Dissertations / Theses on the topic 'Modelica'

OpenModelica is an open-source based development environment for Modelica coordinated by the Programming Environments Laboratory (PELAB) at Linköpings Universitet. Previously an external tool, PtPlot, has been used to create graphics from simulation data. This tool is poorly integrated with OMNotebook, the OpenModelica Notebook, which is a tool for creating interactive documents where Modelica code can be edited and evaluated. This thesis develops and implements a plotting API accessible from Modelica algorithmic code and extends OMNotebook to allow creation of diagrams and other forms of graphics without an external application.These diagrams are more customizable than those generated by PtPlot and allow for example logarithmic scaling. The new Modelica API for graphic programming allows access of graphic functionality from within Modelica models and Modelica functions.

The purpose of this thesis is to examine and present the oportunities of solving

control problems using Modelica. This is done by creating some demonstration

examples with exercises. These examples should cover as many types of control

problems as possible. The exercises are aimed for people with basic knowledge

in modeling and automatic control engineering but with little or no knowledge

in Modelica. There are different types of Modelica implementations and the ones

used in this thesis are OpenModelica and MathModelica.

OpenModelica is a complete environment for developing and simulatingModelica models based on free software. It is promoted and developed bythe OpenModelica Consortium. This thesis details a method for describingand consequently displaying visualizations of Modelica models in OMNote-book, an application in the OpenModelica suite where models can be writtenand simulated in a document mixed with text, images and plots. Two dif-ferent approaches are discussed; one based on Modelica annotations and onebased on creating a simple object hierarchy which can be connected to exist-ing models. Trial implementations are done which make it possible to discardthe annotation approach, and show that an object based solution is the onebest suited for a complete implementation. It is expanded into a working 3Dvisualization solution, embedded in OMNotebook.

Technical systems of today are often complex and integrated. To maintain operational functionality and security it is sometimes necessary to have a surveillance system which can detect a fault in an early stage. The device that detects and locates the faulty component is called a diagnosis system. There are several different approaches to fault diagnosis, this study focus on a part of technical diagnosis that uses a model of the system for assistance to make the diagnosis. In the creation of the model of the system computer tools can be used, in this thesis it is investigated if one such software tool is practical to use in the building of the model of the system.

One aspect of technical diagnosis based on models is the creation of a model of the process in question with support for faults, a fault model. In this thesis, Modelica is used to create fault models. The models produced from Modelica are then analyzed by some existing diagnosis algorithms.

The approach of designing fault models in Modelica and then exporting the corresponding system and perform diagnosis analysis on it in Matlab is considered feasible. But the process falls a bit short of the aim of a automatic model building and and diagnosis analysis procedure.

If the results from this thesis are to be used in the future will depend on if the freedom that Modelica gives in designing fault models are deemed worthwhile to accommodate so that the results from the modeling suits the diagnosis analysis. One way to do ease this transformation of data is to restrict the freedom of model designs in Modelica but then some of the benefit that Modelica brings is negated. It is shown here however that it it possible to design fault models in Modelica and then use the results to analyze the models regarding sensor placement and test design.

Simulations are very important for many reasons, and finding ways of accelerating simulations are therefore interesting. In this thesis the feasibility of automatically generating simulation code for a limited set of Modelica models that can be executed on NVIDIAs CUDA architecture is studied. The OpenModelica compiler, an open-source Modelica compiler, was for this purpose extended to generate CUDA code.

This thesis presents an overview of the CUDA architecture, and looks at the problems that need to be solved to generate efficient simulation code for this architecture. Methods of finding parallelism in models that can be used on the highly parallel CUDA architecture are shown, and methods of efficiently using the available memory spaces on the architecture are also presented.

This thesis shows that it is possible to generate CUDA simulation code for the set of Modelica models that were chosen. It also shows that for models with a large amount of parallelism it is possible to get significant speedups compared with simulation on a normal processor, and a speedup of 4.6 was reached for one of the models used in the thesis. Several suggestions on how the CUDA architecture can be used even more efficiently for Modelica simulations are also given.

