Journal of Waterway, Port, Coastal, and Ocean Engineering

$J$-lay is widely accepted as a favorable method for deepwater pipeline installation. The configuration and internal force of the pipeline during the laying process are key factors for its safety, and the embedment induced during pipeline installation plays an important role for pipeline stability in service. Traditionally, the seabed in the analysis of $J$-lay is assumed to be elastic, whereas deepwater deposits are usually very soft, exhibiting low strength and obvious plasticity. This paper presents an analytical model for pipelaying on plastic seabed. This model simplifies the pipeline as the combination of four segments: a natural catenary in water, a boundary-layer segment, a beam on the seabed (touchdown zone) where the soil deforms plastically, and a freely laid horizontal segment. The comparison with a traditional elastic-seabed model reveals that both models have similar pipeline configurations, although the elastic-seabed model slightly underestimates the maximum bending moment. In contrast, the pipeline embedment depths in the two models differ with deeper ultimate penetration predicted in the plastic-seabed model.

Flexible pile-supported protective structures have been used extensively in the protection of bridge piers against vessel collisions. Their success is dependent on their ability to absorb impact energy through large deflection and yielding. A large soil tank ($15\times 5\times 6\mathrm{m}$) was used to conduct large-scale model tests on protective structures in silt. A lateral static load test on a single pile was carried out to derive $p\mathrm{\text{-}}y$ curves for the piles on the basis of the measured bending moment of the pile shaft. Impact tests with different initial impact energies were then conducted on the protective structures and on a single pile to study the energy transfer mechanism during a collision. Soil damping and the inertia force of the pile shaft have obvious effects on the load-displacement curves of single piles, especially in the initial phase of impact. However, their influence on the maximum bending moment of the pile shaft was weak. Compared with protective structures that consist of free-standing piles or a pile row, a novel protective structure with two rows of piles has a relatively larger lateral stiffness and a much larger energy-absorbing capability. A simplified energy-based analysis method is proposed to estimate the lateral deflection of the flexible pile-supported protective structures that are subjected to a given impact energy. Comparison of the calculations with the test results shows that this simplified analysis method gives conservative results approximately 30% for the energy-absorbing capability.

A small-scale field experiment was conducted on wave forces on upright breakwaters, and the following observations were made. The largest waves in a sea state yield one of two very characteristic time histories of the horizontal force, $F$, according to whether or not there is overtopping. With a large overtopping, $F$ has a very sharp peak at the instant at which water reaches beyond the top of the wall. Without overtopping, $F$ has a smooth history with its maximum when the water reaches the highest elevation on the wall. The sharp peaks of the wave-force per unit of length at a given section of a breakwater are estimated to have a negligible effect on the force on one caisson, provided that the wave crest makes an angle of only a few degrees with the breakwater. The dimensionless pressure distributions are not very sensitive to the ratio between the $H_s$ of the incident waves and the elevation of the wall above the mean water level. Our field experiment confirms that Goda’s model (GM) is very effective for estimating the positive wave pressures, although it is slightly conservative. However, Goda’s model yields some negative wave forces that prove to be smaller than the largest negative forces measured in the course of the experiment. Boccotti’s model (BM), based on a linear theory with virtual wave heights, proves to be very effective for estimating negative wave pressures.

To maintain an optimum balance between security and efficiency of maritime transport in shallow waterways with a lot of deep-draft ship traffic such as in the St. Lawrence Waterway, it is particularly important to accurately estimate the ship squat, which is the reduction of the underkeel clearance between a vessel at rest and in motion. Recently, a squat model based on a regression tree was developed. The skill of this model to predict squat in the St. Lawrence Waterway exceeded the performance of 10 empirical models commonly used by the operational and regularity agencies. Although this approach is promising, two main problems were noticed: (1) the predictions obtained by the regression tree are not smooth and (2) the squat predicted with this model is not always monotonically increasing with ship speed (Froude number). In this paper, a stepwise regression tree algorithm is used to model squat. This approach has the same advantages as the regression tree (allowing the representation of complex and nonlinear relationships) and solves both of the aforementioned problems. Furthermore, the squat predictions of the new stepwise regression model outperform the predictions of the regression tree model and the Eryuzlu model, which is currently used by the Canadian Coast Guard. This new model could provide a handy tool for mariners to get real-time squat predictions in the St. Lawrence River. We also provide an algorithm that can be used to fit a squat model for any other economically important shallow waterway.

