Effects of horizontal mixing on the upper ocean temperature in the equatorial Pacific Ocean

The influence of horizontal mixing on the thermal structure of the equatorial Pacific Ocean is examined based on a sigma coordinate model. In general, the distributions of the temperature and currents simulated by the sigma coordinate model are very close to the climatology. However, the simulated thermocline along the equator is slightly diffusive so that there is a cold bias above the main thermocline, while there is a warm bias under the main thermocline. Both horizontal diffusivity and viscosity have important effects on the upper thermal structure in the equatorial Pacific Ocean, while their detailed dynamics are different. Horizontal diffusivity affects the thermal structure in the upper ocean mainly through regulating the vertical diffusivity, while the horizontal viscosity does mainly through regulating directly the circulate system. A large horizontal diffusivity or a small horizontal viscosity can be in favor of simulating a more realistically thermal structure in the equatorial Pacific Ocean.

Development of A Depth-Integrated Longshore Current Model with Unstructured Grids

A depth-integrated model for simulating wave-induced longshore current was developed with unstructured grids. Effects of surface roller and horizontal mixing under combined waves and currents were incorporated in the numerical model. Recommended values of model coefficients were also proposed based on sensitivity analysis. Field observations and three series of laboratory measurements including two cases conducted on the plane beach and one implemented on the ideal inlet were employed to examine the predictive capability of this model. For the field case and laboratory cases conducted on the plane beach, numerical results were compared favorably with the measured data. For the case with an ideal inlet, simulated circulation pattern is supposed to be reasonable although some deviations between numerical results and measured data still can be detected.

Discrete particle simulation of mixed sand transport

An Eulerian/Lagrangian numerical simulation is performed on mixed sand transport. Volume averaged Navier-Stokes equations are solved to calculate gas motion, and particle motion is calculated using Newton＇s equation, involving a hard sphere model to describe particle-to-particle and particle-to-wall collisions. The influence of wall characteristics, size distribution of sand particles and boundary layer depth on vertical distribution of sand mass flux and particle mean horizontal velocity is analyzed, suggesting that all these three factors affect sand transport at different levels. In all cases, for small size groups, sand mass flux first increases with height and then decreases while for large size groups, it decreases exponen- tially with height and for middle size groups the behavior is in-between. The mean horizontal velocity for all size groups well fits experimental data, that is, increasing logarithmically with height in the middle height region. Wall characteristics greatly affects particle to wall collision and makes the fiat bed similar to a Gobi surface and the rough bed similar to a sandy surface. Particle size distribution largely affects the sand mass flux and the highest heights they can reach especially for larger particles.