NUMERICAL ANALYSIS OF WAVE AND NEARSHORE CURRENT FIELDS AROUND LOW-CRESTED PERMEABLE DETACHED BREAKWATERS

A Boussinesq type numerical model was developed which can simulate both wave fields and current fields around permeable detached breakwaters. The validity of the model was verified through measurements of waves and nearshore currents in hydraulic experiments investigating reflection and transmission capability. The porosity of the structure was accounted by a friction term incorporating turbulent resistance. The combination of turbulent friction model and anisotropic diffusion type wave breaking model was found to reproduce wave fields around the detached breakwaters and nearshore current fields behind the structures with a good accuracy.

Evolution and breaking of parametrically forced capillary waves in a circular cylinder

We present results on parametrically forced capillary waves in a circular cylinder, obtained in the limit of large fluid depth, using two low-viscosity liquids whose surface tensions differ by an order of magnitude. The evolution of the wave patterns from the instability to the wave-breaking threshold is investigated in a forcing frequency range (f= ω/2π = 25–100 Hz) that is around the crossover frequency (ωot) from gravity to capillary waves (ωot/2≤ω/2≤4ωot). As expected, near the instability threshold the wave pattern depends on the container geometry, but as the forcing amplitude is increased the wave pattern becomes random, and the wall effects are insignificant. Near breaking, the distribution of random wavelengths can be fitted by a Gaussian. A new gravity–capillary scaling is introduced that is more appropriate, than the usual viscous scaling, for low-viscosity fluids and forcing frequencies <103Hz. In terms of these scales, a criterion is derived to predict the crossover from capillary- to gravity-dominated breaking. A wave-breaking model is developed that gives the relation between the container and the wave accelerations in agreement with experiments. The measured drop size distribution of the ejected drops above the breaking threshold is well approximated by a gamma distribution. The mean drop diameter is proportional to the wavelength determined from the dispersion relation; this wavelength is also close to the most likely wavelength of the random waves at drop ejection. The dimensionless drop ejection rate is shown to have a cubic power law dependence on the dimensionless excess acceleration ε′dan inertial–gravitational ligament formation model is consistent with such a power law.

The Sensitivity of Set-Up/Set-Down and Wave-Driven Currents to Different Breaking Models

The authors have developed a wave-current interaction model. It includes a wave sub-model based on the elliptic form of the mild slope wave equation with a parabolic mild slope wave equation as a boundary condition. It also includes a hydrodynamic sub-model which has been developed to examine set-up, set-down and currents in the coastal zone. The wave breaking model used in the wave sub-model affects the results of set-up, set-down and current obtained using the hydrodynamic sub-model. This paper examines a number of different breaking models and compares the set-up, set-down and currents obtained using radiation stress values which are calculated from derivatives of velocity potential. The velocity potential is obtained in the wave sub-model using the various breaking models being examined. The results show a number of possible breaking models for set-up and set-down calculation and also shows shortcomings in various breaking models when it comes to calculation of longshore currents.