Discrete Event System Simulation Research Articles

Using a Discrete-Event System Specifications (DEVS) for designing a Modelica compiler

We introduce a new architecture for the design of a tool for modeling and simulation of continuous and hybrid systems. The environment includes a compiler based on Modelica, a modular and a causal standard specification language for physical systems modeling (the tool supports models composed using certain component classes defined in the Modelica Standard Library, and the instantiation, parameterization and connection of these MSL components are described using a subset of Modelica). Models are defined in Modelica and are translated into DEVS models. DEVS theory (originally defined for modeling and simulation of discrete event systems) was extended in order to permit defining these of models. The different steps in the compiling process are show, including how to model these dynamic systems under the discrete event abstraction, including examples of model simulation with their execution results.

Practical Example of the Integration of Planning and Simulation Systems Using the RapidSim Software

In the paper practical implementation of the methodology of production planning systems with discrete event simulation (DES) systems integration has been presented. The required definitions of data structures and functions transformation in the form of XSLT documents have been presented. The functional algorithm and RapidSim software made on its basis, which is practical implementation of the integration methodology was developed. Developed software and parameterising documents have been used for the integration methodology verification. RapidSim system was made in VisualBasic development environment, and by the fact that Data Transformation XSLT documents can be independently developed, the software can be used for any integrated systems. During the verification phase of the implemented methodology, the software has been used for the practical implementation of Production Order Verification System (SWZ) for multi-assortment, concurrent production planning and Enterprise Dynamics simulation system integration.

Simulation of Earthwork Load-and-Carry System Based on GPSS World

Focusing on the complexity and a large number of variable factors of earthworks, to simulate earthworks with discrete event system simulation method is very effective, on the basis of analyzing the current developed simulation software, GPSS World discrete event simulation system was used in the simulation; For the one-way path optimization in the Earthwork Load-and-Carry System, an optimization strategy was put forward and put into a series of recycling process including simulation, verification, modification, re-simulation and re-verification with the simulation system, to achieve the optimization of the simulation model. Finally, through the verification of simulation concrete example, the method is proved effective and feasible, and has a wide applicability and a strong guiding significance for actual projects.

The Application of Computer Simulation Technology in the Queuing System Optimization

The optimization Problem of queuing system is an important research subject in the queuing system.There are two ways to solve this problem:one is the traditional theoretical analysis, the other is the application of computer simulation. This thesis introduces the queuing theory and the simulation technique of discrete event system, including fundamental conceptions, methods, performance index and classical model of queuing system, as well as the definition of simulation and the procedure of the simulation of discrete event system. And procedure and parameters set of general modeling methods are analyzed.

A vectorial DEVS extension for large scale system modeling and parallel simulation

In this article we introduce an extension to the Discrete Event System (DEVS) formalism called Vectorial DEVS (VECDEVS) that allows to represent large scale systems in a graphic block diagram way. A pure VECDEVS model basically consist in an array of identical classic DEVS models that may differ in their parameters. The interconnection of VECDEVS models with some special classic DEVS models that can handle VECDEVS events allows us to easily represent large systems of arbitrary structure. A noticeable feature of this extension is that VECDEVS models can be easily split for parallel simulation. For that purpose, we developed an algorithm that automatically splits VECDEVS models into an arbitrary number of sub-models for parallel simulation. The implementation of VECDEVS and the partitioning algorithm in a DEVS simulation tool is also described and its usage is illustrated through some application examples.

Event Step Method on Computer Simulation of Discrete Event System

Discrete event system is driven by event, and system status is discrete on time and space, so it is difficult to solve by using equation model and theoretical analysis method. Computer simulation technique provides an effective mean in order to solve these problems. Contents of this study provide technical and methodological support for computer simulation of discrete event. Firstly, the paper illustrated the basic concept of discrete event system; then, time step method mechanism described by mathematical model and graphical method; finally, we can research on the control flow of event step method when it promotes simulation, and then describe the three scanning methods of event step method, the first is clock value of type event; the second is clock value of dominant entity; the third is event tables. The result showed that the simulation model constructed by event step method has the advantages of short running time, the implement of program easily and so on.

