External Modes File

When computing eigen modes using Radioss (/EIG), for example to create an input file for a flexible body, CPU time and memory requirements can be greatly reduced if a set of approximated modes is already available.

These modes can come from experimental analysis or from another vibratory software. They can be defined on a larger part of the structure than the part on which eigen modes are sought in Radioss.

The working subspace to compute eigen modes is reduced by projecting mass and stiffness matrices on the given modes.

Input File Format

External modes are given in a formatted file whose name is entered in the /EIG in Radioss Starter. This file contains three blocks of data, which must be input in the following order. Each line beginning with # is considered as a comment line and is not taken into account.

Data block 1: Dimensions

#FORMAT: (2I8)
#  Nbnod   Nbmod
      15      16
Number of nodes in external modes support
Number of external modes

Data block 2: Support of external modes (list of nodes)

#FORMAT: (10I8)
#  Nodes
21     22     23     24     25     26     27     28     29     30
31     32     33     34     35     36     37     38


The number of nodes in the list must be equal to Nbnod given in data block 1. The order of nodes in the list is the order in which the sets of components of the projection modes are given in data block 3.

Every node of the support of the /EIG corresponding to the current file (see Radioss Starter Manual) must appear in the present list. On the contrary, the list can contain extra nodes which do not belong to the support of the /EIG. Such nodes and associated components in external modes will be ignored in Radioss.

Data block 3: External modes

#FORMAT: (1P5E16.9)
#   1          X               Y               Z              XX              YY
#FORMAT: (1P1E16.9)
#             ZZ
 5.218918830E+01-5.732668966E+00 0.000000000E+00-7.497102620E-14 3.359287911E-14
-1.643492844E+01-5.732668966E+00 0.000000000E+00 7.497076647E-14 5.936317600E-14


Nbmod modes are input by blocks of Nbnod sets of six values (one set for each node of the support defined in data block 2).
X, Y, Z
Components of the mode on the translational DOF of the node
Components of the mode on the rotational DOF of the node (0. if the node has no rotational DOF)