切变流体和旋转流体的动力学相似性

在传统长重力波方程中引入水平基流的作用，导出了带有基流切变效应的平面波解．正如层结流体与旋转流体具有动力学相似性一样，发现切变流体也有类似的动力学相似性．

Numerical Analysis on Magnetic-induced Shear Modulus of Magnetorheological Elastomers Based on Multi-chain Model

Based on the magnetic interaction energy, using derivative of the magnetic energy density, a model is proposed to compute the magnetic-induced shear modulus of magnetorheological elastomers. Taking into account the influences of particles in the same chain and the particles in all adjacent chains, the traditional magnetic dipole model of the magnetorheological elastomers is modified. The influence of the ratio of the distance etween adjacent chains to the distance between adjacent particles in a chain on the magnetic induced shear odulus is quantitatively studied. When the ratio is large, the multi-chain model is compatible with the single chain model, but when the ratio is small, the difference of the two models is significant and can not be neglected. Making certain the size of the columns and the distance between adjacent columns, after constructing the computational model of BCT structures, the mechanical property of the magnetorheological elastomers composed of columnar structures is analyzed. Results show that, conventional point dipole model has overrated the magnetic-induced shear modulus of the magnetorheological elastomers. From the point of increasing the magnetic-induced shear modulus, when the particle volume fraction is small, the chain-like structure exhibits better result than the columnar structure, but when the particle volume fraction is large,the columnar structure will be better.

Effect of surfactants on hydrodynamics characteristics of bubble in shear thinning fluids at low Reynolds number

In this study,the effects of surfactants on the hydrodynamic characteristics of bubbles in shear-thinning fluids at low Reynolds number(Re<50)are investigated.The bubble terminal velocity and drag coefficient of bubble in clean and contaminated carboxymethylcellulose(CMC)solutions are obtained using a high-speed camera for examining differences.The results show that the existence of surfactant could reduce the terminal velocity of bubble at small volume(0.25wt%CMC:<100 mm3;0.50wt%CMC:<110 mm3),attributed to stiffening the bubble interface.However,this negative effect decreases and finally disappears with increasing bubble volume.The drag coefficient curves of the bubble in contaminated CMC solution exhibit behavior similar to that exhibited by a solid sphere at Re<10,indicating that internal circulation flow is absent at the bubble interface as compared to that in clean CMC solution.However,for 10<Re<40,a transition of drag curve from 24/Re to 16/Re in contaminated CMC solution is observed,which is easy at low SDS concentrations and high CMC concentrations.

Numerical simulation of single bubble rising in shear-thinning fluids by level set method

The behavior of single bubble rising in quiescent shear-thinning tlmds was lnvestlgateO numerically by level set metnoa. number of bubbles in a large range of Reynolds number and Eotvos number were investigated including spherical, oblate and spherical. The bubble shape and drag coefficient were compared with experimental results. It is observed that the simulated results show good conformity to experimental results over a wide range of Reynolds number. In addition, the detailed flow field based on the reference coordinate system moving with the bubble is obtained, and the relationship among flow field, bubble shape and velocity is discussed.

Splitting PMMA with Mini Cutting Explosives

In order to improve the present aviation ejection escape system, the application of explosion cutting technique to aviation escape system is proposed to weaken the strength of canopy before ejecting it. A series of mini cutting explosives are designed to investigate the process of splitting PMMA plate. The phenomenon of spallation in PMMA is observed. The effects of different parameters of mini cutting explosives on the cutting depth are obtained. Consequently the appropriate material of half-circular metal covers, explosive types and the ranges of charge quantities are determined. On the other hand, the cutting process of aviation PMMA plate by mini cutting explosives is simulated by means of nonlinear dynamic analysis code LS-DYNA. In finite element analysis,Arbitrary Lagrangian Euler (ALE) algorithm is used to depict the fluid property of high energy explosives. Continuous damage material model is used to simulate the complicate dynamic damage behavior of PMMA due to explosion shock waves. Only sliding contact option is defined to fulfill the fluid-structure interaction between explosives and PMMA plate by distributed parameter methods. Phenomenon of spallation observed in the experiment is presented in the simulation. The relationship between the penetration depth of PMMA plate and charge linear density obtained by numerical simulation agrees well with experimental result.

Vibration and Instability of Third⁃Order Shear Deformable FGM Sandwich Cylindrical Shells Conveying Fluid

The vibration and instability of functionally graded material(FGM)sandwich cylindrical shells conveying fluid are investigated.The Navier-Stokes relation is used to describe the fluid pressure acting on the FGM sandwich shells.Based on the third-order shear deformation shell theory,the governing equations of the system are derived by using the Hamilton’s principle.To check the validity of the present analysis,the results are compared with those in previous studies for the special cases.Results manifest that the natural frequency of the fluid-conveying FGM sandwich shells increases with the rise of the core-to-thickness ratio and power-law exponent,while decreases with the rise of fluid density,radius-to-thickness ratio and length-to-radius ratio.The fluid-conveying FGM sandwich shells lose stability when the non-dimensional flow velocity falls in 2.1-2.5,which should be avoided in engineering application.

Shear and extensional rheology of entangled polymer melts: Similarities and differences

This work extends our previous understanding concerning the nonlinear responses of entangled polymer solutions and melts to large external deformation in both simple shear and uniaxial extension. Many similarities have recently been identified for both step strain and startup continuous deformation, including elastic yielding, i.e., chain disentanglement after cessation of shear or extension, and emergence of a yield point during startup deformation that involves a deformation rate in excess of the dominant molecular relaxation rate. At a sufficiently high constant Hencky rate, uniaxial extension of an entangled melt is known to produce window-glass-like rupture. The present study provides evidence against the speculation that chain entanglements tie up into "dead knots" in constant-rate extension because of the exponentially growing chain stretching with time. In particular, it is shown that even Instron-style tensile stretching, i.e., extending a specimen by applying a constant velocity on both ends, results in rupture. Yet, in the same rate range, the same entangled melt only yields in simple shear, and the resulting shear banding is clearly not a characteristic of rupture. Thus, we conclude that chain entanglements respond to simple shear in the manner of yielding whereas uniaxial extension is rather effective in causing some entanglements to lock up, making it impossible for the entanglement network to yield at high rates.