Direct numerical simulation and large-eddy simulation are developed to investigate water waves propagating over viscous fluid mud at the bottom, with a focus on the study of wave breaking case. In the simulations, the water surface and the water–mud interface are captured with a coupled level-set and volume-of-fluid method. For non-breaking water waves of finite amplitude, it is found that the overall wave decay rate is in agreement with the existing linear theory. For breaking water waves, detailed description of the instantaneous flow field is obtained from the simulation. The time history of the total mechanical energy in water and mud shows that during the early stage of the wave breaking, the energy decays slowly; then, the energy decays rapidly; and finally, the decay rate of energy becomes small again. Statistics of the total mechanical energy indicates that the mud layer reduces the wave breaking intensity and shortens the breaking duration significantly. The effect of mud on the energy dissipation also induces a large amount of energy left in the system after the wave breaking. To obtain a better understanding of the underlying mechanism, energy transport in water and mud is analyzed in detail. A study is then performed on the viscous dissipation and the energy transfer at the water–mud interface. It is found that during the wave breaking, the majority of energy is lost at the water surface as well as through the viscous dissipation in mud. The energy and viscous dissipation in mud and the energy transfer at the water–mud interface are strongly affected by the wave breaking at the water surface.

We simulate the dynamic evolution of nonlinear water waves coupled with wind turbulence. We first investigate simple wave trains to obtain pressure distribution, based on which parameters for wave growth are quantified and their dependence on wave age and wave steepness is shown. We then investigate broadband waves to obtain physical insights to wind forcing for phase-resolved wavefield simulation. It is found that for long wave components, the wave growth parameter can be approximated by the value of the corresponding monochromatic waves; for short waves, stochastic modeling is suggested.

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The influence of feed concentration on the solid/liquid two-phase flow in a mini-hydrocyclone was studied. A phase doppler particle analyzer was used to measure the two-phase flow pattern in a 25 mm hydrocyclone at three different feed concentrations (300 mg/kg (0.136% (v/v)), 800 mg/kg (0.364% (v/v)) and 1200 mg/kg (0.545% (v/v)). The measurements show that the feed concentration has remarkable influence on the velocities in a hydrocyclone. A higher concentration of solid particles leads to lower axial velocities and can suppress the turbulence of the liquid phase in the inner helical flow; in the outer helical flow, however, the influence was complex. In planes in eddy flow, the downward flow of the liquid phase was increased by a higher concentration of particles; at same time, the dimension of circular flow was also decreasing. In the pyramidal zone, however, the higher feed concentration corresponds to lower axial velocities at the wall region. In the whole experimental zone, the particles lead to the decreasing of tangential velocities. The presence of particles has little influence on the basic flow structure, but changes the size of the eddy flow in the cylindrical section. The correspondence between the higher feed concentration and the shift of the line of zero velocity value closer to the core is also observed which probably means more inlet particles would lead to more liquid leaving the hydrocyclone through the circular flow.