Journal of Waterway, Port, Coastal, and Ocean Engineering

Wave transformations over a coral reef with a steep front slope were comparatively studied using both laboratory tests and smoothed particle hydrodynamic (SPH) modeling. In the numerical model, nonreflective generation and absorption of waves were realized by adding a source term and a velocity attenuation term into the governing momentum equation. The physical and numerical models were carefully designed so that the nonphysical rise of the mean water level over the reef was avoided. Experimental and numerical results on the free surface elevations and the spatial distributions of wave height and wave setup over the reef with and without a vertical seawall were compared and good agreements were obtained. The cross-spectral transfer of wave energy from the peak frequency to the lower and higher frequencies, the vertical distributions of wave-induced current over the reef, and the effects of the seawall position on the maximum wave setup and wave run-up are discussed.

It is well known that the waves generated by marine vessels, often referred to as wave wake or wash, can cause many issues when operating in sheltered waterways, including, but not limited to, erosion of shorelines and damage to maritime structures, and present a danger to other waterway users. Much research has been undertaken to understand the characteristics of these waves and their effects better, especially for high-speed vessels that operate in shallow water where particularly large and energetic waves are generated. However, in general, all previous studies have considered only steady-state conditions in which vessel speed remains constant; however, many vessel operations, particularly those of commuter ferries, in which regular passages through the transcritical zone to supercritical speeds (in terms of depth Froude number) are required. The present study describes a novel series of model-scale experiments used to quantify the waves during both acceleration and deceleration phases. Notable transient effects were found to occur during the acceleration phase that significantly increased both the height and period of the maximum wave compared to height and period of the maximum wave occurring at the corresponding steady-state speed. The wave characteristics at constant speed were used when assessing whether a particular vessel met wash criteria, and such criteria were likely significantly exceeded when a vessel accelerated to a supercritical speed, which could lead to the occurrence of wave wake issues. In an interesting finding, the study also found no such increase in wave characteristics when the same vessel decelerated back through the transcritical speed zone.

This paper discusses the settling and consolidation of soft mixtures of mud and sand based on experiments in a set of laboratory settling columns of varying lengths in the range of 0.5–3 m. Two types of natural muds with varying percentages of sand were used in the settling columns. In addition, mud–sand mixtures with relatively high percentages of sand were tested. The theory of the hindered settling and consolidation processes is briefly explained, and a relatively simple simulation model is proposed. The model simulation results are compared to the results of two laboratory tests with reasonably good agreement between measured and computed values. A plot of the dry bulk density as a function of the percentage of clay and sand is presented, which can be used to obtain an estimate of the in situ density of muddy layers to be dredged from navigation channels and harbor basins. Furthermore, a plot of the timescale of the primary consolidation process is presented.

The physical process of scour around pile groups is complex. Due to economical and geotechnical considerations, multiple pile bridge piers have become more common in bridge designs. Various empirical models have been developed to estimate scour depth at pile groups. However, these models are mostly based on the conventional statistical regression approaches and are not able to adequately capture the highly nonlinear and complex relationship between scour depth and its influential factors. In this study, genetic expression programming (GEP) and multivariate adaptive regression splines (MARS) were utilized to estimate clear-water local scour depth at pile groups using the flow, sediment, and pile characteristics. Two combinations of data were used to train the GEP and MARS models. The first combination included dimensional variables (e.g., mean flow velocity and depth, mean grain diameter, pile diameter). The second combination contained nondimensional parameters. Results indicated that GEP and MARS can accurately estimate scour depth. Both models yielded better results when the dimensional data were used. In addition, the MARS model with a root mean square error (RMSE) of 0.0220 m and correlation coefficient (R²) of 0.902 outperformed the GEP model with an RMSE of 0.0285 m and R² of 0.834. Performance of the GEP and MARS models was compared with that of the existing equations. The comparison showed that both models perform better than the regression-based empirical equations. Finally, a sensitivity analysis showed that pile diameter has the most significant impact on equilibrium scour depth.