A predictive, coastal erosion/shoreline change model has been developed for a small coastal segment near Drew Point, Beaufort Sea, Alaska. This coastal setting has experienced a dramatic increase in erosion since the early 2000’s. The bluffs at this site are 3–4 m tall and consist of ice-wedge bounded blocks of fine-grained sediments cemented by ice-rich permafrost and capped with a thin organic layer. The bluffs are typically fronted by a narrow ($\sim 5\mathrm{m}$ wide) beach or none at all. During a storm surge, the sea contacts the base of the bluff and a niche is formed through thermal and mechanical erosion. The niche grows both vertically and laterally and eventually undermines the bluff, leading to block failure or collapse. The fallen block is then eroded both thermally and mechanically by waves and currents, which must occur before a new niche forming episode may begin. The erosion model explicitly accounts for and integrates a number of these processes including: (1) storm surge generation resulting from wind and atmospheric forcing, (2) erosional niche growth resulting from wave-induced turbulent heat transfer and sediment transport (using the Kobayashi niche erosion model), and (3) thermal and mechanical erosion of the fallen block. The model was calibrated with historic shoreline change data for one time period (1979–2002), and validated with a later time period (2002–2007).

The September 2009 tsunami devastated the Samoan Islands. Damages observed in eighteen coastal villages following this natural disaster are presented. Using observations and idealized numerical simulations, four main conclusions are drawn regarding tsunami damage patterns in these communities. First, for coastal regions with steep terrain, damage to structures is a function of distance from the shoreline, elevation, construction, and topographic conditions. Second, in those villages where inundation is confined by topography (steep bluffs or mountains), damage is more severe. Third, when inundation is unconfined by topography, damage potential (capacity to cause damage, should buildings of a certain construction be present) in these villages increases with decreasing mean topographic slope. Fourth, run-up height and flood elevation may not be the best indicator of damage potential in these villages, which are characterized by irregular topography. Finally, a damage potential formulation is presented which considers both hydrodynamic loading and topography. The proposed damage potential formulation can be used as a tool to help governments, emergency planners, and forecasters to prioritize hazard mitigation initiatives, evacuations, and detailed tsunami forecast simulations.

Results are presented from experiments and computational fluid dynamics (CFD) simulations involving the streamlining of suspended underwater pipelines or structures subject to impacts from sediment/water mixtures. The experiments showed that a considerable reduction in force may be achieved by streamlining, and this reduction in force is most significant at lower Reynolds numbers. Several shapes were tested: round, airfoil, and wedge. Of these, the wedge exhibited the lowest drag coefficient—about one-fifth of the cylindrical pipe at low values of the Reynolds number, and about half at higher Reynolds numbers.

A free-surface semicircular breakwater (SCB) has been developed for protecting coastal and marine infrastructures against ocean waves. The hydrodynamic characteristics of the breakwater are investigated in irregular seas through an experimental program. A test model of the semicircular breakwater has been constructed with front wall porosity varied at 0 (i.e., no perforations), 9, 18, and 27%. The wave surface elevations are measured at different locations upstream and downstream of the models, and the coefficients of wave transmission, reflection, and energy dissipation are evaluated. Wave climate in the vicinity of the breakwater models and horizontal wave force on them are also measured. On the basis of the measured data, empirical models are proposed to provide design formulas for wave transmission, wave reflection, and horizontal wave force. The proposed empirical models show good agreement with the measured data; however, sensible engineering judgment must be taken while using these because the equations proposed are based on small-scale laboratory tests. The overall results indicate that the impermeable SCB model is an effective wave reflector, and the permeable SCB models are good energy dissipaters.

This paper focuses on a method to solve the static configuration for a lumped mass cable system. The method demonstrated here is intended to be used prior to performing a dynamics simulation of the cable. Conventional static analysis approaches resort to dynamics relaxation methods or root-finding algorithms (such as the Newton-Raphson method) to find the equilibrium profile. The alternative method demonstrated here is general enough for most cable configurations (slack or taut) and ranges of cable elasticity. The forces acting on the cable are attributable to elasticity, weight, buoyancy, and hydrodynamics. For the three-dimensional problem, the initial cable profile is obtained by solving three equations, regardless of the cable discretization resolution. This analysis discusses regions and circumstances under which failures in the method are encountered.

Fine-grained sediment budgets based on the monthly bed level and net sediment flux monitoring from October 2006 to October 2007 are estimated to examine the relative contributions of tides and river discharge to mud transport on an intertidal flat adjacent to a river mouth in a semiclosed sound. The estimated sediment budgets are interpreted using the water mass balance equation and the horizontal tidal current pattern measured using high frequency (HF) radar. The intertidal flat accreted during normal discharge conditions are primarily attributable to the alongshore sediment flux toward the river mouth. However, the flat was eroded when the large offshore suspended sediment transport occurred on the flat during the large river discharge. The net alongshore tidal current causes alongshore sediment fluxes toward the river mouth on this intertidal flat adjacent to the river mouth. These findings may be specific to this site, but an adopted comprehensive approach may be applicable to other sites.