With the *GREEN keyword card Green functions
can be calculated satisfying
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where is the stiffness matrix of the structure,
the mass matrix,
a scalar frequency and
a unit force at degree of freedom
. The degree of freedom
corresponds to a specific coordinate direction
in a specific node. Consequently, a Green function is the answer of a system
to a unit force at some location in one of the global coordinate directions. Usually, these Green functions are used in
subsequent calculations. The Green function procedure is linear, i.e. the
material properties have to be linear (usually linear elastic properties and
the density) and the parameter NLGEOM on the *STEP
card is not taken into account.
The degrees of freedom in which a unit force is to applied can be defined by use of the *CLOAD card.
is a parameter on the *CLOAD card.
If the input deck is stored in the file ``problem.inp'', where ``problem'' stands for any name, the Green functions, the stiffness matrix and the mass matrix are stored in binary form in a "problem.eig" file for further use (e.g. in a sensitivity step). Furthermore, the Green functions can be stored in the ``problem.frd'' file, using the standard *NODE FILE or *NODE OUTPUT card.
The sensitivity of the Green functions can be calculated in a subsequent *SENSITIVITY step in which the objective function is set to GREEN (cf. *OBJECTIVE).