The drop/drag process of ship anchors poses a severe threat to the underwater facilities lying on or embedded within the seabed/riverbed. To investigate the penetration depth of ship anchors within clayey seabed under emergent dropping conditions, physical and numerical simulations were performed in this study. The model tests were conducted at 1g condition, and the anchor acceleration was measured by an accelerometer sealed in the model anchor. By integrating the measured acceleration, the velocity and penetration depth during the dynamic penetration of the ship anchor in seabed can be determined. Subsequently, three-dimensional large deformation finite-element (3D LDFE) analyses using the coupled Eulerian-Lagrangian (CEL) approach were performed to investigate the anchor penetration depth in rate-dependent uniform clay. The effects of the strain-rate parameter, reference strain-rate, soil undrained shear strength, impact velocity, and anchor mass on the final penetration depth of the anchor were investigated. An analytical model was then established to predict the motion history of the anchor during its dynamic penetration process within seabed. In the analytical model, each force acting on the ship anchor was thoroughly discussed. Finally, an empirical formula in terms of the anchor total energy was put forward for the convenience of quickly predicting the anchor penetration depth in soft clayey seabed.

In the present work, the wave elevation around a floating semisubmersible was experimentally studied in monochromatic and irregular waves. The effect of the direction of incident waves was considered by introducing five directions: head sea, quartering head sea, beam sea, quartering following sea, and following sea. In monochromatic wave tests, the normalized wave elevation, harmonic components, mean, and skewness of wave elevation were used to analyze the response of disturbed wave elevation. In irregular wave tests, a response amplification factor, ratio of the significant height of diffracted and radiated waves to that of incident waves, was used to analyze the amplification effect of diffraction. The wave run-up in monochromatic wave tests was found to respond significantly on the weather side and mildly on the lee side. However, a strong response of wave run-up on the lee side was observed in irregular waves. Moreover, a phenomenon of near-trapping associated with a large magnification of wave crest height was discovered and confirmed in between two upstream columns. The near-trapping phenomenon was only observed in monochromatic wave tests, and this phenomenon was not witnessed in irregular wave tests. The energy distribution of disturbed waves was also investigated by using the wave energy density spectrum. The energy distribution was dominated by the diffraction in cases in which strong diffraction occurred.

This study analyzes low-flow water levels and expansion of waterway depths in the Yangtze River. It focuses on waterways in the middle and lower reaches of the Yangtze River, known as the Golden Waterway, which are key components of the Yangtze River Economic Zone. Data from 2003 to 2016 indicate that long-distance sedimentation and scour occurs in the downstream channel of the Three Gorges Dam (TGD). High scouring leads to increased waterway depths and greatly reduces the low-flow water level, causing a corresponding decrease in the lowest navigable water level despite increases in both minimum discharge and water level. Waterway depths and widths have increased under the combined actions of river scour and waterway engineering projects, achieving the goals set for 2020, 5 years in advance. Moreover, this study found that the dimensions of the waterways downstream of the dam can be further increased. These findings could be a useful reference for assessing the impacts of reservoir impoundment on downstream water levels and depth, and could assist water resource managers with decision-making processes.

Coastal vegetation has a well-known effect of attenuating waves; however, quantifiable measures of attenuation for general wave and vegetation scenarios are not well known, so field and laboratory studies must be performed for individual setups. The standard practice of performing these studies for such scenarios is extremely expensive, and it is difficult to change parameters and setups. We presented and validated a computational model for a wave flume that can be used for studies of wave attenuation over flexible vegetation based on the previously developed immersed-structure method for fluid–vegetation interaction, thereby augmenting field and laboratory studies with a more-flexible and less-expensive alternative. The main advantage of this computational framework is that almost all terms are derived from first principles without requiring a large number of empirically determined parameters. A series of computational experiments were performed, and an analysis of the wave attenuation with respect to wave heights, spectra, and energy was conducted. Results were compared to results from experiments that the computational wave flume was designed to replicate.

