用可动节点有限元模型模拟裂纹扩展过程

本文针对裂纹扩展有限元模拟模型存在的问题,提出一种可动节点模型.使裂尖在单元尺度内任意移动,实现了扩展模拟连续性.加进松弛扩展,突出其所占比重,使模拟更加逼真.用弹塑性有限变形杂交元自编模拟裂纹扩展的通用FORTRAN 程序,对含中心裂纹铝板进行模拟,假定材料各向同性并遵守等向强化规律,采用米赛斯屈服准则和Drucker 塑性势流动理论做增量弹塑性静力分析,得到了与实验符合较好的结果.

可动节点复合单元的基本原理及在一维问题中的应用

着重于开发一种以常规线性单元为基底,附加中间移动节点而构成的新型高精度的复合有限单元方法。移动节点复合单元法作为一种高精度有限单元法,通过调节中间可动节点的位置改变其单元内部的场分布,从而只需少量单元即可达到较高的计算精度。由于此种复合单元的中间移动节点的形函数采用计算机图形学常用的Bezier函数,故可简称为‘Bezier复合单元’(BCE)。应用此Bezier单元对具有解析解的一维受分布载荷作用的等截面杆问题和受集中载荷作用的变截面杆问题进行模拟,并与解析解及采用常规有限单元法的模拟结果进行对照和分析。

蜕化四边形等参元的单元节点挠动

根据蜕化四边形八节点等参元的位移与应变公式分析了单元节点挠动对该单元计算精度影响的原因，并用算例说明节点挠动值ｒ与单元边长Ｌ１比值很小时会对计算结果产生很大影响。

偏心齿轮机构传动比函数的研究

基于Willis定理与渐开线的特性 ,将偏心齿轮机构的传动比函数求解问题转化为求其动啮合线与两齿轮回转中心交点分此线段的比的问题。推导得出关于偏心齿轮机构的传动比函数的微分方程 。

高层建筑幕墙节点力学性能比较分析

基于某高层建筑幕墙的原设计为可动节点和实际施工改为不可动节点的差异,采用通用有限元软件ABAQUS计算,对比分析两种节点的静力承载性能、滞回性能、转动性能、位移变形能力等,研究探讨施工质量对可动幕墙钢结构节点的工作性能的影响。研究结果表明:将该类可动节点中长圆孔的连接钢件与幕墙钢件进行焊接,变为不可动节点后,对其静力承载性能、转动性能影响不大,但耗能能力下降11.3%,相对主体的变形能力下降82.8%。

Research on thermocouple transient thermometry technology based on LabVIEW

Based on LabVlEW platform, a distributed dynamic storage testing system is designed for measuring transient high temperature signals of explosion field. Using a highpower semiconductor laser as heat source, a traceable dynamic calibration system is established to perform dynamic calibration of thermocouples. With quantumbehaved particle swam optimization （QP-SO） algorithm on MATLAB platform, a model of dynamic compensation filter is established. It is used by LabVIEW that calls MATLAB Script nodes or COM components to accomplish the mixed programming of LabVIEW and MATLAB, further to compensate the temperature values of the thermocouples dynamically. The experimental results show that the technique that combines temperature measurement system with LabVIEW platform is applied well in testing the explosion temperature of ther mobaric weaponry and makes the compensation values closer to the actual signals.

