Journal of Waterway, Port, Coastal, and Ocean Engineering

In this study, a new numerical scheme with variable-coefficient dispersive conditions was developed to simulate tsunamis over slowly varying topography. The new model was developed using a novel time-space decoupled numerical scheme that used the classic wave equation. By adapting this model to simulate tsunamis, a variable-coefficient dispersive condition was derived to consider the dispersive effects using a numerical truncation error from the numerical scheme. The stability condition and range of the variable coefficient were analyzed using a stability analysis. Using the specific dispersive condition and the modified time-space decoupled scheme, a uniform grid system can be used to simulate a dispersive tsunami over slowly varying topography. Numerical experiments for wave propagation with Gaussian humps and dipolar sources in uniform and varying topography demonstrate that the scheme is efficient for simulating tsunami propagation over slowly varying water depths with dispersive effects.

In this study, the distribution and variation of the hydrodynamic forces and hydrodynamic coefficients in both inline (IL) and cross-flow (CF) directions on flexible risers experiencing vortex-induced vibration (VIV) in a uniform flow were investigated. The hydrodynamic forces in the CF and IL directions were theoretically calculated by the Euler-Bernoulli beam vibration equation. With the least-squares method, the hydrodynamic coefficients in both CF and IL directions were further investigated. The results indicate that the hydrodynamic force and vibration displacement almost simultaneously reach their maximums. The excitation coefficients obtained in this paper do not always agree with those obtained by the forced-oscillation tests: some excitation coefficients are even negative within the usual defined exciting nondimensional frequency regime and are related with not only the nondimensional frequency and amplitude but also phase angles of the CF and IL displacements. The added-mass coefficient along a flexible riser has a significant variation compared with that of a rigid cylinder oscillating in a pure CF or IL direction. Moreover, compared with the excitation force, added-mass force is found to be the dominant component in the overall hydrodynamic force for the flexible riser undergoing VIV.

The wave interaction at low Keulegan-Carpenter numbers with a group of four large cylinders arranged in the form of a square with one diagonal along the direction of wave propagation is studied with a focus on the hydrodynamic effects of the most upstream and the downstream cylinders in the group. This is studied by removing them and comparing the wave forces and the free surface elevations around the three remaining cylinders with the four-cylinder configuration. The theoretically predicted wave near-trapping in the case of the four-cylinder group is also investigated for low- and high-steepness incident waves. The numerical results are compared with analytical formulas based on potential theory, and differences are observed between the results for high wave steepnesses. It is observed that the downstream cylinder has a significant influence on the wave forces acting on the cylinders in the four-cylinder group. It is also found that the numerical model correctly represents the wave near-trapping predicted by the analytical formula at a low incident wave steepness. For a high incident wave steepness, the diffraction regime is found to be different, with significant wave radiation from the cylinders and, consequently, the conditions for wave near-trapping breakdown.

This study applies the numerical model GPUSPH, an implementation of the weakly compressible smoothed particle hydrodynamics (SPH) method on graphics processing units, to simulate nearshore tsunami processes. Two sets of laboratory experiments that involve violent wave breaking are simulated by the three-dimensional numerical model. The first set of experiments addresses tsunamilike solitary wave breaking on and overtopping an impermeable seawall. Comparison with free-surface profiles and laboratory images shows that GPUSPH satisfactorily reproduces the complicated wave processes involving wave plunging, collapsing, splash-up, and overtopping. The other set of experiments investigates tsunamilike solitary wave breaking and inundation over shallow water reefs. The performance of GPUSPH is evaluated by comparing its results with (1) experimental data including free-surface measurements and cross-shore velocity profiles, and (2) published numerical results obtained in two mesh-based wave models: the nonhydrostatic wave model CCHE2D and the Boussinesq-type wave model FUNWAVE. The capability of GPUSPH to simulate nonlinear wave phenomena, such as wave shoaling, reflection, and refraction, is confirmed by comparing the wave field predicted by CCHE2D. Although all three models correctly simulate the solitary wave propagation offshore and the bore due to the broken wave run-up nearshore, GPUSPH outperforms CCHE2D and FUNWAVE in terms of resolving wave plunging and collapsing. The conducted two case studies show that the meshless SPH method is reliable for predicting tsunami breaking in the nearshore zone.

Indian River Lagoon (IRL) is a restricted estuary along the east coast of Florida. Although Banana River, a 50-km-long subbasin of IRL, has an outlet to the ocean through the Port Canaveral Locks, the locks remain closed when there is no passing vessel, resulting in limited circulation, long flushing time, and poor water quality. The purpose of this study was to determine the extent to which constructing a low-crested weir adjacent to Port Canaveral can improve flushing in this region. A computer program was used to simulate the hydrodynamic properties of the study area and determine the two-dimensional (2D) depth-averaged velocity field. Then, passive particles were placed in the Banana River, and their movement was tracked using the Lagrangian particle-tracking model (LPTM). Transport timescales were then computed. Results indicate an improvement in flushing in both the Banana River and the central IRL. In the portion of the Banana River to the south of the port complex, the flushing time was decreased from over 200 days down to 38 days as a result of an induced southerly current caused by the proposed low-crested weir.

This article presents an optimized setup for a numerical wave/current facility that allows for fast and efficient generation and absorption of random directional waves, in the presence of uniform noncollinear ambient currents. In this study, the generation of waves was optimized, in terms of computational effort, by replacing the built-in sine and cosine functions with a Taylor series approximation. The mesh in the absorption zone was also optimized with the use of a mesh grading that resulted in larger cells toward the outflow boundary. Results show that the numerical cost is reduced by 70% for the wave generation and by 90% for wave absorption. Results compare very well for wave generation with and without currents with respect to regular wave/current and random wave theories. Wave reflection was generally less than 1% for linear waves, less than 4% for nonlinear waves, and less than 5% for random waves.