Suppression of asymmetric flow behavior downstream of two side-by-side circular cylinders with a splitter plate in shallow water

The flow downstream of a pair of circular cylinder in a side-by-side arrangement normal to the free stream is known to exhibit intermittently bistable structure for the range of G/D = 1.2–2.2 where G is the center-to-center distance between the cylinders and D is the diameter of the cylinder. Eventually, the wake downstream of one of the two cylinders can be wider or narrower than the one downstream of the other cylinder depending on the direction of gap-flow deflection. In the present study, such an asymmetric flow behavior downstream of two side-by-side cylinders, which were vertically located in shallow water, was passively controlled with a splitter plate with a length of L   (1?L/D?5$1?L/D?5$). The center of splitter plate was just coincided with the mid-height of the gap between centers of the cylinders. The investigations were carried out in a water channel using dye visualization and particle image velocimetry, PIV for qualitative and quantitative measurements, respectively. The diameter of the cylinder, D was 40 mm while the depth of water was 20 mm so that the shallow flow condition was provided through the experiments. The Reynolds number, Re based on D was 5000 and the cylinder’s center to center spacing to the cylinder diameter ratio (G/D  ) was equal to 1.25. The results demonstrated that the deflection of the wake and thereby the bistability of the wake was considerably prevented with the presence of the splitter plate for L/D?3$L/D?3$ which resulted in two well symmetric, stable wakes having approximately the same order of magnitudes of vortex shedding frequencies around the cylinders.     

Pressure casting of a zirconia-toughened alumina fiber-reinforced NiAl composite

A pressure-cast NiAl composite reinforced with polycrystalline alumina (PRD-166) fibers containing 0.2 weight fraction of partially stabilized zirconia was examined by optical and transmission electron microscopy (TEM). Fibers in the preform used for casting were forced into contact, and fiber bonding occurred in a number of instances. Fiber volume fraction was increased from an initial value of 0.4 to 0.6 as a consequence of the applied pressure. An explanation is offered for the interaction of applied pressure, wetting angle, and the rigidity of the fiber preform on the final volume fraction of the fibers in the composite. At the fiber/matrix interface, the alumina was free of zirconia particles. It is proposed that alumina grain growth forced the zirconia into the molten NiAl, where it dissolved. As solidification took place, the concentration of zirconium in the molten NiAl increased to a point where zirconium reacted with alumina to form zirconia again.     

Oxidation behavior of single-crystal Al2O3-fiber-reinforced Ni3Al-based composites

A series of single-crystal Al₂O₃-fiber-reinforced Ni3Al-based intermetallic matrix composites were fabricated by pressure casting. The matrices employed were binary Ni₃Al, Ni₃Al-0.5 at. pct Cr, and Ni₃Al-0.34 at. pct Zr. The development of microstructure upon oxidation in air at either 1100 °C or 1200 °C was investigated by optical, scanning, and transmission electron microscopy. In air-oxidized binary Ni₃Al, some of the fibers were fully or partially covered with a layer of oxide. A weak fiber/matrix bond in this system, which led to fiber debonding during composite processing, is believed to be responsible for the ingress of O into the composite and oxidation of the matrix in the debonded regions at the fiber/matrix interface. Addition of Cr to Ni₃Al resulted in an almost threefold increase in fiber/matrix bond strength. No oxidation of the interface was observed. A thick layer of oxide was formed around all the fibers when the composite was thermally cycled prior to isothermal annealing. Addition of Zr to Ni₃Al resulted in the formation of a layer of ZrO₂ on the surface of the fibers during composite processing. The ZrO₂ layer provided a fast path for the diffusion of O, which led to the formation of a rootlike oxide structure around the fibers. The rootlike structure consisted of a network of Al₂O₃-covered ZrO₂.     

Design of a just-in-time periodic material supply system for the assembly lines and an application in electronics industry

The purpose of the paper is the development of a mathematical model and a heuristic approach where the routes are constructed and the service period is determined for the design of an internal milk-run material supply system. The material supply by this system occurs on a just-in-time basis from a central warehouse to several stations of an assembly line. The objective of the proposed mathematical model is the minimization of the total material handling and inventory holding cost. Besides, the proposed heuristic approach intends to construct routes based on an initial service period value and attempts to improve the solution by considering different period values. The most suitable solution is decided on the basis of the least total material handling and WIP/inventory holding cost. The application of the proposed heuristic in a TV assembly plant demonstrates the utility of it to the real practice.     