Performance evaluation from stochastic statecharts representation of flexible reactive systems: A simulation approach

This paper focuses on the performance analysis of flexible reactive systems. The performance analysis consists of two phases: first system modeling, second performance evaluation. The paper models the flexible reactive system by the stochastic statecharts method, and uses the simulation method to evaluate the performance. To make use of the feature of event-triggered state transitions in the statecharts, a new method of simulation is proposed based on the techniques of the discrete-event system simulation. The new method solves the problem of computer implementation of stochastic events, probabilistic transition, concurrent states, parallel actions, and broadcast communication mechanism in the stochastic statecharts. An example of a flexible manufacturing system is presented. The simulation result of the example is consistent with the analytical result, which shows the feasibility of the proposed new simulation method.

Unified Modeling of Discrete Event and Control Systems Applied in Manufacturing

For the development of both a simulation model and a control system, it is necessary to build, in advance, a conceptual model. This is what is usually suggested by the methodologies applied in projects of this nature. Some conceptual modeling techniques allow for a better understanding of the simulation model, and a clear descriptionof the logic of control systems. Therefore, this paper aims to present and evaluate conceptual languages for unified modeling of models of discrete event simulation and control systems applied in manufacturing. The results show that the IDEF-SIM language can be applied both in simulation systems and in process control.

Mission Reliability Assessment of Space TT&C System by Discrete Event System Simulation

Based on the analysis of system characteristics and mission process, space tracking, telemetry and command (TT&C) system can be viewed as a phased‐mission system (PMS). A general methodology using discrete event system simulation is proposed to quantitatively assess mission reliability of space TT&C system, because the traditional method is difficult to solve such complex problem. By dividing the time sequence of TT&C mission profile into several phases, the fault tree model of PMS is built to represent the system logical structure in each phase. In order to efficiently build simulation models, unified modeling language static class diagram is used to describe simulation model architecture. Extensible markup language is adopted to represent the mission reliability model in standard format for simulation input. By randomly generating the failure and repair events of the system components, the changes of the system state are simulated. The logic structure function of fault tree and observation data of the system state change jointly determines the mission reliability. A case study is given to illustrate the approach and validate its effectiveness. Copyright © 2013 John Wiley & Sons, Ltd.

Discrete-Event Simulation for Estimating Emissions from Construction Processes

AbstractWhereas estimating emissions from construction processes is crucial to evaluating emission-reduction plans, current approaches can only estimate emissions from an average rather than operational perspective due to an inability to model uncertainties or randomness for reflecting application characteristics. A discrete-event simulation (DES) method is presented for estimating construction emissions by addressing existing problems. An investigation on the load factor reflecting the application characteristics of some construction equipment is performed, and then an emissions-calculating model able to consider uncertainties or randomness regarding various activities in the equipment duty cycle is proposed. To implement the emissions-calculating model, an available DES system is modified regarding the modeling capabilities for emissions-related factors and the simulation strategy incorporating the emissions-calculating model. The presented DES method is expected to help evaluate the emissions-reduction...

Implementation and Analysis of DEVS Activity-Tracking with DEVSimPy

This paper deals with the implementation of Activity-Tracking (AT) paradigm in the DEVSimPy environment. DEVSimPy has been developed at the SPE UMR CNRS6134 (University of Corsica) in order to facilitate the modeling and the simulation of discrete-event systems described with the DEVS formalism. The AT paradigm is increasingly being used by DEVS modelers for example to improve structural aspects of models (modeling level) or to make simulation more efficient using distributed or parallel algorithm (simulation level). Although DEVSimPy can be used as a software providing some features reusable for the implementation of AT paradigm (simulation profiling or step-by-step simulation), the object oriented way used to develop DEVSimPy makes it a powerful tool to implement AT paradigm in a generic manner. DEVSimPy may be viewed as an experimental framework allowing the implementation of new AT techniques while opening up new perspectives in the field of activity modeling and simulation theory.

