NUMERICAL SIMULATION OF FREE MIXING LAYER WITH CROSS SHEAR

A spectrum method is used to simulate the time-developing free mixing layerwith cross shear which is introduced in different stages. The results show that the properties of flow are nearly the same for situations whether the cross shear is introduced in theinitial time or in early stage. If cross shear is introduced in the stage that the roll-up ofmixing layer occurs, the turbulent intensities of now will increase and mixture of now willbe enhanced.

THREE DIMENSIONAL NONLINEAR NUMERICAL MODEL WITH INCLINED PRESSURE FOR SALTWATER INTRUSION AT THE YANGTZE RIVER ESTUARY

A three-dimensional nonlinear numerical model with inclined pressure was developed to compute the saltwater intrusion at the Yangtze River Estuary. The σ-transformation was introduced in the vertical plane to achieve the same lattices in the whole domain of interest. The mode-splitting technique can be used to split the three-dimensional governing equations into the surface gravity waves (external mode) and the internal gravity waves (internal mode). And the external mode was solved by the improved double-sweep-implicit (DSI) finite difference method and the internal mode was solved by the Eulerian-Lagrangian method. The Eulerian-Lagrangian method can not only reduce the numerical diffusion but also increase the computational accuracy through the improvement of the finite difference scheme in the vertical direction. The application of the model to the Yangtze River Estuary was carried out for the calculation of the saltwater intrusion and the null point. Results of the temporal and spatial distribution of the flow velocity and the salinity coincide with the measured data quite well. The formation and location of the underwater sandbars in the North Channel of the Yangtze River Estuary are closely related to the local salinity, the null point, the predominant current and the residual flow.

Modified porous silica antireflective coatings with laser damage resistance for Ti:sapphire

Porous SiO2 antireflective (AR) coatings are prepared from the colloidal silica solution modified with methyltriethoxysilane (MTES) based on the sol-gel route. The viscosity of modified silica suspensions changes but their stability keeps when MTES is introduced. The refractive indices of modified coatings vary little after bake treatment from 100 to 150℃. The modified silica coatings on Ti:sapphire crystal, owning good homogeneity, display prominent antireflective effect within the laser output waveband (750-850 nm) of Ti:sapphire lasers, with average transmission above 98.6%, and own laser induced damage thresholds (LIDTs) of more than 2.2 J/cm2 at 800 nm with the pulse duration of 300 ps.

Static light scattering properties of a ZnO nanosphere aqueous suspension at visible and near-infrared wavelengths

The scattering properties of ZnO nanospheres with four different particle diameters of 10, 50, 100, and 200 nm suspended in water are investigated theoretical and experimentally in the spectral range of the entire visible range and part of the near-infrared region. The scattering properties of ZnO nanospheres suspended in water are described by employing three main parameters： the angular distribution of the scattering intensity I, the scattering extinction coefficient ascat, and the scattering cross section ascat. The results indicate that （i） at a certain wavelength, the angular distribution of the scattering intensity appears as an obviously forward- propagating feature, and the forward-scattering intensity is dominant gradually when the particle diameter in- creases from 10 to 200 nm, and （ii） the scattering extinction coefficient and cross section can be determined by using the measured transmittance changes of a pure water sample and a given ZnO sample; they all are shown to be dependent on the particle size and incident wavelength. The experimental results of four different scattering samples agree well with the theoretical predictions within the given wavelength range.

BOUNDARY LAYER EFFECTS ON SOLID PARTICLE MOTION AND EROSIVE WEAR

Lagrangian motion equation of a solid particle suspended in 2-D turbulent boundary layer flows has been modified. The effects of boundary layer on particle motion were studied. The critical nondimensional incidence velocities and angles to the wall from the edge of a 2-D incompressible turbulent boundary layer were presented for various nondimensional particle sizes and initial velocities. The numerical results clearly show that the effects of boundary layer on particle motion and particle impact erosive wear are very great. The presence of boundary layer decreases particle impact velocity and impact erosive wear.

RESEARCH ON THE MOTION CHARACTERISTICS OF FIBER SUSPENSIONS IN A WEDGE-SHAPED FLOW

The motion of cylindrical particles in a wedge-shaped flow was studied. The velocity distribution of wedge-shaped flow was simulated and then the Euler-Lagrange model was used to calculate the motion of cylindrical particles. The evolution of particle location, velocity and orientation with time was examined. The trajectories of the particles with different particle Stokes number, rate of flow and initial particle orientation were drawn. The results indicate that the Stokes number and initial orientation are important parameters which mainly affect the particle motion.

VELOCITY DISTRIBUTIONS OF SUSPENDED SEDIMENT-LADEN FLOWS IN OPEN CHANNELS

Analysis on velocity distributions of steady, uniform suspended sediment-laden flow in open channels was presented. The sediment particle-particle interactions and the buoyancy effects due to density stratification were taken into account through a water sediment mixture's constitute relationship and an adapted Monin-Obukhov length scale to validate the theory for a wider spectrum of sediment concentrations. The developed model with the same Von Karman coefficient as that of a single phase flow was shown to be in the excellent agreement with the measurement results in the controlled experiments with both the low and heavy sediment concentrations.