新型弹性侧支撑长轨枕式减振轨道结构力学特性研究

新型弹性侧支撑长轨枕式减振轨道和既有轨枕式减振轨道的弹性支撑方式不同,重点对新型弹性侧支撑长轨枕式减振轨道力学特性和关键参数展开研究。在轮载作用条件下,对比分析两种减振轨道的应力分布情况,找出道床的应力集中区域及最不利位置,研究载荷施加在新型弹性侧支撑长轨枕式减振轨道不同位置时部件的应力分布特征,并对道床的减振特性加以研究。针对荷载作用于轨枕正上方时的最不利位置,进行道床承轨槽折角处的应力分布分析,以及减振轨道整体道床的配筋设计与检算。采用试验与仿真相结合的方发,研究了侧支撑式弹性垫板的厚度、空间倾斜量和材料硬度对轨枕节点动刚度和垂向最大位移的影响。研究结果表明,新型弹性侧支撑长轨枕式减振轨道道床的最大应力出现在承轨槽两侧下部靠近折角的区域,与既有轨枕式减振轨道的最大应力出现在承轨槽底部中间区域截然不同,且减振效果较显著。道床结构参考既有纵向承轨台整体式道床的配筋方案可以满足受力要求,承轨槽两侧下端折角处不会开裂。侧支撑式弹性垫板的厚度、空间倾斜量和材料硬度是影响新型弹性侧支撑长轨枕式减振轨道节点动刚度的三个关键,其中厚度和材料硬度的变化对节点动刚度的影响较大,增加侧垫厚度,降低材料硬度使节点动刚度降低,载荷-位移滞回曲线的面积增大,消耗的振动能量更多;空间倾斜量的影响较小,与节点刚度之间存在正比例变化关系;在三个关键参数的研究范围内取值可以获得满足规范要求,并具有不同减振等级的节点动刚度。

三种单节点摄动对混合值逻辑网络极限集的影响

研究了三种单节点摄动对混合值逻辑网络不动点和极限环的影响.受布尔网络单节点摄动的启发,文章首先在结构矩阵的基础上提出了混合值逻辑网络中单节点摄动的定义,并利用矩阵半张量积的方法得到了单节点摄动下混合值逻辑网络的代数形式.然后,研究了结构矩阵与状态转移矩阵间的关系,并提出了三种特殊类型的单节点摄动.最后,得到了三种单节点摄动对混合值逻辑网络的不动点及极限环影响的充分必要条件.

Para-aortic node involvement is not an independent predictor of survival after resection for pancreatic cancer

To analyze the importance of para-aortic node status in a series of patients who underwent pancreaticoduodenectomy (PD) in a single Institution. METHODSBetween January 2000 and December 2012, 151 patients underwent PD with para-aortic node dissection for pancreatic adenocarcinoma in our Institution. Patients were divided into two groups: patients with negative PALNs (PALNs-), and patients with metastatic PALNs (PALNs+). Pathologic factors, including stage, nodal status, number of positive nodes and lymph node ratio, invasion of para-aortic nodes, tumor’s grading, and radicality of resection were studied by univariate and multivariate analysis. Survival curves were constructed with Kaplan-Meier method and compared with Log-rank test: significance was considered as P < 0.05. RESULTSA total of 107 patients (74%) had nodal metastases. Median number of pathologically assessed lymph nodes was 26 (range 14-63). Twenty-five patients (16.5%) had para-aortic lymph node involvement. Thirty-three patients (23%) underwent R1 pancreatic resection. One-hundred forty-one patients recurred and died for tumor recurrence, one is alive with recurrence, and 9 are alive and free of disease. Overall survival was significantly influenced by grading (P = 0.0001), radicality of resection (P = 0.001), stage (P = 0.03), lymph node status (P = 0.04), para-aortic nodes metastases (P = 0.02). Multivariate analysis showed that grading was an independent prognostic factor for overall survival (P = 0.0001), while grading (P = 0.0001) and radicality of resection (P = 0.01) were prognostic parameters for disease-free survival. Number of metastatic nodes, node ratio, and para-aortic nodes involvement were not independent predictors of disease-free and overall survival. CONCLUSIONIn this experience, lymph node status and para-aortic node metastases were associated with poor survival at univariate analysis, but they were not independent prognostic factors.

Relay movement control for maintaining connectivity in aeronautical ad hoc networks

As a new sort of mobile ad hoc network(MANET), aeronautical ad hoc network(AANET) has fleet-moving airborne nodes(ANs) and suffers from frequent network partitioning due to the rapid-changing topology. In this work, the additional relay nodes(RNs) is employed to repair the network and maintain connectivity in AANET. As ANs move, RNs need to move as well in order to re-establish the topology as quickly as possible. The network model and problem definition are firstly given, and then an online approach for RNs' movement control is presented to make ANs achieve certain connectivity requirement during run time. By defining the minimum cost feasible moving matrix(MCFM), a fast algorithm is proposed for RNs' movement control problem. Simulations demonstrate that the proposed algorithm outperforms other control approaches in the highly-dynamic environment and is of great potential to be applied in AANET.