This paper evaluates the lateral performance of a monopile reinforced by a gravel wheel for offshore structures via centrifuge tests and three-dimensional finite-element (FE) modelings. The gravel wheel comprises a ring frame placed on the pile head and filled with large particles to potentially utilize gravel or crushed stone in offshore areas. The results of centrifuge tests and FE analyses demonstrate that the lateral loading capacity of the monopile increases when combined with a gravel wheel, and the improvement depends on the diameter and thickness of the wheel. By means of FE methods, the interaction between the pile and surrounding soils and gravel fill are illustrated to explain how the gravel wheel contributes to the lateral resistance of the hybrid system. Furthermore, an equivalent layer method adopting the conventional p-y curves is suggested to predict the lateral response of the hybrid foundation. This method is validated by comparisons with the centrifuge tests results. Finally, a case study of the monopile-gravel wheel foundation indicates that the gravel wheel is less efficient in configurations where the ultimate capacity of the hybrid system is dictated by the bending capacity of structures rather than the strengths of soils.

The purpose of this article is to investigate near trapped-mode occurrences by arrays of truncated cylinders. The basic question that this article tries to answer is whether near trapped modes (peak loading wave numbers) are indeed stimulated for arrays of truncated cylinders, such as in arrays of bottom-seated cylinders. Arrays of truncated cylinders are conceived as possible wave-energy-extraction mechanisms given that their modules are allowed to oscillate in surge (or sway) and heave, in contrast to bottom-seated cylinders, which are fixed. Hence, an additional question that should be answered is which actual mode of motion is important. To tackle these tasks, the governing hydrodynamic diffraction problem is considered. Different velocity potentials are defined for the liquid regions formed by the geometry of the truncated cylinders. The sought ultimate solution is achieved using the eigenfunction expansion technique combined with the direct approach, which, in contrast to the multiple-scattering method, is unquestionably more efficient and robust.

This study presents a computational tool for the analysis of commercial navigation capacity of rivers by a fast-time two-dimensional vessel–current interaction model. Different scenarios of rivers and vessels can be simulated, and the model can be used during early-stage design and overall management of inland fairways. The mathematical description relies on the 6DOF equations, where Eulerian flows and a Lagrangian ship-tracking approach is used, coupling river features and the main characteristics of ships. For each time step, the resultant linear and angular momenta were calculated through analytical equations to measure the ship movement and other relevant parameters such as velocity and drift angle. An autopilot system was also developed to reproduce the necessary maneuvers during navigation. A German section of the Rhine River was used for verification. The model reproduced the main movements of vessels in restricted regions; therefore, one can estimate the set of parameters and necessary adaptations in rivers and ships that optimize safe commercial navigation for waterways projects.

In this research, the effect of plate length on the power absorbed by a submerged plate that serves as a wave energy converter was examined numerically. To provide a better understanding of the effect of plate length on power absorption, plate efficiency was obtained at different opening areas beneath the plate and with different wave periods, wave heights, and distances of the plate from the sea bottom. Validation was also performed through a comparison of the current work results with those of theoretical and experimental approaches, and reasonable concordances were observed. The results show that with a low opening area, higher plate efficiency was obtained, and the effect of a change in the plate length on the plate efficiency was found to be remarkable. The numerical findings show that at low values of opening area and wave period, a criterion based on the relative length between the incident wavelength and plate length can be introduced to realize the plate length at which the plate efficiency deteriorates. The results indicate that with a low opening area, at each plate length, an increase in the wave height, wave period, or distance of the plate from the bottom has a favorable effect on the plate efficiency. It is also shown that a nonlinear relation occurs between the opening area below the plate and plate efficiency.

Most existing methods for separation of two-dimensional (long-crested) waves into incident and reflected components are based on linear wave theory. Recently, a new method for separation of incident and reflected nonlinear regular waves was presented including separation of bound and free superharmonics. The present paper extends this method to irregular waves. Irregular waves are much more complicated to separate because bound components are caused by interaction of many different frequencies, thus, some simplifications are needed. The presented nonlinear separation method is based on narrowband approximation. Second-order wave theory is used to demonstrate that errors for more broad-banded spectra are acceptable. Moreover, for highly nonlinear waves, amplitude dispersion occurs and is included by a simplified amplitude dispersion correction factor. Both assumptions are evaluated based on numerical and physical model data. The overall conclusion is that existing reflection separation methods are reliable only for linear and mildly nonlinear nonbreaking irregular waves, whereas the present method seems reliable for the entire interval from linear to highly nonlinear nonbreaking irregular waves. The present method is shown to be an efficient and practical approximation for an unsolved theoretical problem in the analysis of waves in physical models.

