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Multibody dynamics in a vehicle instrument
VDO commissioned CADFEM with the simulative multibody analysis of a vehicle instrument in order to achieve a desired vibration amplitude of 5 g.

Rigid and flexible transient analyses in Ansys

Sector: Automotive supplierSpecialist field: Structural mechanics

The drive mechanism of a VDO vehicle instrument, specifically the drive torque, should be designed to achieve a certain vibration amplitude. For a dynamic multibody analysis using simulation, VDO turned to CADFEM.

Summary

Task

A rigid-transient analysis for the multibody system (MBS) is created in Ansys. After importing the CAD model into Ansys DesignModeler, rigid assemblies are grouped, and the rigid parts are connected by joints. Various types of joint elements (spherical, translational, universal, etc.) can be configured by setting appropriate kinematic constraints for each or any of the six relative degrees of freedom of two components. After loading the swivel joint of the eccentric by a transient moment signal, the desired acceleration behavior of the component can be calculated.

Solution

A rigid-transient analysis for the multibody system (MBS) is created in Ansys. After importing the CAD model into Ansys DesignModeler, rigid assemblies are grouped, and the rigid parts are connected by joints. Various types of joint elements (spherical, translational, universal, etc.) can be configured by setting appropriate kinematic constraints for each or any of the six relative degrees of freedom of two components. After loading the swivel joint of the eccentric by a transient moment signal, the desired acceleration behavior of the component can be calculated.

Customer benefits

Even complex assemblies such as a vehicle instrument can be efficiently analyzed thanks to the ability to perform both rigid and flexible multi-body dynamics within a unique, convenient Ansys Workbench user interface.

Project Details

Task

The drive mechanism of a vehicle instrument, specifically the drive torque, should be designed in such a way that vibration amplitudes of 5 g are achieved. An electric motor gives a short impulse (blue arrow in the figure) to an eccentric. The rotation is converted into translational motion by an elastic beam and the vibrating device is suspended from the ground by a spring-damper mechanism. After switching off the torque, the free amplitude of vibration should start at 5 g.


Customer Benefit

Even complex assemblies such as a vehicle instrument can be efficiently analyzed thanks to the ability to perform both rigid and flexible multi-body dynamics within a unique, convenient Ansys Workbench user interface.


Solution

TThe vibration behavior is dominated by the coil spring. The elastic modes of the device itself are assumed to be much higher. For this reason, a rigid-transient analysis for the multibody system (MBS) is set up in Ansys (see feature tree in the figure). After importing the CAD model into Ansys DesignModeler, rigid assemblies are grouped, and the rigid parts are connected by joints. Various types of joint elements (spherical, translational, universal, etc.) can be configured by setting appropriate kinematic constraints for each or any of the six relative degrees of freedom of two components. After loading the swivel joint of the eccentric by a transient moment signal (blue curve in the figure), the desired acceleration behavior of the component can be calculated (red curve in the figure). Modeling the flexibility of a component can be of moderate importance, but it can also be of critical importance. Here, it was suspected that the long, slender mobile beam would have some influence on the final result. Ansys allows switching between rigid and flexible bodies within the same user interface. In this case, the beam was marked as flexible, resulting in an FE meshed part (see figure). A modal analysis yields the first desired behavior of the vibrating spring-mass system at 60 Hz, followed by the first elastic beam behavior at 800 Hz (see figure). This large frequency gap is the first indication that the assumption of neglecting flexibility qualifies for the rigid transient solution. Performing a flexible transient analysis in Ansys provides a final confirmation, as the displacement results are almost identical compared to the rigid case.

Images: © VDO


Head of Professional Development
Dr.-Ing. Marold Moosrainer

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