Dynamic wrinkling in sandwich beams

Facings of sandwich structures employed in typical applications are often subject to parametric periodic loading. Such loading can cause local dynamic instability of the facings, i.e. large-amplitude small wavelength lateral vibrations. This phenomenon, called in the paper dynamic wrinkling, may result in fatigue damage or immediate failure. The problem of dynamic wrinkling of the facings is analyzed in the present paper for sandwich beams and for large aspect ratio wide panels that vibrate forming a cylindrical surface. The solution is obtained for the case of a relatively thick or compliant core where the Winkler elastic foundation model of the core is applicable. In addition, the problem is formulated as an extension of the Plantema core model that may be preferable for thinner and stiffer cores. In addition, a new simplified elasticity model is introduced in the paper that is based on the assumption that both facings experience simultaneous and interactive dynamic wrinkling instability. Numerical results shown for the elastic foundation model include the criterion for the onset of dynamic wrinkling and the critical value of the damping coefficient of the facing that is sufficient to prevent such wrinkling. As follows from these results, dynamic wrinkling is unlikely in most engineering applications, except for the case in which the maximum stresses in the facing approach the static wrinkling value.     

Reliability through consistency

In many distributed computing environments, failures are reported in a way that violates even the simplest notions of consistency. The authors argue that such practices are at the root of reliability problems, examine some distributed computing technologies in terms of consistency, and present strategies for implementing consistent failure reporting     

Vibrations of plates with superelastic shape memory alloy wires

The article illustrates an approach to the passive vibration control of thin plates utilizing prestressed superelastic shape memory alloy (SMA) wires. The SMA wires can freely slide within protective sleeves that are either embedded within the structure or bonded to its surface. The vibration control mechanism combines an effective continuous elastic foundation representing the support provided by SMA wires to the structure with the energy dissipation as a result of the hysteresis occurring in the wires. The other approach to the vibration control employs superelastic wires attached to the structure at discrete points. The mathematical formulation of the problem presented in the article can be adopted for a rigorous computational analysis. In particular, a closed form expression is obtained for the loss factor in large aspect ratio plates supported at the midspan by a system of parallel SMA wires. As follows from numerical examples presented for such plates, the proposed method offers a significant damping, far exceeding that observed in conventional engineering structures.     

利用Agent实现新的电网后备保护

提出了一种新的利用Agent实现的电网后备保护系统.它优于由传统第Ⅲ段保护构成的后备保护系统,动作更快而且更具有选择性,其自检和纠错能力能减少保护的不正确动作.阐述了:Agent的基本思想,分析了Agent保护通信特点,提出了基于Agent的电网后备保护系统原理结构、算法和IP通信实现,利用电力和通信系统同步仿真平台EPOCHS在一简单电力系统上对所提出的保护系统进行了仿真实现,证明了所提出的方法的有效性.     

Live Distributed Objects: Enabling the Active Web

Distributed computing has lagged behind the productivity revolution that has transformed the desktop in recent years. Programmers still generally treat the Web as a separate technology space and develop network applications using low-level message-passing primitives or unreliable Web services method invocations. Live distributed objects are designed to offer developers a scalable multicast infrastructure that's tightly integrated with a runtime environment.