Journal of Waterway, Port, Coastal, and Ocean Engineering

This paper experimentally investigates the nonlinear hydrodynamic forces on a semisubmerged floating collar under full-scale Reynolds number (R) and Keulegan-Carpenter number (KC) oscillatory flow alone and combined with a current. The collar was forced to oscillate harmonically in the direction of the current within a wide range of oscillation amplitudes and frequencies. The first five orders of the horizontal hydrodynamic forces are obtained using Fourier transformation techniques. The influence of the KC, the frequency parameter ($\beta$), and the reduced velocity (Vr) on the high-order components of the hydrodynamic force were investigated. The results show that, under oscillatory flows, the first five harmonics of the hydrodynamic force coefficients increase with an increase of KC and $\beta$. As the reduced velocity (Vr) increases, the first- and second-order components are greatly affected. These first two order components contribute greatly to the overall hydrodynamic force in the combined flow condition, with no apparent slamming, whereas the last three orders contribute less. The first two harmonics agree well with the experimental results when overtopping occurs; however, differences are apparent where slamming occurs.

A method for expedient characterization of maximum nearshore wave heights due to hurricanes is described. This method, referred to as the wave response function (WRF) method, relates hurricane parameters to maximum wave heights by fitting coefficients from the modified Shore Protection Manual (SPM) forecasting method to results from numerical surge-wave models. The method was applied to numerous locations along the U.S. Gulf Coast: Corpus Christi, Texas; Gulfport, Mississippi; and Panama City, Florida. The WRF method is shown to have the most skill of all similar methods tested. Similar accuracy levels were obtained across all test sites. Data from Hurricane Ike in 2008 provided validation for the method. Although not intended for forecasting, this approach can be applied to risk analysis and extreme value statistics with significantly less computational effort than the use of numerical models.

Numerical models are a key component of methodologies used to estimate tsunami risk, and model predictions are essential for the development of tsunami hazard assessments (THAs). By better understanding model bias and variability and, if possible, minimizing them, more reliable THAs will result. In this study, the authors compare run-up height, inundation lines, and flow-velocity field measurements between an open-source tsunami model and the method of splitting tsunami (MOST) model predictions in the Sendai Plain in Japan. Run-up elevation and average inundation distance are, in general, overpredicted by the models. However, both models agree relatively well with each other when predicting maximum sea surface elevations and maximum flow velocities. Furthermore, to explore the variability in numerical models, MOST is used to compare predictions from six different grid resolutions (90, 60, 30, 20, 15, and 10 m). Results of this work show that predictions of statistically stable products (run-up, inundation lines, and flow velocities) do not require the use of high-resolution (<30-m) digital elevation maps at this particular location. When predicting run-up heights, inundation lines, and flow velocities, numerical convergence was achieved by using the 30-m resolution grid. In addition, the Froude number variation in overland flow and a MOST sensitivity analysis are presented. Also, run-up height measurements and elevations from the digital elevation map were used to estimate model bias. The results provided in this paper will help provide an understanding of the bias and variability in model predictions and locate possible sources of errors within a model.

Turbidity currents are often the main processes of sediment transport in deep waters and reservoirs. To prevent sedimentation in critical locations, various methods, such as placing solid obstacles in the path of these flows, have been proposed. In the present study, the effect of inlet concentration on the behavior of turbidity currents in the presence of two consecutive triangular obstacles was investigated experimentally. For this purpose, a series of laboratory experiments were conducted with various inlet concentrations. In each experiment, velocity and concentration profiles were measured using an acoustic Doppler velocimeter. The velocity of the current head and local Froude number were also determined along the test channel. The results show that a region with negligible velocity and a notable concentration develops upstream of each obstacle, and as the inlet concentration increases, this region becomes larger. In addition, the results also indicate that the sediment deposition rate is higher upstream of the first obstacle compared to that of the second obstacle. Furthermore, observations show that three recirculation regions are developed between the obstacles.

