Journal of Waterway, Port, Coastal, and Ocean Engineering

The submarine flow slides and their hydraulic effects are studied by numerical means. These types of landslides are assumed to separate into a dense flow close to the bed and a turbulent dispersion above it. A two-dimensional fluid mechanics mixture model based on Navier-Stokes' equations has been developed to study water waves generated by these landslides. The dense part is considered as a viscoplastic fluid, whereas the dispersed part is modeled by an ideal fluid. The rheological parameters of the model comprise a diffusion coefficient, a Bingham yield stress, a viscosity coefficient, and friction on the slope. First, the numerical model is validated with an analytical solution for a viscous and a Bingham flow. Then, it has been tested for a rigid box sliding into water along an inclined plane. The results of this simulation have been compared with experiments conducted in a channel. Finally, laboratory experiments consisting in the slide of a gravel mass have been carried out. The results of these experiments have shown the importance of the sediment rheology and the diffusion. The model parameters are adjusted by trial and error to match the observed “landslide” flow.

Fluctuations of the Caspian Sea's mean monthly surface water level for the period of January 1986 to December 1993 were studied. The time series data showed an increasing trend and seasonal variations. Artificial neural network (ANN) and multiplicative autoregressive integrated moving average (ARIMA) modeling were used to predict the time series data. The ANN's input and output consisted of the last 12 months and the current month surface water levels, respectively. The selected ARIMA model required one-month regular differencing, 12-month seasonal differencing, and had a moving average component of lag 12. The ANN and ARIMA predictions for the period of January to December 1993 were very reasonable when compared with the recorded levels. On average, the ANN model underestimated the sea level by three cm, whereas the ARIMA model overestimated it by three cm. The monthly predictions for January to December 1994 presented a continuation of the Caspian Sea water surface level rise that would have various adverse effects or its neighboring countries.

The problem of oblique water wave diffraction by two equal thin, parallel, fixed vertical barriers with gaps present in uniform finite-depth water is investigated here. Three types of barrier configurations are considered. A one-term Galerkin approximation is used to evaluate upper and lower bounds for reflection and transmission coefficients for each configuration. These bounds are seen to be very close numerically for all wave numbers and as such their averages produce good numerical estimates for these coefficients. Only the bounds for the reflection coefficient are numerically computed. These are also numerically compared with the results obtained by using multiterm Galerkin approximations involving Chebyshev polynomials for a wide range of parameters. Numerical results for the reflection coefficients for the three barrier configurations are presented graphically. It is seen that total reflection occurs only for the surface-piercing barriers while total transmission occurs for all the three configurations considered here. It is also observed that the introduction of an equal second barrier to a submerged barrier increases the reflection coefficient considerably in some frequency bands and as such submerged double barrier configurations are preferable to a submerged single barrier for the purpose of reflecting more wave energy into the open sea.

Conventional floating breakwaters are examined and the feasibility of developing a cage floating breakwater is explored. Earlier studies on floating breakwaters reveal that, to achieve a transmission coefficient (K_t) less than 0.5, the breakwater width to wave length ratio (W/L) should necessarily be greater than 0.4 for most of the configurations. Recent studies on cost-effective floating breakwaters indicate that by fixing a row of pipes below the floating body, the W/L requirement can be reduced to 0.15 without any compromise in the performance. This concept has been adopted in developing a new configuration to serve as: (1) a floating breakwater; and (2) as a possible shallow water cage culture unit. Experiments were conducted to study the performance of the cage floating breakwater under wave and wave-current environment. The results on transmission and reflection coefficients are presented and compared with those reported in the literature. The variation of water surface oscillations and velocities within the cage, the effect of mooring line stiffness, and initial tension on transmission characteristics are also discussed.

Analytical solutions provide a simple and economical means of quickly estimating qualitative and quantitative responses of the shoreline to a wide range of environmental and engineering conditions. This paper presents analytical solutions for shoreline evolution in the vicinity of coastal structures, including detached breakwaters, seawalls, and jetties with and without wave diffraction. The solution for a detached breakwater illustrates the growth of a salient with time behind the breakwater and the associated initial shoreline retreat at locations across from the breakwater tips. A simple solution describing flanking of a seawall is obtained by using two different solution areas where the longshore sand transport rate and breaking-wave angle vary. A similar technique is used to model diffraction downdrift of a groin or jetty by allowing the wave angle to vary with the distance alongshore according to a specified function or by employing a large number of solution areas. Cases are also presented for the accumulation updrift a groin and the shoreline response in a groin compartment with a breaking wave angle that varies sinusoidally in time. A solution for a single groin illustrates the impact of bypassing on the updrift accumulation.

A new parabolic equation is derived from the mild-slope equation. It is used as the governing equation for the propagation of periodic surface water waves without wave reflection. For the problem of forward wave propagation, the equation can be solved very efficiently by the parabolic equation method, without the angle limitation as for other parabolic models. Several cases involving incident wave angles up to 70° are adopted to test the model. The numerical results confirm that the new parabolic model is very stable, highly accurate, and economical to use. Finally, a parabolic equation for wave-current interaction based on the wave model developed in this paper is also presented.

Deformation and dissipation of different classes of breakers ranging from a spilling breaker to a strong plunging breaker are studied. Experiments are carried out to investigate spatial changes of the wave profile and wave height attenuation of solitary waves after breaking over a reef. Moreover, the KdV-type equation in which diffusion and bottom friction are considered is numerically solved as an inverse problem to estimate the value of the eddy diffusion coefficient κ* for different classes of breakers. The results reveal that postbreaking wave deformation, wave decay, and the transmission coefficient are closely related to the breaker type. Further, it is shown that the breaker type effect on these phenomena can be evaluated quantitatively.

Wave data on H_1/3, H_max, etc. observed in the sea area around Japan are analyzed to investigate the probability distribution of H_max/H_1/3 and the occurrence properties of giant freak waves with wave heights exceeding 2H_1/3 and 10 m. The analyzed results show that the occurrence probability of the giant freak waves could be argued generally under the Rayleigh extreme distribution, although it varies from area to area. Four-ninths of the extreme waves having the largest maximum individual wave height (H_max)_max at each observation point are occupied by the giant freak waves and moreover, they occur in lower sea states rather than in the severest one.