PIV and PTV measurements in hydro-sciences with focus on turbulent open-channel flows

PIV is one of the most popular measurement techniques in hydraulic engineering as well as in fluid sciences. It has been applied to study various turbulent phenomena in laboratory experiments related to natural rivers, e.g., bursting phenomena near the bed, mixing layers observed at confluences, wake turbulence around dikes and piers, and so on. In these studies, PIV plays important roles in revealing the space-time structure of velocity fluctuations and coherent vortices. This review article focuses particularly on the applications of PIV to turbulent open-channel flows, which have been conducted for the past decade in Hydraulics Laboratory of Kyoto University. In Section 2, we introduce our experimental setup and PIV/PTV algorithm. In Section 3, we apply the PIV measurements to reveal turbulence characteristics and coherent structures in open-channel flows as well as in vegetated canopy flows. For complex flow situations, various applications of PIV to compound open-channel flows and wind-induced water waves are considered to reveal coherent vortices. In Section 4, we discuss some advanced PIV measurements in open-channel flows. The free-surface-elevation fluctuations and velocity components were measured simultaneously with two sets of cameras to examine phase-averaged parameters of turbulence. A multi-layer scanning PIV was developed to reveal 3D turbulence structure in compound open-channel flows. Our discriminator PIV/PTV was applied successfully to sediment-laden open-channel flows and revealed the fluid/particle interaction and the relationship between coherent structures and sediment concentration. Finally, we conducted simultaneous measurements of velocity and dye concentration with a combination of PIV and LIF in vegetated open-channel flow, which enables us to examine turbulent scalar flux of a passive contaminant.     

Occurrence and formation potential of N-nitrosodimethylamine in ground water and river water in Tokyo

N-nitrosodimethylamine (NDMA), a disinfection byproduct of water and wastewater treatment processes, is a potent carcinogen. We investigated its occurrence and the potential for its formation by chlorination (NDMA-FP_2Cl) and by chloramination (NDMA-FP_2NHCl) in ground water and river water in Tokyo. To characterize NDMA precursors, we revealed their molecular weight distributions in ground water and river water. We collected 23 ground water and 18 river water samples and analyzed NDMA by liquid chromatography-tandem mass spectrometry. NDMA-FP_2Cl was evaluated by chlorinating water samples with free chlorine for 24 h at pH 7.0 while residual free chlorine was kept at 1.0-2.0 mgCl₂/L. NDMA-FP_2NHCl was evaluated by dosing water samples with monochloramine at 140 mgCl₂/L for 10 days at pH 6.8. NDMA precursors and dissolved organic carbon (DOC) were fractionated by filtration through 30-, 3-, and 0.5 kDa membranes. NDMA concentrations were <0.5-5.2 ng/L (median: 0.9 ng/L) in ground water and <0.5-3.4 ng/L (2.2 ng/L) in river water. NDMA concentrations in ground water were slightly lower than or comparable to those in river water. Concentrations of NDMA-FP_2Cl were not much higher than concentrations of NDMA except in samples containing high concentrations of NH₃ and NDMA precursors. The increased NDMA was possibly caused by reactions between NDMA precursors and monochloramine unintentionally formed by the reaction between free chlorine and NH₃ in the samples. NDMA precursors ranged from 4 to 84 ng-NDMA eq./L in ground water and from 11 to 185 ng-NDMA eq./L in river water. Those in ground water were significantly lower than those in river water, suggesting that NDMA precursors were biodegraded, adsorbed, or volatilized during infiltration. The molecular weight of NDMA precursors in river water was dominant in the <0.5 kDa fraction, followed by 0.5-3 kDa. However, their distribution was inconsistent in ground water: one was dominant in the <0.5 kDa fraction, and the other in 0.5-3 kDa. Molecular weight distributions of NDMA precursors were very different from those of DOC. This is the first study to reveal the widespread occurrence and characterization of NDMA precursors in ground water.     

Photocarrier generation in organic thin-film solar cells with an organic heterojunction

Photocurrent–voltage characteristics for organic solar cells with a heterojunction formed between copper phthalocyanine and a perylene derivative (or C₆₀) were studied. The photocurrent was observed under both reverse and forward biases. From the analysis of the photocurrent action spectra, the origin of the reverse photocurrent was attributed to the excitons formed in both the organic layers, whereas that of the forward photocurrent was attributed to the excitons formed in the perylene derivative (or C₆₀) layer. The photocurrent density under reverse bias increased at higher temperatures, suggesting that the charge recombination possibility was lowered at higher temperatures. On the basis of the time responses of the photocurrents observed after pulsed photoirradiation, the charge separation and transport processes are discussed.     