A complete Java interface to OpenModelica has been created, supporting both standard Modelica and the metamodeling extensions in MetaModelica. It is bidirectional, and capable of passing both standard Modelica data types, as well as abstract syntax trees and list structures to and from Java and process them in either Java or the OpenModelica Compiler.It currently uses the existing CORBA interface as well as JNI for standard Modelica. It is also capable of automatically generating the Java classes corresponding to MetaModelica code.This interface opens up increased possibilities for tool integration between OpenModelica and Java-based tools, since for example models or model fragments can be extracted from OpenModelica, processed in a Java tool, and put back into the main model representation in OpenModelica.

A first version text generation template language for MetaModelica is also presented. The goal for such a language is the ability to create a more concise and readablecode when translating an abstract syntax tree (AST) to text.

VehProLib is one of many libraries being developed for the object oriented multi-domain language Modelica. The layout and the current status of the library are shown. The aims of the library are to provide the user with a number of different components with different levels of complexity. The components included range from mean value engine components to in-cylinder models. An efficient way to handle parameters using records is provided. Different bus systems are implemented and discussed. Furthermore are replaceable fluid models introduced in the library. It will be shown that Modelica is a very efficient way to create an advanced modelling library.

This thesis is about Model Predictive Control (MPC) method for process control. It describes how this method could be implemented using some different open source software components, describing functionalities of each one and showing how the implementation has been done. Finally the code is tested to demonstrate effectiveness of this software in front of this kind of problems and to demonstrate MPC main characteristics. The main goals of this thesis are these last ones, code development and tests, so all mathematical and theoretical background are described but not as in detail as development and tests. Globally describing, MPC is a process control method where a previous knowledge of the plant is needed, so the controller have a model to simulate and predict the behavior of the system to calculate the best command signal. It has an optimization algorithm determining the optimal trajectory to bring system from initial state to desired state. Optimization is done by iterative simulation and solved online periodically at each sample time, initializing values at each time with measured feedback.

Two ecological models of nitrogen processes in treatment wetlands have been evaluated and compared. These models have been implemented, simulated, and visualized in the Modelica language. The differences and similarities between the Modelica modeling environment used in this thesis and other environments or tools for ecological modeling have been evaluated. The modeling tools evaluated are PowerSim, Simile, Stella, the MathModelica Model Editor, and WEST.

The evaluation and the analysis have been performed using McCall’s factors for software quality (McCall et al, 1977), a correlation analysis and the Constant Comparative Method (Glaser&Strauss, 1999). The results show that the modeling tools and the models can both be separated into two categories: Simple Components and Complex Components for the modeling tools, and Simple Models and Complex Models for the models. The major difference between the Simple Components and the Complex Components is the higher possibility of the Complex Components to create and reuse separate components and the higher complexity in these components. The similarities between the categories are that they are consistent, easy to overview and use, if no new components are to be created. The major difference between the Simple Models and the Complex models lies in the number of functions and in the possibility of reuse and expansion. The similarities between all the models are that they are all consequent, logical, valid, specialized, and easy to use if the user has programming skill.

To conclude thisthesis, the nitrogen decrease in a constructed treatment wetland can well be simulated using the Nitrification/Denitrification model expressed in Modelica and the MathModelica Model Editor. However, some changes to the Model Editor are recommended to make the creation of the model easier. The most important of these changes are the addition of a tutorial, the ddition of useful error handling and messages, and the removal of unnecessary Visio features.

When launching a satellite a separation system is used to keep the satellite attached to a launch vehicle during ascent and to separate it from the launch vehicle while in space. In separation analysis the separation is studied by simulations to see if requirements on the system can be fulfilled. The purpose of this master’s thesis is to investigate if separation analysis can be done using the modeling program OpenModelica and to evaluate OpenModelica and compare it to other modeling programs.

OpenModelica is free software implementing the Modelica language, which is an object-oriented language for modeling and simulation of complex physical systems. Modelica uses equation-based modeling, this means that the physical behaviour of a model is described by differential, algebraic and discrete equations and no particular variable needs to be solved manually.

