Shape morphing of laminated composite structures with photostrictive actuators via topology optimization

In this paper, a new design method is presented for achieving remote wireless shape morphing of laminated composite structures using topology optimization methods. A recently emerging family of smart materials, photostrictive materials, is introduced as the actuation discipline to implement the active control of optical structures by utilizing the photostriction mechanism, which arises from the superposition of photovoltaic effect and converse piezoelectric effect when exposed to the illumination of near ultraviolet light. In terms of the Mindlin plate theory of first-order shear deformation, a finite element formulation including multiphysics effects of photovoltaic, pyroelectric and thermal expansion is developed to model composite structures of ferroelectric materials polarized in 0–1 and 0–3 directions, respectively. The design is formulated as a multi-constrained optimization problem with a least square objective function to minimize structural shape errors. The topology optimization method is used as a systematic design approach to seek the optimal topologies of material layouts for both the photostrictive and host layers as well as the actuator light distribution. In terms of design sensitivity analysis, many gradient-based optimization algorithms can be applied to solve the problem effectively. Numerical examples are presented to demonstrate the effectiveness of this method in the field of active photonic control of laminated composite structures.     

两级树模型无线传感网络在制造现场的应用

针对制造现场信息采集和传送的特点,采用基于Zigbee标准的两级树模型无线传感网络来实现制造现场信息的实时准确的采集和传送,开发了简洁实用的协议栈软件。最后建立了B／S架构的制造现场系统软件平台,在基手网络公共数据库的基础上实现现场信息的系统集成。     

一种200W LED路灯电源推荐解决方案

该文介绍了一种200WLED路灯电源推荐解决方案。这种电源由基于FAN6961的PFC预调节器和基于FSFff2100的谐振LLC变换器组成,并且有6路输出,每路最大输出为0．7A／48V。     

IP级网络拓扑测量技术的研究与实现

对现有的常用的两种网络拓扑测量技术进行了分析研究,实现了基于traeeroute技术的网络拓扑测量系统并用其测量了中国网络,通过与Iplane的测量结果对比评价了其可用性。首先讨论了基于SNMP协议的拓扑测量方法,并指出其优缺点。随后讨论了基于traceroute技术的拓扑测量方法,描述了基于traeeroute技术的拓扑测量系统的设计构架和关键技术。最终利用拓扑测量系统测量了中国网络拓扑,然后将其测量结果同Iplane测量的中国网络拓扑进行复杂网络特征分析。通过特征对比发现,测量系统挖掘出的拓扑呈现出更显著的非相称性、更弱的聚集和更短的距离,证明了该系统的可用性。     

MST-based topology control with NLOS location error compensation for location-aware networks

The topology control algorithms can improve the network capacity and network lifetime in location-aware networks. The topology control algorithms require accurate locations of mobile nodes or distances between each of the mobile nodes. The IEEE 802.15.4a-based location-aware networks can provide precise ranging distance between two mobile nodes. The mobile nodes can obtain their accurate locations by using accurate ranging distances. However, in the IEEE 802.15.4a networks, the ranging distance has a large measurement error in non-line-of-sight (NLOS) conditions. In this paper, we propose MST-based topology control with NLOS location error compensation algorithm to improve location accuracy and prevent mobile nodes from connecting to unstable links in NLOS condition. Performance evaluation shows the proposed algorithm constructs a topology map which has low location errors with considering the instability of NLOS links in NLOS condition.     

无线传感器网络多业务仿真平台的实现方案

在无线传感器网络中,由于传感器节点的能源十分有限,节能是设计的首要因素。然而,无线传感器网络的多业务在现实生活应用中对QoS(服务质量)都有不同的需求,这就使得WSN网络的QoS研究成为了专家学者们的主要研究方向。在WSN网络拓扑结构和业务类型的研究基础上,使用网络模拟器(Network Simulator Version 2,NS2)来搭建基于多业务共存的星型以及对等结构两种WSN网络仿真平台,建立多种业务流量模型,实现以无线传感器网络协议、流量模型、拓扑为基础的功能模块化设计;并对无线传感器网络关键性能进行了仿真模拟,实现延时、吞吐量、能耗等关键性能的分析。     