Prediction of the single-phase turbulent mixing rate between two parallel subchannels using a subchannel geometry factor

This paper presents a simple method for predicting the single-phase turbulent mixing rate between adjacent subchannels in nuclear fuel bundles. In this method, the mixing rate is computed as the sum of the two components of turbulent diffusion and convective transfer. Of these, the turbulent diffusion component is calculated using a newly defined subchannel geometry factor F^* and the mean turbulent diffusivity for each subchannel which is computed from Elder's equation. The convective transfer component is evaluated from a mixing Stanton number correlation obtained empirically in this study. In order to confirm the validity of the proposed method, experimental data on turbulent mixing rate were obtained using a tracer technique under adiabatic conditions with three test channels, each consisting of two subchannels. The range of Reynolds number covered was 5000–66 000. From comparisons of the predicted turbulent mixing rates with the experimental data of other investigators as well as the authors, it has been confirmed that the proposed method can predict the data in a range of gap clearance to rod diameter ratio of 0.02–0.4 within about ±25% for square array bundles and about ±35% for triangular array bundles.     

A power flow tracing method focused on reactive power and SC

“Tracing the power flow of electricity” is a concept that has become the focus of attention recently, as the deregulation or the liberalization of the electric power market proceeds. Although a number of methods, such as “tracing method by power flow contribution,” have already been published, reactive power contribution has been little studied to date. However, applying “tracing the power flow of electricity” to ancillary service, for example compensation of reactive power, is very important. In this paper, we focus on line flows and static capacitors in particular, and study how to deal with the problem. We perform a computer simulation using a simple system and show the tracing results. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 156(1): 33–43, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/ eej.20118     

Some results on subclass containment problems for special classes of DPDA'S related to nonsingular machines

A content-free language is said to be weakly (w-)nonsingular if it is accepted by a nonsingular deterministic pushdown automaton in the sense of Oyamaguchi, Inagaki and Honda (1980). It is undecidable whether a deterministic pushdown automaton (dpda) accepts a w-nonsingular language and whether a dpda is nonsingular in the sense of Valiant (1973). Next, the class of super-nonsingular dpda's (which is a subclass of w-nonsingular dpda's) is introduced. It is decidable whether a dpda is super-nonsingular and whether a dpda accepts a super-nonsingular language. As a consequence, the problem of deciding whether a dpda accepts an LL(k) language reduces to the problem of deciding whether a super-nonsingular dpda accepts an LL(k) language.     

Preferred orientation of crystallite in carbons heat-treated under high pressure

A soft carbon and a hard carbon which were prepared from Polyvinylchloride and phenolformaldehyde resin, respectively, both by carbonizing to about 700°C, were obtained as sintered cakes by heat-treatment up to about 1800°C under the quasihydrostatic pressure of 5 kbar. Preferred orientation of crystallites relative to the compressing direction in these cakes was determined by X-ray difraction technique by using the (004) or (002) diffraction line. The soft carbon showed remarkable preferred orientation of crystallites, but the degree of orientation was dependent only a little on heat-treatment temperature (HTT). At 1200°C under 5 kbar, the hard carbon gave a sintered cake which had no appreciably preferred orientation. The degree of preferred orientation of crystallites in the cake of the hard carbon greatly increased with the increase in HTT. The difference in the dependence of preferred orientation of crystallites in the soft and hard carbons on HTT was interpreted by referring to the texture of the original carbons.     

Theoretical L-shell Coster-Kronig energies 11 ≤ Z ≤ 103

Relativistic relaxed-orbital calculations of L-shell Coster-Kronig transition energies have been performed ab initio for all possible transitions in atoms with atomic numbers 11 ≤ Z ≤ 103. Hartree-Fock-Slater wavefunctions served as zeroth-order eigenfunctions to compute the expectation of the total Hamiltonian. A first-order approximation to the local approximation was thus included. Quantum-electrodynamic corrections were made. Each transition energy was computed as the difference between results of separate self-consistent-field calculations for the initial, singly ionized state and the final two-hole state. The following quantities are listed: total transition energy, “electric” (Dirac-Hartree-Fock-Slater) contribution, magnetic and retardation contributions, and contributions due to vacuum polarization and self energy.