### Tech Briefs

In conventional multibody simulations, all components are considered to be rigid. However, in many practical applications, it is crucial to take into account the flexibility of some structural components. The ADINA to SIMPACK interface is available in ADINA 8.5 for users to introduce the required flexibility.

In the first step of this process, ADINA is used to perform a finite element analysis of a flexible component decoupled from the rest of the multibody system. This analysis may consist of a frequency solution and various nonlinear static analyses. ADINA creates a file containing the following information

• Frequencies and mode shapes
• Linear stiffness and mass matrices
• Geometric stiffness matrices due to reference forces, gravity loads, centrifugal loads, etc.

This file is then read into SIMPACK to perform the multibody dynamic analysis [1]. This solution includes the calculation of the Frequency Response Modes (FRMs), based on the stiffness and mass matrices provided by ADINA, to enhance the solution accuracy [2].

We present a dynamic simulation to demonstrate this new ADINA feature. An anti-roll bar model of a car's front suspension is considered, see Figure below. A 19-beam element model is defined in ADINA and the 9 lowest non-zero natural frequencies and mode shapes are provided to SIMPACK for the multibody simulation.

Finite Element Mesh of an Anti-roll Bar (Courtesy of INTEC GmbH)

Calculated Displacements at Node 20 Using Different Number of Modes
(With and Without FRM)

Node 20 is subjected to a vertical harmonic load. The response at that node is shown above. Accurate results are obtained by passing only the first 9 eigenmodes (calculated by ADINA) to SIMPACK, particularly if the FRMs are included.

The use of ADINA in multibody simulation to account for flexibility of components can clearly be very important.

References

1. SIMPACK FEMBS documentation
2. Shabana, A. A. Dynamics of Multibody Systems, 2nd Ed. Cambridge University Press, Cambridge, 1998.