Journal of Waterway, Port, Coastal, and Ocean Engineering

An experiment was performed to examine the utility of a pile fence in reducing dune erosion and overwash during a storm. Six tests consisting of 58 runs of 400 s each were conducted to compare the effectiveness of six different pile fences arranged in a single row and staggered double rows. The preliminary experiment suggests that the pile fence with a porosity of about 0.5 should be placed near the toe of the dune foreslope with a sufficient burial depth to avoid toppling. A cross-shore numerical model is adjusted to simulate the drag force acting on the pile fence. The adjusted model is compared with the beach and dune profile evolution and the wave overtopping and sand overwash rates measured in the six tests. The model is expanded to predict the extreme (5, 1, and 0.013% exceedance probabilities) of the free-surface elevation and onshore velocity for the future design of the pile fence against the wave forces. The proposed pile fence appears promising but will need to be tested at a field site.

This paper presents the results of an experimental investigation of the flow and turbulence at the armor layer of rubble-mound breakwaters during wave action. The study focused on the details of the flow and turbulence in the armor layer and on the effect of the porous core on flow and stability. To isolate the processes involved with the flow in the porous core, experiments were conducted with increasing complexity. Specifically, three parallel experiments were performed including (1) an impermeable smooth breakwater slope, (2) an impermeable breakwater slope with large roughness elements added to the breakwater, and (3) a porous breakwater where the porous core was added below the breakwater front. One breakwater slope of 1:1.5 was applied. In this paper the focus is on the details of a single sequence of wave approach, run-up, and rundown. To isolate this sequence the experiments were performed applying a solitary wave. The individual sources of turbulence generation were distinguished using Laser Doppler anemometry measurements, and the effect of the armor layer and porous core was described in terms of a reduced impact of the rundown process, production of lee wake turbulence, and less transport of turbulence above the armor layer. The shear stresses were evaluated from the measurements of turbulence, and they were associated with the run-up and rundown phases. The Shields parameter, determined from the shear stresses, was found to be reduced by 30% as a result of the porous core material.

Short rigid large-diameter monopiles have been widely used for offshore wind turbines. The rotation of the piles is strictly controlled to render safe operation of the wind turbines. Consequently, the determination of the bearing capacity within an allowable angular rotation of the monopiles is an important issue. In this study, six lateral loading tests (at 1 g) were conducted on a rigid model pile in low liquid limit silt (ML) soil (with two relative densities). The tests reveal a rotational center at a depth of $(0.75–0.85)L$ ($L=$ embedded length of the pile) and work-hardening load–displacement curves (a continual increase in soil pressures even at a very large rotational angle). The test results were used to establish new $p–y$ curves using a coefficient of subgrade reaction $n_h$ that is correlated to the local pile displacement. In particular, an analytical expression is developed to estimate the net lateral soil resistance $p$ on a circular pile using peak-on-pile radial stress. The new $p–y$ curves and analytical solutions capture the measured $p–y$ curves and the load–displacement relationship of the monopiles in cohesionless soils.

Huanghua Harbor, a semiclosed harbor with three 13.32–23.4 km-long breakwaters forming a coal port and a general port, is located on the silt-muddy coast of the Bohai Sea in China. Frequent gales cause thick sedimentation at the entrance and in the outer waterway. In this study, a two-dimensional depth-averaged horizontal version of the Delft3D software is used to formulate a hydrodynamic suspended sediment transport and bed evolution model. This model is validated by field data, including the tidal level, the tidal current, and the concentration of suspended sediment. The validated model is applied to predict the suspended sediment transport for three different wind scenarios and the short-term morphological evolution from a gale and a wave. The suspended sediment concentrations largely increase from gale-induced currents and waves. The predictions from the gale and its induced wave in 2003 and in 2012 indicate that suspended sediments are driven by the current along the jetties and can be easily deposited at the harbor entrance and outer waterway after the gale, forming a barrier that would impede normal navigation. The maximum deposition thickness from the gale appears at two port entrances and is approximately 10 times the 1-year deposition thickness under normal weather conditions. This implies that the occurrence of a gale is a key factor for sedimentation in Huanghua Harbor because of its induced current and wave.

Separating turbulence from orbital motion under breaking waves in the surf zone is essential to understanding wave-energy dissipation. In this study, velocity data under monochromatic and random waves in the large-scale sediment-transport facility were analyzed using ensemble averaging (EA), high-pass filtering (HPF) and moving averaging (MA) to extract breaking-induced turbulence. Moving averaging provides a simple method for extracting turbulence from velocity measurements under random breaking waves collected at a reasonably high frequency. Various MA time intervals were examined. Three approaches were used to evaluate the ability of MA to extract turbulence, including (1) testing the ability of MA in extracting turbulence from artificially synthesized signals, (2) comparing turbulence strength of monochromatic wave case using MA and EA, and (3) comparing turbulence strength obtained from MA and Butterworth HPF for the random-wave case. The results indicate that approximately 30–42° phase angle (relative to the peak wave period) MA allows reasonable extraction of turbulence. The turbulence extraction particularly at the wave crest and trough can be improved by adjusting the averaging interval. An adaptive MA with variable averaging time is developed. The MA method is further examined and verified using velocity measurements in the inner surf zone at two sites along the west–central Florida coast.

The process of wave refraction in nearshore zones can result in an asymmetric directional distribution of spectral energy when oblique, multi-directional wave fields propagate into shallow water areas. Here the effect of this directional asymmetry on the net wave-induced radiation stresses is analyzed. The net radiation stresses are calculated for a shoaled JONSWAP frequency spectrum with both symmetric and asymmetric directional distributions and then compared with those calculated from the commonly-used monochromatic formulation (appropriate for spectra that are narrow-banded in frequency and directions). Past studies have demonstrated that the use of the monochromatic approximation in radiation stress calculations results in a significant overestimation of the radiation stress components $S_{\mathit{xx}}$ and $S_{\mathit{xy}}$ in broad-banded seas. The present results show that the inclusion of directional asymmetry in radiation stress calculations reduces this overestimation for $S_{\mathit{xx}}$ but increases the overestimation for $S_{\mathit{xy}}$ for a range of dominant wave directions. Thus, directional asymmetry is an additional factor that contributes to overestimation when the monochromatic approximation is used for $S_{\mathit{xy}}$ and can therefore also lead to an overestimation of associated parameters such as alongshore current velocities and alongshore sediment transport rates.

A series of comprehensive research and development projects has validated the novel concept of the bucket foundation as an alternative to piled foundations, and bucket foundations are rapidly becoming a viable option for offshore wind farms and marginal fields.

Within the last decade, experimental studies have indicated the possibility of defining foundation response using plasticity theory. Results of multiple loading tests addressing the effect of embedment on the strain-hardening behavior of shallow bucket foundations under combined loading are reported. The kinematic mechanisms accompanying pre-failure are presented. It is argued that the drained capacity of offshore bucket foundations and the ratio of plastic increments are largely influenced by embedment depth and the preload ratio $V/V_{\text{peak}}$.