Browsing by Subject "Petri nets"
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Item A flexible control system for flexible manufacturing systems(Texas A&M University, 2004-09-30) Scott, Wesley DaneA flexible workcell controller has been developed using a three level control hierarchy (workcell, workstation, equipment). The cell controller is automatically generated from a model input by the user. The model consists of three sets of graphs. One set of graphs describes the process plans of the parts produced by the manufacturing system, one set describes movements into, out of and within workstations, and the third set describes movements of parts/transporters between workstations. The controller uses an event driven Petri net to maintain state information and to communicate with lower level controllers. The control logic is contained in an artificial neural network. The Petri net state information is used as the input to the neural net and messages that are Petri net events are output from the neural net. A genetic algorithm was used to search over alternative operation choices to find a "good" solution. The system was fully implemented and several test cases are described.Item A graphical user interface for the analysis of task graphs(Texas Tech University, 1999-08) Krishna, SanthoshThis thesis describes a flexible graphical user interface (GUI) tool designed and developed for the analysis of task graphs. The interface tool takes the task graph along with parameters such as execution times of the tasks, number of processors, and communication costs, as input and gives the average completion time and the probability distribution of the completion times for the task graph as output, using a numerical analysis tool and a simulation analysis tool. The interface provides access to heuristic algorithms to generate an allocation matrix that maps tasks into processors. The solution tools uses this matrix along with the parameters to generate results. The GUI is developed in such a way that the user can configure it by adding new heuristics or any other solution scheme.Item A petri net based tool for the analysis of task graph systems(Texas Tech University, 1998-05) Dova, HemchandThe goal of this research is to develop a software tool for the analysis of task graph systems with a graphical user interface. PN's directly incorporate the topological information of the input task graph and also accommodate means to include parameters such as the processor heterogeneity, allocation schemes, communication costs, and random execution times. A technique for the analysis of a task graph systems using PN's has been reported in [6]. The methodology described in this thesis provides a graphical user interface tool for the analysis of the task graph system. The technique reported in [6] and [14] has been used in this thesis for the numerical and simulation analysis of the input task graph systenL The limitation of the numerical method of analysis is that tasks having only exponentially distributed execution times can be analyzed. This restriction is overcome in the simulation method of analysis where tasks having normal distributions can also be analyzed. The results from the numerical and simulation analysis are used to validate the tool. The software is implemented using JAVA. In this thesis three allocation heuristics are also implemented. The allocation heuristics are part of the topology of task graph systems. The Petri net tool generates the allocation of the tasks onto the processors. The software tool is called TASK GRAPH SYSTEM ANALYZER (TGSA). Furthermore, the implementation methodology of the present thesis can also be easily adapted to accommodate additional methods of analysis that use the same topology for the task graph system. Additional factors that could help in the study of task graph systems can also be incorporated.Item Audio browsing of automaton-based hypertext(Texas A&M University, 2004-09-30) Ustun, SelenWith the wide-spread adoption of hypermedia systems and the World Wide Web (WWW) in particular, these systems have evolved from simple systems with only textual content to those that incorporate a large content base, which consists of a wide variety of document types. Also, with the increase in the number of users, there has grown a need for these systems to be accessible to a wider range of users. Consequently, the growth of the systems along with the number and variety of users require new presentation and navigation mechanisms for a wider audience. One of the new presentation methods is the audio-only presentation of hypertext content and this research proposes a novel solution to this problem for complex and dynamic systems. The hypothesis is that the proposed Audio Browser is an efficient tool for presenting hypertext in audio format, which will prove to be useful for several applications including browsers for visually-impaired and remote users. The Audio Browser provides audio-only browsing of contents in a Petri-based hypertext system called Context-Aware Trellis (caT). It uses a combination of synthesized speech and pre-recorded speech to allow its user to listen to contents of documents, follow links, and get information about the navigation process. It also has mechanisms for navigating within documents in order to allow users to view contents more quickly.Item Distributed program reliability based on minimum file spanning trees(Texas Tech University, 2000-12) Krishnan, KirtiThe objective of this thesis was to develop a generalized modeling technique using Petri Nets based on Minimum File Sparming trees and to generate reliability measures for a distributed program in the given distributed