Universität Stuttgart
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Item Open Access Prospects of the German multibody system research project on vehicle dynamics simulation(1992) Schiehlen, WernerThe German Research Council (DFG) decided 1987 to establish a nationwide research project devoted to dynamics of multibody systems. In this project 14 universities and research centers are cooperating with the goal to develop a general purpose multibody system software package. This concept provides the opportunity to use a modular structure of the software, i.e. different multibody formalisms may be combined with different simulation programmes via standardized interfaces. For the DFG project the database RSYST was chosen using standard FORTRAN 77 and an object oriented multibody system datamodel was defined. According to the modular concept the requirements of vehicle system dynamics as tire models or railway wheel-rail models, respectively, are easily met. The Iltis benchmark problem is used to demonstrate some features of the object oriented datamodel.Item Open Access Werkzeuge zur Simulation von Mehrkörpersystemen(1992) Leister, Günter; Schiehlen, WernerDas dynamische Verhalten von komplexen mechanischen Systemen beeinflußt maßgeblich die Bauteildimensionierung und die Funktionalität von Konstruktionen. Bei der Konzeption von Fahrzeugen, Maschinen und Robotern muß daher dem dynamjschen Verhalten große Beachtung geschenkt werden. Für den Konstrukteur ist es dabei wünschenswert, in einem möglichst frühen Stadium der Konstruktion zuverlässige Aussagen über das dynamische Verhalten zu haben. Ein bewährtes Vorgehen hierfür ist die Simulation des dynamischen Verhaltens mit Rechenmodellen. Die Aufstellung der Bewegungsgleichungen und die Einbindung der Gleichungen in eine geeignete Simulationsumgebung ist vor allem bei großen Ersatzmodellen aufwendig und fehlerträchtig. In diesem Beitrag werden die speziell für die Mehrkörperdynamik konzipierten Werkzeuge NEWEUL und NEWSIM vorgestellt. Ausgehend von der Mehrkörpersystembeschreibung generiert das Programmpaket NEWEUL symbolische Differentialgleichungen und stellt alle für eine automatische Simulation erforderlichen Informationen bereit. Das Programmsystem NEWSIM verwendet anschließend die symbolischen Bewegungsgleichungen in kompilierter Form für die Simulation. Durch die Verwendung eines obiektorientierten Datenmodells stellen die Programme NEWEUL und NEWSIM Werkzeuge eines modulares Programmpaket für die Mehrkörperdynamik dar. Dieses Vorgeben wird am Beispiel eines Mehrfachpendels und eines Ackerschleppers erläutert.Item Open Access Application of parallel computing to robot dynamics(1993) Schäfer, Peter; Schiehlen, WernerIn this paper an approach for the application of parallel processing to the dynamic analysis of robots based on the multibody system method is presented. The inherent structure of the symbolic equations of motion is used for partitioning those into independent modules for concurrent evaluation. The applied strategies for parallelization include the parallel evaluation of subsystem equations and the parallel computation of the inertia matrix along with its factorization, and of the force vectors and control inputs. The implementation of the parallel structures is discussed with respect to optimal utilization of transputer resources. The presented approach yields a strong reduction of computing time and supports real-time simulations of controlled robots, which is also shown in an example.Item Open Access Ein Baukastenkonzept für Modellerstellung, Simulation und Optimierung von Fahrzeugen(1992) Leister, Günter; Schiehlen, WernerDie Methode der Mehrkörpersysteme wird bei der Simulation von Fahrzeugen seit Jahren mit Erfolg eingesetzt. Dabei sind die zu untersuchenden Ersatzmodelle immer umfangreicher geworden. In der Fahrzeugdynamik werden deshalb Mehrkörpersysteme häufig in Komponenten zerlegt, die sowohl als Einzelmodell aber auch in Verbindung mit anderen Modellen verwendet werden und die einzeln verifiziert sind. Mit Hilfe eines objektorientierten Datenmodells für Mehrkörpersysteme ist die Wiederverwendung derartiger Komponenten, wie beispielsweise kompletten Radaufhängungen, leicht möglich. Eine zentrale Rolle im Gesamtablauf einer Dynamikanalyse spielen Formalismen zur Aufstellung, sowie Integrationsverfahren zur Lösung der Bewegungsgleichungen. Sollen Formalismen und Integrationsverfahren innerhalb einer modularen Software-Umgebung verwendet werden, so müssen die zugrunde liegenden Berechnungsmethoden automatisiert ablaufen. Es werden Methoden zur automatischen Aufstellung und Simulation symbolischer Bewegungsgleichungen von Mehrkörpersystemen vorgestellt. Ausgehend von einem standardisierten Datenmodell für Mehrkörpersysteme werden mit dem Programmsystem NEWEUL symbolische Bewegungsgleichungen in Minimalform aufgestellt und problemspezifische Simulationsprogramme automatisch generiert. Diese werden in compilierter Form innerhalb des Programmsystems