The work is divided into two parts. The main part is to implement a mathematical model of a separation system in OpenModelica, simulate it and study the behaviour of the system. A Monte Carlo method, which randomly generates values for uncertain model parameters, is used when simulating the model. The other part of the work is to evaluate OpenModelica and compare it with other modeling programs, such as Matlab/Simulink, C/C++ and JAVA to see advantages and disadvantages with OpenModelica.

The hot rod and wire rolling process is widely used to produce rolled iron alloys in different shapes and dimensions. This industry has been under a constant development during the last decades. Today, complex geometries are produced at a high speed since it is possible to use several stands in each mill at the same time. A reason for the development is rising demands from customers. The most important demands are to save energy, to get better material properties and higher dimension accuracy. To meet these demands on speed and accuracy, a better control of how the material behaves in the process is needed. There is also a need to be able to quickly find a new setup of the mill in order to be able to produce other geometries.

The purpose with this Master Thesis is to model and simulate the hot rod and wire rolling process with the modeling language Modelica. The model is given the known inputs and the desired final result in order to compute the unknown inputs to the mill. To meet these goals, a model that depends on for example the gap between the rolls, the roll speeds and the tensions between different stands is needed. It should be possible to make simulations to find roll speeds or to calculate the tensions caused by known roll speeds.

With the help of models of the steps in the process, a model has been developed in Modelica. The model can be expanded to a mill with an arbitrary number of stands. In the search for the best way of modeling a hot rod and wire rolling mill, several algorithms have been simulated and analyzed in Modelica. The results from all simulations show that the billet and the groove should be described by different functions for the upper and the lower half. Furthermore, it is not a good solution to use only polynomials to describe the shapes in the process. A function with infinite derivative in the endpoints is needed to describe the billet in an acceptable way. The problem has also been solved using Matlab. In this work it is shown that the Modelica solution is preferred, compared to solving the optimization problems in Matlab. An advantage with the Modelica solution is that the model can be split into several easily connected sub models. Unfortunately it was even hard for Modelica to solve general problems. The describing functions made it hard to find the intersections and to keep the area constant during the rotation. The least square method could lead to bad approximations of the shapes.

Profilvalsning används idag globalt som en process för att tillverka metaller i olika former och har under de senaste årtiondena varit i en lång utvecklingsfas. Numera valsas komplicerade geometrier samtidigt som produktiviteten har ökat drastiskt tack vare möjligheten att valsa med flera valspar samtidigt. Under utvecklingsprocessen har även kraven från kunderna ökat, främst vad gäller energibesparing och noggrannhet på den slutgiltiga produktens dimensioner och materialegenskaper. För att kunna möta dessa krav på snabbhet och noggrannhet krävs större kontroll av hur materialet beter sig i valsningsprocessen och att det snabbt går att bestämma hur valsverket ska ställas in när en ny serie ska tillverkas.

Syftet med examensarbetet som redovisas i denna rapport är främst att modellera och simulera profilvalsningsprocessen med modelleringsspråket Modelica. Modellen ska sedan kunna användas för att utifrån givna indata till processen bestämma olika inparametrar till valsverket för att uppnå önskat slutresultat. För att nå dessa mål krävs en modell som bland annat beror på spelet mellan valsarna, valshastigheterna och dragen mellan olika valspar. Simuleringar ska kunna göras för att både bestämma önskade valshastigheter och för att beräkna vilka drag givna valshastigheter ger upphov till i valsverket.

Med hjälp av modeller och beskrivningar av de olika stegen i valsningsprocessen har en modell tagits fram i Modelica. Modellen har en given inprofil och kan sedan byggas ut till ett valsverk med önskat antal valspar. I Modelica har olika modeller och algoritmer simulerats och analyserats för att kunna svara på hur ett profilvalsverk modelleras på bästa sätt. Resultaten från de olika simuleringarna visar att heta och valsspår bör beskrivas med olika funktioner för den övre och för den undre delen av profilen. Det är ingen bra lösning att endast använda polynom för att beskriva de olika formerna. En basfunktion med oändlig derivata i ändpunkterna är nödvändig för att beskriva hetan på ett bra sätt. En fördel med Modelica är även att modellen enkelt kan delas upp i flera enkelt sammankopplade delmodeller. Tyvärr var det svårt även för Modelica att lösa generella problem. Funktionerna som användes för att beskriva de olika formerna gjorde det svårt att hitta skärningspunkter och att hålla arean konstant under rotationen. Minsta kvadratmetoden resulterade ibland i dåliga approximationer av de olika formerna.

