Journal of Waterway, Port, Coastal, and Ocean Engineering

Random wave forces consisting of drag and inertia components are analyzed. The forces were measured in a wave tank experiment with circular cylinders at low Keulegan‐Carpenter numbers. The values of the hydrodynamic coefficients were chosen from the corresponding tests in regular waves. The method used in choosing these values applicable to the case of random waves is discussed. The nonlinear drag force contribution is linearized so that the spectral approach may be applied directly. Good correlations between the measured force spectra and the computed spectra were obtained in several cases of random waves. The short‐term distribution of the in‐line and transverse forces is shown. It is found that the in‐line force amplitudes follow the Rayleigh distribution reasonably well. The relations of the transverse force to an exponential distribution are exhibited.

Eight test runs using a 1:3 glued gravel slope with an impermeable base were conducted in a wave tank to evaluate and calibrate the numerical model developed previously. For each run with the specified incident wave train generated in a burst, measurements were made of the free surface oscillation at the toe of the slope, the waterline oscillation on the slope, the temporal variation of dynamic pressure on the base of the slope, and the displacements of loose gravel units placed on the glued gravel slope. First, the friction factor associated with the rough slope is calibrated within a relatively narrow range using the measured waterline oscillation. The calibrated numerical model is shown to predict the measured hydrodynamic quantities fairly well. Second, the coefficient for the lift force acting on a sliding gravel unit is calibrated in the range 0.18‐0.4 by comparing the measured and predicted displacements of loose gravel units on the 1:3 glued gravel slope. The computed results based on the calibration of the lift coefficient alone are shown to be in reasonable agreement with the measured gravel displacements. However, these comparisons also indicate the limitations of the calibrated numerical model.

A numerical two‐line model is developed to predict the erosion at the bend of a curved gravel causeway caused by the offshore and longshore gravel transport inside the breaker line on the side slope of the causeway. The two‐line model is based on a simplified erosion profile characterized by the landward displacement of the shoreline due to erosion and the seaward displacement of the breaker line due to deposition. The variations of the shoreline and breaker‐line displacements with time along the curved causeway are computed numerically using the continuity equations of sediment for the eroded and deposited regions on the side slope. Longshore and offshore gravel transport rates are estimated by modifying empirical formulas for straight sand beaches. The developed model is compared with the observed erosion at the West Dock Causeway in the southern Beaufort Sea north of Alaska. The calibrated numerical model is shown to explain the observed erosion well, although more detailed data are required to evaluate the model more rigorously.

It is conjectured that the low‐frequency turbulence in alluvial channels is engendered at the separation points of the large eddies in the lee of bedforms. These points are taken as the locations of point sources of pressure disturbances, and their influence throughout the flow region is determined using the normal‐mode analysis of the linear hydrodynamic stability theory for inviscid fluids. The analysis predicts that the spatial rate of decay, with respect to depth, of the standard deviation of velocity fluctuations is closely related to the bedform length. The theoretical predictions are borne out reasonably well by the observed data.

A model is developed to simulate the effect that surface waves have on the mixing of submerged buoyant discharges. The model is Lagrangian in nature and solves simultaneous equations that describe the motion of the plume relative to the ambient. It is demonstrated that the model agrees well with the experimental results and may be used to study the effect of waves on buoyant jets for a much wider range of source and ambient conditions than has so far been studied experimentally.

Experimental results for hydrodynamic loading from the combined effect of oscillatory motion and current on two productionriser configurations are presented. The riser systems tested consist of a single cylinder and a large center pipe surrounded by twelve satellites. The current is superimposed on the oscillatory motion in three directions: parallel; perpendicular; and oblique with a 45° angle. The experimental study showed a significant reduction in the drag coefficients when the oscillatory motion and the added current were parallel. The magnitude of this reduction depends primarily on the ratio of the maximum velocity of oscillatory motion to the steady current speed. The prediction of forces on marine risers using Morison's formula in a coexisting environment at low Keulegan‐Carpenter numbers yields unsatisfactory results due to vortex shedding. However, the use of this equation at high Keulegan‐Carpenter numbers in a coexisting environment was demonstrated to be safe and appropriate. The data and results of this study have shown that current strongly influerces the fluid loading of risers in the drag‐inertia dominated regime. Current has a profound effect on the drag and inertia coefficients used in the Morison equation.

Recreation boating on rivers can create conflict and crowding which detract from both the safety and the enjoyment of the boating environment. Travel over water by boat is inherently risk-prone, and demands a special category of skills. In recreation boating, especially, these skills are often absent. Speed and operational characteristics of boats, as well as the physiography of the river landscape, are some of the variables which influence boating conflict. Difference in speed is a particularly significant contributor to boating conflict. A method is developed to measure the impact of recreation boating on a river, suitable especially for a narrow water configuration and a relatively high flow of traffic. A complementary part to impact assessment is the physiography of the river environment. A method to map the visibility down a river channel, in order to identify locations of potential boating hazards, is described. The policy implications are discussed. The case study is the Rideau River in Ottawa, Ontario, Canada.

A series of laboratory tests were made of the erosion of a dune due to a single wave uprush. The uprush is generated by a sudden release from a head tank which runs up an inclined beach to a vertical dune. Fifty tests were run for ten different elevations in the head tank. The same sand-dune grain size was used for all of the tests. Results indicate that there is a strong correlation between the force of the uprush at the dune and the volume eroded.

The numerical solution of the linear dispersion relation for water waves is considered for the case of the evanescent modes. A two-point Padeó approximation is constructed based upon correct asymptotic behavior at both high and low frequencies. This overcomes some difficulties experienced with a previous one-point Padeó approximation based on correct behavior at low frequencies. The two-point approximation is quite accurate but entails considerable preliminary work to obtain the coefficients. A completely different approach is also presented which only involves the solution of a quadratic equation. The results of this method are accurate to better than 0.35% for the first evanescent mode and are considerably better for the higher modes. They form reliable first estimates for use in the Newton iteration if very accurate results are required.