‐empirical model for the vortex‐induced oscillation of cylindrical structural elements in Water is presented. The model is based upon force measurements for forced cylinders in a uniform aqueous flow. The frequency and amplitude of response of flexibly‐mounted cylindrical elements as well as the stability of steady state oscillation is inferred from the model. The model response is compared with experimental data for both water and air. The results raise some strong doubts about the validity of mixing experimental data obtained in such different media.

Floating breakwaters are inventoried. The various types are separated into 4 general categories, which are Box, Pontoon, Mat, and Tethered Float. The Tethered Float was identified as a special category but lacked sufficient prototype experience for detailed analysis. Advantages and disadvantages of the Box, Pontoon and Mat are presented. Hydraulic model test results and prototype experience for these 3 types are presented. Alternative mooring systems and anchorage methods are summarized. The engineering studies usually needed for a suitable design are outlined. Costs and design data for selected prototype installations are tabulated.

The effect of sudden convergence of a rectangular channel on the scattering of a solitary wave and the subsequent evolution is assessed. Separation loss is treated approximately by invoking a hydraulic loss formula for steady state flows in a nonuniform conduit and by equivalent linearization. The semi‐empirical theory is compared with existing experiments.

Observational evidence is provided to show that positive storm surges are damped more than negative surges by ice. Data on the influence of an ice layer on tides and circulation is reviewed as supportive evidence for dissipation of long waves by ice. A mechanism is suggested as to why positive surges are more strongly damped. The crest and trough of the surge wave (which is a long gravity wave) are respectively referred to as the positive and negative surge. The observations consisted of tide gage data from 23 locations in eastern Canadian water bodies for the period 1965–1975. Classical studies, while recognizing the dissipation of long gravity waves by ice, do not account for the asymmetric dissipation of the crests and troughs. Here, we suggest a mechanism involving surface contraction and dilation as responsible for the asymmetric damping. This asymmetric damping occurs during the propagation of the surge in the shallow coastal waters and not during the generation. Open water or leads play an important role in this asymmetric dissipation process.

A method is described for solving transient responses of structural members of variable cross‐section subjected to wave forces. The member is divided into small segments andsthe transfer matrix and the Laplace transform method are applied to the equation of motion of the segments including fluid inertias. Since it is difficult to perform the Laplace transformation when the wave force is a complicated function of the time, the analysis utilizes the Fourier series expansion procedure to obtain the result for general dynamic loads, Then the transformed solution becomes a function of the coordinate of the position. The transfer matrix method derives the solution of the member by the combination of the solution of each segment which is expressed in terms of the Laplace transform parameter. The Laplace transform inversion integral transforms the solution in the image domain into the time domain when the residue theorem is applied. As an example, numerical calculations are carried out for the response of a circular variable cross‐section pipe in a fluid subjected to conoidal wave forces.

Wharf facilities which are constructed and administered by public authorities of seaports are regarded as social overhead capital. Since the services that they furnish are not brought to the market, the optimum distribution of services from the viewpoint of social benefits is difficult to quantify. Specifically, ships arriving at a port inevitably bring about external diseconomies resulting from congestion in a port. Evidently, it is important to decrease or eliminate such external diseconomies. In this study, a port with public wharfs which handles general cargoes is treated; and the congestion at a port is analyzed both from economic and engineering points of view. Furthermore, preliminary examinations are made of the method for determining the optimum degree of usage of the wharf facilities, and the method for realizing the optimum degree by means of an adequate pricing system.

An analytical technique is developed for correcting the time‐averaged net sediment transport rate under oscillatory flows for the effects of the cessation of transport whenever the magnitude of the near‐bottom velocity is less than some threshold value. This estimation scheme eliminates the analytical complexity of incorporating the threshold effect directly into the transport model. The threshold speeds are calculated using an empirical formulation. Using a simple model of longshore transport across the surf zone and employing some recent findings on velocity distributions, the magnitudes of threshold effects are explored for both broadband and monochromatic waves. An explanation for the observed difference in longshore transport efficiency for laboratory and field observations is suggested. A simple model for cross‐shore transport is used to explore the effects of threshold of motion on this transport mechanism. [Graphical presentations are used to show under what combinations of wave height, wave period, and sand size threshold effects are significant for various transport regimes.

A system is described for sampling coastal data from a remote central station under computer control. The data gathering network handles wave measurements from offshore buoys and nearshore pressure sensors, and velocity components from current meters and anemometers. Coastal station locations range from Hawaii to North Carolina with system interconnection through ordinary dial up telephone lines. Data are objectively edited automatically, analyzed and are available for remote display within a few minutes of the observation. Measuring instruments, system hardware, operations, and reports are described.

A representation for nonlinear random waves is obtained from a perturbatioh expansion method. The first‐order wave solution is assumed to be a zero‐mean, Gaussian process. The skewness measure and the skewness kernel for the nonlinear second‐order waves are examined numerically and are compared with hurricane‐generated, real ocean waves. These skewness measures are shown to always be positive and to increase as the water depth decreases. The effects of the angle of intersection between interacting wave trains are also examined numerically.

A numerical model describing wave‐induced mean sea level variations and coastal currents in the nearshore region is developed by the finite element method. The model includes nonlinear convective accelerations, lateral mixing and bottom friction. To specify the wave refraction field, a wave model is also developed with a semi‐discrete Galerkin method. The numerical accuracy of the model is verified with the analytic solutions for one‐dimenional longshore currents and two‐dimensional rip currents. The numerical model is also applied to predict realistic meandering currents occurring on a periodic rip channel. Due to the nonlinear inertial effect, the unaccelerated longshore current profile is stretched and causes a decrease in the magnitude of maximum velocity. A comparison with the analytic solution of a one‐dimensional longshore current velocity distribution indicates that the linear analytic solution significantly overestimates the maximum velocity. The numerical results quantitatively demonstrate the relative importance of the nonlinear convective terms in the nearshore current problem.

Two approximate methods are presented for the calculation of the wave induced forces and moments on a vertical, surface‐piercing cylinder of elliptic cross section. Both methods provide a substantial reduction in computational effort when Compared with the exact solution which involves the numerical evaluation of Mathieu functions. One method involves the expansion of the exact expressions for the forces and moments for small values of the elliptic eccentricity parameter. The second method is based on Green's theorem and gives rise to an integral equation for the fluid velocity potential on the cylinder surface. Numerical results are presented for a range of relevant parameters and show excellent agreement with the computed values of the exact solution.

The internal wave problem in a circular cylindrical tank is solved by the standard method of separation of variables. Numerical results for the surface displacement at the interface, as well as the pressure distribution at the wall, are obtained.