Journal of Waterway, Port, Coastal, and Ocean Engineering

This study investigates runup heights of random waves on a small diameter circular pier installed on a uniform slope bottom, by laboratory experiments under various conditions of waves, bottom slopes, and installed water depths of the pier. The main purpose of the study is to propose a prediction formula for the 2% excess runup height on a pier. The formula is expressed by the exponential function. The correlation coefficient between the predictions and observations is 0.98. Since the maximum and one-third maximum runup heights are found to be related linearly to the 2% excess runup height, those are estimated through the prediction formula. By employing the prediction formula, one can also estimate the water depth where the runup on a pier becomes maximum.

Experiments were conducted with periodic wave groups incident on a plane beach with a slope of 1:35. The wave groups were composed of a series of cnoidal waves with varying wave heights. Emphasis was on obtaining a number of measurements inside the surf zone. The analysis of the data shows that the location of the start of breaking of the individual wave in a group is affected by the groupiness of the waves. The H/h ratio at breaking was seen to have a wider variation for the individual waves in the group than for monochromatic waves. In all cases, some groupiness was conserved inside the surf zone, but in some cases it was reversed in the sense that the higher waves in the group before breaking became the smallest after and vice versa. It was also found that even inside the surf zone, nonlinear interactions result in energy at frequencies that are multiples of the group frequency, although, as expected, the energy is more evenly distributed between the different frequencies than in the waves originally generated.

A new time-domain method for separating incident and reflected waves in wave flumes using any number of wave gauges is presented. The method (named LASA) is based on a local approximation model considering linear and Stokes II nonlinear components, and a simulated annealing algorithm to calculate the parameters of the local approximation model. The LASA method is directly applicable to experiments in wave flumes with an arbitrary number of wave gauges, but the LASA concept may be extended to laboratory and field three-dimensional experiments by selecting the appropriate local approximation model. The LASA method has been compared to the two-point and Kimura's method and has proved to be very robust. The application of the LASA method to physical experiments using nonstationary regular and random waves generated estimations of incident and reflected waves with relative mean squared errors lower than 3% for regular waves and ranging from 4 to 16% depending on the spectral shape.

The effectiveness of a boom is associated with the hydrodynamics in the vicinity of the oil slick that it is attempting to contain, especially under open-sea conditions. A comprehensive investigation of oil containment is provided under various current, wave, and wind conditions. In this paper, a local two-phase nonlinear hydrodynamic numerical model is developed to simulate oil containment by a fixed boom under open-sea conditions. The shape of an oil slick is a function of time, and unstable waves may develop along the oil-water interfacial boundary. This paper describes a simulation of the behavior of the oil slick and deals with important interfacial boundary conditions. A nonhydrostatic pressure is introduced to accommodate the complicated local flow near the oil slick and a successive overrelaxation method is used to solve the pressure equation. A comparison is made of the oil slick shape with and without the hydrostatic pressure assumption. Some simple simulations of free-surface elevations under a number of wave conditions are performed to verify the numerical model. The computed results are in general agreement with those obtained from previous experiments.

In the first of these companion papers, a two-phase numerical model was described and tested for some simple cases under wave conditions. This paper applies that numerical model to simulate the interfacial waves and oil free-surface waves under a number of key hydrodynamic conditions. The characteristics of oil-water interfacial waves and free-surface waves are discussed. Effects of currents and waves on the interfacial waves (interfacial elevation, oil-water relative velocity, and interfacial velocity components) are investigated. The variation of the oil thickness under current and wave conditions is also discussed. The computational results indicate that an increase in the incoming wave height and period may (1) cause instability of the oil-water interfacial waves near the front of the oil slick and this may promote entrainment failure; (2) increase the interfacial waves and free-surface waves at the boom; (3) lower the trough of the oil-water interface at the boom and thus promote drainage failure if the oil thickness exceeds the boom draft; and (4) decrease the freeboard of the boom and thus encourage oversplashing failure.

The numerical simulation of interfacial waves and waves on the free surface of an oil slick under combined current and wave conditions is presented in a companion paper. The present paper focuses on the application of a numerical model developed by Fang and Johnston that numerically predicts the relationship between oil containment failure velocity and wave/wind parameters. Comparative laboratory experiments have been undertaken in a 24-m-long, 0.4-m-wide, 0.4-m-deep wave flume. Detailed comparisons and discussions of the computed and experimental results are provided. The effects of oil viscosity and density on oil containment failure velocity receive particular attention, and the influences of other parameters such as oil volume and boom draft are also quantified. It is concluded that the developed numerical model provides an economic, convenient, and effective method of predicting oil containment failure under various sea conditions.

A 2D numerical model was applied to study tide-induced currents in the Thane Creek. The model was forced by the tide at Apollo Bunder, calibrated with the observed tide at Pir Pau, and verified with the tide data collected at Vashi and Airoli. Predictions of amplitudes are in fair agreement with the observations. Even though the predictions are more or less in agreement in phase at high tide, it differs at low tide by nearly 30 min. A comparison of the modeled currents with data at Vashi suggests that the current values are reasonably accurate. The circulation pattern indicates the maximum velocities during the neap and spring are 0.4 and 1.5 m/s, respectively, in the vicinity of the Elephanta Island. The water mass passing through the eastern side tends to move toward Panvel Creek, whereas the orientation of water mass passing through the western side is toward the main channel of the creek depending on the tidal excursion. The study on residual current reveals that two anticyclonic eddies are present around Elephanta and Butcher islands. These eddies and high residual current values show intense mixing capacity in the southern region.

Under a standing wave two types of bed response can occur depending on the relative size of the sediment: L-type, which occurs for relatively fine sediment, and “N-type,” which occurs for relatively coarse sediment. The specific concern of the present note is with the N-type response, which involves scour in the area of bed between the node and antinode of the standing wave field and accretion under the node. The conditions necessary for the N-type response to occur are examined and a new method for predicting the equilibrium N-type scour profile is described. The method is based on a general characterization of N-type profile geometry and on physical reasoning applied to available experimental data. Predictions of field-scale scour using the new method are generally much greater than scour predictions based on existing interpretation of wave flume experimental results.