Yuji Sugihara

Quantitative properties of oscillating-grid turbulence in a homogeneous fluid

Oscillating-grid turbulence in a homogeneous fluid is in equilibrium between the diffusion of turbulent energy and the dissipation rate of the energy. Such a field has been investigated experimentally and analyzed by using the k– turbulence model. Vertical and horizontal components of fluctuating velocity have been measured under the vertical oscillation of a square grid. Vertical profiles of five characteristic quantities, the turbulent energy k, the dissipation rate , the vertical energy flux F, the eddy viscosity νt and a lengthscale lt, have been obtained from the measurements. In the model analysis, the governing equations and the boundary conditions have been non-dimensionalized by using the turbulent energy k0 and the dissipation rate 0 which are given virtually at the center of the grid oscillation as boundary conditions. Dimensionless analytical solutions of k,,F,νt and lt have been derived. The experimental data show some relationships existing between the analytical solutions. This shows the application of the k– model to the oscillating-grid turbulence to be valid. The analytical solutions include three model parameters. Their values have been determined from the experimental data. The values of k0 and 0 have been evaluated by superposing the analytical solutions of k, and F on their experimental data, and have been related empirically to the experimental parameters. Using the empirical relations for k0 and 0 and the analytical solutions, we can estimate k,,F,νt and lt of the oscillating-grid turbulence.

Experimental observation of internal symmetric solitary waves in a two-layer fluid

Water tank experiments were conducted on the internal symmetric solitary waves generated by gravity flow intrusion at the horizontal interface of a two-layer fluid. Velocity distributions in the waves were first measured using an image processor. Flow visualization studies revealed some new features of the solitary waves, including a marked decrease in the phase velocities of two large-amplitude, oppositely propagating waves after their head-on collision.

Treatment and regeneration of nano-scale zero-valent iron spent in water remediation

Nano-scale zero-valent iron (nZVI) has shown its promising treatment technique to decontaminate nitrate from water. However, research reports lack the treatment and regeneration of the spent reagent from the treatment process. This research utilized different derivatives of nZVIs in the purpose of nitrate treatment in its aqueous solution to show their different reactivities in applied batch experiments. Selected nanoparticles were investigated via transmission electron microscopy, surface characterization analyzer, X-ray diffraction and laser-scattering particle size analyzer. The fresh synthesized nZVI had the highest performance with complete nitrate removal within 60 min. Treated nZVI succeeded to regain the lost reactivity of aged nZVI and boosted its removal efficiency 10 times. On the other hand, the regenerated nZVI, recovered from spent synthesized nanoparticles, regained full and complete removal efficiency of nitrate, the same as the synthesized nZVI. The obtained result gives a great competitiveness of nZVI reagent to treat nitrate against any other treatment technology.

VARIABILITY OF HEAT-ISLAND INTENSITY IN FUKUOKA METROPOLITAN AREA

The influences of meteorological factors on the variability of heat-island structure in the Fukuoka metropolitan area are investigated on the basis of observation data and numerical simulation by using a meteorological numerical model, i.e., Weather Research and Forecasting (WRF). The present results show spatial patterns of the heat island to be controlled by local wind systems. The heat-island intensity varies temporally depending on the formations of sea and land breezes, whereas the variation becomes relatively small under background wind dominated condition. The heat-island intensity takes a maximum value in nighttime and the value depends on the amount of the global solar radiation in daytime.

Turbulent Properties of an Atmospheric Boundary Layer in Day and in Night

A field observation was made to investigate turbulent characteristics in the lower region of an atmospheric boundary layer in day and in night. Horizontal and vertical wind speeds, and wind direction were measured by using a doppler sodar at 13 points in the range of 55m to 425m above the ground. Vertical profiles of the mean wind speeds, the Reynolds stress and the turbulent intensities were obtained from the measured data. The diurnal profiles were compared with the nocturnal ones. Their profiles show that the diurnal boundary layer had a strong convection caused by the solar-heating and the nocturnal layer was relatively stable. The Reynolds stress decreased linearly with height both in day and in night.

QUANTITY OF SPRAY TRANSPORTED BY STRONG WIND OVER BREAKING WAVES

A special reflecting wall 12 m long and 2.1 m high was built off the beach at Reggio Calabria, and 30 wave gauges were assembled before the wall and were connected to an electronic station on land. It was possible to observe the reflection of wind waves generated by a very stable wind over a fetch of 10 Km. The experiment aimed to verify the general closed solution for the wave group mechanics (Boccotti, 1988, 1989), for the special case of the wave reflection.Significant features on Wadden Sea wave climate are evaluated in respect of the state of the art. Main emphasis was laid on an analysis of the governing boundary conditions of local wave climate in island sheltered Wadden Sea areas with extensions being sufficient for local wind wave growth. Explanatory for significant wave heights a reliable parametrization of local wave climate has been evaluated by using generally available data of water level and wind measurements.