Action > Eigen

Calculation of eigen frequencies and eigenvectors (natural modes) of the structure. A reference load case containing the definition of effective masses must essentially be specified. If the natural modes shall be calculated for the deformed system, the reference load case and/or the summation load case also contain the relevant effective loads.

After the calculation, a number of n load cases may be accessed from the load case pool (named ‘Outputfilename#n’, with n being the eigenmode, eg. Eigen01#3.mod). The load cases contain normalized eigenvectors as displacements and may be used for graphic presentation etc.

Setting	Description
Action	Code of the selected Action. It is possible to switch to another action without leaving and re-entering the input function.
Action will be skipped (Option)	The action will be skipped in the calculation process if the option is selected.
Input-1 > Number of natural modes	Number of natural modes of vibration
Input-2 > Reference load case name	Load case including the effective masses for calculating the eigenvalues. In case of non-linear analysis, also static deformations (and internal forces if the option P-Delta effects is set) are used for calculating the tangent stiffness matrix. Note: If a summation load case SumLc is specified, the respective deformations (and stresses if appropriate) are considered for calculating the tangent stiffness in addition to the respective values of the reference load case, if the option Accumulate stiffness or Erection control is set. I.e. you must take care to avoid specifying loads in the reference load case which already have been previously accumulated in the summation load case. The option Accumulate permanent loads includes all previously calculated permanent load cases in the reference load case.
Input-3 - (Subspace)	In some cases, the number of calculated eigenmodes is smaller than expected. In such cases, the dimension of the iteration matrix may be increased by additional iteration vectors (Subspace). This may lead to better iteration results and a higher number of eigenmodes found.
Input-3 - (Damping table name)	Optional generation of a variable (table) of modal damping ratio.
Output-1 > Modal file name (*.mod)	Name of the binary modal file, where eigenvalue and natural modes are stored.
Output-2 > List File	List file name to list load case results. Note: With the default '*' , the name Eigen.lst will be automatically used. If the field remains empty, no list file will be created Results in the list file are: Results of the static calculation of the reference load case Eigenfrequencies and mass participation factors Diagonal entries in the mass matrix Sum of masses and loads Note: The eigenvectors are not output in the standard list file. An alphanumeric presentation can be generated with using the action ListMod.
Delta-T	Duration of the Action (not applicable for this action)
Description	Descriptive text for the selected Action (max. 80 characters)