Victorino Sanz

Hybrid System Modeling: Using the Parallel DEVS Formalism and the Modelica Language

The objective of the presented work is to facilitate the description of discrete-event models and the discrete-event part of hybrid-DAE models. It is achieved by combining the Parallel DEVS formalism, the process-oriented modeling approach and the Modelica language. This objective not only includes the description of P-DEVS and process-oriented models in Modelica, but also developing interface models which will facilitate the combination of these models with other continuous-time or discrete-event Modelica models. The development of this work includes the identification and analysis of the requirements needed to describe P-DEVS and process-oriented models in Modelica, the description and implementation of a message passing mechanism in Modelica, the implementation of the requirements analyzed into new Modelica libraries that facilitate the description of models using current Modelica functionalities, the combination of these new libraries with other Modelica libraries and the validation of the developed models using case studies and benchmarking systems.

Modeling of the ARGESIM “Crane and Embedded Controller” System using the DEVSLib Modelica library

Abstract DEVSLib is a free Modelica library, developed by the authors, that supports the Parallel DEVS formalism. The library is mainly designed to model discrete-event systems. It also includes interfaces to communicate the DEVSLib models with the rest of the Modelica libraries. Thus, the library can be used in the development of multi-domain and multi-formalism hybrid models. This manuscript discusses the modeling of the system “Crane and Embedded Controller,” proposed by ARGESIM, using Modelica and DEVSLib. The crane system is composed of a car that moves along a rail and a load connected to the car by a cable. A discrete controller controls the position of the car and its movement. The crane system is implemented in Modelica as a continuous-time model and the discrete controller is constructed using DEVSLib. The communication between the continuous-time and the discrete-event parts is performed using the DEVSLib interfaces. DEVSLib is freely available for download at http://www.euclides.dia.uned.es.

Integrating Parallel DEVS and equation-based object-oriented modeling

The benefits of integrating the Parallel DEVS (P-DEVS) formalism with the Equation-Based Object-Oriented modeling languages (EOOL), which constitute the state-of-the-art for continuous-time system modeling, are discussed. The characteristics of the Equation-Based Object-Oriented (EOO) methodology are presented. The requirements to describe P-DEVS models using an EOOL are evaluated. These requirements are detailed for the case of the P-DEVS formalism and the Modelica language, with the introduction of the DEVS-Lib Modelica library. DEVSLib facilitates the description of P-DEVS models in Modelica, and allows the combination of DEVS models together with other Modelica libraries in order to construct multi-formalism hybrid models. DEVSLib has been developed by the authors and is freely available at http://www.euclides.dia.uned.es.

DEVS specification and implementation of SIMAN blocks using Modelica language

Modelica is a general object-oriented simulation language mainly based on non-causal modeling with mathematical equations. The aim of our work is to develop a Modelica library, ARENALib, for discrete process-oriented system modeling with comparable functionalities to Arena Basic Process panel. It will provide, combined with the current Modelica components for continuous system modeling, a good tool for modeling hybrid systems. A first version of the library, with basic capabilities, is freely available under GPL license. In this contribution a specification of the Create, Dispose, Queue, Seize, Delay and Release SIMAN blocks using DEVS formalism is presented. The implementation, in Modelica, of SIMANLib library is based on these specifications. Create, Process and Dispose modules of ARENALib have been reimplemented using SIMANLib blocks. A single server system model is also discussed. Future work will consist of the development of more SIMAN blocks to complete ARENALib modules and functionalities.

CellularAutomataLib2: improving the support for cellular automata modelling in Modelica

ABSTRACT CellularAutomataLib is a library developed by the authors to facilitate the description of Cellular Automata (CA) models in Modelica. It supports the description of 1D and 2D CA and their combination with other Modelica models. Modelling versatility and scalability are the main focus in the design. The internal behaviour of CA models is programmed in C, that is consequently hidden to the modelling tool and not considered in the causalization and manipulation of the model. A new version, named CellularAutomataLib2, is presented in this manuscript. The library has been extended to improve the simulation performance, by only evaluating active cells, and to support Lattice Gas Cellular Automata (LGCA) models. The library design and use are discussed. Two models, forest fire spread and the ARGESIM C17 ‘SIR-type Epidemic Spread’, are used to illustrate the functionality of the library. CellularAutomataLib2 is freely available at http://www.euclides.dia.uned.es (under the Modelica License 2).

