Siemens Railway Engineering  Award for Georg Prinz’s master’s thesis on the topic:


Integration of flexible bodies in multi-body systems

Georg Prinz, who researches in the field of rail systems at the VIRTUAL VEHICLE Research Center in Graz, received the Siemens Railway Engineering Award for his pioneering master’s thesis on the “Integration of flexible bodies in multi-body systems”.

Picture (from the left): Diemo Wojik (Siemens Mobility, Head of Engineering), Mike Rabanser (3rd place), Georg Prinz (first place), Julian Torggler (first place), Stefan Erlach (Siemens Mobility, Head of Bogies), Horst Bischof (TU Graz, Vizerektor)

(Photograph: Oliver Wolf)

When creating multi-body simulation models (MBS models) in development projects, it is necessary to integrate simplified flexible bodies into the model. Basically, a multibody system consists of rigid components that are connected to each other by coupling elements. For certain investigations, elasticity must be taken into account, which is why flexible bodies must be integrated into the MBS model according to a reduction procedure. Usually, a finite element method (FEM) is used for this, which is often not available to the users of the MBS.

With the FEM method, the CAD model is broken down into a limited number of small elements. The FEM model consists of several thousand nodes and degrees of freedom, but the MBS software can only handle a few hundred degrees of freedom efficiently. For this reason, it is necessary to reduce the flexible body before integrating it into the multi-body simulation.

Figure 1: Integration of flexible bodies

Figure 1: Integration of flexible bodies

The aim of the master’s thesis was to create a toolbox based on freely usable software that can be used to create and prepare flexible bodies for MBS. This enables the application of MBS models even without special knowledge of FEM and allows MBS developers to independently create flexible components and integrate them into the simulation. In addition, alternative reduction methods (MOR methods) were implemented in the toolbox that are not available in commercial software. These reduction methods were compared and evaluated to determine their practicality. Finally, simulations were carried out to investigate the influence of flexible components on the driving dynamics of rail vehicles.

Fig. 2 shows the process of the toolbox with the different modules:

Figure 2: Toolbox flowchart

Figure 2: Toolbox flowchart

First a 3D model of the flexible component is created and saved as a STEP file. This file is read into PYTHON and sent to the mesher. For the generation of the solver input file, the coordinates of the main nodes, i.e. the nodes of the reduced model, are also specified. The positions of these nodes should be chosen so that they coincide with the markers of the (possibly already existing) MBS model and are distributed as evenly as possible over the body. Based on the FE mesh and the definition of the main nodes, a solver input file is generated and sent to the FE solver. The solver performs a modal analysis and stores the mass and stiffness matrix, which are subsequently reduced using a MOR method. Various validation methods can still be used to check the quality of the reduced system. In the next step, the reduced matrices are used to create the interface file, which can be read into the MKS software, whereupon the component has flexible properties.

By using PYTHON as the programming language, the toolbox can be easily extended and adapted to specific tasks in the future.

The toolbox created can be used in all areas that require flexible MBS and is therefore not limited to the rail vehicle sector.