Effective process times for multi-server flowlines with finite buffers

An Effective Process Time (EPT) approach is proposed for the building of aggregate models to represent multi-server tandem queues with finite buffers. EPT distributions of the workstations in the flow line are measured without identifying the contributing factors. A sample path equation is used to compute the EPT realizations from arrival and departure events of lots at the respective workstations. If the amount of blocking in the line is high, the goodness of fits of the EPT distribution determines the accuracy of the EPT-based aggregate model. Otherwise, an aggregate model based on just the first two moments of the EPT distributions is sufficient to obtain accurate predictions. The approach is illustrated in an industrial case study using both simulation and analytical queueing approximations as aggregate models.     

两类排队网络的逼近研究

本文给出了两类排队网络。一类是容量有限的队列网络,我们证明了在高负荷下,标准化的队长过程弱收敛于半鞅反射的布朗运动：另一类是带有反馈的多类顾客多服务台队列网络,我们获得了队列网络中负荷过程的扩散逼近。     

Performance evaluation of two-stage multi-product kanban systems

We propose an approximate evaluation procedure for a kanban-controlled production system with two stages and multiple products. In the first stage, single-product manufacturing facilities produce items that are the input material for a single multi-product manufacturing facility in the second stage. Each manufacturing facility is controlled by a distinct kanban loop with a fixed number of kanbans. Processing and setup times are exponentially distributed, demand arrivals at the output store of the second stage are Poisson and independent for each product. If a customer's demand cannot be met from stock, the customer either waits or leaves the system, depending on the admissible number of backorders and the current number of waiting customers (partial backordering). We describe a new decomposition-based approximation method for the evaluation of such systems in steady state. We focus on the performance measures average fill rate, average fraction of served demand, and average inventory level. We report the results of several numerical tests. The results indicate that the approximation is sufficiently accurate for a large variety of systems. We also illustrate the effects of increasing the maximum number of backorders on the performance of the system.     

Performance modelling of a fault-tolerant real-time multiprocessor using stochastic Petri nets

The fault-tolerant multiprocessor (ftmp) is a bus-based multiprocessor architecture with real-time and fault-tolerance features and is used in critical aerospace applications. A preliminary performance evaluation is of crucial importance in the design of such systems. In this paper, we review stochastic Petri nets (spn) and developspn-based performance models forftmp. These performance models enable efficient computation of important performance measures such as processing power, bus contention, bus utilization, and waiting times.     

Performance evaluation and capacity planning in a metallurgical job-shop system using open queueing network models

In this paper, we apply performance evaluation and capacity allocation models to support decisions in the design (or redesign) and planning of a job-shop queueing network of a metallurgical plant. Approximate parametric decomposition methods are used to evaluate system performance measures, such as the expected work-in-process (WIP) and production leadtimes. Based on these methods, optimisation models are then applied for the allocation (or reallocation) of capacity to the stations of the job-shop network. These models are also used to generate approximate trade-off curves between capacity investment and WIP or leadtime, which are valuable for a production manager to estimate how much capacity should be allocated to the stations to reach some targeted performance measures. These curves are also useful for the sensitivity analysis of the solutions to changes in the input parameters, such as the variability of the product demands, the mix of the production and the throughput rate of the network.     

Solving coupled task assignment and capacity planning problems for a job shop by using a concurrent genetic algorithm

The problems of task assignment and capacity planning of manufacturing systems have been researched for many years. However, in the existing literature, these two types of problems are researched independently. Namely, when solving the task assignment problem, it is usually assumed that the production capacity of the manufacturing systems has been determined. On the other hand, when solving the capacity planning problem, the production tasks assigned to the workstations in the manufacturing system have also been determined. Actually, the task assignment problem and the capacity planning problem are coupled with each other. When we assign production tasks to workstations, production capacities of these workstations should be regulated so that they are enough for completing the tasks. At the same time, when planning the production capacity, we must know what production tasks are assigned to what workstations. This research focuses on the coupling relations between the two problems for a closed job shop, in which the total work-in-process (WIP) is assumed to be constant. The objective of the task assignment problem is to balance the workloads of the workstations and the objectives of the capacity planning problem are maximising the throughput and minimising total costs of machine purchasing and WIP inventory. We construct the fundamental system architecture for controlling the two coupled optimisation processes, and propose a concurrent genetic algorithm (CGA) to solve the two coupled optimisation problems. The influences of the decision variables of one problem on the objective function of the other problem are taken into consideration when the fitness functions of the CGA are constructed. Numerical experiments are done to verify the effectiveness of the algorithm.     

