| 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. |
- 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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| 3. |
- Fransson, Åsa, 1971, et al.
(författare)
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Characterization of fractured crystalline rock: two Swedish in situ field experiments
- 2014
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Ingår i: 1st International Discrete Fracture Network Engineering Conference, 20-22 oct 2014, Vancouver, Canada.
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Konferensbidrag (refereegranskat)abstract
- Construction of a nuclear waste repository requires information and an understanding of the fractured rock. The Swedish concept for nuclear waste deposition that is currently being developed by the Swedish Nuclear Fuel and Waste Management Co (SKB) includes a natural barrier in the form of crystalline rock, and engineered barriers in the form of bentonite and a copper canister. This paper aims to present two in situ field experiments: the first is the Large fractures experiment and the second is BRIE, the Bentonite Rock Interaction Experiment. Important issues include possible deformation (shearing) of fractures and deformation zones influencing the localization of canisters, and fluid flow, resulting in hydration of the bentonite. The aim of Large fractures is to further develop strategies and integrated investigation and modelling methodology for the identification and characterization of geological structures to ensure that (size) determination of large fractures or minor deformation zones to a greater extent can be based on real properties and to a lesser degree on a criterion related to the existence of a full perimeter fracture – tunnel intersection. BRIE is a field experiment which addresses the hydraulic interaction between the system components of compacted bentonite and the near-field host rock composed of hard and fractured bedrock. The above experiments are presented in terms of investigations performed to obtain discrete fracture descriptions. Grouting of fractures intersecting the investigation borehole of the Large fractures experiment was designed based on field data and a decrease in flow from above 200 liters/min to below 1 liter/min was achieved. The magnitude of the transmissivity of the fracture/deformation zone that was grouted indicates a large fracture size. This is also indicated by the ongoing integrated interpretation (geology, hydrogeology and geophysics). Results from BRIE show that hydration is uneven and is controlled by the main conductive fracture, highlighting the need for a relevant fracture description.
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| 4. |
- Iwase, Masami, et al.
(författare)
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Analysis of safe manual control by using Furuta pendulum
- 2006
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Ingår i: 2006 IEEE Conference on Computer Aided Control System Design.
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Konferensbidrag (refereegranskat)abstract
- This paper focuses on the interaction of manual and automatic control in a demanding task where the process is unstable and has actuator limitation. The problem is inspired by control of high performance aircrafts but which is similar to controlling the arm of a Furuta pendulum while maintaining the stability of the pendulum. The task is to control the position of the pendulum arm manually while maintaining the pendulum in the upright position. The analysis of regions for safe maneuvers is important to realize the desired control system.
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| 5. |
- Ylikiiskilä, Johan, et al.
(författare)
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Improving Newton's method for Initialization of Modelica models
- 2011
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Konferensbidrag (refereegranskat)abstract
- Initializing a model written in Modelica translates to finding consistent initial values to the underlying DAE. Adding initial equations and conditions creates a system of non-linear equations that can be solved for the initial configuration. This paper reports an implementation of Newton's method to solve the non-linear initialization system. This implementation also uses a regularization method to deal with singular Jacobians as well as sparse solvers to exploit the sparsity structure of the Jacobian. The implementation is based on the open-source projects JModelica.org and Assimulo, KINSOL from the SUNDIALS suite and SuperLU.
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| 6. |
- Åkesson, Johan, et al.
(författare)
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Manual Control and Stabilization of an Inverted Pendulum
- 2005
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Ingår i: Proceedings of the 16th IFAC World Congress. - 008045108X
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Konferensbidrag (refereegranskat)abstract
- The problem of stabilizing an inverted pendulum on a cart while enabling manual control of the cart velocity is treated. Introduction of an input saturation nonlinearity makes the problem challenging in the sense that the system may be driven to a state where recovery is not possible. A controller based on the controllability set of the inverted pendulum, which ensures stability and tracking of constant reference velocities for the cart is developed. The controller also offers a trade-off between performance and robustness.
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| 7. |
- Åkesson, Johan, et al.
(författare)
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Safe Manual Control of the Furuta Pendulum
- 2001
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Ingår i: Proceedings of the 2001 IEEE International Conference on Control Applications, 2001. (CCA '01).. - 0780367332 ; , s. 890-895
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Konferensbidrag (refereegranskat)abstract
- This paper deals with the manual control of unstable systems, subject to control signal saturation. In particular we consider the Furuta pendulum, where the problem is to control the orientation of the arm manually while stabilizing the inverted pendulum. This paper presents an analysis which leads to an insight into the problem as well as the control strategy. This control strategy has been implemented on the real Furuta pendulum. Aspects of the implementation as well as experimental results are discussed
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| 8. |
- Andersson, Christian, et al.
(författare)
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Derivative-free Parameter Optimization of Functional Mock-up Units
- 2012
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Ingår i: [Host publication title missing].
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Konferensbidrag (refereegranskat)abstract
- Representing a physical system with a mathematical model requires knowledge not only about the physical laws governing the dynamics but also about the parameter values of the system. The parameters can sometimes be measured or calculated, however some of them are often difficult or impossible to obtain in these ways. Finding accurate parameter values is crucial for the accuracy of the mathematical model. Estimating the parameters using optimization algorithms which attempt to minimize the error between the response from the mathematical model and the physical system is a common approach for improving the accuracy of the model. Optimization algorithms usually requires information about the derivatives which may not always be available or not be appropriate for estimation which forces the use of derivative-free optimization algorithms. In this paper, we present an implementation of derivative-free optimization algorithms for parameter estimation in the JModelica.org platform. The implementation allows the underlying dynamic system to be represented as a Functional Mock-up Unit (FMU), thus enables parameter estimation of models designed in modeling tools following the standardized interface, the Functional Mock-up Interface (FMI), such as Dymola.
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| 9. |
- 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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| 10. |
- 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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