| 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. |
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| 4. |
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| 5. |
- Führer, Claus, et al.
(författare)
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Integration av numeriska metoder i kemiteknikutbildningen
- 2005
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Ingår i: [Host publication title missing].
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Konferensbidrag (refereegranskat)abstract
- Kemiteknikprogrammet fick en ny utbildningsplan 2001. Enligt den gamla utbildningsplanen fanns det en valfri kurs i numerisk analys under årskurs 4 med ett fåtal studenter. I den nya utbildningsplanen integrerades numeriska metoder med kemiteknik redan under första terminen. Metoder undervisas där problemställningen finns. Vi har valt att kalla undervisningen i numeriska metoder för beräkningsteknik. Den beräkningsmässiga delen av kursen i kemiteknik tillsammans med beräkningsteknik omfattar ca 6 poäng av en 12 poängs kurs. I kemiteknik tränas teknologerna att ställa upp modeller för kemitekniska system. För att lösa dessa krävs i flera fall hjälp av numeriska metoder. I kemiteknik används huvudsakligen färdiga funktioner för att lösa modellerna. Beräkningsteknik lär ut principen bakom de använda metoderna. Vi diskuterar de fördelar vi ser i integrerade och ämnesövergripande upplägg av kursen samt våra erfarenheter av undervisningen efter kursen har gått i fyra år. Vi avslutar med att diskutera hur denna ändring har påverkat programmet i sin helhet.
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| 6. |
- Ghandriz, Toheed, et al.
(författare)
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Structural Optimization of Multibody Systems
- 2015
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Ingår i: Proceedings of the ECCOMAS Thematic Conference on Multibody Dynamics 2015. - 9788494424403 ; , s. 828-838
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Konferensbidrag (refereegranskat)abstract
- Flexible multibody dynamics (FMD) has found many applications in control, analysis and design of mechanical systems. FMD together with the theory of structural optimization can be used for designing multibody systems with bodies which are lighter, but stronger. Topology optimization of static structures is an active research topic in structural mechanics. However, the extension to the dynamic case is less investigated as one has to face serious numerical difficulties. One way of extending static structural topology optimization to topology optimization of dynamic flexible multibody system with large rotational and transitional motion is investigated in this paper. The optimization can be performed simultaneously on all flexible bodies. The simulation part of optimization is based on an FEM approach together with modal reduction. The resulting nonlinear differential-algebraic systems are solved with the error controlled integrator IDA (Sundials) wrapped into Python environment by Assimulo. A modified formulation of solid isometric material with penalization (SIMP) method is suggested to avoid numerical instabilities and convergence failures of the optimizer. Sensitivity analysis is central in structural optimization. The sensitivities are approximated to circumvent the expensive calculations. The provided examples show that the method is indeed suitable for optimizing a wide range of multibody systems. Standard SIMP method in structural topology optimization suggests stiffness penalization. To overcome the problem of instabilities and mesh distortion in the dynamic case we consider here additionally element mass penalization.
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| 7. |
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| 8. |
- Modin, Klas, et al.
(författare)
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Geometric Integration of Weakly Dissipative Systems
- 2009
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Ingår i: Numerical Analysis and Applied Mathematics, Vols 1 and 2. - 1551-7616 .- 0094-243X. ; 1168, s. 877-877
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Konferensbidrag (refereegranskat)abstract
- Some problems in mechanics, e.g. in bearing simulation, contain subsystems that are conservative as well as weakly dissipative subsystems. Our experience is that geometric integration methods are often superior for such systems, as long as the dissipation is weak. Here we develop adaptive methods for dissipative perturbations of Hamiltonian systems. The methods are "geometric" in the sense that the form of the dissipative perturbation is preserved. The methods are linearly explicit, i.e., they require the solution of a linear subsystem. We sketch an analysis in terms of backward error analysis and numerical comparisons with a conventional RK method of the same order is given.
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| 9. |
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| 10. |
- Mohammadi, Fatemeh, et al.
(författare)
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Restarting algorithms for simulation problems with discontinuities
- 2014
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Ingår i: Linköping Electronic Conference Proceedings. - : Linköping University Electronic Press. - 9789175193809 ; , s. 819-826
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Konferensbidrag (refereegranskat)abstract
- Modelica has in its language support for describing discontinuities; so-called events. Modern integrating environments; like Assimulo; provide elaborated event detection and event handling methods. In addition; the overall performance of a simulation of models with discontinuities (hybrid models) depends strongly on methods for restarting integration after event detection. The presented paper reviews two restarting methods; based oRunge--Kutta starters for multistep methods; and presents first experiments on a hybrid system described in Modelica and simulated by JModelica.org/PyFMI and Assimulo.
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