Mathematical models possible to simulate are of great importance in order to make successful projects in the aircraft manufacturing industry. An aircraft fuel system is very complex, containing pipes, tanks, orifices, valves and pumps. The principal of this thesis is using the tool Easy5, which no longer is considered reliable enough in terms of development and support. This thesis tries to evaluate the Modelica language as a possible alternative to Easy5. To make this evaluation, the components concerned in the fuel library in Easy5 are implemented to the Modelica language. Small hydraulic systems are built up in Dymola, and verified against Easy5 through simulation with high accuracy.

A model of the fuel system of an unmanned aerial vehicle (UAV) is built from the implemented Modelica components to examine how Dymola manage a large model. The simulation made in Dymola was considerably more time efficient than the one made in Easy5, in the range of minutes instead of hours. Thus, much time can be saved if Dymola is used instead of Easy5.

Finally, the components in the fuel library handle a two phase flow of fuel and air. Modeling a two phase flow is not trivial and discontinuous mass flow and pressure values are also implemented and discussed.

För att driva framgångsrika projekt inom flygindustrin är det av stor vikt att ha matematiska modeller som kan simuleras. Ett bränslesystem till ett flygplan kan ses som ett komplext system bestående av bl.a. rör, tankar, ventiler och pumpar. För närvarande använder uppdragsgivaren till detta examensarbete modeller till dessa komponenter i verktyget Easy5, vars framtid anses osäker med avseende på nyutveckling och support. Syftet med detta examensarbete är därför att utvärdera modelleringsspråket Modelica som möjligt alternativ till Easy5. För att kunna göra en utvärdering implementeras berörda komponenter i Modelica med utgångspunkt från Easy5s bränslebibliotek. Mindre hydrauliska system skapas i verktyget Dymola, och dessa verifieras mot Easy5 genom simuleringar. Simuleringsresultaten visar på hög överensstämmelse mellan de båda verktygen.

För att undersöka hur verktyget Dymola hanterar en stor modell skapas bränslesystemet till ett obemannat flygplan (UAV) utifrån de implementerade Modelicakomponenterna. Resultat tyder på att simuleringstiden kan kortas betydligt om Dymola används gentemot Easy5; storleksordningen minuter istället för timmar.

Avslutningsvis hanterar komponenterna i bränslebiblioteket ett massflöde av både bränsle och luft. Att modellera ett 2-fasflöde stöter på vissa simuleringstekniska komplikationer i form av diskontinuerliga massflöden och tryck, vilket visas och diskuteras.

During the most recent decades modern equation-based object-oriented modeling and simulation languages, such as Modelica, have become available. This has made it easier to build complex and more detailed models for use in simulation. To be able to simulate such large and complex systems it is sometimes not enough to rely on the ability of a compiler to optimize the simulation code and reduce the size of the underlying set of equations to speed up the simulation on a single processor. Instead we must look for ways to utilize the increasing number of processing units available in modern computers. However to gain any increased performance from a parallel computer the simulation program must be expressed in a way that exposes the potential parallelism to the computer. Doing this manually is not a simple task and most modelers are not experts in parallel computing. Therefore it is very appealing to let the compiler parallelize the simulation code automatically. This thesis investigates techniques of using automatic translation of models in typical equation based languages, such as Modelica, into parallel simulation code that enable high utilization of available processors in a parallel computer. The two main ideas investigated here are the following: first, to apply parallelization simultaneously to both the system equations and the numerical solver, and secondly. to use software pipelining to further reduce the time processors are kept waiting for the results of other processors. Prototype implementations of the investigated techniques have been developed as a part of the OpenModelica open source compiler for Modelica. The prototype has been used to evaluate the parallelization techniques by measuring the execution time of test models on a few parallel archtectures and to compare the results to sequential code as well as to the results achieved in earlier work. A measured speedup of 6.1 on eight processors on a shared memory machine has been reached. It still remains to evaluate the methods for a wider range of test models and parallel architectures.