The oscillating wave surge converter (OWSC) is a type of ocean wave power device typically consisting of a flap, or arm, hinged at the bottom to allow forward and backward movement by surging waves, and is efficient in generating electricity from waves due to its capability in operating at a wide range of wave spectra. The power generated from the OWSC could be further maximized by arranging the devices in an array at their optimal spacing. This paper addresses the optimization of device configuration within an array by using the genetic algorithm (GA) scheme, for which the spacings between devices are taken as the optimization variables, and the maximum q-factor is chosen as the objective function. The q-factor is a performance assessment parameter that quantifies the average total power produced by an array compared to an individual device. Three array layouts—namely, the single-, double-, and triple-array, each comprising 12 OWSCs—were considered. The pitch response amplitude operator (RAO) of each device in the array was evaluated, from which the power generated and q-factor were determined. The influence of different wave periods and their propagation directions on the array optimal spacing and q-factor was investigated. This study shows that the optimal spacing is highly correlated to the scattering parameter. The results presented here will aid engineers in selecting appropriate spacing that would maximize the power production. The results also provide an enhanced understanding of the performance of the OWSC array when arranged in different configurations.

Accurate estimation of storm surge along the coasts subject to extreme storm conditions requires proper wind and pressure forcing and quantification of the wind waves resulting from local and far-field energy sources. This paper summarizes the steps involved in accurately representing the offshore wave climate for the North Atlantic Coast Comprehensive Study (NACCS) domain, defined from the United States–Canadian border in Maine to the Virginia–North Carolina border. The motivation of the regional wave modeling is to provide offshore boundary conditions for the simulation of extreme extratropical and synthetic tropical events to drive the nearshore wave and surge modeling efforts within the NACCS. The offshore wave conditions were estimated using the third-generation WAve Modelling (WAM) model. Value-added wind fields were defined for each of the four wave model grids (North Atlantic Ocean Basin, U.S. Coastal Regional scale, and two subregional-scale grid systems covering the NACCS coastal domain). Five tropical events (Hurricanes Sandy, Irene, Isabel, and Gloria and Tropical Storm Josephine) and 17 extratropical events were simulated to evaluate WAM’s performance. Model results were compared with 30 point-source measurements available during these storm events. Time, scatter, and quartile-quartile plots; Taylor diagrams; and a battery of statistical tests were used in the evaluation process. The WAM provided quality zero-moment wave height estimates, with biases in the range of −0.07 to −0.14 m, RMS errors (RMSEs) of about 0.40 m, scatter indexes (SIs) around 25%, and a correlation of 0.95 compared with the measurements. The wave period results contained the greatest errors with peak period biases of −0.26 to 0.06 s, RMSEs from 2.4 to 2.7 s, SIs near 25%, and a correlation between 0.47 and 0.59. The mean period biases were about −0.70s, RMSEs were about 1.5 s, and there was a correlation of 0.6–0.7. The mean wave direction biases ranged from 4.5 to −0.34° with RMSEs of 55°.

Marine structures are sometimes represented in coastal ocean circulation models as a porous plate that exerts drag on the flow and dissipates energy. Such a representation requires that a loss coefficient be specified to reduce the flow speed to some prescribed fraction of the upstream incident flow. To provide guidance and a framework for this problem, the case of a uniform channel that is partially blocked by a porous structure is considered. Drawing on existing results from actuator disc theory, simple analytical relations are presented for the dependence of the flow speed through a porous plate on the loss coefficient. It is shown that limitations on representing structures with high hydrodynamic loading using an actuator disc in an unbounded region can be avoided by allowing for weak geometrical blockage by lateral boundaries.

Driven piles are the main foundation system for offshore oil and gas facilities. They are installed through the jacket legs or at the bottom of the structure. Driven piles can, however, experience premature refusal. In this case, drilling solutions may be needed, such as drilling to remove the plug ahead and below the pile toe. Because time is important during offshore operations, offshore bored piles are rarely used. Unlike pile drivability analysis, which is based on wave analysis and hence reliable, there is no established pile-drillability assessment. This paper extends the findings of previous research in which the specific excavation energy (SEE) was estimated in subsoils from Turin, Italy, at a small scale. Two subsoil classes were considered and compared in this study. The SEE was linked to different friction-angle and cohesion values, and using the Nishimatsu and Evans cutting models, preliminary theoretical net drilling penetrations were estimated. The results should be considered as theoretical values.

Wave variability and connections with climate indices along the U.S. West Coast were analyzed in this study. Monthly significant wave height data from five buoy stations that have an observation period ranging 18–37 years along with large-scale climate indices were used in the analysis. The dominant modes of significant wave height variability were determined using continuous wavelet transforms. There is a significant power at the annual scale during the whole measurement period of all stations. Cross-wavelet power spectra was used to explore the possible effects of El Niño Southern Oscillation (ENSO) events on the wave climate variation. Correlation between the significant wave heights and large-scale climate indices at different temporal scales showed that there is a relationship between significant wave heights and indices. This finding indicates that positive ENSO events lead to larger wave heights in the region.