Create Flexible Body Input File without Radioss

Computes the required data to write a flexible body input file without using Radioss.

Follow these steps:
  1. Using a vibration code, compute the mass and stiffness matrices on the model corresponding to the flexible body, then compute the local reduction modes. The modes family can be of any kind (free eigen modes, Craig & Bampton modes, refer to Dynamic Analysis in the Radioss Theory Manual for further details).

    Orthogonalize the reduction modes with respect to the mass matrix so that the local projected mass matrix is diagonal for matters of efficiency.

  2. Choose the locations of the points defining the orthonormal local frame. For example, the origin can be placed at the center of mass if known. Compute the components of the modes defining the finite rigid motion of the flexible body from the coordinates of the nodes in the local frame. Add to the family the modes associated with rotational DOF, if necessary.

    Store the rotation matrix from the local frame to the global frame (it is simply the coordinates of the vectors of the local triedra expressed in the global frame). It is needed to input the initial orientation of the flexible body.

  3. Compute the projected matrices M R , M L , and K L . Separately store the full symmetric part and the diagonal part of the local projected stiffness matrix. Compute the maximum eigen frequency of the local dynamic system from M L and K L .
  4. Compute the nine T k l matrices and transform all the vectors of the local modes family and of the finite rigid body modes family through these matrices.

    Compute the nine mass coupling matrices M C k l and the nine stiffness coupling matrices K C k l .