浅析"开关稳压电源"(二)

文中进一步对开关电源两种主要电路结构——“串联型”／‘‘变压器耦合并联型”开关电源作了比较详尽的介绍,且对比了两者性能的优劣。文章用较大的篇幅分析了一种典型的实用开关稳压电源——BC机芯彩电应用的关键点与难点：激励脉冲产生电路、自动调节过程与过载保护电路。     

Flexible Multibody Systems Models Using Composite Materials Components

The use of a multibody methodology to describe the large motion of complex systems that experience structural deformations enables to represent the complete system motion, the relative kinematics between the components involved, the deformation of the structural members and the inertia coupling between the large rigid body motion and the system elastodynamics. In this work, the flexible multibody dynamics formulations of complex models are extended to include elastic components made of composite materials, which may be laminated and anisotropic. The deformation of any structural member must be elastic and linear, when described in a coordinate frame fixed to one or more material points of its domain, regardless of the complexity of its geometry. To achieve the proposed flexible multibody formulation, a finite element model for each flexible body is used. For the beam composite material elements, the sections properties are found using an asymptotic procedure that involves a two-dimensional finite element analysis of their cross-section. The equations of motion of the flexible multibody system are solved using an augmented Lagrangian formulation and the accelerations and velocities are integrated in time using a multi-step multi-order integration algorithm based on the Gear method.     

Coupling losses in a rectangular multifilamentary superconducting composite

Coupling current losses between filaments of a superconducting multifilament composite subjected to a transverse varying field is highly dependent on the shape of the conductor. The ac loss is evaluated in a conductor of rectangular cross sectional area. It is shown that the loss per unit volume is somewhat different from the loss in an elliptical shaped composite of the same aspect ratio. In addition, the loss in the outer copper sheath is less sensitive to the aspect ratio than the inner filamentary region. Numerous experimental results are given on losses in as-received conductors and in conductors where the outer copper sheath has been partially removed. The anisotropy in the losses caused by a changing field perpendicular or parallel to the wide side of a conductor is in very good agreement with the theory.     

甲烷活化机理研究进展

对近年来CH4活化机理方面的研究做了综述。在甲烷氧化偶联(OCM)反应中,催化剂表面上究竟何种氧负离子(O2-(超氧)、O22-(过氧)、表面晶格氧O2-)是参与活化CH4的活性氧物种仍然是一个存在争议的问题。在不同金属表面上CH4的直接活化模式被认为有两种,一种是形变模式,另一种是伸缩模式。在通过中间体途径活化CH4的研究中,发现“三中心两电子”脱氢反应和与有机金属阳离子络合物的络合交换反应是两种在温和条件下活化CH4的很有前景的活化方式。     

Superconductivity in MgB2: A Case Study of the “Flat Band–Steep Band” Scenario

The electronic structure of MgB₂ is analyzed in terms of the flat band–steep band scenario for superconductivity. Good agreement between the Fermi surfaces obtained from de Haas–van Alphen measurements and from TB-LMTO and FP-LMTO calculations was achieved. The decomposed electron–phonon coupling (q) reveals a pronounced peak-like structure along the –A and –M directions.     

Modeling multiaxial impact behavior of a glassy polymer

In many applications of polymers, impact performance is a primary concern. Impact tests experimentally performed on molding prototypes yield useful data for a particular structural and impact loading case. But, it is generally not practical in terms of time and cost to experimentally characterize the effects of a wide range of design variables. A successful numerical model for impact deformation and failure of polymers can provide convenient and useful guidelines on product design and therefore decrease the disadvantages that arise from purely experimental trial and error. Since the specimen geometry and loading mode for multiaxial impact test provides a close correlation with practical impact conditions and can conveniently provide experimental data, the first step of validating a numerical model is to simulate this type of test. In this paper, we create a finite element analysis model using ABAQUS/Explicit to simulate the deformation and failure of a glassy ABS (acrylonitrile-butadiene-styrene) polymer in the standard ASTM D3763 multiaxial impact test. Since polymers often exhibit different behavior in uniaxial tensile and compression tests, the uniaxial compression or tensile tests are generally not representative of the three-dimensional deformation behavior under impact loading. A hydrostatic pressure effect (controlled by the parameter γ) is used to generalize a previously developed constitutive model ("DSGZ" model) so that it can describe the entire range of deformation behavior of polymers under any monotonic loading modes. The generalized DSGZ model and a failure criterion are incorporated in the FEA model as a user material subroutine. The phenomenon of thermomechanical coupling during plastic deformation is considered in the analysis. Impact load vs. displacement and impact energy vs. displacement curves from FEA simulation are compared with experimental data. The results show good agreement. Finally, equivalent stress, strain, strain rate and temperature distributions in the polymer disk are presented. Electronic Publication     

高转速冲击载荷下柔性板式联轴器的使用寿命

针对典型柔性板式联轴器在高速小型单缸发动机试验台上应用时使用寿命极短的问题,分析了柔性板产生周向和径向变形的原因,研究了连接方式、结构参数和材料对寿命的影响。设计出的压环式连接方式有助于延长柔性板寿命,并具有安装方便、运转噪声低等优点。通过发动机台架试验证明:柔性板式联轴器采用压环式连接可延长柔性板寿命4倍多。     

Experimental excitation and detection of angular harmonics in a step-index optical fiber

As an alternative to classical LP-modes used as a signal carrier in the optical fiber, we propose a superposition of angular harmonics that can be obtained as a special combination of LP-modes, which also shows modal properties in an optical fiber. Results of a number of natural experiments on selective excitation of both individual angular harmonics and their superposition are discussed. The text was submitted by the authors in English.     

偏振耦合测试在分布式应力传感中的理论分析

对高双折射保偏光纤内部的分布式偏振模式耦合在分布式应力传感中的应用进行了理论分析.根据光弹理论和弹性力学理论,建立了横向应力作用下保偏光纤的偏振耦合模型,推导出应力下的偏振耦合强度公式.偏振耦合强度对应力的大小,方向,作用长度以及保偏光纤的拍长都敏感.详细分析了每一个因素对耦合强度的影响.当横向应力的作用方向角为45°,作用长度为保偏光纤的一半时,这时保偏光纤耦合强度对应力传感最敏感.     

柔性储液容器跌落碰撞仿真方法的研究

基于多物质的ALE有限元法,利用罚函数方式实现了两种流体与结构间的耦合作用,并完成了大变形柔性储液容器跌落碰撞过程的三维动态模拟。在分析柔性储液容器碰撞过程力学行为的同时,比较不同装水量对其结果的影响,为该类柔性储液容器结构的设计提供了重要的参考依据。