computing environment. A global repair state was also incorporated into the final model to measure the availability of the program. (The idea proposed features the concept of using Minimum File Spanning trees as the major component in the Petri Net model rather than the individual components of the system, thereby achieving a reduction in the state space and improved efficiency in the generation of reliability results.Item Modeling and analysis of concurrent processing systems by temporal petri nets(Texas Tech University, 1987-05) Lu, Harngdar ATemporal Petri nets, a new class of Petrinets in which timing constraints are represented by the operators of temporal logic, have recently been proposed. Due to the versati1ity of the temporal logic operators to express temporal Tempora1 Petrinets, a new class of Petrinets in which timing constraints are represented by the operators of temporal logic, have recently been proposed. Due to the versati1ity of the temporal logic operators to express temporal assertions, temporal Petri nets are expected to be suitable for describing causal and temporal relationships between events of a system, including eventuality and fairness. In this thesis we investigate the potential of temporal Petrinets as a design/verification tool for concurrent systems through modeling and analysis of the handshake daisy chain arbiters and the alternating bit protocol. We present some methods for analyzing temporal Petri nets. A brief comparison of temporal Petri nets with other verification methods is a1so given.Item Modeling and analysis of hybrid dynamic systems(Texas Tech University, 1996-12) Gotesman, MosheA modeling technique for hybrid dynamics systems, using high-level Petri nets, is presented. A hybrid dynamics system is a continuous dynamics system in which discrete events occur. Modeling of hybrid dynamics systems is difficult since continuous dynamics and discrete event dynamics have entirely different mathematics. The dissertation presents techniques for converting a hybrid dynamics system, represented mathematically or by means of a block diagram into a Petri net. The resulting Petri net. called the Hybrid Dynamics Petri Net (HDPN). captures both the continuous and discrete event phenomena in the system. This provides a single formalism for modeling hybrid dynamics systems. Procedures are also provided for converting a Petri net into a block diagram and into a mathematical representation. Some examples are implemented to demonstrate the capability of the Petri net formalism to correctly model hybrid dynamics systems. The examples demonstrate the modeling power of Petri nets for continuous and hybrid systems, including non-linear systems and MIMO systems.Item Optimization algorithms applied to large petri nets(Texas Tech University, 2001-08) Tarek, AhmedPetrinets (PNs) are important modeling tools for many practical control problems which include concurrent, asynchronous systems. Analysis of reachability is important in connection to the characterization of PN models and many important properties of P-Ns are related to it. Very little work has been reported which combines optimization theory with PNs, Computation of legal firing sequences (LFSs) to decide the reachability using well-established optimization techniques is the main focus of this dissertation. The fundamental problem of deciding the reachability with a pre-specified firing count vector u and the total firing instances d = Óm ui is considered. Related computational issues are also considered. Different optimization techniques are investigated. Some of these techniques appear to be extremely elegant. .A set of problems related to the reachability analysis in PNs are identified. Starting with the basic reachability equations, the straightforward Single step LP method which uses only one iteration of linear programming (LP) is derived. .Another important method is based on the Optimality Principle (OP) which is combined with LP to derive the OP-based LP method. With considerable problem sizes, the combinatorial state-space-explosion-problem remains as a major computational barrier for a LP method which computes a LFS in one step. From elementary net equations, the dynamic programming (DP) algorithm to compute LFSs of PNs is derived. To avoid the state-space-explosion-problem, the reversed net N~1of an original PN TV has been used and the basic DP algorithm is modified to compute on the reversed net. The original problem is subdivided into d recursive parts and each part is solved using LP This is the principle of the DP-based LP method. To improve computation time, a forward recursive DP-based LP method is derived. Firing of the sink transition in a critical siphon is a major problem for the DP-based LP method, since it deadlocks a computational process. To avoid this, an approximation algorithm which involves Pontryagin's Minimum Principle (PMP)-based LP for a known firing count vector u and the total firing instance d is introduced and discussed. The method computes on an original PN A^. A heuristic algorithm which supports the computation of the PMP-based LP method is derived. This heuristic algorithm suppresses firing of the sink transition of a potential critical siphon. The complete method avoids potential critical transitions and computes complex problems. Analysis of complexity is important for the computer implementation of a computational method. Therefore, time and space complexities are considered in order to compute LFSs of PNs. Time complexity becomes about d~3 times to that of a single step LP method if a complete problem is subdivided into d subproblems. This technique is adopted with the FDP-based LP method, the