6. Useful notes for use

• Need for a static mode and type of dynamic modes:

In the case of forced displacement excitation, the dynamic modes are calculated using blocked supports and the presence of the static mode is mandatory.

In other cases, the dynamic modes are calculated using free supports, and the presence of a static mode is no longer justified.

The dimension of the interspectral matrix is given by the sum of the static modes and dynamic modes (if any) taken into account.

Thus, for a structure with five dynamic modes, excited in movement by two supports, the dimension of the interspectral modal response matrix is 7.

If the excitation is given in imposed force, there are no static modes and the dimension of the interspectral matrix is 5.

• Use of the keyword **** MODALsous the factor key**** EXCIT: **

In the case of using the keyword MODAL under the keyword factor EXCIT to directly introduce the modal spectral density matrix as an excitation, all the arguments that were used to create this modal interspectral matrix (supported nodes and degrees of freedom) must be returned under the keywords EXCITBASE_MODALE and MODE_STAT.