非线性Kelvin-Helmholtz不稳定性

本文用导数展开法对液体薄层与亚音速气流接壤时的界面稳定性作非线性分析.文中考虑了液体的表面张力与体积力,故非线性的Rayleigh-Taylor不稳定性可作为特例而导出;液体与气体均不计粘性.虽然Nayfeh曾算过这一情况,但其三阶方程有遗漏(如213页的式(2.29)).同时解也不自洽(如其一阶解(2.31)并不满足他的初始条件(2.20)),此外,在截止波数附近,对行波他并未考虑.本文弥补了这些,并得出了新的结论.

Tokamak中的Kelvin-Helmholtz不稳定性

<正> Tokamak中的一个重要问题是加热。中性束注入加热是加热的一个有效手段,它使美国PLT上的离子温度达到7.1KeV.但PLT上的中性束注入的不对称性引起等离子体的快速环向旋转,转速可达1×10~7厘米/秒。1979年5月Suckewer等在PLT上测量了速度分布。 在具有速度剪切进行旋转的等离子体中,会不会形成新的磁流体力学不稳定性?1980年

Thermal stress wave and spallation induced by an electron beam

Thermal stress wave and spallation in aluminium alloy exposed to a high fluency and low energy electron beams are studied theoretically. A simple model for the study of energy deposition of electrons in materials is presented on the basis of some empirical formulae. Under the stress wave induced by energy deposition, microcracks and/or microvoids may appear in target materials, and in this case, the inelastic volume deformation should not vanish. The viscoplastic model proposed by Bodner and Partom with corresponding Gurson's yield function requires modification for this situation. The new constitutive model contains a scalar field variable description of the material damage which is taken as the void volume fraction of the polycrystalline material. Incorporation of the damage parameter permits description of rate-dependent, compressible, inelastic deformation and ductile fracture. The melting phenomenon has been observed in the experiment, therefore one needs to take into account the melting process in the intermediate energy deposition range. A three-phase equation of state used in the paper provides a more detailed and thermodynamical description of metals, particularly, in the melting region. The computational results based on the suggested model are compared with the experimental test for aluminium alloy, which is subjected to a pulsed electron beam with high fluency and low energy. (C) 1997 Elsevier Science Ltd.

Wave pattern characteristics of a two-phase nozzle flow by shock propagation

In this paper, the wave pattern characteristics of shock-induced two-phase nozzle Hows with the quiescent or moving dusty gas ahead of the incident-shock front has been investigated by using high-resolution numerical method. As compared with the corresponding results in single-phase nozzle flows of the pure gas, obvious differences between these two kinds of flows can be obtained.

Effect of nonlinear wave-current interaction on flow fields and hydrodynamic forces

A fifth-order theory for solving the problem of interaction between Stokes waves and exponential profile currents is proposed. The calculated flow fields are compared with measurements. Then the errors caused by the linear superposition method and approximate theory are discussed. It is found that the total wave-current field consists of pure wave, pure current and interaction components. The shear current not only directly changes the flow field, but also indirectly does sx, by changing the wave parameters due to wave-current interaction. The present theory can predict the wave kinematics on shear currents satisfactorily. The linear superposition method may give rise to more than 40% loading error in extreme conditions. When the apparent wave period is used and the Wheeler stretching method is adopted to extrapolate the current, application of the approximate theory is the best.

Shock-induced two-phase flows in an aligned baffle system filled with suspended particles

This paper describes the shock propagation through a dilute gas-particle suspension in an aligned baffle system. Numerical solution to two-phase flows induced by a planar shock wave is given based on the two-continuum model with interphase coupling. The governing equations are numerically solved by using high-resolution schemes. The computational results show the shock reflection and diffraction patterns, and the shock-induced flow fields in the 4-baffle system filled with the dusty gas.

A new dynamic model for study of dislocation pattern formation

Based on the principle given in nonlinear diffusion-reaction dynamics, a new dynamic model for dislocation patterning is proposed by introducing a relaxation time to the relation between dislocation density and dislocation flux. The so-called chemical potential like quantities, which appear in the model can be derived from variation principle for free energy functional of dislocated media, where the free energy density function is expressed in terms of not only the dislocation density itself but also their spatial gradients. The Linear stability analysis on the governing equations of a simple dislocation density shows that there exists an intrinsic wave number leading to bifurcation of space structure of dislocation density. At the same time, the numerical results also demonstrate the coexistence and transition between different dislocation patterns.

Parameter-transformation relations for traveling-wave solutions of kdv-burgers equation

 Burgers suggested that the main properties of free-turbulence in the boundless area without basic flow might be understood with the aid of the following equation, which was much simpler than those of fluid dynamics, 更多还原

Reflection of shock-wave in pur foam from rigid wall

Keller proposed that a building, a mechanical installation or a body wrapped bya layer of foam plastics may be an efficient means for protection from damage ofblast wave. However, the practical effect was beyond expectation. For example, agunner wearing the foam plastics-padded waistcoat was injured more seriously by theblast wave from a muzzle. Monti took the foam plastics as homogeneous two-phasemedium and analyzed it with the theory of dusty flow. The obtained results showthat the peak pressure behind the reflected shock wave from rigid wall with foamcoat exceeds obviously that without foam coat under the same condition. Gel'fand,Patz and Weaver made experimental observations by means of shock tubes and veri-

3-dimensional transient wave response in a cracked elastic solid

The three-dimensional transient wave response problem is presented for an infinite elastic medium weakened by a plane crack of infinite length and finite width. Tractions are applied suddenly to the crack, which simulates the case of impact loading. The integral transforms are utilized to reduce the problem to a standard Fredholm integral equation in the Laplace transform variable and sequentially invert the Laplace transforms of the stress components by numerical inversion method. The dynamic mode I stress intensity factors at the crack tip are obtained and some numerical results are presented in graphical form.