Visualization and laser measurements on the flow field and sand movement on sand dunes with porous fences

The installation of windbreak sand fences around sand dunes is one of the most promising methods to suppress windblown sand movement. In the study reported in this paper, we investigated the influence and validity of a small fence mounted on a model sand dune, in order to understand the fence’s suppression mechanism on the sand movement. The flow field around the dune and the process of sand-dune erosion were measured using LDV, PIV, and laser-sheet visualization techniques. A non-porous fence was found to suppress sand movements in its upstream area, but to enhance erosion downstream of the fence. This intensive erosion was caused by separated shear flow from the leading edge of the fence. In this study, four levels of porosity rate of the fence were tested. The fence-porosity dependences of the turbulent flow field and the erosion were discussed. The shapes of eroded sand dunes were found to depend on the porosity rate. The relationship between the sand-dune erosion and the flow field around the dune was illustrated with schematic diagrams. We concluded that the most desirable fence porosity should be 30% in order to avoid dune erosion if installed at a middle height on the stoss surface of a dune. This porosity provides a mean velocity reduction with avoiding a separated flow, although the flow bleeding through the porous fence is accompanied by grid turbulence and induces serious erosion in a narrow space behind the fence. Furthermore, we confirmed that the empirical correlation of the critical friction velocity can be applied to sand movements influenced by a fence.     

Microstructures and rheology of micellar surfactant solution by Brownian dynamics simulation

In this paper, three-dimensional Brownian dynamics simulation has been conducted for dilute micellar surfactant solution under a steady shear flow. The rodlike micelle in surfactant solution is assumed as a rigid rod made up of lined-up beads. The Lennard–Jones potential and soft-sphere potential are employed and taken as the inter-bead potentials for end–end beads and interior–interior beads, respectively. The motion of the rodlike micelles is determined by solving the translational and rotational equations for each rod under hydrodynamic drag force, Brownian force and inter-rod potential force. Velocity Verlet algorithm has also been exerted in the simulation. The micellar network structure is formed at low shear rates and destroyed by high shear rates. The computed shear viscosities and the first normal stress coefficient represent shear thinning characteristics. The paper reveals the relation between rheology and microstructure of surfactant solution at different shear rates. The effect of surfactant solution concentration rested on the micellar structures and rheological properties has also been investigated.     

Results of 0.5% cold-leg small-break LOCA experiments at ROSA-IV/LSTF: Effect of break orientation

Three 0.5% cold-leg small-break loss-of-coolant accident (SBLOCA) experiment were conducted at the ROSA-IV Large Scale Test Facility (LSTF) to investigate the effects of break orientation on system thermal-hydraulic responses. In these three experiments, the break hole was located at the side, bottom, and top of the horizontal cold leg, respectively. Although the key phenomena observed in the three experiments were basically the same, the break flow rate was affected by the break orientation when phase stratification occured in the cold leg; the break flow rate was largest for the side break and smallest for the top break. The RELAP5/MOD2 code failed to predict the difference in the break flow rate observed in the experiments. Modification to the break flow calculation models, for both subcooled and two-phase flow discharge conditions, resulted in good agreement between data and predictions.     

H Nmr Spectra of Oligosaccharide Substituted Cyclodextrins

ABSTRACT

¹H NMR spectra of some oligosaccharide substituted cyclodextrins composed of only α-D-glucose units are analysed. Chemical shifts of protons of each glucosyl group of the chain were determined by experiments with the HOHAHA pulse technique. In spite of the similar kinds of protons, dispersion of chemical shifts is observed. The most dispersed proton is the anomeric proton, and the largest change in the chemical shifts is 0.5 ppm.     

Structural development of ultra‐high strength polyethylene fibers: Transformation from kebabs to shishs through hot‐drawing process of gel‐spun fibers

Structural development of ultra‐high strength polyethylene fibers via hot‐drawing processes of as‐spun gel fibers was investigated by means of transmission electron microscopy. It is found that the shish‐kebabs developed in both the as‐spun and drawn fibers can be transformed continuously into the micro‐fibril structure composed mostly of the shish structure through the hot‐drawing process. The structure transformation involves a drastic decrease in diameter of the kebab plus the shish but almost no change in the shish diameter. This result suggests that the chains in the kebabs are incorporated into the shishs and consumed to extend the longitudinal dimension of the shishs during the drawing process. The proposed new deformation model well explains the relationship between the fiber morphology and their mechanical properties: the tensile strength and modulus of the fibers can be determined by the number of the shish in the fiber and the macroscopic diameter of the fiber, which are apriori determined at the spinning process. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1861–1872, 2010     

EPMA line analysis of chemical states of chromium

A novel technique for determining the chemical states of elements with a heterogeneous distribution in samples involving EPMA line analysis is proposed. LLS (linear least squares) calculation was applied to a set of reduced spectra measured in the line analysis. The reduced spectra which have several energy points (including two points for backgrounds) were measured in order to save measuring time. The LLS calculation gives the mole fraction of each chemical state. We applied this method to the analysis of corrosion products formed on Cr-containing steel after corrosion tests. EPMA mapping revealed that Cr is enriched only in the inner layer of the corrosion products. From the results of the LLS calculation, it was determined that Cr in the corrosion products exists in the trivalent Cr state whereas in the steel Cr is in the metallic state. This result corresponds to the spectra of characteristic x-rays from the corroded steel. Copyright © 2001 John Wiley & Sons, Ltd.