一种基于Petri网的工程管理模型

提出了用Petri网建立工程管理模型.为了适应在工程管理中的应用,对Petri网理论进行了扩充,提出了判定库所的概念,设计了托肯移动的规则,使用优先矩阵描述了托肯的移动.     

非肯定型工程问题的 Petri 网方法

一项工程一般都包含着多道工序.如果知道了各工序的工期以及工序之间的衔接关系,就可以画出工程的流程图.从工序流程图可以求出完成这项工程的最短时间和每个工序的最晚必须开工时间,并确定主工序线.这样便于统筹安排,提高施工效率.这就是统筹方法.我们提出解决这类工程问题的另一种方法:Petri 网方法.在[2]中我们定义了一类含时间因素的 Petri 网,并用这种网及其可达标识图对肯定型工程问题进行了分析和讨论.本文作为[2]的续篇,我们用 Petri 网方法讨论和分析非肯定型工程问题.     

K(0,1)-TPN方法在三防系统安全性分析应用

三防系统软件是坦克装甲车辆防护系统中的安全关键软件,对其安全性分析是十分必要的.定义了k(0,1)—时间Petri网(K(0,1)-TPN),该网是对时间Petri网的一种扩展,对于输入不同、运行过程相同及其控制机构相同或不同的系统分析建模具有普遍的应用价值.应用k(0,1)—时间Petri网及其动态的运行规则,并采用合成技术建立起了三防系统的模型.通过对运行时序、状态转移等的分析,得出了若干个三防软件系统存在的危险状态,并对软件及其系统的修改提出了建议.     

基于模糊随机系统动力学模型的矿区环境质量评价

为了解决矿区环境质量评价问题,将模糊Petri网(FPN)和随机Petri网(SPN)相结合,并扩展成具有状态转移计算功能和可信度计算功能的模糊随机函数函数Petri网(FSFPN);然后,将FSFPN与系统动力学(SD)模型相结合,提出了一种FSFPN-SD模型,该模型很好地继承了SD模型的全部特征,同时又将FSFPN网的全部特征融入到FSFPN-SD模型中。FSFPN-SD模型的评价过程是基于被评价系统的自主动态演变而进行的,从而避开了因选择不合理评价指标而带来的评价结果不准确的困扰;基于Petri网的评价模型图中的节点具有明确的物理含义且具有运行状态表示,节点之间具有明确的因果关联关系,该特点可方便于评价模型的构建。应用结果表明,FSFPN-SD模型能获得评价结论及其可信度、能获得影响评价结论的关键因果路径、能获得评价结果与各影响因素之间的相关性变化曲线。根据这些信息,可以制定具有针对性的控制对策。     

基于随机Petri网的震后次生灾害演化模型研究

针对震后次生灾害的演化问题,本文采用多案例分析方法提取地震及其次生灾害事件的属性,从属性层次按照“事件类型、关键属性、从属属性、环境属性和危害评估属性”对其进行结构化描述,分析震后次生灾害事件的属性特征,绘出了震后次生灾害演化Petri网模型。在此基础上,以渐变型次生灾害事件——震后瘟疫为例,根据随机Petri网与马尔科夫链的同构关系,构建了震后瘟疫事件演化系统随机Petri网模型。最后,通过马尔科夫链及相关数学方法对震后瘟疫事件演化系统进行了评估,分析其中的均衡状态及其变动规律,验证了模型的有效性,为应对地震次生灾害事件提供科学的应急决策支持。     

基于Petri Net的需求流动网组建模型及其稳定性分析

针对供应链概念不足,提出需求流动网概念,并论述了需求流动网概念模型,运用Petri网理论建立需求流动网模型,并对模型进行了分析,随后在分析需求流动网稳定性内涵的基础上,进一步运用Petri网理论分析了需求流动网稳定性,并最终得出了相应结论.     

基于面向对象Petri网的业务流程建模方法研究

在信息系统开发过程中，信息系统建模的方法和模型的表示问题十分重要。本通过对面向对象Petri网的讨论，阐述了利用面向对象Petri网建立业务流程模型的基本问题，并给出了模型的计算机表示和存储方法。     

出现网的同步距离

六十年代初期,C.A.Petri(西德)开始用有两类节点的网模拟系统.这种网后来被称为Petri网,廿多年来已得到广泛应用.七十年代初Petri和他的同事们着手研究通用网理论(General Net Theory),八十年代初通用网论的文献开始大批出现,其应用领域包括物理、化学、工程、法律、逻辑、计算机科学等三十几个学科,并将对数学本身的发展产生积极的影响.     

有界Petri网的进程表达式

提出了有界Petri网的进程表达式的概念,并给出了求有界Petri网进程表达式的一个算法.一个有界Petri网的进程表达式是以该网的基本子进程集为字母表的正规表达式.它所表示的正规集是该Petri网全体满进程的集合.所谓满进程,是指每个s切对应着Petri网的一个可达标识的那类进程.     

