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991.
A numerical model based on the smoothed particle hydrodynamics method is developed to simulate depth‐limited turbulent open channel flows over hydraulically rough beds. The 2D Lagrangian form of the Navier–Stokes equations is solved, in which a drag‐based formulation is used based on an effective roughness zone near the bed to account for the roughness effect of bed spheres and an improved sub‐particle‐scale model is applied to account for the effect of turbulence. The sub‐particle‐scale model is constructed based on the mixing‐length assumption rather than the standard Smagorinsky approach to compute the eddy‐viscosity. A robust in/out‐flow boundary technique is also proposed to achieve stable uniform flow conditions at the inlet and outlet boundaries where the flow characteristics are unknown. The model is applied to simulate uniform open channel flows over a rough bed composed of regular spheres and validated by experimental velocity data. To investigate the influence of the bed roughness on different flow conditions, data from 12 experimental tests with different bed slopes and uniform water depths are simulated, and a good agreement has been observed between the model and experimental results of the streamwise velocity and turbulent shear stress. This shows that both the roughness effect and flow turbulence should be addressed in order to simulate the correct mechanisms of turbulent flow over a rough bed boundary and that the presented smoothed particle hydrodynamics model accomplishes this successfully. © 2016 The Authors International Journal for Numerical Methods in Fluids Published by John Wiley & Sons Ltd 相似文献
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Electrochemical intercalation of lithium into multiwall carbon nanotubes produced by the arc-electric technique has been carried
out in button cells to estimate the solid state diffusion coefficients of lithium. An extension of the Galvanostatic Intermittent
Titration Technique (G.I.T.T.) of Weppner and Huggins and further developed by Honders is employed. The results are interpreted
providing that the lithium species enter the nanotubes perpendicularly to their walls and thus give rise to a necklace structure
as observed by Transmission Electron Microscopy (TEM). Finally, the results are compared with the data obtained for different
kinds of carbon: carbon fiber, petroleum coke and graphite.
Paper presented at the 6th Euroconference on Solid State Ionics, Cetraro, Calabria, Italy, Sept. 12–19, 1999. 相似文献
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Electrically-induced optical storage effects in smectic polysiloxanes A variable transmission device
Changes in the optical transmission induced by electric fields have been studied in a smectic side-chain polysiloxane liquid crystal. The transmission varied from effectively zero, for a highly scattering (opaque) texture, to total, for a homeotropic texture, on increasing the applied voltage across the material. The field-induced textures were durably stored in the smectic phase, enabling the order parameter of the side groups to be studied by dielectric relaxation measurements. For the highly transparent texture, a side group order parameter of 0-92 has been observed. 相似文献
1000.
In this paper we consider an open queueing network having multiple classes, priorities, and general service time distributions.
In the case where there is a single bottleneck station we conjecture that normalized queue length and sojourn time processes
converge, in the heavy traffic limit, to one-dimensional reflected Brownian motion, and present expressions for its drift
and variance. The conjecture is motivated by known heavy traffic limit theorems for some special cases of the general model,
and some conjectured “Heavy Traffic Principles” derived from them.
Using the known stationary distribution of one-dimensional reflected Brownian motion, we present expressions for the heavy
traffic limit of stationary queue length and sojourn time distributions and moments. For systems with Markov routing we are
able to explicitly calculate the limits. 相似文献