DP-based LP method and the PMP-based LP method with known u and d. Computation time curves for the Single step LP, the DP-based LP and the PMP-based LP methods with a prespecified u and d which use the Revised Simplex DLPRS subroutine are obtained. Certain subclasses of PNs have well-defined reachability criteria. Computation time curves for these subclasses of PNs are obtained using a two-phase simplex subroutine. Some application issues are considered in this dissertation. The identified problems are addressed. Future research directions are outlined.Item Robust manufacturing system design using petri nets and bayesian methods(Texas A&M University, 2008-10-10) Sharda, BikramManufacturing system design decisions are costly and involve significant investment in terms of allocation of resources. These decisions are complex, due to uncertainties related to uncontrollable factors such as processing times and part demands. Designers often need to find a robust manufacturing system design that meets certain objectives under these uncertainties. Failure to find a robust design can lead to expensive consequences in terms of lost sales and high production costs. In order to find a robust design configuration, designers need accurate methods to model various uncertainties and efficient ways to search for feasible configurations. The dissertation work uses a multi-objective Genetic Algorithm (GA) and Petri net based modeling framework for a robust manufacturing system design. The Petri nets are coupled with Bayesian Model Averaging (BMA) to capture uncertainties associated with uncontrollable factors. BMA provides a unified framework to capture model, parameter and stochastic uncertainties associated with representation of various manufacturing activities. The BMA based approach overcomes limitations associated with uncertainty representation using classical methods presented in literature. Petri net based modeling is used to capture interactions among various subsystems, operation precedence and to identify bottleneck or conflicting situations. When coupled with Bayesian methods, Petri nets provide accurate assessment of manufacturing system dynamics and performance in presence of uncertainties. A multi-objective Genetic Algorithm (GA) is used to search manufacturing system designs, allowing designers to consider multiple objectives. The dissertation work provides algorithms for integrating Bayesian methods with Petri nets. Two manufacturing system design examples are presented to demonstrate the proposed approach. The results obtained using Bayesian methods are compared with classical methods and the effect of choosing different types of priors is evaluated. In summary, the dissertation provides a new, integrated Petri net based modeling framework coupled with BMA based approach for modeling and performance analysis of manufacturing system designs. The dissertation work allows designers to obtain accurate performance estimates of design configurations by considering model, parameter and stochastic uncertainties associated with representation of uncontrollable factors. Multi-objective GA coupled with Petri nets provide a flexible and time saving approach for searching and evaluating alternative manufacturing system designs.Item Semi-formal verifcation of analog mixed signal systems using multi-domain modeling languages(2013-05) Ramirez, Ricardo, active 2013; Abraham, Jacob A.The verification of analog designs has been a challenging task for a few years now. Several approaches have been taken to tackle the main problem related to the complexity that such task presents to design and verification teams. The methodology presented in this document is based on the experiences and research work carried out by the Concordia University's Hardware Verification and the U. of Texas' IC systems design groups. The representation of complex systems where different interactions either mechanical or electrical take place requires an intricate set of mathematical descriptions which greatly vary according to the system under test. As a simple and very relevant example one can look at the integration of RF-MEMS as active elements in System-On-Chip architectures. In order to tackle such heterogeneous interaction for a consistent model, the use of stochastic hybrid models is described and implemented for very simple examples using high level modeling tools for a succinct and precise description.Item Systematic generation and evaluation of stochastic petri net models for the performance analysis of task graphs(Texas Tech University, 1995-05) Decker, Jeffrey FloydThe main thrust of this work is to develop a mechanism to generate a Stochastic Petri Net from a given task graph. The task graph corresponds to a particular job that has been broken down into several tasks. The problem is to find the average completion time of any job represented by a task graph using an unlimited number of processors as v^ell as a limited number of processors. Currently, there are models that solve the problem for an unlimited number of processors [10]. However, there is no model available to solve this problem for a limited number of processors. Work has been done using Queuing Networks [13], but not Stochastic Petri Nets. To analyze a particular task graph using a Petri Net with a limited number of processors, the Stochastic Petri Net(SPN) model must be generated manually. Once the Stochastic Petri Net is generated, its evaluation can be carried out using a tool such as the Stochastic Petri Net Package (SPNP) [1] developed at Duke University.Item The reliability of distributed computer systems(Texas Tech University, 1998-12) Nadgir, Neelakanth MalhariNot available