A Moving Grid Framework for Geometric Deformable Models

Geometric deformable models based on the level set method have become very popular in the last decade. To overcome an inherent limitation in accuracy while maintaining computational efficiency, adaptive grid techniques using local grid refinement have been developed for use with these models. This strategy, however, requires a very complex data structure, yields large numbers of contour points, and is inconsistent with the implementation of topology-preserving geometric deformable models (TGDMs). In this paper, we investigate the use of an alternative adaptive grid technique called the moving grid method with geometric deformable models. In addition to the development of a consistent moving grid geometric deformable model framework, our main contributions include the introduction of a new grid nondegeneracy constraint, the design of a new grid adaptation criterion, and the development of novel numerical methods and an efficient implementation scheme. The overall method is simpler to implement than using grid refinement, requiring no large, complex, hierarchical data structures. It also offers an extra benefit of automatically reducing the number of contour vertices in the final results. After presenting the algorithm, we demonstrate its performance using both simulated and real images. This work was supported in part by NSF/ERC Grant CISST#9731748 and by NIH/NINDS Grant R01NS37747.     

Study of impact energy propagation phenomenon and modal characteristics of an armored vehicle undergoing high velocity impact

A new manufacturing technology is being employed to build a new type of armored vehicle. While thick panels are welded together in the old manufacturing technology, relatively thin panels are welded to a frame structure in the new manufacturing technology. The structural integrity of the new type of armor vehicles can be maintained mainly by the frame structures while the panel thickness is reduced significantly to reduce the total vehicle weight. Since the dynamic characteristics of a frame-panel hybrid structure are different from those of the old type of structure which consists of only thick panels, they should be identified to achieve a good performance of the vehicle. For this purpose, a proper FE model of the hybrid type of structure needs to be developed. In the present study, FE models are proposed to represent the frame-panel hybrid type structure efficiently. The impact energy propagation, the transient response and the modal characteristics are investigated with the FE models. This paper was presented at the 4th Asian Conference on Multibody Dynamics(ACMD2008), Jeju, Korea, August 20–23, 2008. Hong-Hee Yoo received a B.S. and M.S. degree in Mechanical Engineering from Seoul National University in 1980 and 1982. He then went on to receive his Ph.D. degree from Michigan State University in 1989. Dr. Yoo is currently a Professor at the School of Mechanical Engineering at Hanyang University in Seoul, Korea. His research interests are in the area of Flexible body dynamics, vibration.     

Quantitative relationships between composition, particle size, triple phase boundary length and surface area in nickel-cermet anodes for Solid Oxide Fuel Cells

The present study is focusing on the elaboration of the quantitative relationships between the primary microstructural parameters (i.e. the phase volume fractions Φ, the particle and pore sizes and the corresponding size distributions PSD) with the more complex topological features (triple phase boundary length TPB_L, and specific surface area SSA) in porous Ni-cermet anodes. These relationships are crucial for the microstructure optimization and for the improvement of the corresponding electrode performance.In the first part of the study a pristine anode material with a graded microstructure is analyzed. The results from the different zonations indicate that the TPB_L correlates well with the volume fraction of the coarsest phase which is nickel. However the volume fractions also correlate with the particle size after sintering due to stronger particle coalescence at higher nickel volume fractions. Since the larger particle size leads to a decrease of the TPB_L this coarsening effect partly neutralizes the advantage of a higher nickel volume fraction. Furthermore, the TPB_L is also linked with the nickel surface area and with the corresponding pore-nickel interface area. The pore-nickel interface is the least abundant internal surface and therefore it represents the microstructural feature which predominantly limits the TPB formation in our nickel-cermet anode.In the second part the effects of microstructural degradation during exposure in a humid gas environment at 950 °C are investigated. During the early period (<200 h) the rapid decrease of the TPB_L is directly linked with the kinetics of nickel grain growth. At longer periods (>1000 h) the nickel coarsening ceases whereas the decrease of the TPB_L continues at a lower rate. During longer exposure time the reduction of TPB_L is most probably caused by a slight volatilization of the nickel phase and by the formation of continuous CGO layers which are shielding the surface of the nickel grains.     

Multi-objective topology optimization of end plates of proton exchange membrane fuel cell stacks

End plates of the proton exchange membrane fuel cell (PEMFC) need to be well designed because their strength and rigidity directly affect the clamping pressure distribution and thus affect the performance and lifetime of fuel cell stacks. In this paper, a multi-objective topology optimization model of the end plates in a PEMFC stack with nonlinear contact boundary conditions was established to obtain an optimized structural design. It was found that the design improved with topology optimization is not only light but also meets manufacturability requirements. This provides good guidance for the design of a high-performance end plate.