Home About us Contact
|
Home About us Contact | ||
|
|
||
Straight Channel (straight + channel)
Selected AbstractsProcesses and mechanisms of dynamic channel adjustment to delta progradation: the case of the mouth channel of the Yellow River, ChinaEARTH SURFACE PROCESSES AND LANDFORMS, Issue 6 2003Changxing Shi Abstract This paper analyses the processes and mechanisms of a three-stage channel adjustment over a cycle of the Yellow River mouth channel extension based on data comprising hydrologic measurements and channel geometric surveys. Rapid siltation in the mouth channel takes place in the young stage when the channel is being built by deposits and in the old stage when the channel cannot further adjust itself to keep sediment transport in equilibrium. It is disclosed that the bankfull width,depth ratio, bed material size and slope decrease in the young and mature stages but do not change in the old stage. The reduction of bankfull width,depth ratio and bed material size during the young and mature stages is found to be able to offset the effect of the slope reduction on sediment transport due to continuous mouth progradation. They reach their limits in old stage, and a constant slope is kept by unceasing sediment accumulation. The grain size composition of incoming sediment and the fining mechanism are responsible for the occurrence of lower limit of bed material size. The reason for the existence of a limit of bankfull cross-sectional shape is that the large flows can fully transport the sediment load they are carrying, and siltation in the channel in the old stage takes place mainly in the low flows. It is suggested that the bankfull discharge plays an important role in shaping the channel but that the entire channel form is the product of both the large and low flows plus the effects of interaction between them. Channel pattern change shows a process from a braided pattern in the young stage to a straight pattern in the mature and old stages, and the straight channel becomes gradually sinuous. The occurrence and transformation of the channel patterns are supported by two planform predictors, but are also facilitated by some other conditions. Copyright © 2003 John Wiley & Sons, Ltd. [source] Adaptive finite elements with large aspect ratio for mass transport in electroosmosis and pressure-driven microflowsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 9 2010Virabouth Prachittham Abstract A space,time adaptive method is presented for the numerical simulation of mass transport in electroosmotic and pressure-driven microflows in two space dimensions. The method uses finite elements with large aspect ratio, which allows the electroosmotic flow and the mass transport to be solved accurately despite the presence of strong boundary layers. The unknowns are the external electric potential, the electrical double layer potential, the velocity field and the sample concentration. Continuous piecewise linear stabilized finite elements with large aspect ratio and the Crank,Nicolson scheme are used for the space and time discretization of the concentration equation. Numerical results are presented showing the efficiency of this approach, first in a straight channel, then in crossing and multiple T-form configuration channels. Copyright © 2009 John Wiley & Sons, Ltd. [source] Transient free-surface flow of a viscoelastic fluid in a narrow channelINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 6 2004Roger E. Khayat Abstract The interplay between inertia and elasticity is examined for transient free-surface flow inside a narrow channel. The lubrication theory is extended for the flow of viscoelastic fluids of the Oldroyd-B type (consisting of a Newtonian solvent and a polymeric solute). While the general formulation accounts for non-linearities stemming from inertia effects in the momentum conservation equation, and the upper-convected terms in the constitutive equation, only the front movement contributes to non-linear coupling for a flow inside a straight channel. In this case, it is possible to implement a spectral representation in the depthwise direction for the velocity and stress. The evolution of the flow field is obtained locally, but the front movement is captured only in the mean sense. The influence of inertia, elasticity and viscosity ratio is examined for pressure-induced flow. The front appears to progress monotonically with time. However, the velocity and stress exhibit typically a strong overshoot upon inception, accompanied by a plug-flow behaviour in the channel core. The flow intensity eventually diminishes with time, tending asymptotically to Poiseuille conditions. For highly elastic liquids the front movement becomes oscillatory, experiencing strong deceleration periodically. A multiple-scale solution is obtained for fluids with no inertia and small elasticity. Comparison with the exact (numerical) solution indicates a wide range of validity for the analytical result. Copyright © 2004 John Wiley & Sons, Ltd. [source] 3-D simulation and visualization of laminar flow in a microchannel with hair-pin curvesAICHE JOURNAL, Issue 7 2004Y. Yamaguchi Abstract The purpose of the present study was to investigate fluidic behavior in a microchannel with hair-pin curves, using a three-dimensional (3-D) computational fluid dynamics simulation, and to observe the 3-D flow pattern, to validate the simulation. The microchannel used was fabricated on a PMMA plate using a flat-end mill. The channel width and depth were 210 and 205 ,m, respectively, and the radius of each hair-pin curve was 500 ,m. Two liquids; purified water and an aqueous solution of 50 ,mol/L fluorescein, were introduced into the microchannel through different inlets and were merged, forming a side-by-side parallel flow in the straight channel. When the average velocity was 25 mm/s, the liquid was thrust outward by centrifugal force and, as a result, the vertical line that crossed the central axis was distorted after passing the first hair-pin curve. At the second hair-pin curve, the centrifugal force was exerted in the opposite direction, and the distorted line returned nearly to an initial vertical