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61.
This paper is concerned with a numerical study of the three-dimensional Honji instability that can arise in an oscillatory flow impinging on a circular cylinder. It is well known that when the fluid motion far from the cylinder is perpendicular to its axis then the flow is liable to a three-dimensional breakdown via this instability which initially appears as an axially periodic mushroom-like structure attached to the surface of the cylinder. Here the focus is on examining the Honji instability under an oblique inflow. The obliqueness of the free stream is represented by an angle of attack through introducing an axial flow component. It is found that the Honji mode is suppressed by increasing the axial flow component, and when this component is sufficiently large the instability mechanism is no longer operative so that all that remains is a featureless two-dimensional columnar flow. At smaller values of angle of attack, though the Honji structure remains, it is deformed by the axial flow component. The developed two-layer near-cylinder vortical structures can be related to the energy and momentum transfer between the two layers. 相似文献
62.
Chaoyang GuoXinglong Gong Shouhu XuanLuhang Zong Chao Peng 《Journal of magnetism and magnetic materials》2012,324(6):1218-1224
The normal forces of magnetorheological fluids under oscillatory shear are investigated by a commercial magneto-rheometer with plate-plate geometry. At the constant strain amplitude and frequency, the normal forces almost keep a steady value with the testing time if the strain amplitude is smaller than the critical value. When a larger strain is applied, they will fluctuate periodically. Under the strain sweep mode, the relationships between normal forces and strain amplitude can be divided into three regions: linear viscoelastic region, nonlinear viscoelastic region and the viscoplastic region. Under the frequency sweep method, it is found that the angular frequency show little influence on the normal forces. At last, the normal forces increase with increasing of the temperature under a low magnetic field, while they decrease under a high magnetic field. 相似文献
63.
An electromechanical system with flexible arm is considered. The mechanical part is a linear flexible beam and the electrical
part is a nonlinear self-sustained oscillator. Oscillatory solutions are obtained using an averaging method. Chaotic behavior
is studied via the Lyapunov exponent. The synchronization of regular and chaotic states of two such devices is discussed and
the stability boundaries for the synchronization process are derived using the Floquet theory. We compare the results obtained
from a finite difference simulation to those from the classical modal approach. 相似文献
64.
S.R.VEMPATI A.B.LAXMI-NARAYANA-GARI 《应用数学和力学(英文版)》2010,31(12):1481-1496
The objective of the present study is to investigate the effect of flow parameters on the free convection and mass transfer of an unsteady magnetohydrodynamic flow of an electrically conducting, viscous, and incompressible fluid past an infinite vertical porous plate under oscillatory suction velocity and thermal radiation. The Dufour (diffusion thermo) and Soret (thermal diffusion) effects are taken into account. The problem is solved numerically using the finite element method for the velocity, the temperature, and the concentration field. The expression for the skin friction, the rate of heat and mass transfer is obtained. The results are presented numerically through graphs and tables for the externally cooled plate (Gr 〉 0) and the externally heated plate (Gr 〈 0) to observe the effects of various parameters encountered in the equations. 相似文献
65.
We prove global wellposedness for the one-dimensional cubic non-linear Schrödinger equation in a space of distributions which is invariant under Galilean transformations and includes L2. This space arises naturally in the study of the restriction properties of the Fourier transform to curved surfaces. The Lp bounds, p≠2, for the extension operator, dual to the restricition one, plays a fundamental role in our approach. 相似文献
66.
本研究分段常数变量线性中立型泛函微分方程的振动性。用不同的方法研究所考虑的方程,获得存在振动解的两个判定定理。 相似文献
67.
从理论和实验上研究了非理想性对B-Z反应体系时间自组织行为的影响,重点考察了加入惰性电解质对B-Z反应体系振荡周期的影响,按照Oregonator模型,通过小寄生参数法动力学理论分析表明,非理想性对B-Z反应体系振荡周期的影响体现在振荡周期与铈离子的活度系数成反比,而且惰性电解质的加入使得振荡周期进一步加长.通过一系列实验观测,原则上得到了与理论分析一致的结论. 相似文献
68.
This paper has introduced a pseudo-potential in bond-fluctuation model to simulate oscillatory shear flow of multiple self-avoiding
chains in three dimensions following our previous work under simple shear flow. The oscillatory flow field was reasonably
reproduced by lattice Monte Carlo simulation using this pseudo-potential neglecting hydrodynamic interaction. By sampling
the configuration distribution functions, the macroscopic viscoelasticity of semi-concentrated polymer solution was determined.
Both Newtonian and non-Newtonian regimes were studied. The complex modulus and dynamic viscosity exhibit a reasonable power
relation with oscillatory frequency, which is consistent with present theories and experiments. Consequently, lattice Monte
Carlo simulation has been extended to model free-draining self-avoiding multi chains subject to oscillatory shear flow and
to investigate associated viscoelasticity on the molecular level.
Received: 1 October 1999 Accepted: 19 October 1999 相似文献
69.
70.
采用热线风速仪测量受吹吸扰动的壁湍流边界层的流向速度,用傅里叶变换和子波变换研究
吹吸扰动对壁湍流能谱的影响,结果显示施加的低频扰动使边界层内层大尺度结构的能量减
少,小尺度结构的能量有所增强,远离壁面时扰动强度逐步衰减直到在外层中消失;通过VITA
法和子波变换法检测猝发事件,表明该扰动降低了猝发强度,使猝发周期延长,条件平均速
度波形的幅值降低、持续时间变短,说明扰动明显抑制了相干结构的猝发过程. 利用子波变
换可以实现湍谱分析,能有效检测猝发中的湍流结构,是一种客观的分析工具. 相似文献