On shapes of body waves in periodically inhomogeneous, magnetostrictive, dielectric materials

The shapes of shear body waves in periodically inhomogeneous, magnetostrictive, dielectric media are studied with emphasis on the partial (elastic and magnetostrictive) wave motions coupled to produce magnetoelastic waves __________ Translated from Prikladnaya Mekhanika, Vol. 42, No. 7, pp. 57–63, July 2006.     

A criterion for the onset of growth of two shear cracks in an elastic body under plane-strain conditions

The Wiener-Hopf method is used to find a solution to a symmetric problem that gives a criterion for the onset of growth of long shear cracks emanating from a corner point on the boundary of a hole and filled with a plastic material __________ Translated from Prikladnaya Mekhanika, Vol. 42, No. 4, pp. 83–90, April 2006.     

MHD Turbulence at the Laboratory Scale: Established Ideas and New Challenges

The properties of MHD turbulence in the electrically conducting fluids available in the laboratory (where the magnetic Reynolds number is significantly smaller than unity) may be summarised as follows:(1) The Alfven waves, even under their degenerated form at this scale, are responsible for a tendency to two-dimensionality. Eddies tend to become aligned with the applied magnetic field and inertia tends to restore isotropy. The competition between these mechanisms results in a spectral law t^-2k^-3.(2) When insulating walls, perpendicular to the magnetic field, are present and close enough to each other, two-dimensionality can be established with a good approximation within the large scales, and the predominant mechanism is the inverse energy cascade.(3) These columnar eddies are nevertheless submitted to a dissipation within the Hartmann boundary layers present at their ends, whose time scale is independent of the wave number. When this damping effect is negligible, ordinary 2D turbulence is observed with k^-5/3 spectra. On the contrary when this (ohmic and viscous) damping is significant this 2D turbulence exhibits k^-3 spectra.Besides these homogeneous (except within the Hartmann layers) conditions, for instance in shear flows such as mixing layers, almost nothing is known except that two-dimensionality may be well established. The first results of a recent experimental investigation (still in development) are presented. Some challenging questions are raised, such as the interpretation of a surprising difference between the transport of momentum and the transport of a scalar quantity (heat) across that layer. A video was shown during the oral presentation of this paper, illustrating the energy transfer toward the large scales and the weakness of the dissipation suffered by this 2D velocity field.     

结构优化设计的KFD方法及其在电除尘器本体结构优化中的应用

电除尘器本体结构优化设计是一个规模大,设计变量数多而具有相当难度的几何可调和拓扑可调优化设计问题。对这样一个大型复杂的结构优化问题,本文在文[1]的工作基础上,充分利用结构的力学特性,应用有效设计变量的概念,建立了不用求偏导数且不必解线性规划的可行方向法—KFD方法。该方法具有收敛速度快、占用内存少的优点,比通常ε有效约束可行方向法提高速度数十倍。实际应用的结果表明文中的方法是很有效的。     

Transient response of a finite crack in an orthotropic strip under the in-plane shear impact

The transient response of a central crack in an orthotropic strip under the in-plane shear impact loading is studied by using the dual integral equation method proposed by Copson and Sih. The general formula for the shear stress intensity factor near the crack tip is derived. Numerical results of with in various cases are obtained by solving the second kind Fredholm integral equation and by performing the inverse Laplace transform.     

Threshold-type shear-thickening in polymeric solutions

Threshold-type shear-thickening has been reported in the literature for relatively complex mixtures and one of the most famous is a solution of poly(vinylalcohol) in water in which a substantial amount of sodium borate is added. As far as we know, relatively few polymer solutions have been shown to be shear-thickening, even less of the threshold type. Two cases of threshold-type shear-thickening are examined. One of them is reversible [HPAM Pusher 700 or partially hydrolyzed poly(acrylamide) aqueous solution], the other one (in vitro-synthesized native dextran aqueous solution) leads to the formation of an irreversible structure provided sufficient strain is applied. In both cases, the occurrence of shear-thickening above a critical value of shear rate is related with a change in macromolecular conformation. This conformational change (reversible) can be followed by the formation of intermolecular bonds (irreversible).Presented at the 57^th Annual Meeting of the Society of Rheology, Ann Arbor, Michigan, Oct. 1985     

非高斯随机激励下工程结构可靠性估计的一种方法

本文将工程结构考虑为振动系统,把随机载荷及在结构上的载荷效应作为随机过程,分析状态函数的高阶矩,进行最大熵概率分析,得到结构在随机载荷作用下失效的概率。此法为随机环境下工作的结构、构件或设备的安全设计、可靠性检验提供了一个可行的方法。     

Three views of viscoelasticity for Cox–Merz materials

A slight rearrangement of the classical Cox and Merz rule suggests that the shear stress value of steady shear flow, , and complex modulus value of small amplitude oscillatory shear, G^∗(ω) = (G^′2 + G^″2)^1/2, are equivalent in many respects. Small changes of material structure, which express themselves most sensitively in the steady shear stress, τ, show equally pronounced in linear viscoelastic data when plotting these with G^∗ as one of the variables. An example is given to demonstrate this phenomenon: viscosity data that cover about three decades in frequency get stretched out over about nine decades in G^∗ while maintaining steep gradients in a transition region. This suggests a more effective way of exploiting the Cox–Merz rule when it is valid and exploring reasons for lack of validity when it is not. The τ −G^∗ equivalence could also further the understanding of the steady shear normal stress function as proposed by Laun.     

Stability conditions of prestressed pin-jointed structures

Pin-jointed structures are first classified to trusses, tensile structures, and tensegrity structures in view of their respective stability properties. A sufficient condition for stability of an equilibrium state is derived for tensegrity structures. The condition is based on the bilinear forms of the linear and geometrical stiffness matrices considering the flexibility of members. The stability is defined by the positive definiteness of the tangent stiffness matrix, whereas the definition of prestress-stability is based on the geometrical stiffness matrix and the infinitesimal mechanisms. Numerical examples verify that the so-called super-stability condition might not be satisfied by a stable tensegrity structure, and that a prestress-stable structure can be unstable if the prestresses are moderately large.