A Trust Management Scheme Based on Behavior Feedback for Opportunistic Networks

In the harsh environment where n ode density is sparse, the slow-moving nodes cannot effectively utilize the encountering opportunities to realize the self-organized identity authentications, and do not have the chance to join the network routing. However, considering m ost of the communications in opportunistic networks are caused by forwarding operations, there is no need to establish the complete mutual authentications for each conversation. Accordingly, a novel trust management scheme is presented based on the information of behavior feedback, in order to complement the insufficiency of identity authentications. By utilizing the certificate chains based on social attributes, the mobile nodes build the local certificate graphs gradually to realize the web of "Identity Trust" relationship. Meanwhile, the successors generate Verified Feedback Packets for each positive behavior, and consequently the "Behavior Trust" relationship is formed for slow-moving nodes. Simulation result shows that, by implementing our trust scheme, the d elivery probability and trust reconstruction ratio can be effectively improved when there are large numbers of compromised nodes, and it means that our trust management scheme can efficiently explore and filter the trust nodes for secure forwarding in opportunistic networks.

Buffer and Switch： Road-to-Road Routing Scheme for Intermittently Connected Vehicular Networks

Due to the road-constrained data delivery and highly dynamic topology of vehicle nodes in a Vehicular Ad Hoc Network (VANET), it is better to construct routing based on the road-to-road pattern than the traditional node-to-node routing pattern in MANETs. However, the challenging issue is the opportunistic forwarding at intersections. Therefore, we propose a novel routing scheme, called Buffer and Switch (BAS). In BAS, each road buffers the data packets with multiple duplicates propagation in order to provide more opportunities for packet switching at intersections. Different from conventional protocols in VANETs, the propagation of duplicates in BAS is bidirectional along the routing path. Moreover, BAS's cost is much lower than other flooding-based protocols due to its spatio-temporally controlled duplicates propagation. Different from recent researches, BAS can deliver packets not only to a stationary node, but also to the stationary or mobile nodes in a specified area. We conduct the extensive simulations to evaluate the performance of BAS based on the road map of a real city collected from Google Earth. The simulation results show that BAS can outperform the existing protocols, especially when the network resources are limited.

RSA-based Proxy Signature for Media Independent Handover

This paper proposes an Authentication Interworking Protocol （AIP） based on IEEE 802.21 Medi Independent Handover （MIH） in the heterogeneous networks. The proposed AIP with the RSA-based proxy signature reduces handover delay time and communication message overhead when the mobile node moves between the heterogeneous networks. It defines new AlP Type Length Value （AlP TLV） in MIH frame format and uses the MIH Information Server （MIHIS） for issuing signature. The MIHIS can generate a signature on behalf of the AAA server and then the signature can he used by mobile node for a pre-authentication. For low handover delay, the proposed AIP performs pre-authentication processes with MIP protocol before layer 2 handover. Also, this paper analyses the performance of the handover and compares with the non-secure MIH.

A Universal Fairness Evaluation Framework for Resource Allocation in Cloud Computing

In cloud computing,fairness is one of the most significant indicators to evaluate resource allocation algorithms,which reveals whether each user is allocated as much as that of all other users having the same bottleneck.However,how fair an allocation algorithm is remains an urgent issue.In this paper,we propose Dynamic Evaluation Framework for Fairness(DEFF),a framework to evaluate the fairness of an resource allocation algorithm.In our framework,two sub-models,Dynamic Demand Model(DDM) and Dynamic Node Model(DNM),are proposed to describe the dynamic characteristics of resource demand and the computing node number under cloud computing environment.Combining Fairness on Dominant Shares and the two sub-models above,we finally obtain DEFF.In our experiment,we adopt several typical resource allocation algorithms to prove the effectiveness on fairness evaluation by using the DEFF framework.

