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81.
82.
针对传统的桥式PWM可逆整流器直流侧工作电压要求较高的限制,提出一种新型PWM可逆整流器拓扑,运用状态空间平均法进行了建模和稳态理论分析,并给出该变流器的参数选择方法。MATLAB数值仿真与样机实验结果证实了该拓扑、模型及理论的正确性。 相似文献
83.
由组播网的特点,根据接收节点处丢包的统计,可以推算出组播网络的拓扑结构。文章在组播网络拓扑发现算法BLT的基础上提出了一种基于丢包和跳数的拓扑发现算法HBLT。通过仿真研究表明,HBLT算法比BLT算法有更高的准确性。 相似文献
84.
IPv6地址路由机制研究综述 总被引:2,自引:0,他引:2
IPv6协议是在IPv4的基础上发展起来为了解决现有网络问题的协议。其地址路由机制是下一代网络运行的基础。该文介绍了IPv6协议现有的地址路由的一些机制和标准,在这些机制的基础上总结了现今IPv6路由的热点问题,并参考了国内外的一些研究文档,对这些问题的一些解决方案进行了概括描述和分析。最后对于目前研究的方向和解决方法进行归纳。 相似文献
85.
利用双向渐进结构优化法对结构固有振型的优化 总被引:6,自引:1,他引:5
利用双向渐进结构优化法研究结构的固有振型优化问题,双向渐进结构优化法(bi—directional evolutionary struetural optimization,简称BESO)是一种拓扑优化方法,它基于这样一个简单的优化程序:从结构中一步步地删去对结构目标性能低效或无效的材料,同时增加对结构目标性能高效的材料,从而使材料布局趋于优化。文中分别采用近似重分析思路的方法和基于变分法推导的公式计算单元特征向量灵敏度,并简单阐述BESO法对结构固有振型(特征向量)进行拓扑优化的一般过程。数值算例表明,用该方法对结构固有振型的优化是行之有效的,且用变分法计算特征向量灵敏度进行优化较之近似重分析法效率更高。 相似文献
86.
87.
《Fullerenes, Nanotubes and Carbon Nanostructures》2013,21(3):245-255
Abstract Several dimers: C120, C140, C130 and their oxygen‐containing derivatives as well as some oligomers or polymers of the well known spherical fullerenes have been synthesized so far. Some of the formulas attributed to such compounds represent the first steps in a more complex fate leading to trivalent capped tubulenes. Such a way could even be followed by functionalized fullerenes. A detailed network transformation is given for C60 and its mono‐ and di‐epoxy derivatives. Semiempirical calculations support the presented findings. 相似文献
88.
There is significant interest today in integrating additive manufacturing (AM) and topology optimization (TO). However, TO often leads to designs that are not AM friendly. For example, topologically optimized designs may require significant amount of support structures before they can be additively manufactured, resulting in increased fabrication and clean-up costs.In this paper, we propose a TO methodology that will lead to designs requiring significantly reduced support structures. Towards this end, the concept of ‘support structure topological sensitivity’ is introduced. This is combined with performance sensitivity to result in a TO framework that maximizes performance, subject to support structure constraints. The robustness and efficiency of the proposed method is demonstrated through numerical experiments, and validated through fused deposition modeling, a popular AM process. 相似文献
89.
Topology synthesis of multi-rigid-body mechanisms has always been a very important stage in the mechanism design process. In most cases, the topology of the multi-rigid-body mechanism for particular task is obtained by designers’ experience and ingenuity, rather than automatic approach. In this work, an approach of topology optimization of multi-rigid-body mechanisms is investigated. The core process of the approach is an automatic optimization design process. In this approach, we construct kinematics mapping from truss structures to the joint-linked mechanisms, which transforms the topology optimization problem of multi-body system into the truss structure optimization problem. We also develop a new strategy for topology optimization of statically determinate truss, the advantage of which lies in the ability dealing with statically determinate truss topology optimization problem compared to the existing methods. By automatically optimizing the topology of the truss structure, the topology of the multi-rigid-body mechanism is optimized automatically, accordingly. Here, we utilize the investigated approach to design suitable layout for multi-rigid-body micro-displacement amplifying mechanisms (MMAMs) with a large amplification ratio (>50). The layout consists of not only the topology information of the mechanism, but also the dimension parameters of the mechanism. The procedure of the approach is carried out in steps, and a human–computer interaction program has been developed for it. Using the developed program, different MMAMs are achieved. Meanwhile, the direct kinematics analysis of the MMAMs is achieved automatically, the existence of dead point position in the mechanism within movement range is checked and the micro-displacement amplification ratio is calculated out. The computing results are validated by the ADAMS® motion simulation, which proves that the achieved MMAMs fully fulfill the functional requirement. Along with two of the achieved MMAMs, the approach is explained, its functionality is shown, its advantages, limitations, some open problems and future works are discussed. 相似文献
90.
The equations that govern the various transport phenomena occurring in a polymer electrolyte membrane fuel cell (PEMFC) were formulated and implemented in a commercial finite element software, in order to predict the fuel cell current density with respect to the operating conditions. The numerical model showed polarization curves in accordance with literature. The catalyst utilization was then improved by optimizing the platinum distribution (design variable) in the fuel cell, so as to maximize current density (objective function) for a fixed total amount of platinum (constraint). The first analysis showed that, for equal anode and cathode catalyst layer thicknesses, maximal current density was achieved by placing more catalyst in the cathode than in the anode. The second analysis showed that, for equal anode and cathode catalyst layer density, maximal current density was achieved by using a catalyst layer that is thicker on the cathode side than that on the anode side. Finally, a topological optimization of the platinum density within the cathode catalyst layer was performed with a gradient based algorithm, and the results showed that at a high stoichiometric ratio, the best design has most of its platinum placed where the reaction rate is the highest, i.e., close to the membrane layer. 相似文献