STOCHASTIC OBJECT-ORIENTED PETRI NETS (SOPNS) AND ITS APPLICATION IN MODELING OF MANUFACTURING SYSTEM RELIABILITY

Object-oriented Petri nets (OPNs) is extended into stochastic object-oriented Petri nets (SOPNs) by associating the OPN of an object with stochastic transitions and introducing stochastic places. The stochastic transition of the SOPNs of a production resources can be used to model its reliability, while the SOPN of a production resource can describe its performance with reliability considered. The SOPN model of a case production system is built to illustrate the relationship between the system's performances and the failures of individual production resources.

A Simulation Engine for Stochastic Timed Petri Nets and Application to Emergency Healthcare Systems

In many service delivery systems,the quantity of available resources is often a decisive factor of service quality.Resources can be personnel,offices,devices,supplies,and so on,depending on the nature of the services a system provides.Although service computing has been an active research topic for decades,general approaches that assess the impact of resource provisioning on service quality matrices in a rigorous way remain to be seen.Petri nets have been a popular formalism for modeling systems exhibiting behaviors of competition and concurrency for almost a half century.Stochastic timed Petri nets(STPN),an extension to regular Petri nets,are a powerful tool for system performance evaluation.However,we did not find any single existing STPN software tool that supports all timed transition firing policies and server types,not to mention resource provisioning and requirement analysis.This paper presents a generic and resource oriented STPN simulation engine that provides all critical features necessary for the analysis of service delivery system quality vs.resource provisioning.The power of the simulation system is illustrated by an application to emergency health care systems.

Modeling of Testability Requirement Based on Generalized Stochastic Petri Nets

Testability design is an effective way to realize the fault detection and isolation.Its important step is to determine testability figures of merits(TFOM).Firstly,some influence factors for TFOMs are analyzed,such as the processes of system operation,maintenance and support,fault detection and isolation and so on.Secondly,a testability requirement analysis model is built based on generalized stochastic Petri net(GSPN).Then,the system's reachable states are analyzed based on the model,a Markov chain isomorphic with Petri net is constructed,a state transition matrix is created and the system's steady state probability is obtained.The relationship between the steady state availability and testability parameters can be revealed and reasoned.Finally,an example shows that the proposed method can determine TFOM,such as fault detection rate and fault isolation rate,effectively and reasonably.

Using Stochastic Colored Petri nets for Designing Multi-Purpose Plants

Designing of a multi-purpose plant as one of the well-known manufacturing systems is more challenging than other manufacturing systems. This paper applies a stochastic colored Petri net (CPN) to design and analyze multi-purpose plants. A simple approach is proposed to determine the utilization of shared resources and to reduce the equipment’s idle times. Three scenarios are presented to describe the proposed model. Generally, according to desire of a decision maker, different scenarios can be considered in the model to achieve to the expected design or plant configuration. The main characteristics of the proposed model are flexibility, the easiness of practical application and the simulation of the model in an easy way.

Generalized stochastic Petri nets based models for performance analysis of communication networks of IEC61850 system

In this paper, data streams are classified into four types conforming to a standardized infrastructure of communication networks for a substation automation system （SAS） based on IEC61850 system. The data exchanged on the net are demonstrated to be stochastic according to investigation on the Ethemet communication principles. Four generalized stochastic Petri nets （GSPN） based models for performance analysis of communication networks of IEC61850 system are developed based on the three-level structure of SAS, different time requirements of the four data streams and different networks topology for different voltage level. The GSPN-based model associated with immediate and exponential transitions is proven to be theoretically isomorphic with Markov chain; hence we apply the mathematic methods of performance evaluation contained in Markov chain to the GSPN models proposed. The computer simulation of the model including only sample value data streams shows that it can meet performance evaluation needs of communication networks of IEC61850 system. Further researches should be focused on the pe^ormance of the other three models to explain clear how those different data streams are interrelated to and interact on each other.

Research on Production Process Control Method Combined Stochastic Process Algebra and Stochastic Petri Nets

A hierarchical closed-loop production control scheme integrating scheduling,control and performance evaluation is discussed.Firstly,the production process is divided into two main hierarchies:the lower level is the physical operation level and the upper one is the management level.Secondly,the schedule template for the management level and the activity template for the physical operation level are constructed separately,the tasks in the schedule have the ability to make partial decisions,and the per- formance parameters are introduced into activity template.Thirdly,the two levels use different model representations:stochastic process algebra for the management level whose output is the control commands and stochastic Petri net for the physical operation lev- el which is the execution of the control commands.Then,the integration of the two levels is the control commands mapping into the lower physical operations and the responses feeding back to the upper decision-making that are defined by some transition functions. Under the proposed scheme,the production process control of a flexible assembly is exemplified.It is concluded that the process con- trol model has partial ability to make decision on-line for uncertain and dynamic environments and facilitates reasoning about the be- haviors of the process control,and performance evaluation can be done online for real-time scheduling to ensure the global optimiza- tion.

