9. FFlex

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Figure 9.1 FFlex example

In many multibody dynamics models, it is important to include one or more flexible bodies in order to obtain accurate results. Since the mid-1980s the most popular approach for adding flexible bodies is using a modal definition. The advantage of the modal method is that a complex meshed finite element can be reduced to a series of modes that could be efficiently used in multibody dynamics software. However, the modal flexible body has several restrictions that make it difficult to find a correct solution.

  • It is difficult to:

  • Model contact with the modal flexible body accurately because the contact represents a virtual “attachment point” and the associated static correction modes needed for accuracy are not available.

  • Keep the modal flexible body definition currently because of the necessity of using external FEA to:

  • Change the mesh

  • Rerun the modal analysis

  • Redo the import process

These restrictions have been addressed with a new method for working with flexible bodies, RecurDyn/FFlex. You can define a flexible body by reading a FE mesh using industry-standard file formats. The FFlex body includes the element details and has the following benefits. It accurately represents a local deformation due to contact force. It only requires a mesh update as design changes occur. It represents accumulated nonlinear deformations in a flexible body while linear behavior is maintained in each element. This could also be done by defining a series of modal flexible bodies, but that would be too tedious to be practical.

Above all, the FFlex body is easy to use and comfortable to understand. RecurDyn/FFlex should be used in a model with flexible bodies in contact or where it would be helpful to assess the nonlinear deformation.