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41.
N. Phan-Thien 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》1992,43(1):207-215
This note reports some analytic Stokes solutions to the flows outside a rotating corrugated cylinder and between two rotating corrugated cylinders of either epitrochoidal or hypotrochoidal cross-sections. The results are obtained by using conformal mappings and general biharmonic solutions inside and outside of a unit circle. 相似文献
42.
The paper is concerned with the flow of a dilute suspension of monosized spheroids past a sphere placed at the centerline of a cylindrical tube. The suspension is modeled by the transversely isotropic fluid model and the numerical solution is obtained by a time-dependent boundary element method. No steady-state solution to the problem was found. However, the amplitude of the long-time oscillations in the drag force on the sphere is only about 1% of its mean value at a solid volume concentration of 0.01 and an aspect ratio of 10 for the spheroids. The initial orientation of the microstructure has a small effect on the drag force: it can give rise to a ±1 % variation in the drag force at large time. 相似文献
43.
N. Phan-Thien 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》1990,41(3):431-440
The paper reports an exact three-dimensional similarity solution for the Oldroyd fluid B. The flow involved is generated by closing as well as sliding the boundaries of a two-dimensional wedge. It is found that the squeezing motion is independent of the sliding motion, but not vice-versa. The squeezing load is shown to be a decreasing function of the Weissenberg number, while the frictional coefficient is only weakly-dependent on the Weissenberg number. 相似文献
44.
A boundary element method is used to simulate the unsteady motion of a sphere falling under gravity along the centreline of a cylindrical tube containing a viscoelastic fluid. The fluid is modelled by the upper-convected Maxwell constitutive equation. Results show that the viscoelasticity of the liquid leads to a damped oscillation in sphere velocity about its terminal value. The maximum sphere velocity, which occurs in the first overshoot, is approximately proportional to the square root of the Weissenberg number when the ratio of the sphere radius to the tube radius is sufficiently small. Particular attention is also paid to the wall effects. It is shown that a closer wall reduces the oscillatory amplitude of the sphere velocity but increases its frequency. The results suggest that the falling-ball technique, which is now widely used for viscosity measurement, might also be used for the determination of a relaxation time for a viscoelastic fluid. 相似文献
45.
This paper describes an implementation of a Boundary Element method to solve a general three-dimensional viscoelastic flow problem. The Boundary Element method is formulated in terms of unknown boundary velocity and traction fields. The fluid is incompressible and is modelled by a differential constitutive equation. The steady-state stress field is obtained by a time marching process of integration. For the first time, some results for steady state isothermal creeping flow extrusion of a viscoelastic fluid from triangular and square dies are described. The concept of an axisymmetric-equivalent swell ratio is introduced to compare the present results with the results of axisymmetric extrusion studies reported in the literature. It is shown that reasonable agreement is achieved. 相似文献
46.
The main goal of this work is to study an initial boundary value problem for a quasilinear parabolic equation with logarithmic source term. By using the potential well method and a logarithmic Sobolev inequality, we obtain results of existence or nonexistence of global weak solutions. In addition, we also provided sufficient conditions for the large time decay of global weak solutions and for the finite time blow-up of weak solutions. 相似文献
47.
Truc T.T. Duong Truong N.V. Do Hai X. Nguyen Tho H. Le Phu H. Dang Nhan T. Nguyen Tuyen N.T. Nguyen Thao D. Nguyen Mai T.T. Nguyen 《Tetrahedron letters》2017,58(23):2280-2283
Two new neolignans, named rebaneolignan A (1) and B (2), were isolated from the stem of Mangifera reba (Anacardiaceae), together with six known compounds (3–8). Their structures were elucidated on the basis of NMR spectroscopic analysis and the absolute configurations of 1 and 2 were determined by NOESY and CD data. All isolated compounds were found to possess more potent inhibitory activity, with IC50 values ranging from 28.5 to 162.8 µM, than the positive control acarbose (IC50, 214.5 µM). Plausible biosynthetic pathways for the formation of 1 and 2 were proposed based on the oxidative β-5′ coupling reactions. 相似文献
48.
Extrudate swell through an orifice die 总被引:2,自引:0,他引:2
The extrudate swell of a viscoelastic fluid through an orifice die is investigated by using a mixed finite element and a streamline integration method (FESIM), using a version of the K-BKZ model. The free surface calculation is based on a local mass conservation scheme and an approximate numerical treatment for the contact point movement of the free surface. The numerical results show a vortex growth and an increasing swelling ratio with the Weissenberg number. Convergence with mesh refinement is demonstrated, even at a high Weissenberg number of O(587), where the swelling ratio reaches a value of about 360%. In addition, it is found that the effective flow channel at the entrance region next to the orifice die is reduced due to the enhanced vortex growth, which may be a source of flow instability. 相似文献
49.
AbstractThe aim of the present paper is to introduce and study the dual concepts of weakly automorphism invariant modules and essential tightness. These notions are non-trivial generalizations of both weakly projectivity, dual automorphism invariant property and cotightness. We obtain certain relations between weakly projective modules, weakly dual automorphism invariant modules and superfluous cotight modules. It is proved that: (1) for right perfect rings, every module is a direct summand of a weakly dual automorphism invariant module and (2) weakly dual automorphism invariant modules are precisely superfluous cotight modules. 相似文献
50.