/EIG

Block Format Keyword Defines the eigen modes and static modes computation for flexible bodies.

Format

(1)	(2)	(3)	(4)	(5)
/EIG/`eig_ID`/`unit_ID`
`eig_title`
`grnd_ID`	`grnd_bc`	`Trarot`	`Ifile`
`Nmod`	`Inorm`	`Cutfreq`		`Freqmin`
`Nbloc`	`Incv`	`Niter`	`Ipri`	`Tol`
`Filename`

Definitions

Field	Contents	SI Unit Example
`eig_ID`	Mode identifier (Integer, maximum 10 digits)
`unit_ID`	Unit Identifier (Integer, maximum 10 digits)
`eig_title`	Mode title (Character, maximum 100 characters)
`grnd_ID`	Node group to which the modes will be computed = 0 Modes are computed for the entire structure. (Integer)
`grnd_bc`	Node group to which specific eigen modes are applied 3 = 0 Free eigen modes are computed. ≠ 0 The node group defines a set of interface nodes. (Integer)
`Trarot`	Codes for translations and rotations (6 Booleans)
`Ifile`	Additional modes file flag5 (Integer)
`Nmod`	Maximum number of modes to be computed Default = 100 (Integer)
`Inorm`	Eigenvector normalization method flag = 0 (Default) Eignvectors are normalized to the unit value of the generalized mass. = 1 Eigenvectors are normalized to the unit value of the largest displacement in the analysis set. (Integer)
`Cutfreq`	Maximum eigen frequency = 0 All `Nmod` eigen modes whose frequencies are higher than `Freqmin` are computed. ≠ 0 At most `Nmod` eigen modes whose frequencies lie in the frequency range `Freqmin`, `Cutfreq` are computed. (Real)	$[Hz]$
`Freqmin`	Minimum eigen frequency7 Default = 0.001 Hz (Real)	$[Hz]$
`Nbloc`	Number of eigen modes per block 9 ≠ 0 The modes are computed per block of `Nbloc` eigen modes. = 0 All eigen modes are computed at the same time. (Integer)
`Incv`	Factor to obtain the number of Lanczos basis vectors to use throughout the computation 10 Default = 2 (Integer)
`Niter`	Maximum number of Arnoldi iterations Default = 300 (Integer)
`Ipri`	Printout level for ARPACK Default = 0 (Integer)
`Tol`	Relative accuracy to which eigen values are to be computed = 0 The tolerance for eigenvalues accuracy is set to machine precision. Default = 0.0 (Real)
`Filename`	Additional modes file name (Character, maximum 100 characters)

Comments

This functionality is implemented for the purpose of the generation of flexible bodies. For detailed normal modes analysis of a model the use of the Bulk Data Format is strongly recommended.
The use of the implicit option /IMPL/LINEAR in the Radioss Engine is required to compute normal modes.
Boundary condition corresponding to the codes for translations and rotations are added to these nodes for the computation of eigen modes. Static modes, one for each additional blocked DOF, are computed.
A static mode corresponds to the static response of the structure, all DOF of the set of interface nodes concerned by additional boundary conditions being blocked; except one taking the one value.
The codes for translations and rotations follow the same rule as for the /BCS option.
If Ifile ≠ 0: An additional file is provided containing pre-computed modes from a normal modes analysis, either experimental or numerical. These modes are used to reduce the dimension of the space in which eigenvalues are sought and thus enhance efficiency.
If Ifile = 1, the additional file is given in a format defined in External Modes File.
Multi-level condensation is no longer supported.
The default (if set blank or zero) for Freqmin is 0.001 Hz. If a value other than zero is entered, that value defines a frequency in the unit system set for /EIG. The capability of computing rigid body modes is not fully implemented. It is recommended to either sufficiently constrain the model or to select a value for Freqmin that is high enough to eliminate all rigid body modes.
Eigen modes are computed using ARPACK software (R. Lehoucq, K. Maschhoff, D. Sorensen, C. Yang).

Figure 1.
Better precision is achieved when only a small number of eigen modes are computed simultaneously.
The number of Lanczos basis vectors to use through the course of the computation is given from the number of required eigenvalues per block (or total if Nbloc = 0) by the formula:
N_{Lanczos vectors} = N_{required eigenvalues} * Incv.
For the post-processing of modes shapes in HyperView, Radioss Starter input file (*000.rad) should be chosen in the Load Model panel and the first output animation file (*A001 which contains the first mode) in the Load Result panel.