Universität Stuttgart
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Item Open Access Analyzing and optimizing multibody systems(1992) Bestle, Dieter; Eberhard, PeterOptimization of holonomic as well as non-holonomic multibody systems is presented as a nonlinear programming problem that can be solved with general-purpose optimization codes. The adjoint variable approach is used for calculating design derivatives of a rather general integral type performance measure with respect to design parameters. The resulting equations are solved by numerical integration backward in time. A multi-step integration algorithm with order and step-size control is adapted for this application by including an interpolation scheme. Numerical experiments and a comparison to the common approach of approximating the gradient of the performance measure by finite differences show that high efficiency, accuracy, and reliability are achievable.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 Cooperative search by combining simulated and real robots in a swarm under the view of multibody system dynamics(2013) Tang, Qirong; Eberhard, PeterThis paper presents a new approach for cooperative search of a robot swarm. After modeling the robot, the mechanical Particle Swarm Optimization method is conducted based on physical robot properties. Benefiting from the effective localization and navigation by sensor data fusion, a mixed robot swarm which contains both simulated and real robots is then successfully used for searching a target cooperatively. With the promising results from experiments based on different scenarios, the feasibility, the interaction of real and simulated robots, the fault tolerance, and also the scalability of the proposed method are investigated.Item Open Access A note on the predictive control of non‐holonomic systems and underactuated vehicles in the presence of drift(2023) Ebel, Henrik; Rosenfelder, Mario; Eberhard, PeterMotion planning and control of non‐holonomic systems is challenging. Only very recently, it has become clear how model predictive controllers for such systems can be generally furnished in the driftless case, where the key is to design a cost function conforming to the geometry arising from the non‐holonomic constraints. However, in some applications, one cannot neglect drift since the time needed to accelerate is non‐negligible, for example, when operating vehicles with high inertia or at high velocities. Therefore, this contribution extends our previous work on the class of driftless non‐holonomic systems to systems with simple kinds of actuator dynamics that allow to represent the boundedness of acceleration in the model. Moreover, we show in a prototypical example of a simple boat‐like vehicle model that a similar procedure can also work for systems that are not non‐holonomic but still under‐actuated. While the contribution is rather technical in nature, to the knowledge of the authors, it is the first time that MPC controllers with theoretical guarantees are proposed for these kinds of models. Moreover, we expect that the resulting controllers are directly of practical value since even the simpler driftless models are employed successfully in various approaches to motion planning.Item Open Access Closing conditions and reaction forces of multibody systems(1992) Schiehlen, Werner; Blajer, WojciechOver the years a considerable effort has been focused on the development of methods and computational algorithms for mathematical modelling and simulation of multibody systems. The methods are mainly concerned with effective formulation and numerical treatment of the dynamical equations of a general multibody system.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 3D FEM simulation of titanium alloy (Ti6Al4V) machining with harmonic endmill tools(2023) Kalu-Uka, Abraham; Ozoegwu, Chigbogu; Eberhard, PeterUsually, end milling operations have been carried out using conventional uniform helix tools with fixed helix angles. Thus, many studies have been conducted to study the effects of these tools on the thermomechanical properties of a milling process. Recently, there have been works that point to the benefits of using harmonic endmills. Harmonic endmills consist of cutting edge profiles that have continuously harmonically varying helix angles. The variation is described using a harmonic function of axial position (elevation) of points on the cutting edge. In this work, a 3D finite element simulation using ABAQUS, is carried out for the complex milling process of Titanium alloy Ti6Al4V. The envelope of the harmonic tool is first generated using a set of MATLAB codes and stored in a Standard Triangle Language (.stl) format. The machine tool is introduced into an FEM program which has been designed to provide for dynamic effects, thermo‐mechanical coupling, material damage law and the criterion for contact associated with the milling process. A Johnson‐Cook material constitutive equation which combines the effects of strain hardening, strain softening, and temperature softening is used. To account for the chip separation criterion, the Johnson Cook damage evolution equation is used. The milling process simulation for Ti6Al4V is then carried out. In the end, the stress distribution and the cutting forces are obtained.Item Open Access Broadband damping properties of particle dampers mounted to dynamic structures(2022) Schönle, A.; Gnanasambandham, C.; Eberhard, P.Background: The background of this work is the classification of the broadband properties of particle dampers (PDs). This broadband characteristic has experienced little systematic investigation in experiments. Objective: So the primary objective of this paper is to find a measure to quantify the broadband damping properties of PDs. Also the demonstration of applicability to technical structures is a desired goal and the experiments provide a sound basis. Methods: The methods for evaluating the performance of particle dampers and tuned mass dampers target the reduction of vibration amplitudes over the frequency range. The test bench consists of a mechanical frame structure with multiple eigenfreqencies up to 200 Hz harmonically excited with an electrodynamic shaker. From the differences in the dynamic behaviour the performance metric will be derived and evaluated. Results: As a result, a dynamic structure is set up as an effective test bench for different damper configurations. Differences of the tested concepts in regard to the dynamic behaviour over a wide frequency range are observed. From the experimental data a performance metric is deduced to quantify these differences. Conclusion: The conclusions drawn from this paper are, that PDs provide high damping over a wide frequency range. Furthermore, with a suitable performance metric this broadband damping properties can be quantified for the use in further development of PDs.Item Open Access Optimierung von Konstruktionsparametern am Beispiel ungefederter Fahrzeuge(1993) Langenbeck, Bernhard; Leister, Günter; Schiehlen, Werner; Kutzbach, Heinz-DieterAm Beispiel eines Ackerschleppers wird ein Verfahren zur Optimierung dynamisch beanspruchter Konstruktionen vorgestellt, wobei das dynamische Verhalten mit Mehrkörpermodellen approximiert wird. Die Autoren beschreiben das Ersatzsystem und die Bewertungskriterien: die Optimierung läuft weitgehend automatisiert ab.