• Journal of the Korea Society for Simulation
• /
• v.20 no.1
• /
• pp.87-96
• /
• 2011

DEVS(Discrete Event Systems Specification) is a set theoretic formalism developed for specifying discrete event system. For execution of DEVS, we need an execution environment, which consists of simulation engine and models interpreted by the simulation engine. Common existing environments use hierarchical scheduling algorithm for DEVS execution. This hierarchical scheduling is a proper algorithm for DEVS execution because of hierarchical and modular characteristics. But this algorithm has overheads owing to message passing and time management. To overcome these overheads, we apply event-oriented simulation to DEVS execution and we remove hierarchical overheads. In eventoriented simulation, the scheduling of model execution is performed by events and event list. We propose three event-oriented execution environments for DEVS and experiment about the performance of our proposed environments in comparison with the existing execution environment using the hierarchical scheduling. The experimental results show our environments works better than existing environment using the hierarchical scheduling.

• Journal of the Korea Society for Simulation
• /
• v.15 no.2
• /
• pp.1-12
• /
• 2006

As the needs of intelligent systems increase, there have been diverse approaches that combine artificial intelligence (AI) and simulation in the last decade. RG-DEVS, which is the basis for this paper, embedded AI planning techniques into the simulation modeling methodology of DEVS, in order to specify dynamically a simulation model. However, a hierarchy concept, which is used for various types of problem solving systems. is not included in the planning of RG-DEVS. The hierarchy concept reduces the computational cost of planning by reducing the search space, and also makes it easy to apply the hierarchical process flow of a target system to planning. This paper proposes Hierarchical RG-DEVS (HRG-DEVS) in an attempt to insert hierarchical planning capability into RG-DEVS. For the verification of the proposed modeling methodology, HRG-DEVS is applied to model the block's world problem of ABSTRIPS, which is a classical planning problem.

• Journal of the Korea Society for Simulation
• /
• v.19 no.3
• /
• pp.45-54
• /
• 2010

The inherent complexity of semiconductor fabrication processes makes it hard to solve well-known job scheduling problems in analytical ways, which leads us to rely practically on discrete event modeling simulations to learn the effects of changing the system's parameters. Meanwhile, unpredictable disturbances such as machine failures and maintenance diminish the productivity of semiconductor manufacturing processes with fixed scheduling policies; thus, it is necessary to adapt job scheduling policy in a timely manner in reaction to critical environmental changes (disturbances) in order for the fabrication process to perform optimally. This paper proposes an adaptive job control framework for a wafer fabrication process in a control system theoretical approach and implements it based on a DEVS modeling simulation environment. The proposed framework has the advantages in view of the whole systems understanding and flexibility of applying new rules compared to most ad-hoc software approaches in this field. Furthermore, it is flexible enough to incorporate new job scheduling rules into the existing rule set. Experimental results show that this control framework with adaptive rescheduling outperforms fixed job scheduling algorithms.

• Journal of the Korea Society for Simulation
• /
• v.27 no.1
• /
• pp.91-99
• /
• 2018

Discrete event simulation environments often need to be modified because additional questions to systems may become apparent while observing the simulation results repeatedly. It leads to increasing development budget and depreciating the effectiveness of the environment. To avoid the modifications and to generate the altered results, this paper applies an Event Control Model (ECM) with control functions that modulate, delete and generate the events at the simulation time. In addition, this paper suggests an easier approach for domain-users, who do not want to program at source code level, by using ECM templates. The simulators with the ECMs can have better extensibility because it becomes more adaptable to possibly unanticipated changes. It prevents increasing development costs due to modifications or development of new models by M&S experts, and it provides a new alternative step to domain users. To support the effectiveness of this approach, this paper describes a relevant example, which is composed of an initial simulation model based on our empirical studies. It will show that there exist the uncountable benefits because the existing simulator is reused by domain users without new projects.