Storm-surge and wave models are routinely used to assess the impact of hurricanes/cyclones for emergency preparedness. Although these models are forced by wind fields, generated by meteorological models in hindcast or forecast mode, selecting a wind model that can accurately resolve the wind field, especially near the hurricane/cyclone core, is a challenging task. This study used several wind hindcast models to force a coupled wave and storm-surge model for selected hurricanes, including Bob (1991), Irene (2011), and Sandy (2012). The resulting simulated storm-surge and wave parameters were compared with observations at a number of observational stations. The wind models include the European Center for Medium-Range Weather Forecasts (ECMWF), the Northeast Coastal Ocean Forecasting System (NECOFS) based on the Weather Research and Forecasting (WRF) model, and parametric wind based on National Hurricane Center (NHC) data sets. The results show that a wind model that has an error in prediction of peak wind speed of more than 20% (when compared with observations) can lead to significant errors in hydrodynamic simulations; using a poor wind model can result in errors as high as 50% for storm-surge and wave predictions. Further, although no single best wind model for all hindcast applications can be recommended (for every region), a wind model that can simulate the environmental wind field and the internal structure of a hurricane (e.g., NECOFS in this study) can better address this uncertainty compared with conventional parametric wind models. The location of a hurricane track relative to the region of interest is a key factor in selecting the proper wind model.

Due to the complex topography in a fjord, wave conditions differ from those of ocean waves. In this study, characteristics of wave conditions in the Bjørnafjorden in Hordaland County, Norway were thoroughly investigated based on field measurements. Bjørnafjorden is approximately 4,600 m wide and more than 500 m deep, with a complex hydrography and topography. Three Datawell Waveriders (DWRs, Datawell, Haarlem, Netherlands) were deployed to measure the wave data. Due to two ferry routes nearby, the measured raw data were found to be influenced by ship waves. Thus, a band-pass filter based on wavelet and inverse wavelet analyses was proposed and developed to detect and remove ship waves from raw data. The wave data analyzed were measured over approximately 19 months. The wave conditions measured by each DWR were characterized by several parameters, such as significant wave height, average zero upcrossing period, and dominant direction. The values of each wave parameter at each DWR usually differed, which indicates that the wave field in Bjørnafjorden is inhomogeneous. The statistical values of these parameters among the three DWRs were correlated to some extent. Their distribution could not be fitted by a suitable distribution function unless more data were available. The coherence among the three DWRs was fairly low.

This study focused on scour beneath and adjacent to submarine pipelines with spoilers on a cohesive seabed. Field data about the seabed bathymetry and seabed subbottom imagery along the pipeline length direction in the Hangzhou Bay, China were collected between 2005 and 2016 for analysis. Results showed that during the last 12 years, self-buried pipelines increased from 40 to 90%; while distributions of scour pits changed randomly with time. Statistical parameters (depth and length of free span) of the scour pits beneath the pipeline in this study were roughly consistent with the values published in previous studies. However, scour adjacent to pipelines was different from that beneath pipelines in that it was much larger, and the formation of it was related to the erosion of the silt loam of the seabed. Three factors (decreased sediment supply, seabed scouring, and installation of spoilers), which probably led to the scouring, were investigated. Sediment supply to the Hangzhou Bay was reduced remarkably during the last 30 years, and the decrease of sediment load in the Yangtze River was the primary cause. In the Hangzhou Bay, the seabed near deep channels was continuously eroded, and the extent of erosion near the pipelines was the largest. Spoilers on pipelines could increase the degree of local turbulence and stimulate the suspension and transportation of sediment. Under the measured spring tidal current condition, the dimensionless scour depth calculated by Goncharov’s equation was relatively large; for example, the 273.1-mm (10.75-in.) diameter pipeline as an example, it was in the range of 0.33–2.49. According to the easily erodible property of silt loam, a hypothesis about the random distribution of scour pits was presented.