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Alter for Initial Conditions in Modal Transient Analysis


Alter Name     mica.v2001


Purpose

To allow the use of initial conditions in a modal transient analysis. 
This DMAP Alter imposes user-specified displacement and velocity
initial conditions in a modal transient solution.  In order to get a
"match" on the initial conditions, the DMAP appends one or two
vectors onto the modes.  These vectors represent the amount of the
initial conditions which the modes are not capable of representing. 
(They are automatically orthogonalized to the modes.)


Solution Sequence

SOL 112.


Input
 
Executive Control

Include 'mica.v2001'.
 
Case Control

A second SUBCASE for the solution.  This subcase should
contain a METHOD pointing to an EIGR Bulk Data entry that
requests the calculation of a number of modes greater than or
equal to the number of system modes plus 2.
 
Bulk Data

PARAM,MIC,ii

If ii >= 0, then no special action is taken (default).
If ii <  0, then the DMAP Alter includes initial conditions in the
solution.

DMIG,MIC,....

A 1- or 2-column matrix containing the initial conditions.  The
first column is the initial displacements, and the second
column is the initial velocities (either may be 0.0 if desired).

EIGR,xx,AGIV,,,aaa

where aaa is the number of modes found in the system
eigenvalue solution plus 2.  (Simply placing a large number
here may be preferable since it does not require prior
knowledge of the number of modes).


Output

Standard output from a modal transient solution plus a second
eigenvalue summary table.  The second table contains the original
modes plus one (high-frequency) pseudo-mode for each initial
condition (displacement or velocity).


Limitations

Not supported for automatic restarts.

Initial conditions may only be specified for the a-set DOFs, and these
DOFs must have mass.

It is recommended to apply modal damping to the high-frequency
pseudo-modes for stability.

The DMAP Alter forces the coupled solution method to be used rather
than the preferred uncoupled method.


Sample Files

Three files are included to demonstrate the use of this DMAP Alter.

mic1.dat        A static run that uses a modified version of the
`pchdispa.v2001' alter to punch the displacements
resulting from a static solution.  These displacements
are used as initial conditions in the following files.

mic2.dat        Modal transient analysis using the results of mic1 as
the initial conditions.  An `include' statement is used to
include the DMIG from mic1.

mic3.dat        Direct transient analysis using the results of mic1 as
initial conditions.  The file `mic1.pch' is edited to
create TIC entries based on the static solution.

The results of runs mic2 and mic3 may be compared to validate the
method.


Additional Documentation

T. Rose, "A Method to Apply Initial Conditions in Modal Transient
Solutions," 1991 MSC World Users' Conference Proceedings, Vol. 1,
Paper No. 13, March 1991.