| 1. |
- Andersson, Christian, et al.
(författare)
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A Workbench for Multibody Systems ODE and DAE Solvers
- 2012
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Ingår i: Proceedings of the IMSD2012 - The 2nd Joint International Conference on Multibody System Dynamics. - 9783927618329
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Konferensbidrag (refereegranskat)abstract
- During the last three decades, a vast variety of methods to numerically solve ordinary differential equations (ODEs) and differential algebraic equations (DAEs) has been developed and investigated. Few of them met industrial standards and even less are available within industrial multibody simulation software. Multibody Systems (MBS) offer a challenging class [5] of applications for these methods, since the resulting system equations are in the unconstrained case ODEs which are often stiff or highly oscillatory. In the constrained case the equations are DAEs of index-3 or less. Friction and impact in the MBS model introduce discontinuities into these equations while coupling to discrete controllers and hardware-in-the-loop components couple these equations to additional time discrete descriptions. Many of the developed numerical methods have promising qualities for these types of problems, but rarely got the chance to be tested on large scale problems. One reason is the closed software concept of most of the leading multibody system simulation tools or interface concepts with a high threshold to overcome. Thus, these ideas never left the academic environment with their perhaps complex but dimensionally low scale test problems. In this paper we will present a workbench, ASSIMULO, which allows easy and direct incorporation of new methods for solving ODEs or DAEs written in FORTRAN, C, Python or even MATLAB and which indirectly interfaces to multibody programs such as Dymola and Simpack, via a standardized interface, the functional mock-up interface. The paper is concluded with industrial relevant examples evaluated using industrial and academic solvers.
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| 2. |
- Andersson, Christian, et al.
(författare)
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Import and Export of Functional Mock-up Units in JModelica.org
- 2011
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Ingår i: [Host publication title missing]. - 9789173930963
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Konferensbidrag (refereegranskat)abstract
- Different simulation and modeling tools often use their own definition of how a model is represented and how model data is stored. Complications arise when trying to model parts in one tool and importing the resulting model in another tool or when trying to verify a result by using a different simulation tool. The Functional Mock-up Interface (FMI) is a standard to provide a unified model execution interface. In this paper we present an implementation of the FMI specification in the JModelica.org platform, where support for import and export of FMI compliant models has been added. The JModelica.org FMI import interface is written in Python and offers a complete mapping of the FMI C API. JModelica.org also offers a set of Pythonic convenience methods for interacting with the model in an object-oriented manner. In addition, a connection to the simulation environment Assimulo which is part of JModelica.org is offered to allow for simulation of models following the FMI specification using state of the art numerical integrators. Generation of FMI compliant models from JModelica.org will also be discussed.
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| 3. |
- Andersson, Joel, et al.
(författare)
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CasADi -- A symbolic package for automatic differentiation and optimal control
- 2012
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Ingår i: Recent Advances in Algorithmic Differentiation. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 9783642300226 ; , s. 297-307
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Konferensbidrag (refereegranskat)abstract
- We present CasADi, a free, open-source software tool for rapid, yet efficient solution of optimization problems in general and dynamic optimization problems in particular. To the developer of algorithms for numerical optimization and to the advanced user of such algorithms, it offers a level of abstraction which is notably lower, and hence more flexible, than that of algebraic modeling languages such as AMPL or GAMS, but higher than working with a conventional automatic differentiation (AD) tool. CasADi is best described as a minimalistic computer algebra system (CAS) implementing automatic differentiation in eight different flavors. Similar to algebraic modelling languages, it includes high-level interfaces to state-of-the-art numerical codes for nonlinear programming, quadratic programming and integration of differential-algebraic equations. CasADi is implemented in self-contained C++ code and contains full-featured front-ends to Python and Octave for rapid prototyping. In this paper, we show how CasADi can be used for optimal control using either a collocation approach or a shooting approach.
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| 4. |
- Andersson, Joel, et al.
(författare)
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Dynamic optimization with CasADi
- 2012
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Ingår i: IEEE 51st Annual Conference on Decision and Control (CDC), 2012. - 0743-1546. - 9781467320658 ; , s. 681-686
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Konferensbidrag (refereegranskat)abstract
- We demonstrate how CasADi, a recently devel- oped, free, open-source, general purpose software tool for nonlinear optimization, can be used for dynamic optimization in a flexible, interactive and numerically efficient way. CasADi is best described as a minimalistic computer al- gebra system (CAS) implementing automatic differentiation (AD) in eight different flavors. Similar to algebraic modeling languages like AMPL or GAMS, it includes high-level interfaces to state-of-the-art numerical codes for nonlinear program- ming, quadratic programming and integration of differential- algebraic equations. CasADi is implemented in self-contained C++ code and contains full-featured front-ends to Python and Octave for rapid prototyping. In this paper, we discuss CasADi from the perspective of the developer or advanced user of algorithms for dynamic optimization for the first time, leaving out details on the implementation of the tool. We demonstrate how the tool can be used to model highly complex dynamical systems directly or import existing models formulated in the algebraic modeling language AMPL or the physical modeling language Modelica. Given this symbolic representation of the process models, the resulting optimal control problem can be solved using a vari- ety of methods, including transcription methods (collocation), methods with embedded integrators (multiple shooting) as well as indirect methods.
