3,539 research outputs found
Enhancing the Supply Chain Performance by Integrating Simulated and Physical Agents into Organizational Information Systems
As the business environment gets more complicated, organizations must be able to respond to the business changes and adjust themselves quickly to gain their competitive advantages. This study proposes an integrated agent system, called SPA, which coordinates simulated and physical agents to provide an efficient way for organizations to meet the challenges in managing supply chains. In the integrated framework, physical agents coordinate with inter-organizations\' physical agents to form workable business processes and detect the variations occurring in the outside world, whereas simulated agents model and analyze the what-if scenarios to support physical agents in making decisions. This study uses a supply chain that produces digital still cameras as an example to demonstrate how the SPA works. In this example, individual information systems of the involved companies equip with the SPA and the entire supply chain is modeled as a hierarchical object oriented Petri nets. The SPA here applies the modified AGNES data clustering technique and the moving average approach to help each firm generalize customers\' past demand patterns and forecast their future demands. The amplitude of forecasting errors caused by bullwhip effects is used as a metric to evaluate the degree that the SPA affects the supply chain performance. The experimental results show that the SPA benefits the entire supply chain by reducing the bullwhip effects and forecasting errors in a dynamic environment.Supply Chain Performance Enhancement; Bullwhip Effects; Simulated Agents; Physical Agents; Dynamic Customer Demand Pattern Discovery
Dynamic hybrid simulation of batch processes driven by a scheduling module
Simulation is now a CAPE tool widely used by practicing engineers for process design and control. In particular, it allows various offline analyses to improve system performance such as productivity, energy efficiency, waste reduction, etc. In this framework, we have developed the dynamic hybrid simulation environment PrODHyS whose particularity is to provide general and reusable object-oriented components dedicated to the modeling of devices and operations found in chemical processes. Unlike continuous processes, the dynamic simulation of batch processes requires the execution of control recipes to achieve a set of production orders. For these reasons, PrODHyS is coupled to a scheduling module (ProSched) based on a MILP mathematical model in order to initialize various operational parameters and to ensure a proper completion of the simulation. This paper focuses on the procedure used to generate the simulation model corresponding to the realization of a scenario described through a particular scheduling
An agent-based dynamic information network for supply chain management
One of the main research issues in supply chain management is to improve the global efficiency of supply chains.
However, the improvement efforts often fail because supply chains are complex, are subject to frequent changes, and collaboration and information sharing in the supply chains are often infeasible. This paper presents a practical
collaboration framework for supply chain management wherein multi-agent systems form dynamic information networks and coordinate their production and order planning according to synchronized estimation of market demands. In the framework, agents employ an iterative relaxation contract net protocol to find the most desirable
suppliers by using data envelopment analysis. Furthermore, the chain of buyers and suppliers, from the end markets to raw material suppliers, form dynamic information networks for synchronized planning. This paper presents an agent-based dynamic information network for supply chain management and discusses the associated
pros and cons
A Petri Nets-based Scheduling Methodology forMultipurpose Batch Plants.
This article presents an optimization methodology of batch production processes assembled by shared resources which rely on a mapping of state-events into time-events allowing in this way the straightforward use of a well consolidated scheduling policies developed for manufacturing systems. A technique to generate the timed Petri net representation from a continuous dynamic representation (Differential-Algebraic Equations systems (DAEs)) of the production system is presented together with the main characteristics of a Petri nets-based tool implemented for optimization purposes. This paper describes also how the implemented tool generates the coverability tree and how it can be pruned by a general purpose heuristic. An example of a distillation process with two shared batch resources is used to illustrate the optimization methodology proposed
Web Application for Visual Modeling of Discrete Event Systems
This research work has resulted in the development of a web application that enables discrete event systems simulation to be created using a Petri-object approach. It provides the development of a model in two stages. In the first stage, the dynamics of the classes of objects are created using Petri net. In the second stage, the model is composed of objects with given dynamics. The simulation algorithm is based on stochastic Petri net with multichannel transitions and is implemented using Ruby. The web application enables the design of the model's dynamics by manipulation with graphics objects and saving it not only as a graphics object but also as a program method. This greatly improves the overall performance of the simulation model development
Towards a Layered Architectural View for Security Analysis in SCADA Systems
Supervisory Control and Data Acquisition (SCADA) systems support and control
the operation of many critical infrastructures that our society depend on, such
as power grids. Since SCADA systems become a target for cyber attacks and the
potential impact of a successful attack could lead to disastrous consequences
in the physical world, ensuring the security of these systems is of vital
importance. A fundamental prerequisite to securing a SCADA system is a clear
understanding and a consistent view of its architecture. However, because of
the complexity and scale of SCADA systems, this is challenging to acquire. In
this paper, we propose a layered architectural view for SCADA systems, which
aims at building a common ground among stakeholders and supporting the
implementation of security analysis. In order to manage the complexity and
scale, we define four interrelated architectural layers, and uses the concept
of viewpoints to focus on a subset of the system. We indicate the applicability
of our approach in the context of SCADA system security analysis.Comment: 7 pages, 4 figure
Computer-aided HAZOP of batch processes
The modern batch chemical processing plants have a tendency of increasing
technological complexity and flexibility which make it difficult to control the
occurrence of accidents. Social and legal pressures have increased the demands
for verifying the safety of chemical plants during their design and operation.
Complete identification and accurate assessment of the hazard potential in the
early design stages is therefore very important so that preventative or protective
measures can be integrated into future design without adversely affecting
processing and control complexity or capital and operational costs. Hazard and
Operability Study (HAZOP) is a method of systematically identifying every
conceivable process deviation, its abnormal causes and adverse hazardous
consequences in the chemical plants. [Continues.
An automated system for batch hazard and operability studies
A widely used hazard identification technique within the process industry is HAZOP (hazard and
operability study). To overcome the repetitive and time-consuming nature of the technique automated
systems are being developed. This work considers batch processes, in which material undergoes
processing in distinct stages within the plant equipment items according to a set of operating
procedures, rather than each equipment item remaining in a âsteady stateâ, as is normal for continuous
plants. In batch plants deviations which can lead to hazards can arise both from deviations from
operating procedures and process variable deviations. Therefore, the effect of operator actions needs to
be considered. CHECKOP is an automated batch HAZOP identification system being developed as a
joint project between HAZID Technologies Ltd and Loughborough University. CHECKOP uses a
state-based approach to HAZOP analysis. CHECKOP takes a plant description and a set of operating
instructions as input and produces a HAZOP report automatically. The overall system architecture and
the details of the major components of the systems will be described. Examples of incorrect plant
operation along with the resulting output generated by CHECKOP will be shown. The advantages and
limitations of CHECKOP will be discussed
SFC++: A tool for developing distributed real time control
WESIC'98, Girona, Spain June 10, 11 and 12, 1998This paper describes a visual tool for developing real time software for the control of distributed manufacturing systems. The aim of this project, currently in progress, is to get a visual programming environment which integrates both the advantages of object oriented modelling for the design and simulation of systems and the power of modern distributed control systems (i.e. computers with real time operating systems interconnected by means of industrial real time networks). To bridge the gap between the object oriented system model and the implementation level, at which we have multiple parallel tasks running over a network, Sequential Function Charts are used as a standard formalism (IEC, 1988; UTE, 1992) for the description of system dynamics and control software programmin
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