Journal of Waterway, Port, Coastal, and Ocean Engineering

Floating offshore wind is a rapidly growing technology that is attracting global interest. To date, most of the demonstrated concepts for offshore floating wind are based on a simple one turbine–one platform system, which might not be the most efficient approach for manufacturing, transportation, and onsite installation. Very large floating structures (VLFS), which allow for operation of multiple turbines, might be an effective alternative to traditional floating foundations. However, the large bending moment caused by waves is a major concern for a VLFS foundation. Adding hinges into the structure might help to alleviate the bending moment. Based on the discrete-module-beam-bending hydroelasticity method, the effects of hinge numbers on the bending moment will be investigated in detail and will be presented in this paper. Overall, the bending moment is reduced when the vertical displacement is increased by the addition of hinges, which indicates a compromise when choosing hinge numbers. In addition, a feasibility study for the application of the multihinged VLFS as a floating wind platform will be provided. It demonstrates that the existence of wind turbines might further reduce the wave-induced bending moment, but they enlarge the total bending moment by introducing a still water bending moment. The effect of wind turbines on the vertical displacement of the multihinged VLFS is insignificant.

In this study, the entrainment mechanisms of unconfined turbidity currents that interact with a linear rectangular obstacle will be investigated and compared with confined studies. Laboratory experiments will be performed in a lock exchange basin, where the width allows unconfined and partially unconfined flows, with varying initial current densities. Ambient fluid entrainment, based on the Morton-Taylor-Turner (MTT) hypothesis, was found to be comparable to previous confined studies; however, in situ current density decreased at a greater rate than the latter. It was shown that this was probably caused by the unconfined lateral spreading of the current before the obstacle. The entrainment parameter had a weak relationship with Froude, Reynolds, and Richardson numbers for nonobstructed tests, which was similar to previous studies. However, this was not the case for obstacle tests, which experienced a greater variance in entrainment velocity and head height. Of note, head height was less than that for equivalent confined tests, which suggested that in a practical setting, confined studies might overestimate the obstacle height needed to block current propagation.

In this work, an analytical solution that models the dynamic response of a poroelastic soil, induced by the action of water waves in a stratified fluid, is obtained. We propose a reduction of the generalized governing equations for the limit when the horizontal displacements of the porous soil are very small compared with the vertical displacements. The results obtained are similar to those calculated with the governing equations in their complete form. We consider that the instantaneous liquefaction depth is unknown; therefore, the boundary value problem is solved as an eigenvalue problem. The instantaneous liquefaction depth is calculated for a wide range of wave frequencies, from long waves to short waves. It is found that liquefaction depth increases with increasing wavelength. For large values of soil shear modulus, the liquefaction depth increases because the pore pressure magnitude is larger than for the case of soils with low shear modulus. This work can be used as a benchmark to identify the effects that the physical parameters of a poroelastic soil have on the liquefaction depth.

The efficiency of dredging, whether with a cutter suction dredger or hydraulic flushing, is closely related to the erodibility of the sediments. It is found that the erodibility of cohesive sediments, which is affected by their rheological properties, could be enhanced by improving their fluidization quality. In this study, a cohesive sediment fluidization and erosion enhancing (CSFEE) device was used to fluidize the sediments during flushing, and the corresponding scour rates of test sediments were investigated. The results indicated that this device, with the combined effects of vibration and air, can significantly enhance the erodibility of cohesive sediments in both the directly and indirectly vibrated areas and that this enhancement is more significant for the sediments with higher initial yield stress. The fluidization of the sediments by mechanical vibration is the key driver for such enhancement. Due to the thixotropy of cohesive sediments, the effects of vibration were time-dependent, whereby the scour rate of test sediments increased with increasing exposure time of the device.

This paper explores the influence of onshore structures' orientations and arrangements during a tsunami impact using the numerical method of smoothed particle hydrodynamics (SPH). Observations from previous tsunami events often reveal variation in the damage and survivability of impacted similar structures. Such variation can be due to shielding effects and other interactions that occur when the tsunami wave incident occurs in an urbanized location. The SPH model used in this work was first validated against previous experimental results and was then used to explore the resulting hydrodynamic behavior to a level of detail hitherto unobtainable from physical experiments. Groups of three and five structures were modeled with varying spatial separation and orientation to the incoming tsunami bore, characterized by the wake clearance angle (A) and the rotation angle (R), respectively. The results reveal significant reductions in total force on a structure can be made via strategic spatial positioning and orientation. Such reductions may mean the difference between superficial damage and wholesale structural collapse and allow the development of more resilient structures in tsunami-prone regions.

