README FILE FOR INERTIA RELIEF ANALYSIS USING RIGID BODY MODES FROM AN EIGENSOLUTION, 
autosupa.v707

M. A. Gockel, February 22, 2000
Revised February 28, 2000 for PARAM, TINY

1.  Background

	This alter package allows inertia relief analysis with any number of rigid body 
modes in a model.  The rigid body modes are computed by an eigensolution.  
You need not know their number prior to the analysis.  This method should be considered 
for initial model checkout runs because it is unlikely that the analysis will fail 
because of matrix singularity.  The automatic constraint removes most causes of 
singularity

2.  Input

	Place include 'autosupa.v707' before the CEND entry. 
	Place param, inrel, -3 in the bulk data section 

The use of SUPORTi entries is optional.  They provides repeatable displacements from 
run to run.  Repeatable internal and external loads are provided regardless of the 
presence of this input.  The DOFs listed should constrain all rigid body modes of the 
model.  If they do not a user warning message will be produced, but the model will run 
to completion.  The DOFs may be on soft or stiff structure, unlike their use with 
param, inrel -1.

Optional Parameters

RBFMAX	Real, default=0.05 hz.  Modes whose natural frequency is below this value 
            are regarded as rigid body modes.  

NDX		Integer, default=13 modes.  The number of modes calculated in the 
            eigensolution.

TINY		Real, default=1.E-3  Tolerance for discarding spcforces.  This is a 		feature of the standard solution sequence.

At least one mode whose frequency is above RBFMAX must be computed to insure that all 
rigid body modes have been computed.  If there are not enough modes computed a fatal 
error exit is taken.  For example, if three disjoint structures are modeled there 
will be 18 rigid body modes.  A minimum value of NDX=19 must be used for this case.  
The present default is adequate for two disjoint components.  The SPC forces are 
computed for all DOFs, to find the error in balancing loads at each grid point.  
All DOFs will tend to have very small but non-zero values.  If TINY is set to a 
non-default value (that is, a number larger than or smaller than 1.E-3) all terms 
smaller than it will be discarded.

3.  Outputs

	The program automatically computes all rigid body modes and the first few above 
param, .  It gives the number of rigid body modes it has determined.  All other output 
is the same as for the built-in capabilities associated with param, inrel values of -1 
and -2.  TAN 4002 describes the differences between these forms of inertia relief.

4.  Limitations

	None.

5.  Test Problem

	File autosup3.dat is a simple verification problem.  It shows all mandatory and 
optional input items.  The TAN describes methods to convert this model to the older 
methods, for reasons of comparison.  File autosup31.dat is a tanker model, based on a 
client suggestion.  It is described in TAN 4438.

6. Revisions
 
February 28, 2000.
1. Discuss function of TINY in readme note.  
2. Put all inputs to READ module to allow faster matrix decomposition using grid 
   point resequencing rather than DOF resequencing.
3. Make processing of RBFMAX parameter more reliable.
4. New test problem added that simulates a model suggested by a client.