On the contact detection for contact-impact analysis in multibody systems

One of the most important and complex parts of the simulation of multibody systems with contact-impact involves the detection of the precise instant of impact. In general, the periods of contact are very small and, therefore, the selection of the time step for the integration of the time derivatives of the state variables plays a crucial role in the dynamics of multibody systems. The conservative approach is to use very small time steps throughout the analysis. However, this solution is not efficient from the computational view point. When variable time step integration algorithms are used and the pre-impact dynamics does not involve high-frequencies the integration algorithms may use larger time steps and the contact between two surfaces may start with initial penetrations that are artificially high. This fact leads either to a stall of the integration algorithm or to contact forces that are physically impossible which, in turn, lead to post-impact dynamics that is unrelated to the physical problem. The main purpose of this work is to present a general and comprehensive approach to automatically adjust the time step, in variable time step integration algorithms, in the vicinity of contact of multibody systems. The proposed methodology ensures that for any impact in a multibody system the time step of the integration is such that any initial penetration is below any prescribed threshold. In the case of the start of contact, and after a time step is complete, the numerical error control of the selected integration algorithm is forced to handle the physical criteria to accept/reject time steps in equal terms with the numerical error control that it normally uses. The main features of this approach are the simplicity of its computational implementation, its good computational efficiency and its ability to deal with the transitions between non contact and contact situations in multibody dynamics. A demonstration case provides the results that support the discussion and show the validity of the proposed methodology.Fundação para a Ciência e a Tecnologia (FCT

Interaction of Vehicles and Flexible Tracks by Co-Simulation of Multibody Vehicle Systems and Finite Element Track Models

Co-Simulation gives a suitable framework for coupling software-tools specialized for the application in different fields of mechanics and/or physics, particularly if based on different mathematical methods. For the computational analysis of a vehicles running behaviour usually a Multibody System approach is used while flexible tracks representing for example a bridge are best examined with the help of Finite Element software. Now, for the simulation of a vehicle running on a flexible track without neglecting the inherent interaction, an obvious and promising strategy is to simulate each of the two subsystems (vehicle and flexible track) with the appropriate software concurrently and to exchange the interfacing data at discrete communication points. To minimize the numerical effort, the tracks finite element model can be reduced modally to a linear description in a pre-processing step additionally; the resulting linear equations of motion of the track can then be solved analytically with high efficiency. An application of the strategy is demonstrated by a truck and the encounter of two railway vehicles each running on bridges

Interaction of Vehicles and Flexible Tracks by Co-Simulation of Multibody Vehicle Systems and Finite Element Track Models

Co-Simulation gives a suitable framework for coupling software-tools specialized for the application in different fields of mechanics and/or physics, particularly if based on different mathematical methods. For the computational analysis of a vehicles running behaviour usually a Multibody System approach is used while flexible tracks representing for example a bridge - are best examined with the help of Finite Element software. Now, for the simulation of a vehicle running on a flexible track without neglecting the inherent interaction, an obvious and promising strategy is to simulate each of the two subsystems (vehicle and flexible track) with the appropriate software concurrently and to exchange the interfacing data at discrete communication points. To minimize the numerical effort, the tracks finite element model can be reduced modally to a linear description in a pre-processing step additionally; the resulting linear equations of motion of the track can then be solved analytically with high efficiency. An application of the strategy is demonstrated by a truck and the encounter of two railway vehicles each running on bridges

Simulation Techniques for Multidisciplinary Problems in Vehicle System Dynamics

Simulation in vehicle system dynamics has its historical origin in the analysis of the purely mechanical behaviour using mechanical multibody system models. In multibody dynamics very efficient numerical methods for the evaluation and for the time integration of the equations of motion are available. These methods have been extended step-by-step to more complex engineering systems that may contain e.g. flexible bodies and mechatronic or adaptronic devices. Multidisciplinary problems like the interaction of mechanical and hydraulic components or the interaction of vehicle dynamics and aerodynamics are handled conveniently by co-simulation techniques. The present paper summarizes some of these recent extensions of classical multibody dynamics such as multifield problems in the simulation of adaptronic devices, advanced models of contact mechanics and coupled problems including multibody dynamics, aerodynamics and structural mechanics

Modular dynamical simulation of mechatronic and coupled systems

Most of the software tools for the analysis and design of mechatronic systems have their origin in classical mechanics. In multibody dynamics very efficient numerical methods for the evaluation and for the time integration of the equations of motion are available. These methods have been extended step-by-step to more complex engineering systems that may contain, e.g., flexible bodies and mechatronic or adaptronic devices. Coupled problems like the interaction of mechanical and hydraulic components or the interaction of vehicle dynamics and aerodynamics are handled conveniently by co-simulation techniques. The present paper summarizes some of these recent extensions of classical multibody dynamics such as multifield problems in the simulation of adaptronic devices, advanced models of contact mechanics and coupled problems including multibody dynamics, aerodynamics and structural mechanics

Die Fokalinstrumentierung des Roentgensatelliten ROSAT

15 figs.SIGLEDEGerman