共查询到20条相似文献,搜索用时 109 毫秒
1.
Changkwon Chung Duwon Choi Ju Min Kim Kyung Hyun Ahn Seung Jong Lee 《Microfluidics and nanofluidics》2010,8(6):767-776
We performed numerical and experimental studies on the viscous folding in diverging microchannel flows which were recently
reported by Cubaud and Mason (Phys Rev Lett 96:114501, 2006a). We categorized the flow patterns as “stable”, “folding,” and “chaotic” depending on channel shape, flow ratio, and viscosity
ratio between two fluids. We focused on the effect of kinematic history on viscous folding, in particular, by changing the
shape of diverging channels: 90°, 45°, and hyperbolic channel. In experiments, the proposed power–law relation (f ~ [(g)\dot]1, f\sim \dot{\gamma }^{1}, where f is the folding frequency, and [(g)\dot] \dot{\gamma } is the characteristic shear rate) by Cubaud and Mason (Phys Rev Lett 96:114501, 2006a) was found to be valid even for hyperbolic channel. The hyperbolic channel generated moderate flows with smaller folding
frequency, amplitude, and a delay of onset of the folding compared with other two cases, which is considered to be affected
by compressive stress when compared to the simulation results. In each channel, the folding frequency increases and the amplitude
decreases as the thread width decreases since higher compressive stress is applied along the thin thread. The secondary folding
was also reproduced in the simulation, which was attributed to locally heterogeneous development of compressive stresses along
the thread. This study proves that the viscous folding can be controlled by the design of flow kinematics and of the compressive
stresses at the diverging region. 相似文献
2.
The notions of $(\overline{\in}, \overline{\in} \vee \overline{\hbox{q}})The notions of ([`( ? )],[`( ? )] ú[`q])(\overline{\in}, \overline{\in} \vee \overline{\hbox{q}})-fuzzy p-ideals and fuzzy p-ideals with thresholds related to soft set theory are discussed. Relations between ([`( ? )],[`( ? )] ú[`q])(\overline{\in}, \overline{\in} \vee \overline{\hbox{q}})-fuzzy ideals and ([`( ? )],[`( ? )] ú[`q])(\overline{\in}, \overline{\in} \vee \overline{\hbox{q}})-fuzzy p-ideals are investigated. Characterizations of an ([`( ? )],[`( ? )] ú[`q])(\overline{\in}, \overline{\in} \vee \overline{\hbox{q}})-fuzzy p-ideal and a fuzzy p-ideal with thresholds are displayed. Implication-based fuzzy p-ideals are discussed. 相似文献
3.
We study some problems solvable in deterministic polynomial time given oracle access to the (promise version of) Arthur–Merlin
class. Our main results are the following:
° BPPNP|| í PprAM||.\circ\quad{\rm BPP}^{{\rm NP}}_{||} \subseteq {{\rm P}^{{{\rm pr}{\rm AM}}}_{||}}. 相似文献
4.
Peter Lammers Jovan Jovanovi? Bettina Frohnapfel Antonio Delgado 《Microfluidics and nanofluidics》2012,13(3):429-440
The concept of a micropatterned surface morphology capable of producing self-stabilization of turbulence in wall-bounded flows is considered in pipes of non-circular cross-sections which act to restructure fluctuations towards the limiting state where these must be entirely suppressed. Direct numerical simulations of turbulence in pipes of polygon-shaped cross-sections with straight and profiled sides were performed at a Reynolds number $Re_\tau \simeq {\mathrm 300}$ based on the wall shear velocity and the hydraulic diameter. Using the lattice Boltzmann numerical algorithm, turbulence was resolved with up to ${\mathrm 540\times 10^6}$ grid points ( ${\mathrm 8,192\times 257 \times 256}$ in the x 1, x 2 and x 3 directions). The DNS results show a decrease in the viscous drag around corners, resulting in a reduction of the skin-friction coefficient compared with expectations based on the well-established concept of hydraulic diameter and the use of the Blasius correlation. These findings support the conjecture that turbulence might be completely suppressed if the pipe cross-section is a polygon consisting of a sufficient number of profiled sides of the same length which intersect at right angles at the corners. 相似文献
5.
The concept of $(\overline{\in},\overline{\in} \vee \overline{q})
6.
Gerti Daschiel Milovan Perić Jovan Jovanović Antonio Delgado 《Microfluidics and nanofluidics》2013,15(5):675-687
The sub-laminar drag effect of microgroove surfaces was studied numerically in a steady two-dimensional channel flow at subcritical Reynolds numbers. Considerations are restricted to grooves of a few viscous length scales in depth, which are assumed not to promote the laminar to turbulent transition process. It was found that the drag reduction effect is due to the layout of grooves with respect to the flow direction and contour geometry. Results of computations show that for grooves of curved contour placed normal to the flow direction, drag arising from viscous and pressure forces is modulated due to the functional dependence of forces on the surface area projected in the flow direction. Such a groove layout leads to a large skin-friction reduction, but a comparable increase in pressure drag results in sub-laminar drag if drag over flat surface is considered as a reference. For a curved groove contour, the drag reduction increases with increasing Reynolds number and reaches about 5 % at Reynolds numbers approaching critical. 相似文献
7.
Given a “black box” function to evaluate an unknown rational polynomial
f ? \mathbbQ[x]f \in {\mathbb{Q}}[x] at points modulo a prime p, we exhibit algorithms to compute the representation of the polynomial in the sparsest shifted power basis. That is, we determine
the sparsity $t \in {\mathbb{Z}}_{>0}$t \in {\mathbb{Z}}_{>0}, the shift
a ? \mathbbQ\alpha \in {\mathbb{Q}}, the exponents 0 £ e1 < e2 < ? < et{0 \leq e_{1} < e_{2} < \cdots < e_{t}}, and the coefficients
c1, ?, ct ? \mathbbQ \{0}c_{1}, \ldots , c_{t} \in {\mathbb{Q}} \setminus \{0\} such that
|