Alfonso Urquia

Development of virtual-labs for education in chemical process control using Modelica

Abstract Virtual-labs are useful tools for education in chemical process control. A novel approach to virtual-lab implementation using the Modelica language is presented. This approach has the following advantages. Firstly, existing Modelica models can be employed to develop virtual-labs. If new models need to be programmed, the use of Modelica reduces considerably the modeling effort. Secondly, as the complete virtual-lab is described in Modelica, virtual-lab developers don’t need to use programming languages. Finally, virtual-labs can be easily distributed to the users, who don’t need to install any additional software. The proposed approach is based on the application of a methodology for interactive model development, and two software tools: a free Modelica library, named Interactive ( http://www.euclides.dia.uned.es/Interactive ), and the Dymola modeling environment. Several virtual-labs have been implemented and successfully applied to education in chemical process control. The development of a virtual-lab based on a complex model of a double-pipe heat exchanger is discussed.

OBJECT-ORIENTED MODELING OF VIRTUAL LABORATORIES FOR CONTROL EDUCATION

Esta tesis se ha centrado en el desarrollo de laboratorios virtuales en el ambito del control usando el lenguaje Modelica. Los laboratorios virtuales son herramientas docentes utiles en la ensenanza del control automatico. Por otra parte, los lenguajes de modelado orientado a sujetos y sus entornos de simulacion constituyen el estado del arte para la descripcion y simulacion de los modelos matematicos usados en el ambito del control. En particular, el lenguaje de modelado orientado a objetos Modelica constituye un estandar para el intercambio de modelos entre diferentes herramientas y desarrolladores. Sin embargo, ni el lenguaje Modelica, ni los entornos de simulacion que soportan Modelica, tales como Dymola u OpenModelica, ofrecen capacidades para la simulacion interactiva. Por tanto, la la aplicacion de Modelica al desarrollo de laboratorios virtuales en el ambito del control es un campo de investigacion abierto. En esta tesis se han propuesto dos enfoques diferentes para el desarrollo de laboratorios virtuales usando el lenguaje Modelica. En primer lugar, se han propuesto las metodologias y se han desarrollado las herramientas software necesarias para el desarrollo de laboratorios virtuales combinando el uso de Modelica/Dymola, y herramientas que permiten la creacion sencilla de la interfaz grafica de usuario, como los entornos Ejs y Sysquake. En este caso, el modelo de laboratorio virtual se desarrolla mediante Modelica/Dymola, y la interfaz grafica del laboratorio mediante Ej y Sysquake. En segundo lugar, se ha desarrollado una metodologia para transformar cualquier modelo escrito en Modelica a una formulacion adecuada para la simulacion interactiva y se ha programado una libreria en lenguaje Modelica, denominada VirtualLabBuilder, posibilita el desarrollo de los laboratorios virtuales usando solo Modelica/Dymola. Esta libreria contiene un conjunto de modelos, escritos en lenguaje Modelica, de elementos graficos interactivos que permiten una creacion sencilla de la interfaz modelo-usuario. Las metodologias propuestas y las herramientas software programadas han sido aplicadas con exito a la adaptacion de librerias existentes en lenguaje Modelica para que sean adecuadas para la simulacion interactiva, tales como la libreria de procesos fisico-quimicos JARA, y al desarrollo de un conjunto laboratorios virtuales para la educacion en control de procesos. Entre los laboratorios virtuales con aplicacion a la ensenanza del control que han sido desarrollados en la tesis cabe destacar los siguientes: laboratorio de un sistema de cuatro tanques, de un evaporador industrial, de un intercambiador de calor, de un reactor quimico, de una casa solar y de una lavadora.

An approach to virtual-lab implementation using Modelica

A novel approach to the implementation of interactive virtual-labs is proposed. The virtual-lab is completely described in Modelica language and translated using Dymola. To achieve this goal, a systematic methodology to transform any Modelica model into a formulation suitable for interactive simulation has been developed. In addition, VirtualLabBuilder Modelica library has been programmed. This library contains a set of Modelica models of visual interactive elements (i.e. containers, animated geometric shapes and interactive controls) that allows easy creation of the virtual-lab view (i.e. the model-to-user interface). This approach has two strong points. Firstly, it allows taking advantage of the Modelica capabilities for multi-domain modelling and model reuse. In particular, existing Modelica libraries for modelling of physical systems can be reused to build the virtual-lab models. Secondly, VirtualLabBuilder library allows describing the virtual-lab view with Modelica, which facilitates its development, maintenance and reuse. The proposed approach is discussed in this manuscript and it is illustrated by means of the following case study: a virtual-lab describing the thermodynamic behaviour of a solar house. VirtualLabBuilder library can be freely downloaded from http://www.euclides.dia.uned.es/

Development of an industrial boiler virtual‐lab for control education using Modelica

The use of the VirtualLabBuilder Modelica library and the Dymola modeling environment facilitates the implementation of virtual‐labs with elaborated user interfaces, and based on large and complex Modelica models. This implementation methodology is applied to develop an industrial boiler virtual‐lab for process control education. VirtualLabBuilder is freely available at www.euclides.dia.uned.es.