• Proceedings of the Korea Society for Simulation Conference
• /
• 1998.03a
• /
• pp.91-95
• /
• 1998

기존의 이산 사건 시스템 시뮬레이션 환경들은 Interoperability의 문제, Portability 문제로 인하여 Internet과 Web상에서 분산 시뮤레이션이 불가능하다. 본 논문에서는 이러한 제약을 해결하고자 자바를 사용하여 DEVS(Discrete Event Systems Specification)형식혼을 구현하여 Internet/Web 상에서 시뮬레이션이 가능한 DEVSim-Java 환경을 설계하고 구현하였다. DEVSim-Java를 사용하여 시뮬레이션 환경을 구현함으로써 원격지에서 개발된 시뮬레이션 모델들을 인터넷을 통하여 재사용 하는 remote model-base(RMB) 개념을 제안된다. DEVSim-Java는 자바의 장점을 이용하여 시뮬레이션 과정을 애니메이션으로 잘 나타낼수 있고, 시뮬레이션의 결과를 Graphical Analyzer를 통해 분석할 수 있게 된다.

• Journal of Korean Port Research
• /
• v.14 no.1
• /
• pp.47-55
• /
• 2000

In order to cope with the changes of container terminal situation in these days, many simulation studies for container terminal have been accomplished. But previous simulation studies using simulation language have limitations in model representation and difficulties in modeling of large scaled container terminal system. To make these problems better, this paper addresses an object-oriented simulation of container terminal system using a DEVS formalism. The DEVS(Discrete Event System Specification) formalism, developed by Zeigler, supports specification of discrete event system in a hierarchical and modular manner. The formalism provides a mathematical basis for studying discrete event systems with better understood and sounder semantics. In a step of system modeling, a DEVS formalism aims at the exact system modeling that has a basis of semantics and utilizing the object-oriented manner can flexibly cope with the changes of system environment. In this study a model is developed and verified through the simulation of some alternatives.

• Proceedings of the KIEE Conference
• /
• 1999.07b
• /
• pp.838-840
• /
• 1999

In this paper, modeling and analysis of discrete event systems by temporal logic frame works and petri net is considered. The reachability tree of the petri net can be used to solve the safeness, boundedness, conservation and coverability problems of discrete event systems. But the reachability tree of the petri net do not solve reachability and liveness problems in general. We proposed a method that synthesised the petri net and the temporal logic frameworks. This method slove some problems of petri net by logical representation of temporal logic frameworks.

• Proceedings of the Korea Society for Simulation Conference
• /
• 1998.03a
• /
• pp.50-55
• /
• 1998

In this paper we use discrete simulation method to get the criteria of system evaluation required in the case of designing the complicated probabilistic event system having discrete probabilistic variables and to search the effective and reliable alternatives to satisfy the objective value of the given system through on-line, single run within the short time period. If we find the alternative we construct the algorithm which change values of decision variables and determining alternative by using the stopping algorithm which end the simulation in the steady state of system. In order to prevent the loss of data when we analyze the acquired design alternative in the steady state we provide the background of the estimation of the autoregressive model and mean and confidence interval for evaluating correctly the objective function obtained by the small amount of output data through the short time period simulation.

• Journal of the Korea Society for Simulation
• /
• v.7 no.2
• /
• pp.137-152
• /
• 1998

One of the components that constitute the simulation models is the state variables whose values are determined by the time related simulation process. Embedding rule-based expert systems into the simulation models should provide a systematic way of handling these time-dependent variables without distracting the essential problem solving capabilities of the expert systems which are well suited for expressing the decision making function of complex cases. The expert system, however, is inefficient in dealing with the time elapsing characteristics of target system compare to the simulation models. To solve the problem, this paper provides an interruptible inference engine whose inferencing process can be interrupted when the variables' value, which are used as the parameters of the rules, are not yet determined due to the time dependent nature of the state variables. The process is resumed when the variables are ready. The elapse of time is calculated by time-advance function of the simulation model to which the expert system has been embedded. The example modeling shown exploits the embedded interruptible inferencing capability for the controlling and monitoring of metal grating process.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
• /
• 1999.10a
• /
• pp.35-42
• /
• 1999

In order to cope with the changes of container terminal situation in these days, many simulation studies for container terminal have been accomplished. But established simulation studies using simulation language have restrictions in model representation and difficulties in modeling of large scaled container terminal system. To make these problems better, in this paper addresses object-oriented simulation of container terminal system using a DEVS formalism. In a step of system modeling, using a DEVS formalism aim at the exact system modeling that has a basis of semantics and utilizing the object-oriented manner can flexibly cope with the changes of system environment. In this study a model was developed and verified through the simulation of some alternatives.