Nastran reference manual : Freq Dynamic Type 1

MENU SEQUENCE:
Data → Loads → Dynamics Loads

Defines a frequency dependent dynamic load of the form:

This type is used in transient response problems, where:
f= independent variable, it is a frequency.
i= imaginary unit.
A= Scale factor
Ft = Frequency delay
= Phase lead
C(f) and D(f) are functions defined by tables of interpolation. Tables have to be created before assigning this condition and associated to the condition using statements "Table Interpolation Values C[f]" or "Table Interpolation Values D[f]".
The user has to define these tables using the following menu sequence: Materials->Tables. More information about table creation can be found in he chapter Tables of this manual.
Finally, the user has to select in which degree of freedom he wants the load to act.
This condition can be assigned over points, lines and surfaces and has effect over nodes of the mesh.