Comparison of Model Order Reduction Techniques for Flexible Multibody Dynamics using an Equivalent Rigid-Link System Approach

In this paper we present a comparison of different model order reduction techniques for flexible multibody dynamics. In particular, we adopt a formulation based on a Equivalent Rigid-Link System (ERLS). This approach is suitable in the case of large displacements and small elastic deformations and it allows the kinematic equations of motion to be decoupled from the compatibility equations of the displacements at the joints. The ERLS approach, recently extended through a modal formulation, is here implemented in combination with different reduction techniques, i.e. Craig- Bampton, Interior Mode Ranking (IMR), Guyan, Least Square Model Reduction (LSMR) and Mode Displacement Method (MDM). In order to assess the advantages and disadvantages of the different methodologies, these techniques are applied to a benchmark mechanism under different input conditions, i.e. gravitational force and step torque input. The accuracy of each reduced model is numerically evaluated through the comparison of computational time, the behaviour in frequency domain and by means of vector correlation methods, i.e. the Modal Assurance Criterion (MAC), the Cross-Orthogonality (CO) and the Normalized Cross-Orthogonality (NCO).