This paper will discuss the variations in wave loads on a vertical seawall structure due to the addition of parapets. A 1:8 model scale experiments on a wall with parapets will be carried out. The models will be tested for monochromatic waves that have different breaking characteristics that are identified based on the amount of air entrapped during breaking. These include slightly-breaking waves (SBW), breaking waves with small air trap (BWSAT), and breaking waves with large air trap (BWLAT). The relative reduction in impact pressure will be used to quantify parapet performance. This paper revealed that with the addition of a parapet, wave force increases compared to a vertical wall (VW) until incident wave height [(H_i < 0.125 m)]. However, with further increases in wave height (H), the wave force reduces for large (LP) and medium parapets (MP) compared with a small parapet (SP). The exit angle of the parapet plays a vital role to decrease the wave loads for higher H; the extent of the decrease is dictated by the movement of deflected water. Based on the tested parapets and wave characteristics, an LP (45°) attracted less load on the overall structure compared with other parapet types for higher H_i (H_i > 0.125 m).

Driven by waves, water surface elevation, and wind conditions, a coupled wave, hydrodynamic, and sediment transport modeling system was developed to investigate the transport of placed dredged material in the surf and nearshore zones of southern Lake Michigan. With the measured bathymetric data and the implementation of a cross-shore transport routine, the modeling study focused on nearshore sediment migration, bed volume change, and subaqueous profile change due to wave action. The field datasets validated the model's capability in properly reproducing longshore and cross-shore current and wave processes that govern nearshore sediment transport. The analysis on survey data and simulation results indicates that time-averaged longshore current dominates the redistribution of sediment. Although the cross-shore transport is an order of magnitude smaller than the longshore transport, including the surf zone cross-shore process in the model contributes to net bed and subaqueous profile changes, and greatly improves the model performance.

Ports are complex engineering systems that have always been evolving to satisfy the new or changing demands of stakeholders. However, the ever-growing complexity in port sectors in a volatile environment creates a high degree of uncertainty in port planning projects. This study presents a structured framework to deal with uncertainties in the port planning process. Stakeholder analysis, different methods of addressing uncertain developments, and SWOT analysis were jointly used to develop the framework. Effective actions were planned in response to opportunities and vulnerabilities derived from uncertainties that manifest in a projected lifetime. Face-to-face interviews with key stakeholders and literature review were conducted to identify uncertainties and planning horizons. The framework was applied to the Ports of Isafjordur Network in Iceland. The results show that demand for aquaculture and cruise activities create the main uncertainties for the port network. Uncertainties mainly present opportunities in the short-term horizon, while in the middle-term horizon the port network is confronted with multiple vulnerabilities. The nonlinearity of dealing with uncertainty by application of the framework provides a robust and better plan toward its success in a dynamic world. The framework supports decision making under uncertainty by facilitating adaptive port planning.

An automatic procedure to identify the bed friction coefficient is tested on a 2D hydrodynamic model of the Gironde estuary (France). The proposed procedure involves an optimization algorithm based on evolution strategy, namely Covariance Matrix Adaptation Evolution Strategy. Without optimization, application of the same friction distribution to different hydrological conditions leads to significant relative error in water level prediction up to 20%–30%. For the tested configuration, 300 runs seemed to be sufficient to reach an optimal value whereas an additional 200 runs would help to gain an accuracy of a few millimeters (or 0.3%). In order to reach the same level of accuracy for the different hydrological configurations, it is necessary to adapt for each configuration of the bed friction coefficient. Such behavior tends to confirm a seasonal variation of the friction coefficient and this is particularly the case in the central part of the estuary. Different relationships of the friction coefficient according to the flowrate have been incorporated inside the 2D hydrodynamic model. These relationships effectively maintain an accurate prediction of the water levels close to 10% for a wide range of hydrological configurations.