Modeling and Analysis of Logistics System Based on Stochastic Petri Net under Supply Chain Circumstances

In order to describe the impacts of adjustment ability of logistics system on the profit and cost of logistics system, we constructed a model of logistics system based on stochastic Petri net （ SPN）, and proposed a theorem for the adjustment ability of logistics system under supply chain circumstances on condition that the payoff of supply chain is a steadily increasing process. Then we put forward that a sequence of MGF （ moment generating function ） of out-of-goods risk process for logistics system is a martingale. The model we proposed can overcome shortcomings of the previous ones that can not describe the characteristics of the adjustment ability of logistics system. The results of simulation experiments are consistent with theoretical analysis.

Survivability analysis of wireless Ad hoc network using stochastic reward nets

To provide services in presence of failures or attacks in a timely manner, the network survivability was analyzed. Based on stochastic Petri nets, we put forward an effective model for ad hoe network and adopt a two-phase approach consisting of the steady-state availability analysis and the system transient performance analysis, then provide a quantitative approach for analysis of the network survivability. The results show that the proposed model is useful for the design and evaluation of the wireless ad hoc network.

Modeling method of hybrid systems using extended Petrinets

In order to model effectively hybrid systems,a new modeling method of extended Petri nets,which is called extended object-orient hybrid Petri net （EOHPN）,is proposed.To deal with the complexity of hybrid systems, object-oriented abstraction mechanisms such as encapsulation and classifications are merged into EOHPN models.To combine the continuous part and discrete part of hybrid systems and to reduce the complexity of hybrid systems,a hybrid Petri net is introduced and extended with object-oriented modeling technology.Development of object models is suggested on the basis of the defined EOHPN.Finally, an application-oriented case is presented to illustrate that how the proposed EOHPN is used to model hybrid systems.The resulting model validates that the EOHPNs can deal with the modeling complexity of hybrid systems.

基于随机Petri网的突发火灾应急预案流程化研究

为提高突发火灾的应急响应效率,根据突发火灾的应急响应流程构建了基于随机Petri网(SPN)的仿真模型,通过仿真计算获取了该模型的状态可达集,由可达集构建与模型同构的马尔可夫链对模型进行计算分析,得到了突发火灾SPN模型所有可达状态的稳态概率,利用库所繁忙率、变迁利用率2个指标对模型进行性能分析。结果表明,突发火灾应急响应流程中应急专家、救援人员、救援物资3个业务单元的繁忙率高达35.36%、39.37%、38.25%,展开应急救援耗时在流程总耗时中占比高达27.74%,制定突发火灾应急预案时需着重对以上业务单元及流程环节进行优化,从而优化应急资源调配,提高应急响应整体效率。

基于随机Petri网的民机审定试飞实施流程建模与分析

审定试飞是民用飞机获取型号合格证书的重要活动,具有高成本、高风险的特点。研究审定试飞的实施流程有利于推动试飞工作有序进行,进而缩短试飞周期及降低试飞成本。目前对试飞流程的研究局限于流程描述与定性分析,缺乏对试飞流程的形式化建模与性能分析,无法检验流程中的关键环节。为解决上述问题,文中研究了审定试飞3个阶段的实施流程,并利用随机Petri网构建了该流程的仿真模型;通过建立与该模型同构的马尔可夫链,对实施流程进行了性能分析,识别出了流程中耗时较多的关键环节,进而分析了关键环节的实施速率对流程平均运行时间的影响。最后通过一个案例验证了模型与方法的可行性。结果表明,制造符合性检查环节与试飞数据处理环节是流程中耗时较多的关键环节,应将其作为流程优化的重点,同时提升上述两个关键环节的实施速率相比提高单环节速率,成本更低且流程运行效率提升幅度更大。

基于petri网的森林火灾应急救援流程网络模型及时效研究

为了对森林火灾的应急救援流程进行优化,以提升应急救援效率,依据森林火灾应急救援预案、有关规定与实际救援案例,从信息传递的角度对森林火灾应急救援流程进行了直观描述。基于petri网相关理论,运用PIPEv5.2.0,构建了森林火灾应急救援随机petri网模型与其同构马尔可夫链,在模型有界、活性、安全且可达的基础上,通过确定模型的库所繁忙率、变迁利用率、平均延迟时间,得到如下结果:①森林火灾应急救援活动早期的灾情信息多且复杂,随着森林火灾的发展呈现动态变化,火灾发生后如何高效地获取过火面积、火线长度、风向、风力、植被载量以及地形等关键信息是优化的重点。②避免信息堆积,基于火灾规模、强度、形式、火头方向等重要任务信息变量,实现实时快速决策、动态处置,是保证森林火灾应急救援活动的时效性的关键。

基于随机颜色Petri网的食物网能量流动建模与分析

为更好地描述能量流动问题,对生物变化做出及时的预测。以食物网中能量流动为例,提出一种随机颜色Petri网模型及可达性分析方法。在颜色Petri网的基础之上针对token引入随机函数和约束函数等属性用来描述token的传递特性;基于随机颜色Petri网提出可达图构造算法和随机概率矩阵;将随机颜色Petri网应用到食物网的能量流动过程中,对能量流动过程进行分析并对传递的物质进行分类,验证该模型的有效性。

