Tetsuo Ueno

A cross-correlation technique for velocity field extraction from particulate visualization

A rapid time series of photographs of the horizontal cross-sections of several y+ locations were taken of a turbulent open-channel water flow with Red = 3,900. A pair of photographic images were obtained with a time difference of 1.3 v/uτ2at each y+ locations. The pictures were digitized into 8 bit data with a spatial resolution of 2.5 viscous scales. Instead of identifying discrete particles, a variable interval spatial correlation technique was used to extract the velocity components. With this technique, two-dimensional spatial cross-correlations of the illumination intensities were taken between a pair of picture images. The correlations were taken over small areas and the peak of the correlation coefficients were used to obtain the convection velocity yielding the u and w components of velocity. Some statistical properties were calculated and are shown to be comparable with previous data. Spatial correlations of the velocity components revealed some unique characteristics related to the structure of turbulence.

Experimental study on the coherent structure of turbulent open-channel flow using visualization and picture processing

Coherent structures of turbulent open-channel flow in the wall region of a channel bed were examined quantitatively using experimental data obtained by flow visualization. Successive pictures of flow patterns in two horizontal cross-sections at different levels near the channel bed were taken, and then were digitized and analysed by a computer. This method of flow visualization and picture processing enabled us to calculate the distributions of the three components of the velocity vectors. The distributions of velocities, streamlines, two-dimensional divergence and three components of vorticity could be calculated and are displayed as graphical output. In our numerical analyses, the idea of a two-dimensional correlation coefficient is introduced, through which the degree of similarity of turbulence structures can be better estimated than with the usual one-dimensional coefficient. Use of the data was based on the premise that the essential element in a turbulence structure is vortex motion. We propose a conceptual model of turbulence structure in which the elementary unit of coherent structure in the buffer layer is presumed to be a horseshoe vortex and in which the characteristics of the multiple structure of turbulence are shown with respect to the scale, arrangement and generating process of horseshoe vortices and longitudinal vortices. Our model clearly explains the generating mechanism and mutual relations of low-speed regions, high-speed regions, ejections, sweeps and localized free-shear layers.

Optical and magnetic studies on the phosphorescent state of phthalazine in polar and non-polar hosts

The optical and magnetic properties of the lowest triplet state (T 1) of phthalazine were investigated in benzoic acid (BAC), p-dichlorobenzene (DCB) and p-dibromobenzene (DBB) by means of phosphorescence spectroscopy, ODMR and E.P.R. at liquid helium temperatures. Well resolved phosphorescence spectra were observed in DCB and DBB and a vibrational analysis of the spectra was made. The transition energies of the T 2(nπ *) and the S 1(nπ *) states were estimated from the excitation spectra. The energy gaps between T 1 and T 2 were estimated to be 2150, 694 and 788 cm−1 in BAC, DCB and DBB, respectively. The sublevel schemes and the zero field splittings (ZFS) were determined. The observed changes of the ZFS on going from the polar to the non-polar hosts are discussed in terms of the vibronic and spin-orbit interactions with the nearby T 2(nπ *) state. The most radiative sublevel was found to be T2 in DCB, but T y in BAC. This difference is attributed to the shifts of the energy levels and the reduction of ...

Influence of Channel Width on the Flood Flows in a Stream Valley

Investigative reports of flood disaster in a stream valley state that the magnitude of flood damages depends on the stream configuration. A meandering stream runs in mountainous basins through narrow valley. Flood damages were serious around the narrow apex of a bend. On the other hands, the damages were little serious around the wide apex. From this point of view, the stream width at the apex of a bend was focused on. The experiments with a doubly meandering compound channel were conducted to investigate the influence of channel width on the flood flows. Water surface flows were visualized, and water level was measured. The channel width influences on the magnitude of water surface velocity and divergence, implying that the scale of bank erosion can be difference. The magnitude is large in the case of narrow apex. On the other hand, the magnitude is small in the case of wide apex. This means that the flood damages can be explained by experimental results. As a result, it is supposed that appropriate river width must be taken into account to reduce the flood damages in a stream valley.

THE EFFECT OF CONFIGURATION ON FLOOD FLOW IN STREAM VALLEY

The flood disaster in a stream valley is discussed with experimental results by water surface flow visualization and water level measurement. From a field survey, it is found that the magnitude of damage is dependent on valley width, which implies the change of flood flow depth on the alluvial plain, and river width at the bend apex. As experimental results, the magnitudes of water surface velocity and divergence around the apex are large for deep condition on the flood plain and narrow channel width at the bend apex, implying that significant erosion can occur around a bend. Thus it is important to understand the effect of configuration on flood flows and appropriate river width at the bend apex to reduce flood damages in a stream valley.

TRIAL OF SEDIMENT DISCHARGE MEASUREMENTS UNDER FLOODS IN THE HII RIVER

The river-bed configurations were measured by a echo-sounder attached to a cross-type float under floods in the Hii River which is the typical sand-bedded river in Shimane Prefecture. At the same time, time series of photographs were taken of the flow patterns on the flow surface, and the vertical distributions of the velocity and turbidity were also measured.In this paper, by using the data, moving velocities of dunes were obtained at every stage of the floods, and approximate estimations of discharge rate of bed load and suspended load were tried.

Picture Analysis of Aerial Photographs of Flood Flows

A pair of aerial photographs of the flood flow in the Agano River on Sept. 25, 1966 was analyzed by the cross-correlation technique to obtain velocity vectors over the area of 1700 × 1000 m of the water surface. About 340 × 400 velocity vectors were obtained at every 5.0 m in streamwise and 2.5 m in spanwise direction.The interval and arrangement of the longitudinal low-speed band and high-speed band appearing alternately in the spanwise direction over the water surface were analyzed and two kinds of spanwise scales of large scale turbulence were found; one is about twice water depth and another is 4 5 times.

Picture Processing of Aerial Photographs of a Flood Flow by the Cross-Correlation Technique

A pair of aerial photographs of flood flow of Ishikari River were analysed by picture processing to obtain two-dimensional distribution of velocity vectors of the flood surface. Streamline patterns, vorticity and divergence were calculated using the obtained velocity data and the structure of the vortices and its relation with river sedimentation were elucidated.Strong upwellings (boils) in the vortices and strong downflows around the edge of the vortices were shown to be the main cause of the formation of the core of scroll bars.

Investigation of the Coherent Structure of Turbulent Open Channel Flow by Two-Dimensional Pattern Recognition

The horizontal cross-sections of the uniform open channel flow was visualized and twodimensional velocity distribution in each cross-section was obtained by picture processing.Two-dimensional pattern recognition method was introduced into the obtained velocity data. Two-dimensional patterns of vorticity distributions was proposed to detect the typical arrangement of vortex motions.Ensemble averaged pattern of two-dimensional distribution of velocity vectors, x- and zcomponents of velocity vectors, vorticity and two-dimensional divergence around the detected points were shown. Based on these patterns, mechanism of sweeps and ejections, and onedimensional methods to detect these events were examined.