line. When the average velocity was 125 mm/s, however, the vertical line, which was distorted at the first hair-pin curve, did not recover to the initial vertical line after the second curve. The interface between the two liquids was permanently waved. The simulation was in good agreement with the experimental data. The results suggest that the diffusion rate through the interface of two liquids in microchannels with hair-pin curves can increase, compared to that in straight microchannels. © 2004 American Institute of Chemical Engineers AIChE J, 50: 1530,1535, 2004 [source] Prediction of the location of stationary steady-state zone positions in counterflow isotachophoresis performed under constant voltage in a vortex-stabilized annular columnJOURNAL OF SEPARATION SCIENCE, JSS, Issue 18 2007Schurie L. M. Harrison Abstract A theoretical model is presented and an analytical expression derived to predict the locations of stationary steady-state zone positions in ITP as a function of current for a straight channel under a constant applied voltage. Stationary zones may form in the presence of a countercurrent flow whose average velocity falls between that of a pure leader zone and of a pure trailer zone. A comparison of model predictions with experimental data from an anionic system shows that the model is able to predict the location of protein zones with reasonable accuracy once the ITP stack has formed. This result implies that an ITP stack can be precisely directed by the operator to specific positions in a channel whence portions of the stack can be removed or redirected for further processing or analysis. [source] A remark on the pressure for the Navier,Stokes flows in 2-D straight channel with an obstacleMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 8 2004H. Morimoto Abstract Let T=,×(-1,1) and &ℴ,,2 be a smoothly bounded open set, closure of which is contained in T. We consider the stationary Navier,Stokes flows in . In general, the pressure is determined up to a constant. Since , has two extremities, we want to know if we can choose the constant same. We study the behaviour of the pressure at the infinity in , and give a relation between the velocity and the pressure difference. Copyright © 2004 John Wiley & Sons, Ltd. [source] Geomorphology of the onset area of a paleo-ice stream, Marguerite Bay, Antarctic PeninsulaEARTH SURFACE PROCESSES AND LANDFORMS, Issue 4 2008John B. Anderson Abstract Geomorphic features indicate that both glacial and melt-water erosion characterize the onset area of the ancestral Marguerite Ice Stream. The large size of these features indicates that they formed over repeated glacial cycles, most recently during the Last Glacial Maximum. Ice drainage within the bay and on the inner continental shelf was strongly influenced by tectonic fabric. Deep, isolated basins surrounded by rugged bedrock bathymetry characterize the innermost part of the bay. Drumlins and other streamlined features occur in the floors of these basins at depths of up to 900 m. The outer bay has three large interconnected basins. Drumlins and megaflutings within these basins indicate ice was grounded at water depths up to 1000 m. The orientations of these features show convergence of drainage from the northeast, east and south into the Marguerite paleo-ice stream. On the inner continental shelf, the ice converged into a single, wide trough dominated by mega-scale glacial lineations. This transition in geomorphic features from drumlins and megaflutings to mega-scale glacial lineations occurs at the location on the continental shelf where sedimentary strata blanket bedrock, and marks a zone of acceleration of the ice stream. The glacially sculptured geomorphic features within Marguerite Bay co-exist with anastomosing, radial and relatively straight channels, which become increasingly focused in a seaward direction. This implies that a well organized subglacial drainage system existed within the bay at some point in the past. Copyright © 2008 John Wiley & Sons, Ltd. [source] Lattice Boltzmann simulation on flow fields connected with multiple side-channelsHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 2 2007Shohji Tsushima Abstract For this study, using the lattice Boltzmann method (LBM), we conducted flow-field analyses in which two straight channels were mutually connected with multiple side-channels. Results showed that calculated flow fields can be categorized into three types of flow pattern depending on flow field geometry and flow conditions. The following typical flow patterns were identified: case 1, the incoming flow passes uniformly through the side channels; case 2, the flow passes preferentially through the side channel in the inlet and the outlet; and case 3, the flow passes mainly through the side channel of the outlet side. Results also indicate that these flow patterns depend on two dimensionless parameters: the ratio of permeability of the side channels to the channel width, and the Reynolds number. © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(2): 96,104, 2007; Published online in Wiley InterScience (www. interscience.wiley.com). DOI 10.1002/htj.20143 [source] Synthesis, structure and photoluminescence of two zinc carboxylate polymers with different coordination architecturesCHINESE JOURNAL OF CHEMISTRY, Issue 10 2003Hong Ding Abstract The hydrothermal reaction of ZnO with benzene-1,4-dicarboxylic add gave Zn·BDC·2H2O (1) and Zn-BDC·H2O (2) (BDC = benzene-1, 4-dicarboxylate), respectively. Polymer 1 (C4H4O3ZH0.5) shows a one-dimensional zigzag chain structure built up from the alternate connection of tetrahedral ZnO4 and BDC units. Polymer 2 (C4H3O2.5Zn0.5) possesses a three-dimensional framework containing infinite zigzag Zn·Zn·Zn pseudochains generated by five-coordinate zinc centers and a rectangular channel system including three groups of different straight channels along the [001], [010] and [60,1] directions. The two metal-organic polymeric compounds exhibit strong photoluminescent emission bands at 402 nm (,ex = 260 nm) (for 1) and at 344 nm and 385 nm (,ex = 279 nm) (for 2) in the solid state at room temperature. [source] | |||||||||||||