10.1.4. RFlex Body Reference Frame

The plot data is the RFlex Body Reference Frame for the RFlex body.

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Figure 10.3 Plot Data for the RFlex body

  • Definition of the RFlex Body Reference Frame

    • The RFlex Body Reference Frame is defined a reference frame of whole data of the RFI file which have followings.

      • Node – ID, initial position, and mass

      • Element connectivity

      • Properties

      • Frequencies (Eigen value)

      • Mode Shapes (Eigen vector, Stress shape and Strain shape)

      • …

    • The reference frame is set by CAD/Mesher program. (The reference frame is set the Ground.Inertia marker on the CAD/Mesher program.) FE software just uses and calculates all data with respect to the reference frame. Therefore, the outputs are written in RFI file. See the Figure 10.4.

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      Figure 10.4 Create procedure of a RFlex body

    • When the RFlex/Import procedure, the first choosing point is located the RFlex Reference Frame.

    • The RFlex Reference Frame is shown in “Origin & Orientation” tabs in the RFlex Properties dialog. The Origin and Euler Angle data is the same with the initial value of RFlex plot data. See Figure 10.5.

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      Figure 10.5 Origin & Orientation in RFlex Properties dialog

  • Why the RFlex Body Reference Frame is used instead RFlex CM?

    • Using the RFlex Body Reference Frame gives following benefits:

      • There’s no converting procedure for using data of the RFI file.

      • The interface for FE Software can be defined easily using the RFlex Body Reference Frame. Followings export functions are already used this assumption: FEA Export, MDF Export, and Durability (FEMFAT) Interface.

    • The EOM of RecurDyn/Solver for MFBD is developed using the RFlex Body Reference Frame. (Therefore, the solver doesn’t calculate the RFlex CM.)

    • RecurDyn/GUI also uses the RFlex Body Reference Frame. (Because, GUI also uses the RFI file.)

  • Theoretical meaning of the RFlex Body Reference Frame

    • Floating Frame of Reference Formulation is a theoretical name of RFlex. (Shabana A., “Dynamics of Multibody Systems”, John Wiley & Sons, New York, 1989.) Therefore, the RFlex Body Reference Frame is changing with simulation condition even though a constraint is set. Because, the RFlex Body Reference Frame is a floating.

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      Figure 10.6 Floating Reference Frame

  • How to get the RFlex CM?

    • Approximation – using RFlex CM marker

      • The RFlex CM marker can be used like as general marker in the Expression and Request. The kinematics is calculated as the same method for the RFlex marker. (The displacement with respect to the Reference Node is constant. The reference node is defined as a nearest node from the marker.)

    • Exact CM position