The Impact of Petri Nets on System-of-Systems Engineering

The successful engineering of a large-scale system-of-systems project towards deterministic behaviour depends on integrating autonomous components using international communications standards in accordance with dynamic requirements. To-date, their engineering has been unsuccessful: no combination of top-down and bottom-up engineering perspectives is adopted, and information exchange protocol and interfaces between components are not being precisely specified. Various approaches such as modelling, and architecture frameworks make positive contributions to system-of-systems specification but their successful implementation is still a problem. One of the most popular modelling notations available for specifying systems, UML, is intuitive and graphical but also ambiguous and imprecise. Supplying a range of diagrams to represent a system under development, UML lacks simulation and exhaustive verification capability. This shortfall in UML has received little attention in the context of system-of-systems and there are two major research issues: 1. Where the dynamic, behavioural diagrams of UML can and cannot be used to model and analyse system-of-systems 2. Determining how Petri nets can be used to improve the specification and analysis of the dynamic model of a system-of-systems specified using UML This thesis presents the strengths and weaknesses of Petri nets in relation to the specification of system-of-systems and shows how Petri net models can be used instead of conventional UML Activity Diagrams. The model of the system-of-systems can then be analysed and verified using Petri net theory. The Petri net formalism of behaviour is demonstrated using two case studies from the military domain. The first case study uses Petri nets to specify and analyse a close air support mission. This case study concludes by indicating the strengths, weaknesses, and shortfalls of the proposed formalism in system-of-systems specification. The second case study considers specification of a military exchange network parameters problem and the results are compared with the strengths and weaknesses identified in the first case study. Finally, the results of the research are formulated in the form of a Petri net enhancement to UML (mapping existing activity diagram elements to Petri net elements) to meet the needs of system-of-systems specification, verification and validation

Scheduling and discrete event control of flexible manufacturing systems based on Petri nets

A flexible manufacturing system (FMS) is a computerized production system that can simultaneously manufacture multiple types of products using various resources such as robots and multi-purpose machines. The central problems associated with design of flexible manufacturing systems are related to process planning, scheduling, coordination control, and monitoring. Many methods exist for scheduling and control of flexible manufacturing systems, although very few methods have addressed the complexity of whole FMS operations. This thesis presents a Petri net based method for deadlock-free scheduling and discrete event control of flexible manufacturing systems. A significant advantage of Petri net based methods is their powerful modeling capability. Petri nets can explicitly and concisely model the concurrent and asynchronous activities, multi-layer resource sharing, routing flexibility, limited buffers and precedence constraints in FMSs. Petri nets can also provide an explicit way for considering deadlock situations in FMSs, and thus facilitate significantly the design of a deadlock-free scheduling and control system. The contributions of this work are multifold. First, it develops a methodology for discrete event controller synthesis for flexible manufacturing systems in a timed Petri net framework. The resulting Petri nets have the desired qualitative properties of liveness, boundedness (safeness), and reversibility, which imply freedom from deadlock, no capacity overflow, and cyclic behavior, respectively. This precludes the costly mathematical analysis for these properties and reduces on-line computation overhead to avoid deadlocks. The performance and sensitivity of resulting Petri nets, thus corresponding control systems, are evaluated. Second, it introduces a hybrid heuristic search algorithm based on Petri nets for deadlock-free scheduling of flexible manufacturing systems. The issues such as deadlock, routing flexibility, multiple lot size, limited buffer size and material handling (loading/unloading) are explored. Third, it proposes a way to employ fuzzy dispatching rules in a Petri net framework for multi-criterion scheduling. Finally, it shows the effectiveness of the developed methods through several manufacturing system examples compared with benchmark dispatching rules, integer programming and Lagrangian relaxation approaches

On the Use of Queueing Petri Nets for Modeling and Performance Analysis of Distributed Systems

Predictive performance models are used increasingly throughout the phases of the software engineering lifecycle of distributed systems. However, as systems grow in size and complex-ity, building models that accurately capture the different aspects of their behavior becomes a more and more challenging task. The challenge stems from the limited model expressivenes

Performance Evaluation of CORBA Concurrency Control Service Using Stochastic Petri Nets