Decomposition without aggregation for performance approximation in queueing network models of semiconductor manufacturing

Accurate and speedy forecasts of production cycle time are key components that support the operation of modern semiconductor wafer fabricators. Estimates of cycle time can be obtained via simulation, but such an approach, though common, requires significant computational investment and model maintenance. Queueing network models and approximations for their performance can provide a viable alternative. As modern semiconductor manufacturing systems exhibit largely reentrant product routing, but contain essential probabilistic routes (for metrology and rework), prior mean cycle time approximation methods are not well suited to the system structure. In this paper, we extend the decomposition without aggregation (DWOA) approach – which is tailored to systems with deterministic routing – to allow for the existence of probabilistic paths. Numerical and simulation studies are conducted with numerous practically inspired datasets to assess the quality of the resulting mean cycle time approximations. The results reveal that our approach outperforms the existing mean cycle time approximations on datasets inspired by the semiconductor industry MIMAC benchmark datasets. For example, in MIMAC dataset 1, our mean cycle time approximations exhibit an average of 10.33% error compared to 18.82% error for existing approaches.     

System performance analysis of flexible flow shop with match processing constraint

Blocking makes the analytical modelling of open queuing networks with finite buffers intractable because the product-form solutions are unavailable. In this paper, about mould manufacturing, a four-stage flexible flow shop with match processing constraint is first modelled as an open queuing network with finite buffers. According to the characteristics of the matching node, the inter-arrival time distributions of parts arriving at the nodes are assumed to be exponential or general. Next, based on approximation of queuing theory, the Decomposition of State Space Method and the Generalized Expansion Method are developed for system performance evaluation. Then, experiments to assess the accuracy of the proposed methods are reported by comparing the analytical results with simulations. Finally, a case of a real-life production system of mould manufacturing is studied to show the application of the proposed methods. The results of experiments reveal that the proposed methods are feasible and effective for system performance evaluation and they can even solve large-size practical problems in a reasonable time. The results in this paper can provide a basis for system design or resource planning, to solve buffer allocation problems and capacity configuration problems.     

纸浆模塑托盘构型三维设计及支腿结构 CAE 分析

运用 Pro/ E 软件对纸浆模塑托盘构型进行了三维设计,完成了托盘支腿和面板的零部件建模及相应的装配。 运用 ABAQUS 有限元分析软件对托盘支腿结构进行了强度计算,模拟分析了纸浆模塑托盘支腿在压缩载荷作用下的弹塑性变形,得到了模型受载变形全过程的载荷-位移曲线,从而确定了支腿的承载能力。     

Knowledge Networks and Innovative Performance in an Industrial District: The Case of a Footwear District in the South of Italy

The traditional district literature tends to assume that: (1) the competitiveness of firms depends on external sources of knowledge; (2) all firms in a district benefit from knowledge externalities; (3) relying on external knowledge relationships necessarily means these are confined to the district area. Our case study of the Barletta footwear district in the South of Italy suggests otherwise. Based on social network analysis, we demonstrate that the local knowledge network is quite weak and unevenly distributed among the local firms. A strong local network position of a firm tended to increase their innovative performance, and so did their connectivity to extra-local firms. So, it mattered being connected either locally or non-locally: being co-located was surely not enough. Having a high absorptive capacity seemed to raise only indirectly, through non-local relationships, the innovative performance of firms.     

基于复合仿真技术的武器装备工业造型设计方法

目的 将仿真技术作为武器装备工业造型设计中的重要手段,使国防武器装备在满足隐身性能和结构强度的要求下,提升装备工业造型的视觉气质.方法 首先依据隐身理论提出武器装备造型的隐身设计策略,然后利用隐身仿真技术与有限元仿真技术对武器装备工业造型方案进行隐身性分析、静力学分析、动力学分析以选出最优设计方案,并找到方案中的结构薄弱部位,最后通过结构优化方法对其薄弱部位进行造型优化设计.结论 以舰载雷达天线座为例验证了基于隐身分析与有限元分析的工业造型设计方法可应用在武器装备领域.     

多位姿焊接焊缝成形尺寸的神经网络建模

根据焊缝成形尺寸受焊件位姿、焊接条件和焊接规范等多种因素的影响，利用人工神经网络－ＢＰ网络的特性，探讨了建立这种多输入多输出非线性系统静态模型的方法，并通过一个实例检验了这种方法是有效的，并具有较高的精度和速度。     

航空电子总线性能分析

以排队论为工具,建立了航空电子综合化网络系统的模型,对以“MIL-STD-1553B”数据传输总线为互联网络接口的航空电子综合化系统的时间性能指标进行了定量的分析和研究,对航空电子综合化网络系统的结构和动态特性进行了描述、分析。