NEWSIM für die Simulation verwendet. Dies wird an einem Beispiel aus der Fahrzeugdynamik verdeutlicht.Item Open Access Multibody systems and robot dynamics(1990) Schiehlen, WernerThe method of multibody system has been developed during the last two decades with application to various engineering topics, including robotics and walking machines. On the other hand, special algorithms for robot dynamics are available featuring the high computational efficiency required for control purposes. This paper shows the close relation between both approaches. Essential criteria for the effeciency of dynamics software are the numbers of coordinates used, which should be minimal. For illustration a two-body system is considered, including open and cIosed loop configurations.Item Open Access Towards learning human-seat interactions for optimally controlled multibody models to generate realistic occupant motion(2023) Fahse, Niklas; Harant, Monika; Roller, Michael; Kempter, Fabian; Obentheuer, Marius; Linn, Joachim; Fehr, JörgItem Open Access Inverse fuzzy arithmetic for the quality assessment of substructured models(2015) Iroz, Igor; Carvajal, Sergio; Hanss, Michael; Eberhard, PeterThe dynamical analysis of complex structures often suffers from large computational efforts, so that the application of substructuring methods has gained increasing importance in the last years. Substructuring enables dividing large finite element models and reducing the resulting multiple bodies, yielding a reduction of, in this case, complex eigenvalue calculation time. This method is used to predict the appearance of friction-induced vibrations such as squeal in brake systems. Since the method is very sensitive to changes in parameter values, uncertainties influencing the results are included and identified. As uncertain parameters, standard coupling elements are considered and modeled by so-called fuzzy numbers, which are particularly well suited to represent epis- temic uncertainties of modeled physical phenomena. The influence of these uncertainties is transferred to undamped and damped eigenfrequencies of a substructured model by means of direct fuzzy analyses. An inverse fuzzy arithmetical approach is applied to identify the uncertain parameters that optimally cover the undamped reference eigenfrequencies of a non-substructured, full model. If a validity criteria is defined, a positive decision in favor of the most adequate model can be performed.Item Open Access Improving the accuracy of musculotendon models for the simulation of active lengthening(2023) Millard, Matthew; Kempter, Fabian; Stutzig, Norman; Siebert, Tobias; Fehr, JörgVehicle accidents can cause neck injuries which are costly for individuals and society. Safety systems could be designed to reduce the risk of neck injury if it were possible to accurately simulate the tissue-level injuries that later lead to chronic pain. During a crash, reflexes cause the muscles of the neck to be actively lengthened. Although the muscles of the neck are often only mildly injured, the forces developed by the neck’s musculature affect the tissues that are more severely injured. In this work, we compare the forces developed by MAT_156, LS-DYNA’s Hill-type model, and the newly proposed VEXAT muscle model during active lengthening. The results show that Hill-type muscle models underestimate forces developed during active lengthening, while the VEXAT model can more faithfully reproduce experimental measurements.Item Open Access On the validation of human body models with a driver-in-the-loop simulator(2018) Kempter, Fabian; Fehr, Jörg; Stutzig, Norman; Siebert, TobiasFor the development of modern integrated safety systems, standard simulation models of anthropometric test devices, often called crash test dummies, are inappropriate for Pre-Crash investigations due to missing activation possibilities, tuned characteristics for one specific accident scenario and high passive stiffness properties. To validate safety concepts getting active prior to the crash new tools like suitable virtual models of human occupants are required. Human Body Models (HBM) provide a higher biofidelity and can be equipped with active muscle elements enabling different muscle activation strategies. To improve the muscle activation strategy and the stiffness properties of active HBMs, validation processes on the basis of low-acceleration experiments are inevitable. In contrast to Post Mortem Human Surrogates only low-severity tests can be performed with real human subjects. This paper presents the workflow of a validation process based on an academic scale Driver-in-the-Loop (DiL) simulator in combination with a synchronized measurement chain consisting of an Optitrack stereo vision and an electromyography detection system.Item Open Access Finite element simulations of motorcyclist interaction with a novel passive safety concept for motorcycles(2021) Maier, Steffen; Doléac, Laurent; Hertneck, Holger; Stahlschmidt, Sebastian; Fehr, Jörg