Design of SPICE Lib: A Modelica library for modeling and analysis of electric circuits

SPICELib is an object-oriented model library, written in the Modelica language, that implements some of the modeling and analysis capabilities of the circuit simulator PSpice. A novel approach has been adopted in the SPICELib design. It arises from considering that the reasons behind the success of PSpice include: the quality of the device models, the variety of supported analyses and the good performance of the numerical simulation. As a consequence, SPICELib is conceived to mimic not only the PSpice device models, but in addition PSpice capability to perform a variety of circuit analyses and the PSpice algorithms to calculate the circuit bias point, which is the most problematic analysis from the numerical standpoint. The fundamental hypotheses and the architecture of SPICELib library are discussed, in addition to the modeling of the supported analyses and devices. A case study is fully developed, in order to illustrate SPICELib use and validation. SPICELib version 1.1 (release October 2003) is free software, and it can be retrieved from the website: http://www.modelica.org/Conference2003/papers.shtml.

Object-oriented Design of Reusable Model Libraries of Hybrid Dynamic Systems -- Part One: A Design Methodology

An object-oriented methodology for the design of reusable model libraries, dedicated to the composition of hybrid simulation models, is proposed. It takes into consideration all the phases of the library life cycle: design, programming, maintenance, modifications, extension, etc. The methodology distinguishes between the role of the library designers and the role of the library users. One of its main goals is guaranteeing that the users are able to use the libraries without having to know their internal details. In particular, users should not be confronted with numerical problems. The library designers should guarantee the numerical efficiency of the models based on the library predefined-models. In this respect, some of the numerical aspects of the model library design are discussed. The concept of library design rules is introduced as the cornerstone of the proposed methodology.

Dynamic modelling of PEM fuel cells using the FuelCellLib Modelica library

FuelCellLib is a free Modelica library for 1D dynamic modelling of PEMFC (proton exchange membrane fuel cells). FuelCellLib models describe the physical–chemical phenomena that take place in the cell cathode and the membrane, including the electrochemical reactions in the catalytic layer, the electron conduction in the catalytic and diffusion layers, the proton conduction in the proton conductor material (e.g. Nafion polymers) of the catalytic layer and the membrane, the coexistence of steam and liquid water, the transport of water in liquid and steam phases, the electro-osmotic drag, the transport of oxygen in steam phase in the catalytic and diffusion layers, the cathode flooding, the membrane drying and the double-layer pseudo-capacitance. The first version of FuelCellLib was released in 2005. The second version of the library, released in 2008, is presented in this article. The modelled phenomena, modelling hypotheses and equations, the library structure and its validation are discussed. Two different validation studies of FuelCellLib PEMFC models have been successfully completed. First, the effect on the simulated cell behaviour of selected electrochemical parameters and operating conditions has been qualitatively analysed, being the obtained results in good agreement with the results reported by other authors. Second, FuelCellLib cell models have been validated using experimental data. The GAPILib Modelica library has been used to fit the PEMFC models to experimental data and to estimate the value of the cell model parameters. FuelCellLib and GAPILib can be freely downloaded from http://www.euclides.dia.uned.es/

Visualization and interactive simulation of Modelica models for control education

An approach to the implementation of virtual-labs well-suited for control education is proposed. The virtual-lab model is described in the Modelica language and it is adapted for interactive simulation by applying a systematic methodology. The virtual-lab view (i.e., the user-to-model interactive interface) is composed by connecting predefined components of Interactive, a free Modelica library presented in this manuscript. Interactive contains a set of ready-to-use Modelica models of visual interactive elements (i.e., containers, animated 3D geometric shapes and interactive controls), intended to facilitate easy definition of the virtual-lab view and the model-to-view communication. Finally, the Modelica description of the virtual-lab is translated into executable code using the Dymola modeling environment. The interactive component models provided in the Interactive library are C++ code generators: when the virtual-lab is executed, the C++ code describing the virtual-lab view and the bidirectional model-to-view communication is automatically generated. The generated C++ code uses the VTK and Qt libraries. The proposed approach is illustrated by means of an example: the development of the virtual-lab of a double-pipe heat exchanger, which is intended for chemical-process control education.

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.