Coastal Engineering Journal

Based on oblique irregular wave physical model tests, the hydraulic characteristics of the semicircular breakwater are studied in this paper. The variations of wave forces on unit length of semicircular breakwater with the main effective factors including wave steepness H_s/L_s, relative wave height H_s/d, d′/H_s and the angle of incidence θ₀ are studied. In addition, the longitudinal distribution of wave forces, and the longitudinal load reduction are analyzed. Some empirical formulae of the longitudinal distribution coefficient and the longitudinal load reduction factor are presented for practical use. Particularly, the conditions for trough values of the total horizontal wave forces are larger than crest values are discussed.

At present, there are a few models to calculate 3D morphology change that have been thoroughly validated and are useful to the engineering community. The 3D models typically consume substantial computational time and resources, which can pose as one of the limitations of applying such models. To overcome this limitation, the present paper introduces an approach for calculating representative waves to be used instead of time series wave climate. The calculation of representative waves is done by assuming equivalence of wave energy and longshore or cross-shore sediment transport between representative and real waves. In this study, a 2D hydrodynamic model and a 3D morphological model are applied with representative waves to calculate morphologies between fishtail groins. It was found that the use of two representative waves can reduce the computational time from 480 hrs using classical methods to 2 hrs, thus saving computational time while providing satisfactory results with typical values of 0.85 and 0.19 m for the statistical measures EI and RMSE, respectively.

Nonlinear water waves propagating over a three-dimensional submerged porous bottom are investigated using depth-integrated model developed by Hsiao et al. In particular, the case of waves over porous submerged trapezoidal mounds is discussed and the results are compared with the experimental data of Cruz et al. The overall comparisons are reasonably good, suggesting that the model equations used in this study can describe diffraction, reflection and refraction effects well.

A two-phase flow model based on the mass and momentum conservation is presented, which can simulate the fluid and sediment movement on a flat bed under sheetflow conditions. The governing equation in the vertical direction is modified by considering the influence of static normal intergranular stress. Horizontal pressure gradient is modified in terms of sediment concentration. A criterion is introduced to decide the temporal variation of the still bed level during a one-wave cycle. Vertically parabolic eddy viscosity and corresponding sediment diffusion coefficient are assumed. Numerical results include initial validation comparisons with the existing experimental data from Horikawa et al. [1982]. All measured properties, such as the concentration, sediment velocity and sediment flux are reproduced quite well. Further investigations on the experimental data of Delft Hydraulics [Ribberink and Al-Salem, 1995; Dohmen-Janssen, 1999] cover a wide range of pure sinusoidal wave and combined wave/current flow conditions for different sediment sizes. The numerical results are satisfactory with respect to the measured time-varying and time-averaged concentration distributions both in the sheetflow layer and the suspended layer. Taking into account the various experimental measurements, the present two-phase flow model shows the significant superiority over an existing two-phase flow model [Mina and Sato, 2004]. Comparison between the measurement and the present simulation for sediment flux and net transport rate is also performed.