Computational dynamics: theory and applications of multibody systems

International audienceMultibody system dynamics is an essential part of computational dynamics a topic more generally dealing with kinematics and dynamics of rigid and flexible systems, finite elements methods, and numerical methods for synthesis, optimization and control including nonlinear dynamics approaches. The theoretical background of multibody dynamics is presented, the efficiency of recursive algorithms is shown, methods for dynamical analysis are summarized, and applications to vehicle dynamics and biomechanics are reported. In particular, the wear of railway wheels of high-speed trains and the metabolical cost of human locomotion is analyzed using multibody system methods

Impactless biped walking on a slope

AbstractWalking without impacts has been considered in dynamics as a motion/force control problem. In order to avoid impacts, an approach for both the specified motion of the biped and its ground reaction forces was presented yielding a combined motion and force control problem. As an application, a walker on a horizontal plane has been considered. In this paper, it is shown how the control of the ground reaction forces and the energy consumption depend on the gradient of a slope. The biped dynamics and the constraints within the biped system and on the ground are discussed. A motion control synthesis is developed using the inverse dynamics principle proven to be most efficient for human walking research, too. The impactless walking with controlled legs is illustrated by a seven-link biped. The “flying” biped has nine degrees of freedom, with six control inputs. During locomotion, the standing leg has three scleronomic constraints, and the trunk has three rheonomic constraints. However, there are three rheonomic constraints for the prescribed leg motion or three scleronomic constraints for reaction forces of the trailing leg, respectively. The nominal control action for impactless walking can be precomputed and stored. The model proposed allows the investigation of several problems: uphill and downhill walking, optimization of step length, stiction of the feet on the slope and many more. All these findings are also of interest in biomechanics

Simulation based design of automotive systems

The design of automotive systems using simulation tools features cost reduction and quality enhancement. This paper presents two basic approaches. The rust approach deals with the application of CAD data bases to the evaluation of input data for multibody system formalisms, most adequate for automotive system modeling. An object oriented data model for multibody systems is presented. The second approach covers the development of an integrated simulation tool for automotive vehicles and the corresponding animation facilities. Driving comfort is related to the human perception of mechanical vibration. A companion paper deals with the optimization of automobile parameters using the multi body systems approach

Lage- und Kraftregelung strukturvariabler mechanischer Systeme

Strukturvariable mechanische Systeme sind in der Fertigungstechnik und bei Transportvorgängen häufig zu finden. Eine wichtige Aufgabe besteht darin, geeignete Regelgesetze für einen sanften Bewegungsablauf ohne Kraftsprünge und Kraftimpulse (Stöße) zu finden. Es werden zunächst die Bewegungs- und Reaktionsgleichungen von Mehrkörpersystemen mit Minimalkoordinaten aufgestellt. Dann werden geeignete Regelgesetze entworfen, welche die Sollbewegung sicherstellen und kleine Störungen in den Sensorsignalen ausregeln. Die Methode wird am Beispiel einer ebenen, aus sieben starren Körpern aufgebauten Gehmaschine verdeutlicht. Der Bodenkontakt des abhebenden Fußes erweist sich als vollständig steuerbar, so daß Kraftsprünge beim Übergang von der Stützphase in die Schwingphase vermieden werden können. Der auftretende Fuß erreicht den Boden ohne Stoß

Nonlinear oscillations in multibody systems : modeling and stability assessment

The method of multibody systems results in highly nonlinear and often high-dimensional dynamical equations featuring a broad variety of nonlinear oscillations. The generation of equations of motion, simulation tools and an approach for the stability assessment of nonlinear oscillations from an engineering point of view are presented

An object oriented data model for vehicle dynamics problems

The design of automotive systems using computer codes for vehicle dynamics problems features cost reduction and quality enhancement. This paper presents two basic approaches. The first approach deals with the application of CAD data bases to the evaluation of input data for multibody system formalisms, most adequate for automotive system modelling. An object oriented data model for multibody systems is presented. The second approach covers the development of an integrated simulation tool for automotive vehicles and the corresponding animation facilities. As an example the dynamical analysis of a van is shown including the choice of optimal suspension parameters

Prospects of the German multibody system research project on vehicle dynamics simulation

The 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

Multibody systems and robot dynamics

The 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

Dynamics and control of nonholonomic mobile robot systems

The positional degrees of freedom of a mobile robot are reduced by nonholonomic constraints further to a smaller number of motional degrees of freedom. It is shown how the equations of motion can be reduced to a minimal number using generalized coordinates and generalized velocities. The theoretical results are applied to an actively controlled robot with stiff tires. One scalar control variable provides full controllability of the position of the robot moving on a plane surface. A control strategy is found for stationary and instationary motions

Uncertainties in road vehicle suspensions

Road vehicles are subject to random excitation by the unevenness of the road. For a dynamical analysis, vehicle models of the vertical vibrations as well as guideway models of the road unevenness are required. The fundamental dynamics of vehicle suspensions can be already modeled by a quarter car featuring the decoupling of the car body motion and the wheel motion. This suspension model is characterized by five design parameters where two of them, the shock absorber and the tire spring, are highly uncertain due to wear and poor maintenance. For the assessment of the vehicles performance three criteria have to be used: ride comfort, driving safety and suspension travel. These criteria depend on all the five design parameters resulting in a conflict or a pareto-optimal problem, respectively. In this paper, the uncertainties of the parameters are projected into a criteria space in order to support the decision to be made on the basis of a pareto-optimal problem. Simulations with uncertainties support the robust suspension design. It is shown that controlled suspension parameters remain uncertain due to the unpredictable decisions made by the driver