A sink moving scheme based on local residual energy of nodes in wireless sensor networks

In the application of periodic data-gathering in sensor networks,sensor nodes located near the sink have to forward the data received from all other nodes to the sink,which depletes their energy very quickly.A moving scheme for the sink based on local residual energy was proposed.In the scheme,the sink periodically moves to a new location with the highest stay-value defined by the average residual energy and the number of neighbors.The scheme can balance energy consumption and prevent nodes around sink from draining their energy very quickly in the networks.The simulation results show that the scheme can prolong the network lifetime by 26%-65%compared with the earlier schemes where the sink is static or moves randomly.

New Approach to Cluster Synchronization in Complex Dynamical Networks

In this paper, a distributed control strategy is proposed to make a complex dynamical network achieve cluster synchronization, which means that nodes in the same group achieve the same synchronization state, while nodes in different groups achieve different synchronization states. The local and global stability of the cluster synchronization state are analyzed. Moreover, simulation results verify the effectiveness of the new approach.

Energy-Efficient Mobile Data Collection Adopting Node Cooperation in an Underwater Acoustic Sensor Network

This paper considers an underwater acoustic sensor network with one mobile surface node to collect data from multiple underwater nodes,where the mobile destination requests retransmission from each underwater node individually employing traditional automatic-repeat-request(ARQ) protocol.We propose a practical node cooperation(NC) protocol to enhance the collection efficiency,utilizing the fact that underwater nodes can overhear the transmission of others.To reduce the source level of underwater nodes,the underwater data collection area is divided into several sub-zones,and in each sub-zone,the mobile surface node adopting the NC protocol could switch adaptively between selective relay cooperation(SRC) and dynamic network coded cooperation(DNC) .The difference of SRC and DNC lies in whether or not the selected relay node combines the local data and the data overheard from undecoded node(s) to form network coded packets in the retransmission phase.The NC protocol could also be applied across the sub-zones due to the wiretap property.In addition,we investigate the effects of different mobile collection paths,collection area division and cooperative zone design for energy saving.The numerical results showthat the proposed NC protocol can effectively save energy compared with the traditional ARQ scheme.

Smart Prediction for Seamless Mobility in F-HMIPv6 Based on Location Based Services

This paper proposed a new scheme for smooth handoff over F-HMIPv6 networks based on Location Based Services(LBS). It uses the available information about mobile node(MN) such as user mobility patterns and MN's velocity to reduce handoff latency. In the proposed scheme, the movement pattern of users plays an important role in the performance analysis. The proposed scheme develops LBS that records a number of mobility patterns based on user daily behavior, and exploits these information to reduce the handoff latency. The proposed scheme is analyzed and compared with F-HMIPv6 protocol. The results show that it improves the performance in terms of handoff latency, packet delivery cost, and location update cost. Specifically, the proposed scheme achieves the tradeoff between realizing a smooth handoff and minimizing the cost that is the demand for all customers of mobile services.

Impact of Heterogeneity on Forwarding Schemes in Opportunistic Networks

In the paper, we concentrate on the infl uence of heterogeneity on the performance of forwarding algorithms under opportunistic networks. Therefore, we first describe two different heterogeneous network models, and capture the heterogeneity which concern mobile nodes' contact dynamics under the individual models and the spatial models. Then we investigate inter-contact time is not fully follow exponential distribution and compare the performance of the delivery delay between direct forwarding protocol and three-hop forwarding protocol under three network models. We illustrate the performance of message delivery delay under the spray and wait protocol and prophet protocol from simulation results. Our simulation results show that the heterogeneity should be considered for the performance of forwarding protocols.

DTMC-based Modeling and Analysis of Obstacle Ad hoc Networks

One of the main characteristics of Ad hoc networks is node mobility, which results in constantly changing in network topologies. Consequently, the ability to forecast the future status of mobility nodes plays a key role in QOS routing. We propose a random mobility model based on discretetime Markov chain, called ODM. ODM provides a mathematical framework for calculating some parameters to show the future status of mobility nodes, for instance, the state transition probability matrix of nodes, the probability that an edge is valid, the average number of valid-edges and the probability of a request packet found a valid route. Furthermore, ODM can account for obstacle environment. The state transition probability matrix of nodes can quantify the impact of obstacles. Several theorems are given and proved by using the ODM. Simulation results show that the calculated value can forecast the future status of mobility nodes.