Synthesis and spectroelectrochemistry of dithieno(3,2‐b:2′,3′‐d)pyrrole derivatives

New π‐conjugated polymers containing dithieno(3,2‐b:2′,3′‐d)pyrrole (DTP) were successfully synthesized via electropolymerization. The effect of structural differences on the electrochemical and optoelectronic properties of the 4‐[4H‐dithieno(3,2‐b:2′,3′‐d)pyrrol‐4‐yl]aniline (DTP–aryl–NH₂), 10‐[4H‐dithiyeno(3,2‐b:2′,3′‐d)pirol‐4‐il]dekan‐1‐amine (DTP–alkyl–NH₂), and 1,10‐bis[4H‐dithieno(3,2‐b:2′,3′‐d)pyrrol‐4‐yl] decane (DTP–alkyl–DTP) were investigated. The corresponding polymers were characterized by cyclic voltammetry, NMR (¹H‐NMR and ¹³C‐NMR), and ultraviolet–visible spectroscopy. Changes in the electronic nature of the functional groups led to variations in the electrochemical properties of the π‐conjugated systems. The electroactive polymer films revealed redox couples and exhibited electrochromic behavior. The replacement of the DTP–alkyl–DTP unit with DTP–aryl–NH₂ and DTP–alkyl–NH₂ resulted in a lower oxidation potential. Both the poly(10‐(4H‐Dithiyeno[3,2‐b:2′,3′‐d]pirol‐4‐il)dekan‐1‐amin) (poly(DTP–alkyl–NH₂)) and poly(1,10‐bis(4H‐dithieno[3,2‐b:2′,3′‐d]pyrrol‐4‐yl) decane) (poly(DTP–alkyl–DTP)) films showed multicolor electrochromism and also fast switching times (<1 s) in the visible and near infrared regions. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40701.     

锂硫电池电解质的研究

文章综述了锂硫电池有机液态、凝胶聚合物和全固态电解质的研究进展;阐述了锂硫电池电解质现阶段研究工作中存在的问题,并展望了锂硫电池电解质未来的研究方向。     

Flow characteristic of the horizontal cylinder placed on the plane boundary

In this study, the flow characteristic of the circular cylinder laid on the free surface is studied quantitatively using the particle image velocimetry technique. The flow phenomena in the upstream and downstream regions of the horizontal cylinder and free surface junctions increase the instability of the vortical flow structure significantly. Since the scour and burial process of the pipelines laid on the seabed depends mostly on the hydrodynamic behavior of the flow, the present investigation concentrates on the characterization of the flow structures using the time-averaged and instantaneous flow data. Distributions of velocity vectors, patterns of streamlines, vorticity contours and corresponding Reynolds stress correlations characterize the flow structure in detail.     

Comparison of abrasive wear behavior of ductile iron with different dual matrix structures

Abrasive wear behavior of ductile irons with different dual matrix structures has been investigated. In order to obtain ductile irons with different dual matrix structures an unalloyed ductile iron specimens were austenitized in the two-phase region (α + γ) at various temperature (795 °C and 815 °C) and then rapidly transferred to a salt bath held at the 365 °C for austempering for 30, 90 and 120 min. Some specimens were quenched from same intercritical austenitizing temperatures and tempered at 550 °C for 60 and 300 min. Some specimens were also conventionally austempered and/or quenched from 900 °C for comparison. Experimental results showed that, the tensile strength increased and ductility decreased with increasing martensite volume fraction in the specimen with martensite dual matrix structure. By increasing the tempering time, the yield and UTS decreased and ductility increased. In addition, the specimens with ausferrite dual matrix structures exhibited much greater ductility than conventionally austempered ones. The tensile strength increased while ductility decreased with increasing ausferrite volume fraction. Furthermore in all austenitized specimens, the abrasive weight loss of austempered specimens (A series) was lower than those of quenched specimens (Q series) irrespective of all loads due to increased AFVFs and total elongation. It was shown that wear loss of both tested materials in abrasive wear was proportional to the applied load. However, there was a decreasing trend in the weight loss of the A795 with dual matrix structure austempered for 30 and 90 min with increasing load. The reason was because of the fact that the specimen surface was work hardened with cutting efficiency of the abrasive reduced through clogging, and attrition jointly leading to less weight loss. Moreover, increasing the austempering time caused more ductile ausferritic structure to displace hard martensite. In all austempered samples, the abrasive weight loss increased with increasing the austempering time. As for the case of Q samples, the abrasive weight loss increased more or less linearly with load since an increase in the applied load might increase the contact stress. Among the Q samples, the highest weight loss was obtained for the Q795-300, Q815-300 sample because of lower martensite volume fraction, but the lowest weight loss was observed for the Q900 sample due to the highest martensite volume fraction. For Q900 samples, the amount of fracture of the abrasives was found to be increase with the harder specimen, and it may have contributed somewhat to the increased wear.Furthermore, microchips were dominant wear mechanism by cutting mode for higher ductile materials while micro-ploughing was predominant wear for harder materials, but wear also occurred by combinations of ploughing and embedding particles into the surface for Q samples. Cross-section examination by SEM through the wear surfaces revealed that a more smoother surface was observed for the A795 sample than that of the Q795 sample. However, a more rougher surface was observed for the A900-120 sample than that of the Q900 sample.