ISA Standard Simulation Model Generation Supported by Data Stored in Low Level Controllers

One of the most widespread techniques to evaluate various aspects of a manufacturing system is discrete-event simulation (DES). However, building a simulation model of a manufacturing system is a difficult task and needs great resource expenditures. Automated data collection and model buildup can drastically reduce the time of the design phase as well as support model reusability. Since most of the manufacturing systems are controlled by low level controllers (e.g., PLCs, CNCs) they inherently store structure and control logic of the system to be modeled by a DES system. The paper introduces an ongoing research of PLC code processing method for automatic ISA standard simulation model generation of a conveyor system of a leading automotive factory. Results of the validation process and simulation experiments are also described through a case study.

Simulation of capacity and cost for the planning of future process chains

One of the most promising approaches in modern microelectronics is the introduction of 3D chip micro systems with through-silicon via (TSV) interconnections. A successful transfer of this technology from the scientific level up to the level of mass production is not least of all a matter of cost-effectiveness and profit, which is directly related to high productivity. The developed technologies therefore have to be feasible for effective mass production. In this paper we introduce a method for planning and evaluating costs in future process chains. This method goes beyond usual mostly Excel-supported solutions, as it is based on a discrete event simulation system. The simulation model is generically generated out of an XML process chain definition file and includes a sophisticated state model for machines. Multiple process scenarios are created with the help of a supporting software tool. These scenarios are investigated for achieving favourable equipment and process chain configurations as well as control strategies to support manufacturing ramp-ups.

Supports for transparent object-migration in PDES systems

It is well known that Parallel Discrete Event Simulation systems may suffer, in terms of delivered performance, from imbalance of the computational load. In case of conservative synchronization we may experience CPU under-utilization and/or excessive communication overhead. On the other hand, for the optimistic paradigm we may even have rollback thrashing effects, with a consequent reduction of the percentage of productive (ie not rolled back) work carried out. This paper presents the design of a global memory management architecture supporting application-transparent migration of simulation objects whose state is scattered across dynamically allocated memory chunks. Our approach is based on a non-intrusive background protocol that provides each instance of the simulation kernel with information on the current mapping of the virtual address space of all the other instances. Dynamic memory requests by the application layer are then locally mapped onto virtual-address ranges that maximize the likelihood of being portable onto the address space of a remote kernel instance. In this way, independently of the load-balancing trigger (or policy), we maximize the likelihood that a desirable migration across a specific couple of kernels can actually take place due to compliance of the corresponding source/destination address spaces. We have integrated the global memory manager within the ROme OpTimistic Simulator (ROOT-Sim), namely a run-time environment based on the optimistic synchronization paradigm which automatically and transparently parallelizes the execution of event-handler-based simulation programs conforming to ANSI-C. Further, we provide a contribution in the direction of widening load-balancing schemes for optimistic simulation systems by defining migration triggers and selection policies for the objects to be migrated on the basis of memory usage patterns. An experimental assessment of the architecture and of memory-oriented load balancing is also provided.

Graphical modeling and simulation of discrete-event systems with CD++Builder

We introduce CD++Builder, an open-source environment that aims at providing easy-to-use graphical modeling tools to simplify the construction of models and the execution of simulations of complex Discrete Event System Specification (DEVS) models. The architecture and implementation of CD++Builder focuses on providing simple definition and reuse of components, offering easy extensibility to support new features. CD++Builder includes graphical editors for DEVS-coupled models, DEVS-Graphs and C++ atomic models; it provides code templates that are synchronized with their graphical versions, and it greatly simplifies the software installation and update procedures. We show how this environment can be used to build and simulate DEVS models, and we compare the process with previous versions and other simulation tools, showing that CD++Builder can improve model development by creating DEVS models in a completely assisted manner, including advanced graphical interfaces.

Study on the Responsiveness of Production Load-Equilibrium Based Order Allocation Strategy

For industry cluster with multiple suppliers and multiple manufacturers, there exist a network of supply and demand relationship among suppliers and manufacturers. By using the balanced production load among suppliers as the main criteria for decision making, an order allocation model for supply chain with multi-suppliers vs. multi-manufacturers based on production load equilibrium-based strategy is proposed in this paper. In the end of paper the discrete event system simulation is used to verify that the production load equilibrium-based strategy can enhance the supplier's responsiveness effectively，which further leads to a satisfied OTD of manufacturers and the optimization of the whole supply chain.

