Influence of swirl on the stability of a rod in annular leakage flow

The influence of swirl (flow rotation) on the stability of a rod in annular leakage flow is investigated. Under the assumption of laminar flow and plane vibrations (no whirling), it is shown that the swirl acts, in effect, as an elastic foundation with negative foundation stiffness, the magnitude being proportional to the mean circumferential flow rate squared. Consequently, swirl always lowers the critical axial flow speed in case of divergence instability of a rod of finite length. Numerical analysis is needed to predict the effect of swirl in case of flutter instability of a finite rod; this is not performed here. However, for the flutter-like instability of travelling waves in an infinite rod-channel system, it is shown analytically that swirl again always lowers the critical axial flow speed. Finally, it is found that by circumferential flow alone, the travelling waves are extinguished at a certain flow rate, followed by a divergence-like instability.     

Density viscous continuum traffic flow model

A new traffic flow model called density viscous continuum model is developed to describe traffic more reasonably. The two delay time scales are taken into consideration, differing from the model proposed by Xue and Dai [Phys. Rev. E 68 (2003) 066123]. Moreover the relative density is added to the motion equation from which the viscous term can be derived, so we obtain the macroscopic continuum model from microscopic car following model successfully. The condition for stable traffic flow is derived. Nonlinear analysis shows that the density fluctuation in traffic flow induces density waves. Near the onset of instability, a small disturbance could lead to solitons determined by the Korteweg-de-Vries (KdV) equation, and the soliton solution is derived. The results show that local cluster effects can be obtained from the new model and are consistent with the diverse nonlinear dynamical phenomena observed in the freeway traffic.     

Constitutive modeling of cyclic plasticity and creep,using an internal time concept

Using the concept of an internal time as related to plastic strains, a differntial stress-strain relation for elastoplasticity is rederived, such that (i) the concept of a yield-surface is retained; (ii) the definitions of elastic and plastic processes are analogous to those in classical plasticity theory; and (iii) its computational implementation, via a “tangent-stiffness” finite element method and a “generalized-midpoint-radial-return” stress-integration algorithm, is simple and efficient. Also, using the concept of an internal time, as related to both the inelastic strains as well as the Newtonian time, a constitutive model for creep-plasticity interaction, is discussed. The problem of modeling experimental data for plasticity and creep, by the present analytical relations, as accurately as desired, is discussed. Numerical examples which illustrate the validity of the present relations are presented for the cases of cyclic plasticity and creep.     

On the nonlinear dielectric function of CuCl in pump and probe experiments

We study the dispersion and the absorption changes of CuCl under high excitation conditions in two-beam experiments with parallel and crossed linear polarizations of both beams. The induced optical non linearities are shown to depend sensitively on the presence of interactions between the degenerate transverse exciton states.     

EFFECTIVE SPECIFIC HEATS OF MULTI-PHASE THERMOELASTIC COMPOSITES

This paper studies the effective properties of multi-phase thermoelastic composites. Based on the Helmholtz free energy and the Gibbs free energy of individual phases, the effective elastic tensor, thermal-expansion tensor, and specific heats of the multi-phase composites are derived by means of the volume average of free-energies of these phases. Particular emphasis is placed on the derivation of new analytical expressions of effective specific heats at constant-strain and constant-stress situations, in which a modified Eshelby’s micromechanics theory is developed and the interaction between inclusions is considered. As an illustrative example, the analytical expression of the effective specific heat for a three-phase thermoelastic composite is presented.     

Influence of switchable magnetic field on the modulation property of nanostructured magnetic fluids

Magnetic fluid is a kind of colloidal material with tunable microstructure and unique optical properties. The tunable magneto-optical modulation property of magnetic fluid under externally switchable magnetic field with various modulation periods is investigated theoretically and experimentally. The transitional modulation period (lower limit of the working frequency) between the square-like and oscillation-like modulation is achieved and found to be magnetic-field- and sample-concentration-dependent. The modulation mechanism is analyzed and ascribed to the dynamic microstructure of magnetic fluid under different modulation periods of external magnetic fields. The result of this work may be helpful for the pragmatic applications of magnetic fluid based on the square-like modulation.     

Optical extensometer and elimination of the effect of out-of-plane motions

A novel optical extensometer is developed to estimate the local uniform strain on planar surface accurately. The proposed system consists of a shared large format lens and two image sensors, which acquire pairs of images of two isolated small regions on the object surface simultaneously. Digital image correlation (DIC) algorithm is applied to determine the relative displacement between gauge points designated on recorded pairs of images. Then local strain can be extracted after dividing the relative displacement by the scale distance. Moreover, a special experimental setup called “correction sheet” is used to eliminate the virtual strain induced by out-of-plane motions. Uni-axial tensile experiments are performed to validate the reliability and resolution of the optical extensometer, and the measurement results demonstrate that the resolution of the optical extensometer achieves 2–3 με.