| 1. |
- Eichberger, Alex, et al.
(författare)
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The befenits of parallel multibody simulation and its application to vehicle dynamics
- 1993
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Ingår i: Advanced Multibody System Dynamics. - Dordrecht : Springer Netherlands. - 0792321928 - 9401706255 - 9789048142538 - 9789401706254 ; , s. 107-126
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Bokkapitel (refereegranskat)abstract
- In summer 1987 most of the multibody dynamics community met at the JPL, Pasadena, to discuss the needs and the open problems in multibody system simulation, especially for space applications. P. W. Likins stated in his survey [16]: “Computational questions focused initially on the selection of subroutines for numerical integration, matrix inversion, or eigensystem analysis,and lately have shifted to preprocessors and postprocessors for user convenience. More fundamental issues are raised by the potential of symbolic manipulation and parallel processing, both of which present the possibility of revolutionizing the field.” Concepts for symbolic implementation have been pursued at various places, e.g. [14, 21]. This paper presents results of our efforts to exploit the potential of parallel computer architectures for multibody simulation. It has its roots in an analysis of the status of knowledge at the time, the above statement was made.
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| 2. |
- 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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| 3. |
- 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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| 4. |
- Ghandriz, Toheed, 1982, et al.
(författare)
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Structural topology optimization of multibody systems
- 2016
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Ingår i: Multibody System Dynamics. - : Springer Science and Business Media LLC. - 1384-5640 .- 1573-272X. ; 39:1, s. 135-148
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Tidskriftsartikel (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 (Andersson et al. in Math. Comput. Simul. 116(0):26–43, 2015). A modified formulation of solid isotropic 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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| 5. |
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| 6. |
- 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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| 7. |
- 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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| 8. |
- Rantil, Jens, et al.
(författare)
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Multiple-Shooting Optimization using the JModelica.org Platform
- 2009
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Konferensbidrag (refereegranskat)abstract
- Dynamic optimization is the problem of finding the minimum of a cost function subject to a constraint comprised of a system of differential equations. There are many algorithms to numerically solve such optimization problems. One such algorithm is multiple shooting. This paper reports an implementation of a multiple shooting algorithm in Python. The implementation is based on the open source platform JModelica.org, the integrator SUNDIALS and the optimization algorithm scipy_slsqp. The JModelica.org platform supports model descriptions encoded in the Modelica language and optimization specifications expressed in the extension Optimica. The Modelica/Optimica combination provides simple means to express complex optimization problems in a compact and user-oriented manner. The JModelica.org platform, in turn translates the high-level descriptions into efficient C code which can compiled and linked with Python. As a result, the numerical packages available for Python can be used to develop custom applications based on Modelica/Optimica specifications. An example is provided to illustrate the capabilities of the method.
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| 9. |
- 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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