Process plan and part routing optimization in a dynamic flexible job shop scheduling environment: an optimization via simulation approach

This paper presents an optimization via simulation approach to solve dynamic flexible job shop scheduling problems. In most real-life problems, certain operation of a part can be processed on more than one machine, which makes the considered system (i.e., job shops) flexible. On one hand, flexibility provides alternative part routings which most of the time relaxes shop floor operations. On the other hand, increased flexibility makes operation machine pairing decisions (i.e., the most suitable part routing) much more complex. This study deals with both determining the best process plan for each part and then finding the best machine for each operation in a dynamic flexible job shop scheduling environment. In this respect, a genetic algorithm approach is adapted to determine best part processing plan for each part and then select appropriate machines for each operation of each part according to the determined part processing plan. Genetic algorithm solves the optimization phase of solution methodology. Then, these machine-operation pairings are utilized by discrete-event system simulation model to estimate their performances. These two phases of the study follow each other iteratively. The goal of methodology is to find the solution that minimizes total of average flowtimes for all parts. The results reveal that optimization via simulation approach is a good way to cope with dynamic flexible job shop scheduling problems, which usually takes NP-Hard form.

Combining optimisation and simulation in an energy systems analysis of a Swedish iron foundry

To face global competition, and also reduce environmental and climate impact, industry-wide changes are needed, especially regarding energy use, which is closely related to global warming. Energy efficiency is therefore an essential task for the future as it has a significant impact on both business profits and the environment. For the analysis of possible changes in industrial production processes, and to choose what changes should be made, various modelling tools can be used as a decision support. This paper uses two types of energy analysis tool: Discrete Event Simulation (DES) and Energy Systems Optimisation (ESO). The aim of this study is to describe how a DES and an ESO tool can be combined. A comprehensive five-step approach is proposed for reducing system costs and making a more robust production system. A case study representing a new investment in part of a Swedish iron foundry is also included to illustrate the method's use. The method described in this paper is based on the use of the DES program QUEST and the ESO tool reMIND. The method combination itself is generic, i.e. other similar programs can be used as well with some adjustments and adaptations.The results from the case study show that when different boundary conditions are used the result obtained from the simulation tools is not optimum, in other words, the result shows only a feasible solution and not the best way to run the factory. It is therefore important to use the optimisation tool in such cases in order to obtain the optimum operating strategy. By using the optimisation tool a substantial amount of resources can be saved. The results also show that the combination of optimisation and simulation tools is useful to provide very detailed information about how the system works and to predict system behaviour as well as to minimise the system cost.

Collaborative Modeling Process for Development of Domain-Specific Discrete Event Simulation Systems

The discrete event systems specification (DEVS) formalism supports the object-oriented (OO) specification of discrete event models in a hierarchical, modular manner. If a system that is to be modeled is domain-specific, the development of models with the use of the DEVS formalism would require domain knowledge about the system as well as to understand DEVS semantics. This paper proposes a collaborative modeling process to compensate for the lack of professional engineers. To compensate, this modeling process utilizes three types of engineers: domain engineer, modeling and simulation (M&S) engineer, and platform engineer. The process consists of four steps: conceptual modeling, model partition, model implementation, and model integration/simulation. The system requirements are used to specify domain models in the conceptual modeling step, and the models are partitioned into two types: discrete event-level model (DEM) and behavioral-level model (BM). The DEM is specified as the DEVS formalism, and the BM is defined as algorithms and equations. Each model is implemented separately, and the implemented models are integrated and simulated flexibly by using a dynamic linking library. The modeling process is then applied to develop a war game simulator. The advantage of this modeling process is that the collaborative work is related to the whole series of steps. This collaboration maximally utilizes the capabilities of the professional engineers by seamlessly separating yet correlating their works.

Dynamic Channel Allocation Control with thresholds in Wireless Cellular Networks using Simpy

New and handoff calls control mechanisms are the key point to wireless cellular networks. In this paper, we present an adaptive algorithm for dynamic channel allocation scheme with guard channels and also with handoff calls waiting queue ensuring that handoff calls take priority over new calls. Our goal is to find better tradeoff between handoffs and new calls blocking probabilities in order to achieve more efficient channel utilization. Simpy is a Python based discrete event simulation system. We use Simpy to build our simulation models to get analytical data.