A systemic approach for modeling biological evolution using Parallel DEVS.

A new model for studying the evolution of living organisms is proposed in this manuscript. The proposed model is based on a non-neodarwinian systemic approach. The model is focused on considering several controversies and open discussions about modern evolutionary biology. Additionally, a simplification of the proposed model, named EvoDEVS, has been mathematically described using the Parallel DEVS formalism and implemented as a computer program using the DEVSLib Modelica library. EvoDEVS serves as an experimental platform to study different conditions and scenarios by means of computer simulations. Two preliminary case studies are presented to illustrate the behavior of the model and validate its results. EvoDEVS is freely available at http://www.euclides.dia.uned.es.

An approach to agent-based modeling with Modelica

Abstract Modelica is a free, general-purpose object-oriented equation-based modeling language. It is mainly designed to describe systems using the physical modeling approach. Our proposal to describe Agent-Based Models (ABMs) in Modelica is discussed in this manuscript. The contribution of the presented work is twofold: firstly, to analyze the conceptual requirements to describe ABMs in Modelica; and secondly, to develop a prototype implementation following the previous analysis. Agents are described using a message passing communication mechanism previously proposed by the authors. Additional extensions to this mechanism are proposed in order to describe agent interactions. The environment, where the agents live, is described as a two-dimensional cellular automaton. A new Modelica library, named ABMLib, developed to support this functionality, is presented. A prototype implementation of the message passing mechanism and ABMLib models has been performed to demonstrate the functionality of the library as a proof-of-concept for this proposal. The library is freely available at www.euclides.dia.uned.es/vsanz .

Modelica extensions for supporting message passing communication and dynamic data structures

Discrete-event modeling methodologies, such as DEVS, Parallel DEVS or the process-oriented approach used by Arena, support the description of systems in a modular and hierarchical fashion. In these approaches, model components communicate by means of message interchange. Messages constitute impulses of information instantaneously sent from one component to another, either individually or arranged in groups, or bags. Dynamic data structures are required to manage bags of messages, either locally or as inputs/outputs of components. This communication approach is conceptually different from the connection between components used in the physical modeling approach supported by Modelica. Improving Modelica to support message passing communication facilitates the description of DEVS models and the development of libraries with analogous functionality to Arena. The authors have previously implemented message passing communication in Modelica using external C functions, but these implementations present some restrictions. The concepts required to describe message passing communication in Modelica are discussed, and a proposal to extend the language is presented. Two simple application examples are also included to illustrate the use of the proposed extensions.

Improving efficiency of hybrid system simulation in Modelica

Modelica supports the modeling of hybrid systems by means of differential and algebraic equations, and discrete-events. The simulation of Modelica models is carried out by solving the continuous-time equations, detecting the occurrence of events and managing the triggered events. After managing an event, the event iteration algorithm is used to find consistent restart conditions before resuming the numerical integration. The objective of the work presented in this manuscript is to describe a procedure to optimize the event iteration algorithm. The structure of the model is analyzed in order to only re-evaluate the equations involved in the management of events. The use of this procedure is described by means of an application example.

Hybrid system modeling using the SIMANLib and ARENALib Modelica libraries

The ARENALib and SIMANLib Modelica libraries replicate the basic functionality of the Arena simulation environment and the SIMAN language. These libraries facilitate describing discrete-event models using the Arena modeling methodology. ARENALib and SIMANLib models can be combined with other Modelica models in order to describe complex hybrid systems (i.e., combined continuous-time and discrete-event systems). The implementation and design of SIMANLib and ARENALib is discussed. The ARENALib components have been built in a modular fashion using SIMANLib. The SIMANLib components have been described as Parallel DEVS models and implemented using DEVSLib, a Modelica library previously developed by the authors to support the Parallel DEVS formalism. The use of Parallel DEVS as underlying mathematical formalism has facilitated the development and maintenance of SIMANLib. The modeling of two hybrid systems is discussed to illustrate the features and use of SIMANLib and ARENALib: firstly, a soaking-pit furnace; secondly, the malaria spread and an emergency hospital. DEVSLib, SIMANLib and ARENALib can be freely downloaded from http://www.euclides.dia.uned.es/.