COMBINING SYSTEM DYNAMICS AND DISCRETE EVENT SIMULATIONS - OVERVIEW OF HYBRID SIMULATION MODELS <s> Type of connection <s> The United States Department of Defense's High Level Architecture for Modeling and Simulation (HLA) provides a standardized interface for distributed simulations. The recent advent of HLA has greatly increased interest in the use of distributed, interoperable simulation model components. This paper focuses on how on-line data (i.e. data from real-time dependent processes) can be used in analytical simulation models and how the use of HLA based components can facilitate the integration of this kind of data into simulations. The paper also discusses the issue of cloning federates and federations and introduces some potential applications of cloning for a public transportation prototype example. <s> BIB001 </s> COMBINING SYSTEM DYNAMICS AND DISCRETE EVENT SIMULATIONS - OVERVIEW OF HYBRID SIMULATION MODELS <s> Type of connection <s> This paper first discusses the basic design approach adopted for the High Level Architecture and the design goals that it addresses in the military simulation arena. Next, the limitations of this architecture are discussed with particular focus on the real-time information requirements needed to support its operation. Finally, the paper discusses HLA's inability to model complex systems with hierarchical command and control structures and the inherent limitations that this deficiency will impose upon the application of futuristic simulation technologies to military applications. <s> BIB002 </s> COMBINING SYSTEM DYNAMICS AND DISCRETE EVENT SIMULATIONS - OVERVIEW OF HYBRID SIMULATION MODELS <s> Type of connection <s> Hierarchical production planning provides a formal bridge between long-term plans and short-term schedules. A hybrid simulation-based production planning architecture consisting of system dynamics (SD) components at the higher decision level and discrete event simulation (DES) components at the lower decision level is presented. The need for the two types of simulation has been justified. The architecture consists of four modules: enterprise-level decision maker, SD model of enterprise, shop-level decision maker and DES model of shop. The decision makers select the optimal set of control parameters based on the estimated behavior of the system. These control parameters are used by the SD and DES models to determine the best plan based on the actual behavior of the system. High level architecture has been employed to interface SD and DES simulation models. Experimental results from a single-product manufacturing enterprise demonstrate the validity and scope of the proposed approach. <s> BIB003 </s> COMBINING SYSTEM DYNAMICS AND DISCRETE EVENT SIMULATIONS - OVERVIEW OF HYBRID SIMULATION MODELS <s> Type of connection <s> Construction systems and projects comprise complex combinations of subsystems, processes, operations, and activities. Discrete Event Simulation (DES) has been used extensively for modeling construction systems, addressing system complexity, and analyzing system behavior. However, while DES is a powerful tool for capturing operations as they occur in reality, DES does have difficulty modeling context and its mutual effects on the operational components of a system. System Dynamics (SD), on the other hand, captures feedback loops that are derived from the context level of a system and that can anticipate system behavior; nevertheless, SD cannot effectively model the operational parts of a system. Hybrid SD and DES modeling provide a set of tools that use the capabilities, while improving upon the disadvantages, of these two approaches. Although initial efforts to develop hybrid SD-DES modeling dates back to the late 1990s, in the construction industry, there are relatively few studies in this area, and there is still no robust architecture for hybrid system developers. This paper addresses these issues by proposing a comprehensive hybrid simulation architecture based on the High Level Architecture (HLA) infrastructure, which can be used by hybrid simulation developers in the construction industry. A typical steel fabrication shop has been modeled based on the proposed architecture, and it has been compared with the ideally developed hybrid simulation architecture. <s> BIB004 </s> COMBINING SYSTEM DYNAMICS AND DISCRETE EVENT SIMULATIONS - OVERVIEW OF HYBRID SIMULATION MODELS <s> Type of connection <s> The idea of combining discrete-event simulation and system dynamics has been a topic of debate in the operations research community for over a decade. Many authors have considered the potential benefits of such an approach from a methodological or practical standpoint. However, despite numerous examples of models with both discrete and continuous parameters in the computer science and engineering literature, nobody in the OR field has yet succeeded in developing a genuinely hybrid approach which truly integrates the philosophical approach and technical merits of both DES and SD in a single model. In this paper we consider some of the reasons for this and describe two practical healthcare examples of combined DES/SD models, which nevertheless fall short of the "holy grail" which has been so widely discussed in the literature over the past decade. <s> BIB005 </s> COMBINING SYSTEM DYNAMICS AND DISCRETE EVENT SIMULATIONS - OVERVIEW OF HYBRID SIMULATION MODELS <s> Type of connection <s> This paper deals with the simulation modeling of the service supply chain and the salinity and its diffusion in the Panama Canal. An operational supply chain model was created using discrete-event simulation. Once complete, a component based on differential equations was added to the model to investigate the intrusion of salt and the resulting salinity diffusion into the lakes of the canal. This component was implemented in the AnyLogic simulation modeling environment by taking advantage of the concept of hybrid modeling that is embedded in AnyLogic. <s> BIB006
Combining the two different models in one hybrid one is one of the most important thing in this whole process. This defines also how the models will communicate, share data, behave at a certain time point etc. Back in the 1999 there were two papers that stress out the possibilities and the advantages when using HLA (High Level Architecture) to combine two or more models BIB001 BIB002 . Some research done so far has employed this tool in order to combine their models BIB003  BIB004 ). Clearly, the benefits are enormous, but also the effort, time and the technicality when using this approach. Some have used a more usual ways to do this, like Excel and Visual Basic for Applications BIB005 ). There are even cases where a specific research has been conducted in order to define a generic module in order for SD and DES models to communicate and function  ). There are even examples where the modellers have a single software solution (Anylogic, <www.xjtek.com>) and combined a DES model with differential equations BIB006 ). Maybe it is not as same as the rest of the cases, but is worth mentioning as an approach.