Modal super-element definition
- @MODAL_SUPERELEMENT_DEFINITION {
- @MODAL_SUPERLEMENT_NAME {MseName} {
- @BULK_NAME {BulkName}
- @REDUCED_MATRICES_FILE_NAME {RedcuedMatrixFileName}
- @NUMBER_OF_MODAL_COORDINATES {N_{δ}}
- @LIST_MODE_NUMBERS {n_{1},n_{2},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
- 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.
- The number of boundary points, N_{bpt}, and modal coordinates, N_{δ}, determines the size of the reduced mass and stiffness matrices: 6N_{bpt} + N_{δ}. If N_{δ} is smaller than the number of modes used to form the reduced matrices stored in the HDF5 ReducedMatrixFileName, only the first N_{δ} modes will be used. Alternatively, an ordered list of desired modes to be used from the HDF5 archive can be specified, e.g., n_{1} = 3, n_{2}= 5. The last entry of this list cannot exceed the number of modes used to form the reduced matrices.
- 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.
- It is possible to attach comments to the definition of the object; these comments have no effect on its definition.
Sensors
- 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).
- 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 ≤ N_{δ}/6. No v value is accepted for the modal super-element.