Modal super-element definition

@MODAL_SUPERELEMENT_DEFINITION {
@MODAL_SUPERLEMENT_NAME {MseName} {
@BULK_NAME {BulkName}
@REDUCED_MATRICES_FILE_NAME {RedcuedMatrixFileName}
@NUMBER_OF_MODAL_COORDINATES {Nδ}
@LIST_MODE_NUMBERS {n1,n2,etc}
@SHAPE_NAME {ShapeName}
@GRAPHICAL_PARAMETERS_NAME {GrfParamName}
@COMMENTS {CommentText}
}
}

Introduction

A modal based super-element is an elastic substructure whose stiffness and mass characteristics are represented in an approximate manner using Herting's modal reduction approach. The super-element takes into account the elastic deformations of the structure by means of a modal representation. In addition, the substructure is allowed undergo large rigid body displacements and rotations. The modal based super-element is associated with a bulk, BulkName, which contains the ordered list of interface vertices. All the interface points must feature six degrees of freedom: three displacements and three rotations.

The geometry of the modal super-element is inherited from bulk, BulkName, which must have an associated triad, TriadName. The displacements and rotations components at the interface points are all measured in this triad.

NOTES

  1. The entries of the reduced symmetric mass and stiffness matrices must be given as the fields ReducedMassMatrix and ReducedStiffMatrix, respectively, of HDF5 archive ReducedMatrixFileName. Optionally, a reduced damping matrix can be specified with the field ReducedDampingMatrix. Typically, these matrices are obtained by applying Herting's transformation to the unconstrained mass and stiffness matrices computed by a finite element package such as NASTRAN.
  2. The number of boundary points, Nbpt, and modal coordinates, Nδ, determines the size of the reduced mass and stiffness matrices: 6Nbpt + Nδ. If Nδ is smaller than the number of modes used to form the reduced matrices stored in the HDF5 ReducedMatrixFileName, only the first Nδ modes will be used. Alternatively, an ordered list of desired modes to be used from the HDF5 archive can be specified, e.g., n1 = 3, n2= 5. The last entry of this list cannot exceed the number of modes used to form the reduced matrices.
  3. An external shape, ShapeName, can be optionally defined for the modal super-element. This external shape is exclusively used in the visualization post-processor and has no effect on the analysis procedure. Modal super-element shapes must be of the SURFACE type.
  4. It is possible to attach comments to the definition of the object; these comments have no effect on its definition.

Sensors

  1. Sensors can be defined to extract information about modal super-elements. The following SensorType and associated FrameName specifications are allowed for modal super-elements: DISPLACEMENTS, MODAL_COORDINATES, CONFIGURATION, VELOCITIES, ACCELERATIONS. (Default value: DISPLACEMENTS).
  2. For SensorType = DISPLACEMENTS, CONFIGURATION, VELOCITIES or ACCELERATIONS, a u value is accepted for the modal super-element; u = 0 refers to the floating frame and u = k referes to the k-th vertex of bulk BulkName. For SensorType = MODAL_COORDINATES, six of the modal coordinates are evaluated as determined by the u value. If u = 1, the first six modal coordinates are evaluated, if If u = 2, the next six are evaluated, etc. u is an integer such that 1 ≤ u ≤ Nδ/6. No v value is accepted for the modal super-element.