Journal of Waterway, Port, Coastal, and Ocean Engineering

Design criteria for absorbing wave makers are presented and their implementation illustrated by reference to the conversion of a conventional wave maker with a wedge‐type paddle. Measurements obtained with both regular and irregular waves demonstate that the requried feedback loop in the wave maker's control circuit can be successfully based on a conventional wage gage. Furthermore, it is shown that good absorption characteristics can be achieved with a lessthan‐perfect circuit design. Comparison of results obtained both with and without absorption highlight some of the dangers of investigating the behavior of reflective coastal structures in a laboratory channel equipped with a conventional wave maker. It is shown that the multiple reflection of irregular waves between a test structure and a nonabsorbing wave maker can produce systematic changes in the incident wave climate that it would be difficult to rectify. Generally the full consequences of such changes will be unknown but they could be very serious. Thus, it is strongly recommended that tests on reflective structures should be carried out only with absorbing wave makers.

Interaction of finite amplitude non‐linear water waves with platforms or docks in constant depth or variable depth medium has been studied theoretically and numerically. Wave uplift forces as well as wave transformation characteristics have been obtained for various conditions. In order to conveniently treat the moving free surface, an isoparametric mapping technique is used to transfer the fluid region and its boundaries into a regular domain. A Galerkin finite element model is developed to model the transformed fluid domain. The resulting discrete equations are solved iteratively by using adaptive line successive over relaxation (SOR) method. Artificial viscosity is introduced in both the dynamic and the kinematic free surface equations to dampen out the free surface oscillations in the front region of the platform or the dock. The Runge‐Kutta method is employed to integrate the time variation in the nonlinear free‐surface equations. The computed time‐history of the total hydrodynamic force per unit width of the platform placed above the horizontal bottom compares quite well with the available experimental data. For the sloping bottom, some time‐history of the total hydrodynamic forces on platforms and docks are also computed to evaluate the effects of the sloping bottom. The sloping bottom significantly increases the uplift forces on platforms or docks.

The stream function theory proposed by Dean for irrotational nonlinear waves is modified and extended for rotational nonlinear waves. Bottom shear stress due to laminar, smooth‐turbulent, and rough‐turbulent flow can be included by introducing the conventional eddy, viscosity model for the latter two. In order to solve the maximum of bottom friction velocity which appears in the stream function, an equation that includes the stream function itself is established and then solved by iteration. Computed velocity profiles are compared with measured results.

Discussions and comparisons are provided of dynamic breaking wave forces on vertical walls predicted by Minikin and Goda methods. Normalized wave forces computed by both methods are plotted as functions of water depth to deepwater wavelength ratio, seabed slope, and superstructure and foundation dimension ratio. The results exhibit distinctly different characteristics of the two predictive methods. The Minikin method is more conservative than the Goda method for large depth to wavelength ratio. With long wave or shallow water depth, the Goda method predicts conservative forces.

Waves impacting on breakwaters, even of rubble‐mounds, are reflected efficiently from them, so producing almost standing waves for normal approach and a complex short‐crested wave system for oblique approach. In the former, sediment is accreted one half wavelength intervals from the face at the expense of material at the nodes, at odd multiples of quarter wavelength intervals. With angled waves similar erosion takes place, either at the nodal or antinodal regions depending upon the obliquity. These are determined in fractions of the distance of island crests, formed at wave interactions, termed the crest length. Kinematics of the water particles exhibit high bed velocities and also vortices at alignments one eighth of the crest length from the structure. The associated mass transport exceeds that of the incident waves. Model studies in Japan have exhibited scouring capacity for waves at all angles, including normal, and those results are re‐examined herein. New relationships exhibit the need for long duration tests.

Studies on the interaction of tide and river flow are scarce, while studies on the simplified characteristics of tides in canals and gulfs are common. This study employs the perturbation method to solve analytically the interaction of tides and river flow, taking into account the nonlinear convective inertia and bottom friction. Appropriate characteristics of the interaction obtained from an analysis of five records along a river are used in the derivation and verification. The study finds that the interaction of the tide and the river flow is well‐described by the analytical solution for implicit doppler shift. Exclusion of convective term yields an underestimation of the tidal damping. The river flow raises the mean water level but damps the tide and reduces its celerity. The raising of the mean water level during a high discharge is more than the damping of the tide, causing flooding at high water level. Application of the analytical solutions for any value of the river flow requires only the bottom condition of the river, which is found to be smooth for the large alluvial river.

This paper examines wave height distributions in connection with wave grouping. The relationship between the groupiness factor, GF, calculated from Smoothed Instantaneous Wave Energy History (SIWEH) and the shape factor, m, of the one parameter Weibull distribution adopted to represent observed wave height distributions is examined by analyzing two field wave data sets and laboratory experimental data of transformation of wave grouping and wave height distributions over a plane beach of 1/20 slope. There is a moderate linear correlation between GF and m with a correlation coefficient of $-0.93\text{,}$ and the standard deviation of the difference between the observations and the results of the equation obtained by the least squares fit is 0.12. The value of GF becomes small in shoaling water, taking a minimum value around 0.8 times the still water depth normalized by the deep water significant wave height, while the value of m becomes maximum there.

Two Collision Tolerant Pile Structure (CTPS) design concepts were developed for the deployment of navigation aids in shallow water. The CTPS concept consists of the marker/light mounted on a single pile hinged just above the mud line. The hinge allows the pile to flex during a vessel/pile collision yet retains a restoring moment to return the pile to an upright position. The two designs presented here are a peripheral stay/central universal joint hinge concept and a central stay concept. For each design, a 4 m physical model was built for testing. Experiments included laboratory restoring moment-angle tests and in-water barge collision experiments and wave response measurements. Field experiments demonstrated that the pile sustains negligible damage during barge collisions, recovery is prompt, and pile motion in large waves is very small. Experiment results were compared with a 2-dimensional computer simulation of the pile dynamics with good agreement.

The theoretical prediction of water particle kinematics and pressure field under a progressive periodic wave in the laboratory requires the use of a suitable wave theory. An improved asymmetric stream function algorithm is proposed to represent measured periodic wave data. Numerical simulation for the periodic wave profile, in a least square error approximation to the free surface boundary condition errors, converges to the measured wave height and the mean water level. This algorithm essentially combines most computational features of Dean's irregular stream function program and Dalrymple's regular symmetric stream function program. The present algorithm is more accurate than the symmetric and asymmetric wave theories in the simulation of measured periodic wave profiles.