基于行为分析的AS/RS有色赋时Petri网模型研究

为了研究如何提高AS/RS系统的性能,有必要构建其模型.提出了库所双重着色的有色赋时Petri网方法,分析了AS/RS系统活动资源的行为特点和要求,并详细阐述了使用有色赋时Petri网分别构建这些行为模型的过程,从而实现整个AS/RS系统框架模型.采用visual c++软件仿真表明,该方法在构建面向资源的离散系统模型时是有效的.     

Removing dead transitions in timed-arc Petri nets

Timed-arc Petri nets (TAPNs) are a timed extension of Petri nets where tokens are assigned an age indicating the time elapsed from its creation, and PT-arcs (place to transition arcs) are labelled with time intervals that are used to restrict the age of the tokens that can be used to fire the adjacent transition. This is a rather pathological model, as reachability is undecidable, whereas some other known properties of Petri nets, like boundedness, coverability and even termination, are decidable. This article focuses on the problem of detecting dead transitions, i.e. transitions that can be removed from the model since they can never become enabled. We prove that this problem is decidable for TAPNs with natural times, and we present an algorithm that can be used to find dead transitions in the particular case of 1-safe TAPNs.     

Decomposing Timed Petri Net Models of Open Queueing Networks

This paper develops a Petri net-based decomposition approach to model and perform steady-state analysis of open queueing networks with multi-class customers. For each customer class we assume deterministic routeing and different service time distribution. The current decomposition may also consider equipment failures, defective units that have to be re-worked and on-line preparations (to switch from one mix of customers to another) as additional customer classes. In contrast to most of the published works on timed Petri nets, their present use is marked by input flows, originating from external sources. A simple method, directly derived from the timed Petri nets theories, is used for calculating the expected utilization of each server and eventually the maximal productivity of the system for the given deterministic routeing. An important application of the model is in validating discrete-event non-terminating simulation models.     

Timed Petri nets and prediction to improve the Chandy–Misra conservative-distributed simulation

The main contribution of this paper shows that distributed simulation of timed Petri nets (TPN) can take advantage of their structure to obtain a significant lookahead which is usually difficult to compute with other models. In this paper, we introduce a conservative-distributed simulation with a reduced number of control messages and without deadlock resolution. This approach is based on a part of optimism computed on the prediction time each logical process can determine for its advancement. Obviously this prediction time must be computed easily according to the structure of the simulated logical process. Timed Petri nets meet these requirements and we use their structure to evaluate the depth of the prediction. In conservative-distributed simulation, it is known that the deeper the prediction, the better the efficiency of the simulation. We present a method we have devised based on channel time prediction. We compare its performance to the Chandy–Misra method and to some related Petri nets approaches (Chiola). Experiments carried out on Sun stations show that there is more parallelism and a reduced number of null messages in the cases of deadlock avoidance. Moreover, considering deadlock detection and resolution technique we observe that in many cases no deadlock occurs with less control messages.     

A Petri net approach to the modelling and analysis of flexible manufacturing systems

In this paper we present an approach for modelling and analyzing flexible manufacturing systems (FMSs) using Petri nets. In this approach, we first build a Petri net model (PNM) of the given FMS in a bottom-up fashion and then analyze important qualitative aspects of FMS behaviour such as existence/absence of deadlocks and buffer overflows. The basis for our approach is a theorem we state and prove for computing the invariants of the union of a finite number of Petri nets when the invariants of the individual nets are known. We illustrate our approach using two typical manufacturing systems: an automated transfer line and a simple FMS.A shorter version of this paper was presented at the 1st ORSA/TIMS Special Interest Conference on FMSs, University of Michigan, Ann Arbor, August 1984.     

A comprehensive approach of planning and scheduling based on petri nets

The main results available on the use of black-and-white Petri nets for modelling, planning and scheduling manufacturing systems are presented. In the first part of the paper, the basics of Petri nets necessary to understand the subsequent presentation are introduced. Particular attention is paid to event graphs, a particular type of Petri nets used for modelling and evaluating ratio-driven systems. The second part of the paper is devoted to ratio-driven systems, their modelling and their scheduling. Job-shops, assembly systems, and KANBAN systems are used to illustrate this section. Finally, the general case is investigated of manufacturing systems subject to changing demands. An approach based on conflict-free Petri nets with input and output transitions is proposed for planning and scheduling this type of system.     

Modeling job shop scheduling with batches and setup times by timed Petri nets

Batch and setup times are two important factors in practical job shop scheduling. This paper proposes a method to model job shop scheduling problems including batches and anticipatory sequence-dependent setup times by timed Petri nets. The general modeling method is formally presented. The free choice property of the model is proved. A case study extracted from practical scheduling is given to show the feasibility of the modeling method. Comparison with some previous work shows that our model is more compact and effective in finding the best solution.