The interest in performance evaluation of middleware systems is increasing. Measurement techniques are still predominant among those used to carry out performance evaluation. However, performance models are currently being defined due to their flexibility, precision and facilities to carry out capacity planning activities. This paper presents stochastic Petri net models for performance evaluation of the CORBA Concurrency Control Service (CCS), which mediates concurrent access to objects. In order to validate the proposed models, CCS performance results obtained using those models are then compared against ones obtained through actual measurements.The interest in performance evaluation of middleware systems is increasing. Measurement techniques are still predominant among those used to carry out performance evaluation. However, performance models are currently being defined due to their flexibility, precision and facilities to carry out capacity planning activities. This paper presents stochastic Petri net models for performance evaluation of the CORBA Concurrency Control Service (CCS), which mediates concurrent access to objects. In order to validate the proposed models, CCS performance results obtained using those models are then compared against ones obtained through actual measurements

Basit bir makine - iki ürün sisteminin petri ağları kullanılarak modellenmesi, analizi ve simulasyonu

As in many engineering fields, the design of manufacturing systems can be carried out using models. Petri nets have been used extensively to model and analyze manufacturing systems. Petri Nets, as graphical and mathematical tools, provide a uniform environment for modeling, format analysis and design of discrete event systems. The modeling, simulation and analysis of simple one machine-two product systems using Petri nets will be presented in this paper. Behavioral and structural properties of the Petri net model will be considered in details. Then, the Petri net model of one machine-two product system will be simulated using a simulation program.Çoğu mühendislik alanlarında olduğu gibi imalat sistemlerinin tasarımı, modeller kullanılarak başarılabilir. Petri ağları imalat sistemlerinin modellenmesi ve analizinde yaygın olarak kullanılmaktadır. Petri ağları, şekilsel ve matematiksel araçlar olarak kesikli olay sistemlerinin modellenmesi, biçimsel analizi ve tasarımı için düzenli, iyi bir ortam sağlar. Bu makalede, basit bir makine-iki ürün sistemlerinin Petri ağları kullanılarak modellenmesi, simülasyonu ve analizi sunulacaktır. Petri Ağı modelinin davranışsal ve yapısal özellikleri ayrıntılı olarak incelenecektir. Daha sonra bir makine-iki ürün sisteminin Petri ağı modelinin bir simülasyon programı kullanılarak simülasyonu gerçekleştirilecektir

Simulating Train Dispatching Logic with High-Level Petri Nets

Railway simulation is commonly used as a tool for planning and analysis of railway traffic in operational, tactical and strategical level. During the simulation, a typical problem is a deadlock, i.e. a specific composition of trains on a simulated section positioned in such a way that they are blocking each other\u27s paths. Deadlock avoidance is very important in the simulation of railways because deadlock can stop the simulation, and significantly affect the simulation results. Simulation of train movements on a single track line requires implantation of additional rules and principles of train spacing and movement as train paths are more often in conflict than on a double track line. A High-level Petri Nets simulation model that detects and manages train path conflicts on a single track railway line is presented. Module for train management is connected to other modules on a hierarchical High-level Petri net. The model was tested on a busy single track mainline between Hrpelje-Kozina and Koper in south-western Slovenia

Modeling, Analysis and Simulation of Simple One Machine - Two Product System Using Petri Nets

Çoğu mühendislik alanlarında olduğu gibi imalat sistemlerinin tasarımı, modeller kullanılarak başarılabilir. Petri ağları imalat sistemlerinin modellenmesi ve analizinde yaygın olarak kullanılmaktadır. Petri ağları, şekilsel ve matematiksel araçlar olarak kesikli olay sistemlerinin modellenmesi, biçimsel analizi ve tasarımı için düzenli, iyi bir ortam sağlar. Bu makalede, basit bir makine-iki ürün sistemlerinin Petri ağları kullanılarak modellenmesi, simülasyonu ve analizi sunulacaktır. Petri Ağı modelinin davranışsal ve yapısal özellikleri ayrıntılı olarak incelenecektir. Daha sonra bir makine-iki ürün sisteminin Petri ağı modelinin bir simülasyon programı kullanılarak simülasyonu gerçekleştirilecektir.As in many engineering fields, the design of manufacturing systems can be carried out using models. Petri nets have been used extensively to model and analyze manufacturing systems. Petri Nets, as graphical and mathematical tools, provide a uniform environment for modeling, format analysis and design of discrete event systems. The modeling, simulation and analysis of simple one machine-two product systems using Petri nets will be presented in this paper. Behavioral and structural properties of the Petri net model will be considered in details. Then, the Petri net model of one machine-two product system will be simulated using a simulation program