A modeling method of semiconductor fabrication flows with extended knowledge hybrid Petri nets

A modeling method of extended knowledge hybrid Petri nets （EKHPNs）, incorporating object-oriented methods into hybrid Petri nets （HPNs）, was presented and used for the representation ~d modeling of semiconductor wafer fabrication flows. To model the discrete and continuous parts of a complex semiconductor wafer fabrication flow, the HPNs were introduced into the EKHPNs. Object-oriented methods were combined into the EKHPNs for coping with the complexity of the fabrication flow. Knowledge anno- tations were introduced to solve input and output conflicts of the EKHPNs. Finally, to demonstrate the validity of the EKHPN method, a real semiconductor wafer fabrication case was used to illustrate the model- ing procedure. The modeling results indicate that the proposed method can be used to model a complex semiconductor wafer fabrication flow expediently.

基于广义随机Petri网的装备战场抢修建模与分析

装备战场抢修是装备保障工作的重要内容,传统的装备战场抢修已经不满足现代条件下作战需要。为提高信息化条件下装备战场抢修的决策科学性和决策效率,运用广义随机Petri网对装备战场抢修过程进行建模分析,通过不变量判断模型的有效性,并根据广义随机Petri网和马尔可夫链同构特性求解模型主要性能指标。最后通过实例分析说明,该方法可以有效求解装备战场抢修的主要性能指标,验证了模型的有效性和合理性,同时也为装备战场抢修决策提供了一定的参考依据。

基于随机Petri网的铁路货运整车卸车流程优化

基于随机Petri网对铁路货运整车卸车流程进行建模,采用马尔科夫方法分析系统性能。在此基础上对现行铁路货运整车卸车流程进行诊断,得出既有铁路货运整车卸车流程存在着作业流程繁琐、智能化水平低、信息传递不畅、作业标准有待加强等问题;在此基础上,基于“提质增效”与“协调有序”两大优化准则对铁路货运整车卸车流程进行优化分析,结果表明:优化后整车卸车随机Petri网系统的响应时间以及吞吐能力均有所提高,系统的平均延时由优化前的414.92min变化为优化后的378.83min,缩短了36.09min,降低8.70%,卸车流程优化措施是有效的,优化后节点的吞吐与响应能力增强,卸车流程效率得到了大大提升。本研究旨在提高铁路货物运输组织效率,为持续深入的铁路货运改革提供参考。

基于Petri网的危险货物道路运输应急协同处置流程建模

为有效提高危险货物道路运输突发事件应急处置效率,基于随机Petri网构建了危险货物道路运输应急协同处置流程模型;通过同构马尔可夫链分析该流程模型的时间等性能,以各标识稳定概率的累计变化值为切入点,确定应急处置流程中的关键环节,并通过边际效益优化实施速率。研究结果表明,构建的危险货物道路运输应急协同处置流程模型能量化确定应急处置的关键点,可有效提高多主体应急联动处置效率。

JIT生产系统PetriNet建模与仿真研究

激烈的全球市场竞争要求企业对动态需求具有较强的反应能力,同时对自身生产系统的随机特性有较强的把握和控制。制造企业倾向于采用JIT看板生产理念来改善企业的QCD。这里首先建立JIT看板生产系统基本流程的PetriNet模型,然后运用WITNESS建立了一个单产品、多阶段、混联的JIT生产系统仿真模型,通过仿真实验,研究和分析了需求和生产两方面的随机变量在不同的组合下,其变异系数对系统绩效指标的影响。

CERNET的Petri网建模及性能指标评估

构造了ＣＥＲＮＥＴ的性能指标评估Ｐｅｔｒｉ网模型，并据现有的统计资料得出了模型的具体参数．提出了一种计数禁止弧的新概念，并给出了它的一系列基本性质．最后，通过对Ｐｅｔｒｉ网模型的求解，给出了未来中国教育科研网的几个重要的性能指标．通过对性能曲线的分析。

基于随机Petri网的多式联运系统致脆因素影响机理研究

多式联运系统运行过程复杂,其运行效能易受多重致脆因素的影响。在分析多式联运系统特征的基础上,提炼其关键致脆因素,并构建多式联运系统致脆因素影响机理的概念模型。通过构建基于概念模型的随机Petri网模型及其同构的马尔可夫链,并引入随机时间变量,刻画不同致脆因素影响下的多式联运系统动态演化过程。最后,以我国南方某生鲜农产品公司的“公-铁-水”冷链物流多式联运项目为例,通过情景仿真,分析不同致脆因素对该项目运作过程的影响。研究发现:征信调查利弊并存,应合理控制其深度与广度;其次应充分考虑货物的实际需求而非仅仅坚持经营人偏好,制定完善的预防措施和政策激励是保障多式联运高效运行的基本要求。