剪力和弯矩共同作用下钢筋混凝土结构的框架单元模型分析

模拟剪力和弯矩共同作用下钢筋混凝土结构的响应,包括发生在开裂后和极限荷载范围时的各项性能。目前的2维(平面应力和平面应变)和3维非线性有限元方程模拟上述结构响应的成本很高,而且不适用于日常工程实践。提出1种新型框架单元模型,结合高效的带梁-柱单元的平面内全耦合剪切-正常节段模型,适用于已得到试验结果验证的结构分析。标准剪切下的应力和应变假定为由一系列多项式形函数组成;每一个应力分布受内部材料状况影响。框架结构的非线性分析采用的是广义矩阵法,利用文献资料验证该模型,通过试验验证剪切应变对结构响应的影响程度。试验结果和模型分析结果吻合较好。该模型得到的混凝土和钢筋的位移、应变和应力及不同的破坏类型,比之前模型的分析结果更精确。     

Flexible asymmetric spinning

Metal spinning is used to form shell components, but is constrained by two features: it can only produce axisymmetric shapes; it requires a dedicated mandrel for each product. Examination of pressures between product and mandrel revealed that contact is limited to three well defined areas. This suggested that the full mandrel could be replaced by three rollers. Furthermore, if these rollers could be controlled, they could represent any symmetric or asymmetric mandrel. A seven-axis machine has been designed, manufactured, and used to spin trial parts. The machine design is described, and preliminary results give an indicator of process capability.     

绿色数据中心的“最后50m”问题

从提高数据中心配电系统的可用性、节能性以及灵活性的角度．探讨了提高数据中心机房内配电效能的新方法，对以往采用传统解决方案带来的技术和管理上的问题给出了机房配电解决方案。     

弹性连杆机构的动态稳定性研究

研究了一般形式的弹性连杆机构的动力稳定性问题，在忽略结构阻尼的情况下，从理论上研究了低价临界转速的分布规律，给出了低价临界转速与机构一个运动周期固有频率平均值的显式关系表达式。用这一关系式求得的低价临界转速和数值方法得到的识别结果进行了比较，说明了本文方法的有效性。     

Metrics for evaluating the forest biorefinery supply chain performance

For sustainable decision-making regarding biorefinery strategies, different criteria, i.e. economic, environmental, social, should be considered. However, the economic criteria typically do not consider market volatility, whereas today's market involves price and demand volatilities. Biorefinery strategies must be flexible to be robust to market volatility. Therefore, relevant metrics must be developed to quantify the system's performance against volatility. This paper presents metrics of flexibility and robustness which analyze the performance of the supply chain in a dynamic environment, providing additional information along with economic metrics. In this paper, the link between the two metrics, and how profitability and robustness change with flexibility are discussed. The results reveal that, although profitability does not always increase with more flexibility and there is an optimum level of flexibility, the system's robustness is improved by increasing flexibility. Moreover, a “conditional value-at-risk” parameter is introduced to show what patterns of sale lead to highest profit and robustnestness.     

Association-Based Active Access Control models with balanced scalability and flexibility

In existing Active Access Control (AAC) models, the scalability and flexibility of security policy specification should be well balanced, especially: (1) authorizations to plenty of tasks should be simplified; (2) team workflows should be enabled; (3) fine-grained constraints should be enforced. To address this issue, a family of Association-Based Active Access Control (ABAAC) models is proposed. In the minimal model ABAAC₀, users are assigned to roles while permissions are assigned to task-role associations. In a workflow case, to execute such an association some users assigned to its component role will be allocated. The association's assigned permissions can be performed by them during the task is running in the case. In ABAAC₁, a generalized association is employed to extract common authorizations from multiple associations. In ABAAC₂, a fine-grained separation of duty (SoD) is enforced among associations. In the maximal model ABAAC₃, all these features are integrated, and similar constraints can be specified more concisely. Using a software workflow, case validation is performed. Comparison with a representative association based AAC model and the most scalable AAC model so far indicates that: (1) enough scalability is achieved; (2) without decomposition of a task, different permissions can be authorized to multiple roles in it; (3) separation of more fine-grained duties than roles and tasks can be enforced.     

Oscillator analogy for modelling the manufacturing systems dynamics

The purpose of this paper is to present an approach of modelling and analysis of the dynamic behaviour of manufacturing systems. The manufacturing system is considered to be responding to an excitation, namely a demand that varies over time, by producing a number of parts over time. This resembles a mechanical system that displaces its mass responding to a varying input force. Based on this analogy, this paper establishes a manufacturing system's modelling method. A system identification technique is used for deriving inertia, damping and stiffness from the manufacturing system's response to different excitations. Based on these attributes, the response of a manufacturing system to any given input can be estimated. Furthermore, a definition for assessing manufacturing flexibility, based on this approach, is being discussed.     

Organizing a virtual manufacturing enterprise: an analytic network process based approach for enterprise flexibility

Virtual manufacturing is a dynamic enterprise structure that will enable future competitiveness in the fast changing business environment. This is made possible through quick IT based integration of flexible and core competent business entities capable of providing value-added product and services. Flexibility elements represent change capabilities of enterprise wide processes and resources in time and cost dimensions. Value chain considerations require synergy among the participating flexible resources. Also decision information synchronization delays need to be managed so that other entity flow processes in the enterprise remain well synchronized. This may require a capability of dynamic changes in flexible structures leading to effective virtual enterprises. There is a need to develop suitable enterprise architectures for virtual enterprises that offer an increasing focus on agility. Infrastructure support for integration of flexible capability to attain synergy among resources is necessary for enterprise agility. We conceptualize virtual manufacturing (VM) as an integrating infrastructure of flexible resources made possible through alliance of enterprises that are individually core competent in specific business function. Such a VM can attain the required cost, flexibility and responsiveness characteristics in its operations to provide solution to the demanding customer in a global dynamic market. Modelling frameworks depicting these composite flexibility states have complex and tacit interrelationship with plural business goals. Analytical network process (ANP) has been used to model the interrelationship of different decision domains with a view to prioritize enterprise wide flexibility dimensions. The ANP modelling framework takes into consideration the interdependency among sub-strategies. We demonstrate through sensitivity analysis that strategic shift is required to accommodate changes due to dynamic condition in the business environment.     

滑板砖柔性检测系统

本文介绍一种滑板砖柔性检测系统。它能胜于节流开关的滑板砖平整度、厚度的自动检测。本文章给出总体方案，测量方法，原理和主要功能。     

关于提高组合机床利用率的实践

介绍大幅度提高组合机床利用率的探索与尝试。经实践证明，所研制的组合机床结构新颖，具有柔性功能，可一机多用，适合我厂的实际情况，收到了显的经济效益。