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| 5. |
- Andersson, Joel, et al.
(författare)
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Integration of CasADi and JModelica.org
- 2011
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Konferensbidrag (refereegranskat)abstract
- This paper presents the integration of two open source softwares: CasADi, which is a framework for efficient evaluation of expressions and their derivatives, and the Modelica-based platform JModelica.org. The integration of the tools is based on an XML format for exchange of DAE models. The JModelica.org platform supports export of models in this XML format, wheras CasADi supports import of models expressed in this format. Furthermore, we have carried out comparisons with ACADO, which is a multiple shooting package for solving optimal control problems. CasADi, in turn, has been interfaced with ACADO Toolkit, enabling users to define optimal control problems using Modelica and Optimica specifications, and use solve using direct multiple shooting. In addition, a collocation algorithm targeted at solving large-scale DAE constrained dynamic optimization problems has been implemented. This implementation explores CasADi's Python and IPOPT interfaces, which offer a convenient, yet highly efficient environment for development of optimization algorithms. The algorithms are evaluated using industrially relevant benchmark problems.
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| 6. |
- Andersson, Niklas, et al.
(författare)
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Calibration of a polyethylene plant for grade change optimisations
- 2011
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Ingår i: 21ST European Symposium on Computer Aided Process Engineering. - 1570-7946. - 9780444538956 ; 29, s. 673-677
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Konferensbidrag (refereegranskat)abstract
- A polyethylene plant model coded in Modelica and based on a nonlinear MPC model currently used at Borealis AB is considered for calibration. A case study of model calibration at steady-state for four different operating points are analysed, both when looking at one operating point separately, but also to calibrate several simultaneously. Both model parameters and reactor inputs are calibrated for true plant measurement data. To solve the parameter estimation problem, the JModelica.org platform is used, offering tools to express and solve calibration problems. Calibration was obtained with narrow confidence intervals and shows a potential to improve the model accuracy by changing the parameter values. The results will be used for dynamic optimisations of grade changes.
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| 7. |
- Blochwitz, Torsten, et al.
(författare)
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Functional Mockup Interface 2.0: The Standard for Tool independent Exchange of Simulation Models
- 2012
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Ingår i: Proceedings of the 9th International Modelica Conference. - : Linköping University Electronic Press. - 9789175198262 ; , s. 173-184
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Konferensbidrag (refereegranskat)abstract
- The Functional Mockup Interface (FMI) is a tool independent standard for the exchange of dynamic models and for co simulation. The first version, FMI 1.0, was published in 2010. Already more than 30 tools support FMI 1.0. In this paper an overview about the recently published version 2.0 of FMI is given that combines the formerly separated interfaces for Model Exchange and Co-Simulation in one standard. Based on the experience on using FMI 1.0, many small details have been improved and new features ease the usability and increase the performance especially for larger models. Additionally, a free FMI compliance checker will become soon available and FMI models from different tools are made available on the web to simplify testing.
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| 8. |
- Blomé, Mikael, et al.
(författare)
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Course Supervision Challenges in PhD Education
- 2012
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Ingår i: 7:e Pedagogiska Inspirationskonferensen 2012. - 2003-3761 .- 2003-377X. ; 7
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Konferensbidrag (refereegranskat)abstract
- A large portion of the PhD education in Sweden is dedicated to courses. This made it interesting to explore potential course supervision challenges in the PhD programme. A multiple-case study was conducted to identify such challenges and explore how these are perceived by students and supervisors at the Faculty of Engineering of Lund University. By interviewing students and supervisors in five different research groups, insights were gained into how the main stakeholders reason about courses. The findings indicate that courses that are to be included in the education are characterized by a large degree of freedom tailored to individual student needs and preferences. However, the type, timing, availability, value, and convalidation of courses are challenges that limit this freedom.
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| 9. |
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| 10. |
- Broman, David, 1977-, et al.
(författare)
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A comparison of two metacompilation approaches to implementing a complex domaispecific language
- 2012
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Ingår i: Proceedings of the 27th Annual ACM Symposium on Applied Computing (SAC). - New York, NY, USA : ACM. - 9781450308571 ; , s. 1919-1921
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Konferensbidrag (refereegranskat)abstract
- Operational semantics and attribute grammars are examples of formalisms that can be used for generating compilers. We are interested in finding similarities and differences in how these approaches are applied to complex languages, and for generating compilers of such maturity that they have users in industry.As a specific case, we present a comparative analysis of two compilers for Modelica, a language for physical modeling, and which contains numerous compilation challenges. The two compilers are OpenModelica, which is based on big-step operational semantics, and JModelica.org, which is based on reference attribute grammars.
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